Michael

SuperDave, RPMS, BLKMGK and others got it exactly right! To paraphrase a famous aria in a famous opera: "Love is like an ill-behaved child; it never does what it is told. Look for it, and you will never find it; don't look, and there it is!" utvolman, you and I are in a similar position: small, backward town inhabited exclusively by married people. I'm 29, and everyone at work is the typical Midwestern upstanding husband-and-father. But that's typical in engineering. And it's also typical that good jobs are located in boring places. What is surprising, both in your case and in mine, is that being single carries more of a stigma than being divorced: "the divorced man was unlucky, or life threw him a curve, or he jumped into an ill-advised marriage when he was too young to know better; but the single guy - he's just a friggin' loser." It's also very true that women have an eerie sense for detecting lack of confidence and composure. If the guy is not at peace with himself, not confident with himself, how can he project the aura of confidence that women crave? "Nice guys finish last" not because they are "nice", but because they question themselves and seek intellectual justification for their behavior, while the "winners" just put their best foot forward. I used to think that going to the gym would help; that women are attracted to weightlifter-types. Experience showed that this assumption was completely false! However, the realization that women don't care about muscles was actually liberating, because then I started to think of exercise as a personal hobby, rather than a job to be done in order to achieve a particular end. Unfortunately, the process of finding and attracting female companionship tends to expose the most insidious weaknesses in a man's character. It's troublesome enough to make a guy want to just give up. But, as some other folks have remarked, perhaps that's precisely what needs to be done: paradoxically, the only way to succeed is to first give up.

At this point we can observe that the remaining justification for suggesting that long-stroke engines have inferior rev performance, is that subject to the ubiquitous "all else being equal", the long-stroke setup will have a higher moment of inertia, implying that it would take longer to spool up. However, there is a straightforward (but expensive) remedy: use lightened components; a lighter flywheel, lightened crank, compact harmonic damper. Considering the costs of getting back the horsepower lost when losing displacement to destroking, this is a reasonable option. When I first wrote this, I guessed that in a light car with a large engine, it is not inconceivable that in first gear the torque needed to spool up the engine is a large fraction of the torque to accelerate the mass of the car (with a given tire radius). A short calculation showed that this is completely false! Example (in S.I. units): 1000 kg car, 0.3m tire radius, accelerating in first gear at 8 m/s^2. Torque at the driveaxle is 2400 Nm. Assume that we begin at 1000 rpm and end at 5000 rpm, and that the ratio of crank rpm to axle rpm is 10:1, and assume constant acceleration (I know, that's a crude assumption, but it makes the math simple). Then the engine has to spool up from 1000 rpm to 5000 rpm in 1.57 seconds, giving an angular acceleration of 267 rad/s^2. Model the crank by two coaxial cylinders: one with 1.25" radius (the "main journals") weighing 40 lbs, and the other with 3" radius (the counterweights), also weighing 40 lbs. Converting to S.I. units and using the formula: moment of inertia = 0.5*mass*r^2 for a cylinder, the crank's moment of inertia is 0.062 kg*m^2. Also, since torque = moment of inertia times angular acceleration, the torque expended at the crank to spool up the crank itself is about 16 Nm, or 160 Nm at the driveaxle. This is a big crank in a light car accelerating rapidly. Even so, the crank spool-up absorbs <7% of the torque! Including the flywheel, the clutch and the harmonic damper of course raises this ratio, say by a factor of 2. Which perhaps explains why race cars tend to feature small-diameter multiple-plate clutches - another option to consider for a "rev-challenged" long-stroke engine. Regarding port sizing - Jim McFarland had some articles a few years ago, discussing "optimum" velocity of the intake charge. According to him, the mean speed of the flow before reaching the valve curtain area should be around 240 ft/s. Given an intake runner volume and geometry, we get a notional cross-sectional area of the intake port. McFarland pointed out the importance of comparing port cross-sectional area instead of volume. Big-block intake ports have much large volume than small-block intake ports, in part because of large area, but also because the runners are longer. From the cylinder displacement and a guess for volumetric efficiency – at a given rpm, we get a figure for the volume of requisite intake charge per intake stroke. From the cam profile one can back out a time interval during which a fictitious mean intake velocity would fill the aforementioned volume - again, at a given rpm - it's not the same as camshaft duration or a simple integral. It does not appear to be a simple calculation. Anyway, ideally, the port cross-sectional area times 240 ft/s, should equal cylinder volume times volumetric efficiency divided by the time interval. Deciding upon the rpm at which we want the best match would then size the port cross sectional area. All that remains is to slog through the calculations.

Just out of curiosity, what's inside the CFD code that runs "very fast" on a PC? If it's a panel method (vortex and source distribution, with flow-tangency boundary condition on each panel - and possibly vortex particles ejected at specific points in each time step, to simulate the "wake"), I would have to be skeptical. For an example of a state-of-the-art family of inviscid codes (tuned to mimic viscous effects), check out www.consultingaviation.com, or send them e-mail at cascd@mindspring.com – but please, don't mention my name. An erroneous answer is WORSE than a wild guess. A “ballpark” estimate can be worse than having absolutely no clue whatsoever – if the ball is in the wrong ballpark. And aerodynamics "improvements" based on specious analysis are likely to be worse than doing nothing at all. There's a reason that most cars have significant positive lift, and it's not because the OEMs are lazy or stupid. A real CFD analysis would be based on a full 3-D unsteady Navier-Stokes analysis. A full "direct numerical simulation" is currently not possible even with the best of computers and the best, most-motivated minds in industry and academia working on the problem, so we're back to the problem of turbulence modeling. I honestly have no idea what to suggest – what model to use. That doesn't mean that the problem can't be solved, of course - but it does justify tremendous skepticism whenever some one proposes a “solution”.

I was amazed how tight that Barracuda's engine bay is! The inner fenders extend so far inboard, that even the stock (or stock-appearing) exhaust is a tight fit - and that does not look like a wide engine. How did people ever shove a 426 Hemi in there? If a Crysler big block can be made to fit into the Barracuda, for sure it will fit in the Z.

Comparing a completely bare 240Z shell to a completely bare 280Z shell (no sound deadener, no glass, no rubber, no doors/hatch/etc., and of course no mechanicals - nothing that doesn't unbolt or scrape off or unplug – the difference is or the order of 50 lbs. The 280 has longer and stronger frame rails, frame reinforcements fore and aft for the bumper shocks, and slight differences in the transmission tunnel, the door hinge mounts, the radiator lower crossmember, the spare tire well, the framing just aft of the mustache bar mounts, and probably in other places in minor amounts. There is some speculation that the floor boards and some other sheet metal components on the 280Z shell are heavier gauge than on the 240, though I have never seen conclusive evidence one way or the other. Cutting up the shell to save weight is not necessarily impractical or extreme, but it will require some courage and finesse. I have done this, with mixed results.

The idea of a rigorous test of the Z in a wind tunnel comes up from time to time.... I think that this would be nice, but prohibitively expensive. It’s not just a matter of renting tunnel time. You would have to build and instrument the model, figure out how to spin the wheels (pretty important), how to run the ground belt (very important), how to attach the various removable components (air dams, side skirts, spoilers,…). Figure maybe $300,000 for a decent model, $1M for a short test and maybe $10M for a serious test with multiple entries (pressure-sensitive paint, probe-rake traverse and maybe particle image velocimetry). These are only guesses, of course – but more likely than not, they’re on the low end. NASCAR, F1, etc. perform minor tweaks of proven designs year after year – and spend more. Just imagine the costs of starting from scratch. Big difference! Of course, reasonable qualitative information can be obtained from MUCH cheaper and simpler experiments. Not to toot my own horn, but that’s what I tried to do in my water tunnel flow visualization tests. But these tests are rather useless for vehicle design. At best, they elucidate general trends. As for belly pans and underbody tunnels, the short answer is that these devices have good potential, but only when many, many other factors are just right. It’s a very “peaky” design. As Terry and others point out, blocking off the flow in the front with a good air dam, altering the hood lip and front grill, and following up with a good hatch lid spoiler are a better compromise solution, because it works over a broad range of scenarios, even if it’s not the “ultimate” in performance.

Terry, Like your friend mentioned – what you saw was the footprint of a shock wave on the wing upper surface. I wish I got to this thread sooner; but at the present point, my post will just be review. In going over the front of the airfoil, the air accelerates to speeds significantly greater than the speed relative to the airplane itself. If the airplane is flying at, say 550 mph (well below Mach 1.0), there will probably be small regions over the wing upper surface where locally the flow is supersonic. Further aft on the wing, the pressure conditions are such that supersonic flow can no longer be sustained. Nature's solution is to introduce a shock wave, which stands like a "curtain" vertically over the wing. It abruptly terminates the region of supersonic flow, beyond which the flow is again subsonic. Almost all modern commercial jetliners cruise fast enough for there to be regions of supersonic flow over the wing. The speed at which this region gets to be so big that overall aerodynamic efficiency is reduced to unacceptable levels is the natural "speed limit" at which the airplane is operated. At somewhat higher speeds, the drag rises to a point where the engines' thrust is no longer sufficient to overcome the drag; that is the absolute speed limit of the airplane in steady level flight. Airlines will operate their planes at speeds somewhat below this absolute limit, in order to be below the point of diminishing return, to keep fuel costs down. For example, the Boeing 777 is rated at a maximum speed at cruise altitude of around 600 mph (probably more, I don't have the exact details), but you will never see a regular commercial flight faster than around 570 mph true air speed. The speed at which a region of supersonic flow first forms (called the critical Mach number) depends on many factors, such as the thickness of the wing and the lift coefficient at which it's flying. Jetliners are very efficient. They cruise at low lift coefficients and have thin wings. The root part of the wing is pretty thick, though - which is why I occasionally see the shock over the wing near the root portion, but not further outboard. In contrast, the upside-down wings of race cars sometimes operate at huge lift coefficients, so their critical Mach number is lower. Nevertheless, even an Indy car doing 240 mph is going too slow for shocks to appear, although more benign effects of air compressibility are still present at speeds in that range. Even with some very clever airplane design approaches, the drag penalty of trying to fly faster than the critical Mach number is so great, that it makes no commercial sense to do so. This is precisely why the speed of commercial jetliners has not changed much from 1969, when the Boeing 747 was introduced. They all cruise at around Mach 0.8 or so. It's really the critical Mach number, and not the magic Mach 1.0, that determines how fast conventional airplanes can fly. The Concorde flies much faster, of course, but it's so woefully inefficient that even at 10x the ticket price of a regular airplane, it still loses money. Boeing is now working on a new jetliner called the "Sonic Cruiser", designed to cruise at Mach 0.98. In my personal opinion, this airplane has no commercial future. Boeing is pursuing this design to keep their engineers busy. Anyway, the aforementioned footprint of the shock on the wing upper surface is due to a change in index of refraction in the air, which produces regions of contrasting illumination. More precisely, what you're seeing is the second derivative of the index of refraction (in the streamwise direction), which itself varies with the second derivative of the air density. Aerodynamicists call this the "shadowgraph effect". At speeds comparable to the speed of sound, significant changes in the thermodynamic variables of the air (density, pressure, temperature, etc.) are caused by changes in air velocity. Gradual changes are not visible. Violent changes, such as in a shock wave, are very visible, because the second derivate of density or temperature inside a shock is huge. Shocks are very thin, so their shadowgraphs are easy to see. Moist air has greater changes in index of refraction for the same change in temperature. This is why when the air is humid, the shadowgraph effect is stronger, and the shock more visible. By the way, the reason that this shock wave is vertical is that locally the flow is nearly parallel to the wing surface. In contrast, the bow shock of a supersonic airplane (under most conditions) is sloped with an angle equal to the arcsine of the inverse of the Mach number. It is caused by an entirely different mechanism.

I want to second the call for “school first, finances second, hobbies third” – but keep in mind that your $40K will not necessarily make you a millionaire, even if you have decades and decades to wait, and “invest wisely”. Look at what happened in the stock market in the past 2 years. And don’t rush into buying that house, either. Houses have a nasty habit of declining in price, just after you buy them…. If you’re a mechanic, don’t hesitate to buy a cheapo stock 240Z. Drive it, maintain it, get used to it – then modify it. The point, I think, can be stated thus: planning ahead won’t necessarily get you ahead. But not planning ahead will almost certainly get you hosed. That’s not a resounding endorsement of delaying that big plunge into the world of V8 Z’s, but it does agree with experience.

My (admittedly biased!) views on Ohio.... I moved to Ohio in the spring of 2000, due to a compulsory job change (Wright-Patterson AFB). Were it not for that, I would never have moved here. My reasons? 1. weather: 90’s in the summer, way way below freezing in the winter. Long summer, long winter, no transitional seasons, always humid. I have lived in Michigan, Northern Virginia, Los Angeles, and New York City; all of these places have better weather, in my opinion. 2. taxes: not as high as New York or California, but certainly higher than average. State income tax is moderate, but local income taxes really hurt you. Townships don’t have local income tax, but most still have “school district tax”. Property taxes, as a percentage of house value, are outrageous, because the tax base is poor. Sales tax is 6-6.5% 3. suburban sprawl: there is plenty of rural land out here, but you have to drive >20 miles from even the smaller cities (like Dayton) to get out into the countryside, because of low-density housing construction ringing the cities. And, because so much land is available for new construction, existing property values are capped. In the towns, there are covenants and homeowners associations that would constrain activities such as a major Z-building operation; this is similar to what one finds along the coasts, except that there the communities are more affluent. 4. mentality: population turnover is low. Variety? Not that I have been able to observe.... This is a conservative, “heartland” type of area, which pulls no punches in promoting a particular kind of lifestyle. 5. police and cars: traffic cops are ubiquitous. Much worse than in Virginia, in my opinion. There is no safety inspection for cars, but there is a smog check that varies county-by-county. Cars older than 25 years are exempt. Unfortunately, the used car market is scarce, especially for foreign cars. Months go by before I see a Z on the road. On the other hand, if you are a young family trying to raise children, this might be a decent place for you. Ohio is “family-friendly” to the point of obsession. If I had to live in Ohio but had my choice as to which area, I would pick the northeast corner. It offers the most cultural opportunities, the best property appreciation, and the least conservative mentality. The southeast corner – “the hills” – is known for being the most economically backward. Property values in Ohio are NOT on the rise, except in Cleveland, Columbus and Cincinnati. The smaller cities in Ohio (Toledo, Dayton, and on down) are experiencing long-term real estate depreciation, relative to inflation. The reason? Ohio just doesn’t have the job base. After every census, Ohio loses another congressman. The bigger cities are doing better, as they have been able to transition to high-tech/the service sector. But the smaller cities, with their decaying industrial infrastructure, are in trouble. Also, as far as I have seen, Ohio’s agriculture is in trouble too: the farms tend to be small (not too many >1000 acre farms), which suggests that they would have trouble competing in modern agribusiness.

The 7-degree thing is true. It’s an empirical fact, and not the result of fancy calculation. Separation of the boundary layer is a response to an adverse pressure gradient. If you do the math, trying to solve for an attached flow, you would find that for sufficiently high adverse pressure gradient, the attached-flow solution is no longer possible. Basically, it’s like trying to drive uphill – if the slope gets too high, eventually you lose traction and roll back downhill. It so happens that 7 degrees corresponds to a particular pressure gradient, which is the threshold at which a conventional diffuser can no longer maintain attached flow. By the way, that’s for turbulent boundary layers. Laminar boundary layers (not practical for street cars) are even MORE sensitive to adverse pressure gradients. Think of it this way: the turbulent boundary layer is like an off-road 4x4 truck with studded tires trying to go uphill, while a laminar boundary layer is like an economy car with narrow, hard-compound tires. The economy car experiences less friction, which means that IF it can make it uphill, it will have less drag. The 4x4 truck has much higher drag, but it can make it up a much steeper hill. The reason that some diffuser designs can exceed 7 degree upslope without separation is “spanwise relief”, A.K.A. 3-D effects. The pressure gradient is locally relieved to keep the flow attached. How is this done? Good question.... It definitely goes on a case-by-case basis. I don’t have a good answer for that one.

Leaning toward a solid flat-tappet cam for the 454 in my 280Z, I have found that solid-cam options in moderate lift/duration ratings are limited. For Chevy big blocks, cams with less than 250 degrees duration (at 0.050”) and/or less than 0.550” lift are almost exclusively hydraulic, unless they’re muscle-car restoration cams, in which case they have healthy duration but comparatively low lift. One exception is Comp Cams’ “Magnum 270S”, which is 224/224 @ 0.050” and 0.530/0.530 lift. Now then, without resorting to the usual discussion of “what do you want to do with the car” [answer: I haven’t a clue, because my expectations will change once the car is built, and I have never owned a “hotrod” before.], and my favorite, “what sort of dynamic compression ratio are you interested in”, I’m wondering how folks out there in HybridZ land would opine regarding this cam; and, are there suggestions for similarly-sized alternatives from other manufacturers? My preference is toward single-pattern cams, as casual observation shows that dual-pattern cams are stopgap measures to correct for poor exhaust ports, but the exhaust side responds better to amateur porting than does the intake side. The car weighs ~2700 lbs, has the 3.54 R200 and a Doug Nash 5-speed.

My car isn’t what one might called “finished” either; currently it lacks an engine, and has a strange suspension alignment problem. Nothing that can’t be fixed – but the fixing is the difference between running car and garage queen. But it is possible to sit in the driver’s seat and make engine noises while some one else pushes the car. I think there’s a lot of “moral support” value from face-to-face meetings between HybridZ people, even if the cars aren’t finished – or for that matter, not even started yet. If any of you local guys want to get together, I can be reached at ol_70@hotmail.com.

I’ve noticed that there are at least 3-4 folks on this list who reside in the North Kentucky – East Indiana – West Ohio – Columbus region. I’m south-east of Dayton, near the halfway point on I-71 between Cincinnati and Columbus. And I was wondering if we might consider a regional HybridZ meet, or perhaps just take a drive every now and then to look at who’s building what. I moved to this area about two years ago, in a forced career-related move. Every since I’ve been trying to make the best of things, often haphazardly. By now it’s finally time to meet by Z-neighbors!

I have nearly the same situation as James: no wife or kids; a decent income, a house, and a Z that mostly just sits there. The sad part is that I bought a house primarily in order to be able to work on the Z – to have a big garage, to be away from neighbors who might get upset by electric grinders buzzing at night, to have a place to spread out my tools. But instead of working on the Z, I’m working on the house, fretting over the stock market, vegetating at work, and pinching every penny.... When I was in grad school, worrying about passing candidacy exams, building my laboratory setup, researching references, etc., there was somehow still time to work on cars. First my daily driver, then my Z. And that was back when I still had faith in the dating game, still went out with friends, occasionally day-traded stocks and even went to the beach. These days I don’t date, don’t go to bars, don’t trade stocks, live hundreds of miles from the nearest beach, have no exams to worry about, and lack even a token social life – but somehow the Z just sits there. Sometimes I wonder: if I spoke better Latin and wore a robe, I’d make a great monk. No, neglecting the Z is not about time. At least, not merely time. Nor is it a matter of conflicted priorities or dissipative interests. It’s really a matter of – faith. Faith that this project makes sense. Faith that it isn’t a little boy’s delusion, that it’s worth making real, getting it on the road, making something of it. Faith that it isn’t a tight-underpants desire to be “faster” than some punk at a stop light. Faith that wanting a fast Datsun is not Freudian angst over a small Johnson. To a large extent, faith rests upon self-confidence. If one does not believe that he has the capacity to do the job, what chance is there for faith that the job would get done? What’s more, the process of doing the job becomes a struggle against second-guessing and timidity, not an enjoyment of the craftsman’s hobby.

I don’t rant too often, but after today’s financial news I can’t contain the impulse.... To all the reasons that folks lose the opportunity to build their V8 Z’s – divorce, poor health, job loss,... may I add losing one’s life savings in the stock market? This market is really going beyond the ridiculous. It seems to me that we have the dubious privilege of living through the greatest financial collapse in human history. The wealth of a generation, down the toilet. Is there anyone on this board old enough to remember the 1920’s? Anyone? Anyone’s parents, maybe? Please, please tell me that the 1929-1932 crash was even worse than what we’re going through now. And please tell me that there was a recovery….

Pete- I gotta chime in with my congratulations! I've known you and your car for less than a third of the time that it took to build it, but even over that time I have been deeply impressed with your engineering and craftsmanship. Being picky and meticulous is unfortunately something that pays off only at the end. During the journey, it can attract doubt and loss of confidence. But now that the next phase of your journey will be in the company of a running beautiful V8Z, the rest of us can only say one thing - you done good, man!

Jonathan, Let me make some “do as I say, not as I did” assertions.... There are some excellent deals of V8 Z’s out there, but from my experience, they are rare. Before I moved to Ohio, I spent about 5 years in LA. Every week I would look for Z’s in the Recycler. Typically, there would be at least one V8 conversion for sale every week. And typically, every one of them would be an abandoned project, or a “running” conversion that runs even worse than stock. One time I drove a "Nordskog" conversion that was for sale - the poor thing accelerated worse than my Corolla, and the brakes were scary even at 15 mph! I have not seen Aaron240Z’s car – it may be exceptional. But it seems to me that if some one pours his spirit into doing a good engine swap, why would he sell the product of his labor, knowing that such a sale nets only pennies on the dollar spent? There are other exceptions, such as when Jim Biondo “got tired” of his immaculate V8 Z some years back, but how often do those come up? Most of the conversions that I saw for sale would have cost more time and money to correct, than it would cost to start from scratch. And if you’re just looking for a source of swappable drivetrain, find a dilapidated Detroit product with a 350. They are not as common as the magazines claim either, but they are out there. A conversion is a difficult procedure. No doubt about it. But my impression is that the main reason that so many folks on this site (including me!) are bogged down in multi-year conversion projects is not because of the swap itself, or because of engine tuning, but because they are making radical modifications to the rest of the car. It begins something like this: you get a good deal on a tired Z. Then you start pulling trim and carpeting, unbolting body panels, scraping off insulation, just to see how the metal really looks. And behold, there’s rust under the battery tray, and in the frame rails, and in the wheel arches, and under the hatch lip,.... “Man, a stout V8 car won’t work with a frame like that!” And so, out comes the sawzall, the channel-lock pliers and metal sheers, and the welder. The coil springs? They sag – so they too need replacement. And to fit those big wheels, you’d get coilovers. The sway bar? Too soft, of course. But the frame rails are too weak to take the reaction from a stiffer bar, so there’s some more frame reinforcement to do. The half shafts? Too weak for that magic 400 or 500 hp. So they to get replaced. And on and on and on. These are all worthy challenges to undertake, but they are for the experienced hot rodder. My point: if you begin with a solid foundation, a proven foundation – you will be vastly further ahead when you finally do the swap. Don’t let installation of the V8 explode into an all-out struggle to build a killer race car (trust me, I speak from experience!). So what does this mean for a fellow that’s just learning about auto mechanics? In my opinion, it means this: drive what you have for now. Learn its weaknesses. Make small, gradual changes, like those springs, or the brakes, or an upgrade of the gauges. But keep the thing driveable all along, and hold off on that swap. That way, you will learn from low-risk mods at a gentle pace, you will gain confidence, and you will have a worthy foundation when you’re finally ready to make the leap into V8-world – your car will be ready, and you will be ready. Whereas if you begin with some one else’s half-baked conversion, suddenly you have a heap of some one elses’s problems to deal with – hidden, annoying problems with unfamiliar components. And you will be dealing with high expectations (it is, after all, a V8 Z, right?), which would make it difficult to concentrate on meticulous, patient repairs.

Of all the big block choices out there, probably the Chevy BBC is the most natural choice (for reasons similar to why the small block Chevy is the most common small block to use). As Brad Barkley, Ron Jones and a handful of others (I believe there are about 5 big block Z's on HybridZ) can attest, the romance of the big block is hard to resist. They do fit - but not without some very clever metal work. You will almost certainly have to dispense with the mounting of the engine from the steering crossmember (instead weld mounting pads to the frame rails), and would need to notch the frame rails to clear the headers - even if you use block huggers. If you are an experienced big block mechanic, there's significant reason to attempt a big block swap. Otherwise, make do with the small block. Perhaps we should start a "big block V8" forum (all makes, not just Chevy)?

I have a roll cage somewhat similar to the one featured in this thread, so I thought I’d comment on some issues…. The X-bars in the car featured above actually tie into the unibody at all four corners of the "X"; I refer in particular to (1) the areas just above and aft of the upper hinges of the doors, and (2) the “corners” of the unibody where a B-pillar would normally be (the latter are tied together by the horizontal bar behind the seats). The continuation of the tubes forward of the firewall is unclear, but they look like "Monte Carlo" bars triangulating the front strut towers. With that in mind, I'd say that in fact the upper half of the roll cage IS doing it's fair share of reacting to the loads of a side-impact. It's true that in a harsh T-bone, the X-bars will deflect into the driver's shoulder/thigh area - and in that sense they are inferior to NASCAR-style straight door bars. But they weigh less and do a better job of stiffening the whole chassis in torsion. So we might conclude that for safety purposes they are not the best design, but for stiffening the car they perform fine. It comes down to a matter of what's the main reason for building the roll cage: safety or stiffness? From what I have heard, a NASCAR-style cage is astonishingly weak in torsion – so much so, that frame deflection is taken into account when computing the suspension dynamics. Regarding the diagonal bars occupying the passenger compartment - my suggestion is to replace them with a single bar running from the midpoint of the dash bar (a node of several intersecting tubes) aft toward the midpoint of the horizontal bar just behind the seats (another node). That is, connect node-to-node. This ties together the rear strut tower triangulations and the front strut tower triangulations (which is what the horizontal-plane X-bar set was evidently designed to do as well), improving the torsional and bending stiffness of the whole car. I have such an arrangement in my car. It looks like an awkward invasion of interior space, but actually it does not interfere with the driver’s movements.

Let me add to the chorus recommending that you consult the JTR book and get a feel for the issues involved in installing the small block Chevy, regardless of your eventual choice. However, I would like to depart from the chorus in this regard: whereas the Chevy swap is probably the better choice from the point of view of upgradability and maximum performance, the Ford 302 swap might make for a better "sorta-stock" hybrid. The reason is that the Ford engine is considerably smaller and lighter. The T5 transmission and the stock clutch assembly should do just fine in the Z (not so for a 400 hp Chevy engine). There are, of course, aggressively built Ford engines too. But it seems to me that if one were to build the "low-buck hybrid" such as the first version that the JTR book recommends, the Ford version would be the more livable combo. Too bad that the Ford's sump is backwards.

A very similar thing happened to me with my 454, when I installed a Comp Cams XE-262 flat-tappet hydraulic camshaft complete with the kit (springs, locks, retainers, timing chain set) on an otherwise stock engine from a 1978 Suburban. I used stock pushrods, stock rockers, ... - everything stock, basically. The cam was installed with the timing chain set dot to-dot (not degreed in). I did NOT check the spring pressure (open or closed), but I did check for coil bind and for sufficient length in the rocker slots (both passed the "paper clip test"). I didn't check the piston-to-valve clearance either, since I did not pull the heads when I installed the cam. The vavles were adjusted by tightening until the pushrods could no longer be spun by hand, then tightening one half more turn. The installation was done in the presence of a guy who has been racing big block Chevies for some 30 years, so I figured that he knew what was going on - although we were pressed for time. The cam was broken in for 20 minutes at 2000 rpm. But very soon after the first drive, the engine started to make noises that sounded like a spun rod bearing, though oil pressure was always at least 10 psi for every 1000 rpm (never exceeded 3000 rpm, by the way). I did a compression check in each cylinder and found 130+ psi everywhere, with maybe 20 psi variation (at most). What eventually happened was that one pushrod (#4 intake) was broken in half, and several other pushrods were in various stages of bending en route to buckling. The engine backfired severely. Several cam lobes look like some one took a grinder to them. The corresponding lifters are so badly worn that they won't come out of their respective lifter bores. However, the valves are in good shape, as are the pistons - which I checked when I finally removed the heads. This whole adventure basically destroyed my confidence in doing any engine internal work....

Folks, Somehow this whole high-performance in a big block thread left me with a jarring feeling of uncertainty. The reason that my post on big block heads may appear scatterbrained is that I have been pondering this issue for a very long time, and have long ago lost sight of the original “goals”. I’ve been through Staeffel’s book, and Currao’s, and various books by Vizard; and on the more technical side, C.F. Taylor’s engine “bible” and Lumley’s recent condensed version. But somehow that is of little help in choosing which brand of which component to buy. The trouble is theory vs. practice. Every time that I go to a machine shop, the first words out of the guy’s mouth are (besides the canonical “speed costs money”), “how much does the car weigh and how fast do you want to go?” So I end up making up a number to placate him, and to get the conversation started. In reality, however, I don’t particularly care how fast the car goes down the quarter mile, so long as it pulls hard enough to scare me. This is why I can only think of a tentative performance number. Then as soon as I mention a number, the machinist starts lecturing me on how “one number does not a race car make”, etc. Then the machinist proceeds to tell me that I don’t need a solid-tappet cam, that stock heads are going to be fine if they are sufficiently modified, that I do need forged rods, etc. Oh, and no one fails to mention that the rear end will grenade as soon as I cast a glance at it, that only stuffed-shirt poseurs run an independent rear suspension, etc. You get the picture. I do not believe that most machinists are obtuse technicians or callous crooks (though some certainly are), but I seem to be unable to avoid “a failure to communicate”. Talking about limiting values of Z-factors doesn’t exactly help. Maybe I should just glue my business card to my forehead? I can’t build the engine myself, because I will forget to pre-lube a rod journal or something like that, and a bearing will spin 20 minutes after I start up the engine. That is just a consequence of the way that I go about doing things. Not smart on a $6000 engine. I can’t even remove the valve springs off my stock heads (the C-clamp style of spring removal tool keeps getting bent, before the spring itself compresses!). I have never driven a car that, to my knowledge, was faster than high 13’s. A few years ago I test-drove a then-new Z28 Camaro, and it was far faster than anything else that I had ever driven. For a number of years I had a Mark III turbo Toyota Supra; I thought that it was fast – but it ran 15.9 at the Pomona track (back when I lived in Los Angeles)! I narrowly lost to a rusted-out ’66 Mustang. So to me, at least at this point, 9.9 or 10.9 or 11.9 or 12.9 or whatever – they are all a jumble of fantasy, pie-in-the-sky, castle-in-the-clouds numbers so divorced from reality that I need not even bother calculating the optimum shift points or figuring whether I should use 0.040” quench or 0.035” or if I would be better off with 3.36’s than 3.54’s in my R200, or for that matter, how many tenth’s of a second I would get from painting the block Chevy orange and gluing Moroso and Jegs stickers to the windshield. Doesn’t it then make sense to just put together the engine that I already have? Maybe, but after 4 years of construction, a frame that’s supposed to pass NHRA tech for a 7.50 car (no kidding), and many other endeavors, it seems only fitting to go the bucks-up route on building an engine. Yet where to stop? Where is the point of diminishing return? Sure, a roller cam will free up some hp. Sure, a knife-edges crank with scalloped rod journals will spool up faster. But is it worth the money? A “stock” rebuild on a 454 costs about $900. But wait, shouldn’t I also get the crank balanced? Yeah, of course. $300. And that 9.5 CR calls for forged pistons, right? Add another $400. Then add ARP rod bolts. And that 2-bolt main could benefit from going to studs in the mains, right? Isn’t a high-volume oil pump a good idea too? Sure, of course. Then add the roller cam and the forged rods, and we’re up to the $3K range on the short block – or more. So why not throw in another $1000 and just get the GMPP 502 short-block? Or for that matter the Merlin II block (more aftermarket support for the 2-piece crank seal, right?), maybe with roller needle bearings on the cam. And the Lunati $2000 crank – the one with the scalloped rod journals. Maybe one of those Keith Black aluminum blocks, or a ZL-1? Up and up the ladder we go, up and up the beanstalk. Or just go find some 70’s GM truck with a big block, pull the engine out of that and call it Version 1.0. Wait a minute – been there, done that. So this is why I want to make up a number, like 500 hp – it is a line in the sand. It is not the belief that one design point will turn my life around and turn me into a happy smiling dude, but that somehow a decision has to be made – and short of throwing darts at my Summit catalog, the “knee in the performance/price curve” strikes me as the most logical approach. Opinions? Thanks! -Michael

Guys, Many thanks for the replies. When I got through writing my follow-up post, I realized that it ended up as more of a rant than a technical point, so I put it in a more appropriate place in the forum (the “I’m tellin’ ya” section). Please look at it if you get a chance, as it hopefully applies to a broader context than just big blocks. One quicky tech question though – has anyone tried "porting" an Edelbrock Performer RPM oval-port manifold to fit rectangle-port heads? This might not be as foolish as it sounds, because the Edelbrock oval manifold’s runner shape tends to be "square shouldered" (I’ve heard it referred to as “roval”) and there ought to be plenty of meat in the port walls. The reason for doing this, besides using what I already have if I go with the AFR heads, is the flow-quality issues for oval-shaped ports that I mentioned earlier, especially with a carburetor. Grumpy – would it be possible to continue this discussion off-line? My e-mail address is ol_70@hotmail.com.

This one is long and loquacious…. For some time now I’ve been tossing around the idea of getting good aluminum cylinder heads for my 454 big block. Currently I have 346236 GM heads – standard equipment on 1970’s trucks. I have been following the various discussions about heads for small blocks, power vs. torque, the significance of cfm ratings, piston speed, etc. – and while the basics of course apply here as well, the particular choices are very different. Granted, it’s the full combo that matters, not the individual parts. But decent aluminum BBC heads are $2000 ($3000 with serious porting), so I first want to get a feeling for the cylinder head selection. I AM in principle willing to spend $3K on heads – or more – but only if the expense is justified. The price vs. performance curve is not a straight line – there is a knee in the curve, which for big blocks evidently occurs at around 500 hp. A cursory summary of my situation: 2700 lbs car (with cast iron heads), to be driven regularly (in good weather) and suitable for occasional drag racing and maybe autocross-type stuff. The transmission is a Doug Nash 5-speed with 3.27 first gear, and the rear is a stock 3.54 R200. I want ferocious off-idle torque with a usable torque band up to maybe 5500 rpm. Anything beyond that is nice, but not important. It must be compatible with 92-octane gas and pull decent vacuum at idle. The goal is, tentatively, the aforementioned 500 hp. The very highest-flowing heads may be overkill, since the rest of the intake-combustion-exhaust flowpath may not be able to make full use of the high flow volumes at this relatively tame hp level. However, when I say 500 hp, I mean a LAZY 500 hp – the engine is not straining, stock cast crank and 2-bolt mains are doing just fine, pistons speeds are comfy low and I don’t have to constantly keep staring at the oil pressure gauge, and maybe even the carb and ignition tuning isn’t 100% there. The point is, there’s plenty of extra power available with the eventually combo – but 500hp is the notional benchmark for the first iteration. There is no particular goal in the quarter mile. This car is so weird that it would not be competitive in any class for which it would qualify (refuses to join any club that would take it as a member ), and I’m not interested in bracket racing. Information on big blocks is MUCH harder to find than on small blocks. Chevy High performance ran a series of cylinder head flowbench articles (available on their web site), also covering big block heads. This is my starting point. I plotted the various flow numbers vs. lift. Of the heads that they considered, I included: GM 049, 156, 236, 290 and 702 oval port heads; Brodix OEFI, Edelbrock Performer RPM, Dart and GM Performance Parts aluminum oval port heads; Merlin iron oval ports heads (they don’t make an aluminum oval head!); and Canfield and Merlin VR rectangular port heads. These were apparently all unported. I excluded the larger rectangular port heads based on the sentiment that their port volume is probably too large for my application (though port cross sectional area, or rather hydraulic diameter is a more significant parameter, I assume comparable port geometries and runner lengths). Of course, this is just a flow rate comparison. Combustion chamber design, spark plug location, etc., are not considered. Bore diameter was 4.250”. Some heads, like the new AFR heads (see below) flow much better with the larger 4.500” bore, for reasons attributed to valve unshrouding. The main results were: * all the stock GM heads, except for the 049, all almost dead equal on both intake and exhaust (especially up to 0.500 lift) and dead last. The 049’s are considerably better, especially on the exhaust side, with numbers half way between the stock GM heads and the aftermarket heads. * Among the oval port heads, the Brodix (and Merlin) heads have good low-lift intake numbers, but become mediocre by 0.400 lift (intake) and are in the back-of-the-aftermarket-pack on the exhaust side. * Among oval heads, Dart heads are middle-of-the-pack for intake at lift below 0.3, but after 0.4 they are clearly in the lead, and have the best E/I ratio because they’re really good on the exhaust side. The Dart heads reach 300 cfm intake flow at 28” of water at 0.550 lift – that is, at about the max lift that plan to run. * Among the oval heads, the GMPP heads are probably all-around second to the Darts (surprising!). * The Canfield and Merlin VR heads have similar intake flow at 0.4 and lower; then the Canfields pull ahead. Both are superior on intake to all the oval port heads. Canfield is also the hands-down winner on exhaust, where the Merlin VRs are mediocre. Not included in the original CHP series were the new AFR BBC heads (available only with rectangular ports). But a recent article in Hot Rod and AFR’s web site give some data for the 305cc (or rather 315cc) head. Unfortunately it’s apples-to-oranges, because these heads were CNC ported. With that in mind, the AFR heads were amazing, reaching 300 cfm intake flow at 0.370” lift, with the best E/I ratio (for 4.5” bore). At this point, if I choose aftermarket oval, the choice is Dart. If I go rectangular, it’s Canfield or 305cc AFR. The sentimental favorite is AFR. First question: what is the potential of my 346236 heads? If I spend some time porting them, and have 2.25/1.88 valves fitted with a good valve job, what hope do they have of supporting 500 hp with the above-mentioned conditions and, say, a .550” lift flat-tappet hydraulic cam? By gut feeling is that money spent on getting these slugs to “perform” is money wasted. Second question: should I limit my choice to oval heads, as the local engine builders recommend? This is a relatively low-rpm engine, and I do want the low-end torque. But in the big block world, mine is a very light car, and it is deeply geared. Third question: why are Canfield heads so rare? Do they have some hidden flaw that racers know about, but don’t divulge? Fourth question: the Dart heads really wake up at large valve curtain areas, despite having among the smallest port volumes (and hence port cross-sectional areas). My guess is that there’s a big loss due to separation at the “pocket” just upstream of the intake valve seat, so that even at moderate valve lift the flow past the seat is not attached (low discharge coefficient, so to speak). Does this imply that pocket porting would really improve these particular heads – more so than their near competitors? Fifth question: I think that there are reasons (consequences of secondary flow) why oval-shaped ports should flow more “cleanly” than rectangular-shaped ports, when normalized to the same flow rate – especially for “wet” flow (carburetor). So then why is it that maximum-effort race big blocks are based on rectangular-port heads, instead of very large oval-port heads? And by the way, how can I post the Excel plots with the port flow data?

I’ve made some front-end modifications to my ’78 280Z that preclude the reinstallation of the stock headlights in the stock location. The likely new location will be in the grill area, where 280Z’s normally have the front amber parking lights. Assuming, for the sake of argument, that such an installation is legal and all that, I still have to make the choice of whether to attempt to install the stock headlight assemblies, or to switch to a set of those compact headlights, such as the high intensity discharge units that have recently become popular (unfortunately, with rice boys). Does anyone have experience with such lights? They’re the ones that are around 2” in diameter. Are they strictly for auxiliary lighting, such as fog lamps and the like, or can they serve as the primary headlights in a “streetable” car? I am referring to a pair that costs maybe $50, not the $600 stuff that was briefly discussed on the forum last year.