Michael

I forgot to mention - that photograph is on page 50.

Brian Long’s book, “Datsun Z: Fairlady to 280Z” (Veloce Publishing, 1998) has a photograph of a 240Z in a wind tunnel. The car is tufted – a crude but often effective way of visualizing the near-surface flow. In the immediate vicinity of the hood lip the tufts show local separation. I’m surprised to see that only a few inches downstream, the flow appears to reattach. Reasons for this might be (1) the car is raised way off the test section floor - a very bad idea; (2) the engine is probably not running, and the flow through the grill is not realistic; (3) wind tunnel free-stream turbulence acts to hasten reattachment behind the hood lip.

Oddly enough, the 240Z was tested in wind tunnels, at least from what I can tell. I have a coffee-table book on Z history, with several pictures of wind tunnel tests. One can only conclude that either there was something wrong about those tests, or the Z’s aerodynamics were knowingly sacrificed for better looks. Regarding the former, I’ve seen a photograph of the 240Z in a wind tunnel test section, with its wheels on pylons off the tunnel floor. And probably that tunnel had no boundary layer splitter/suction upstream of the test section. Two things are wrong here: moving the car away from the floor or ground plate will give a completely wrong result in terms of ground effects, and not sucking the tunnel boundary layer will throw off the data regardless, because the test section isn’t getting clean, uniform air. This winter I toured the 9-meter low-speed wind tunnel in Ottawa, Canada, where they do a lot of NASCAR-type testing. Roush Racing had some full-scale models. In fact, they were actual race cars, with the engines removed and tufting added to the bodies. Technicians would roll a car into the tunnel, take data, then roll it out and replace it with another one. Anyway, in that tunnel, the car sat on a turntable flush with the tunnel floor, but there was a giant boundary layer suction lip upstream of the test section. Underneath the turn table was the balance, which measured lift (or downforce) and drag. A technician showed me two nearly identical cars, but with different-sized bulges over the front fenders. Evidently the car with the more bulbous fenders was for more downforce (shorter tracks, tighter turns perhaps), while the car with the more gently curved fenders was for lower drag (probably for tracks will longer straightaways). Anyway, the point is that a bad wind tunnel test is no better (and maybe worse) than no test at all, while a good wind tunnel test can reveal things that completely slip one’s intuition.

It IS possible to do a big-block swap without completely dispensing with the unibody and building a custom chassis. But it is essential to extensively reinforce the body. In my big block swap, the notional structure of the unibody was retained, but the car was split into three pieces: front clip, firewall/trans tunnel/floor, and everything else. A cage was welded into the “everything else” portion, and then the car was reasseumbled, with the firewall set further back. That involved a lot of custom bending of sheet metal into compound curves, and welding multiple tube intersections in tight quarters. Some drag-only cars achieve reasonable traction without worrying about engine relocation aft of what’s possible with the stock firewall, but those cars are all back-halved, with tubs, solid rear axles and 4-link suspensions. My car retains the stock rear suspension components (for now), though the suspension pick-up points are extensively braced. So basically the choice is: build a street/handling car with the stock or sorta-stock rear suspension, but heavily rework the front and be very wary of weight distribution; or back-halve the car. In either case, you’ll need a pretty stout roll cage. That was for a 280Z, not a ZX. In a 280Z, Chevy big blocks fit between the stock frame rails if you use block-hugger headers and slightly notch the passenger-side rail. Steering linkage clearance becomes an issue – in my car, the steering shaft passed through a hole in the driver’s side engine mount structure. If you build a custom chassis, with custom floor, transmission tunnel, and everything else, the choice of vehicle on which you base the “swap” is largely immaterial. By the way, recently there were links on HybridZ to an ad about a big block ZX, and another about a full tube-frame 280Z. About 5 of us here have big-block swaps in varying stages of completion. Most successful are/were Brad Barkley (Ratsun) and Ron Jones. Mine is the only big block swap that I’m aware of, which retains the independent rear suspension. I drove the car very briefly about 3 years ago, but the engine ate its cam after 20 miles of driving. Since then, the car has been sitting. A few pics are available on Pete Paraska’s site.

Ilkhan, As far as cost, if you avoid the “while I’m at it syndrome” your $8K figure is reasonable – assuming that you do the actual swap yourself, body work is kept to a minimum, and you don’t include the cost of tools. You might spend more, or less, but if your budget can stomach $8K without excessive indigestion, you’re reasonably well set up for undertaking the V8 swap. The debate on 240 vs. 280 will never end (and has been the subject of many threads here); lighter and more svelte vs. stronger and more robust, etc. If you’re in CA, it’s worth holding out for a 240, because the smog situation is much easier for the 240’s, and 240’s are still available without a huge premium. Elsewhere in the U.S. the 280 is the more likely choice.

My ’78 280Z started out in life as an automatic. It now has a Doug Nash 5-speed. I retained the original pedal box, but added a clutch pedal from a parts car – a ’72 240Z. The brake pedal pad on automatics is wider than on stick-shifts, and the curvature of the pedal arm is slightly different. The brake pedal from the ’72 240Z – which was a stick-shift – didn’t fit. So, I reused the original brake pedal, but cut off ~1” of the pedal pad from the edge nearest to the clutch pedal. THe resulting arrangement is a bit awkward, but it works, and didn't involve much modification. A 280Z with no carpet, no spare tire and no front bumper – but otherwise stock – should weigh around 2700-2750 lbs empty, if it still has A/C. ’75-’78 weight is approximately the same (+- 50 lbs at most). It’s hard to really trim down a 280Z unless you start tearing into the sheet metal.

The metalwork looks clean and solid! But since you asked us to "be honest"... one thing that's worth considering is welding a 1/8" plate over the stock frame rails underneath your motor mounts. The mounts themselves are plenty strong, but without reinforcement to the frame rails, the bolts passing vertically through the frame rails might work themselves back-and-forth, eventually tearing the sheet metal.

The simplest swap is to do no swap at all. No, I’m not trying to be facetious – just realistic. If you’re completely new to Z’s – and evidently, to major automotive undertakings in general – the soundest advice is to spend $2000-$4000 on a 1971-1973 240Z (1970’s are too expensive) with minimal rust and good working condition. Don’t go cheap – avoid the $600 Bondo special – because that will cost more in the long run. Spend more upfront, for a car that’s already decent. Drive that car for several months, if not longer. Learning about the car’s strengths and weaknesses will be far more natural once you become an owner. Then commence with minor modifications, such as suspension and brakes – things that can be done over one weekend, ideally. Take the car to the local racetrack and participate in “test and tune” night. So what if it runs 18’s in the quarter mile? – at least you have established a baseline. At that point the decision to swap engines would become a tradeoff of price, preference in torque delivery, drivability characteristics and other practical factors.

Most Craftsman lawn/garden power tools are rebadged imports. Jackstands and jacks - at least, the lower-end variety - are made in China. I have a cheapo Craftsman hydraulic jack that "gets tired" after holding up the car for a minute or so. My Craftsman electric die grinder is moderately effective, until vibration loosens the 4 screws that hold the motor housing to the driveshaft housing. I've had the best luck with Milwaukee eletric power tools - but they are expensive. But my Craftsman hand tools have been holding up well - except for that screwdriver that I cracked in half, when trying to pry off a pump fitting.

To somewhat redirect the discussion... how much does the S2000 engine weigh, with its various accessories, emissions system, etc.? I’m asking the question somewhat rhetorically, because it seems to me that a modern engine strong enough to survive 9000 rpm would need a beefy block, and those can’t be particularly light.

So one has to wonder why all the emphasis on power vs. displacement; why racing organizations group cars based on displacement, why governments tax engines based on displacement (as opposed to, say, horsepower), why bench-racers focus on hp per cubic inch. “It is what it is” certainly summarizes the fact that our little discussion here won’t change the world. But despite that fact, there is merit in discussing whether hp vs. displacement is or is not a relevant measure of efficiency and engineering prowess. I just think that it’s a case of a excessive devotion to a tradition.

By the way, Z-car aerodynamics, underbody tunnels, spoilers and airdams, explanations for the Z exhaust smell inside the cabin, and so forth, come up several times a year on HybridZ. In keeping with the "search before you post" theme that's come up recently, I thought I'd find an earlier post on aerodynamics books, paste the link, and write some smartass remark about the benefits of doing a search. So I tried using the "search" function myself, to find my own posts on aero stuff and recommendations for books, but the posts that I was trying to find didn't appear, despite some effort at keyword creativity. In the end it was easier to write a new post than to attempt looking for older ones. My conclusion is that there's something wrong with the search function. It's not the silver bullet that some people purport it to be. Perhaps all the more reason to work on a FAQ?

Pete - thanks for the advertisement, I suppose.... A pretty decent book on automotive aerodynamics is "Race Car Aerodynamics: Designing for Speed", by Joe Katz. Have a look at the reviews on the Amazon web page for the book, at http://www.amazon.com/exec/obidos/tg/detail/-/0837601428/qid=1060638949/sr=2-1/104-9123135-2731961?v=glance&s=books . I wholeheartedly agree with the review at the bottom of the page: the book tries really hard to cover as much as possible, but is too watered down for engineers, too long-winded for "laymen" and doesn't give enough practical advise for stock-bodied cars (sedans, coupes, etc.). But I did say that it's a pretty decent book - because books on automotive aerodynamics are rare. Another choice (but out of print) is "Automotive Aerodynamics", by A. Scibor-Rylski; Halsted Press, 1984. He gives a 1970's perspective on the downforce revolution and the OEMs' sudden realization that maybe drag does matter. A short and refreshingly cogent older (1965) article on downforce and spoilers is the SAE paper 650135, “Some Considerations of Automobile Lift and Drag”, by Joseph J. Cornish. I have a copy. I'm not sure about the copyright issues, but perhaps I could mail hardcopies if you're interested. To summarize the problem of automotive aerodynamics: figuring out what the air wants to do in going around cars is MUCH HARDER than figuring out the comparable problem for airplanes! Airplanes are streamlined, with smooth walls and large length to width ratios. They don't fly very near the ground, don't have spinning wheels in flight, and modern airplanes don't have giant radiators sticking out in front of them. This is why airplane design is an established, mature science with nth decimal-point accuracy in most cases, but car aerodynamics is still largely a try-it-and-see effort. And why solutions for cars tend to look very different from solutions for airplanes. Example: rear spoilers that look like inverted airplane wings generally don't work well for sedans and hatchbacks, because of the "dirty" flow behind the passenger compartment. Neither does a big wing necessarily mean big downforce. NASCAR-type upturned spoilers do a reasonable job of downforce and slightly! reduce drag (but that depends greatly on the spoiler size and angle, of course), and they look nothing like an airplane wing. Solutions found by trial-and-error by well-funded racing teams will be superior to latest-and-greatest innovations based on speculation. So there's no shame in copying a 30-year-old design like the BRE spoiler and airdam, especially if you're starting out with a stock street car and you are interested in a little firmer steering feel and less wandering at 100 mph. Whatever you do, don't slap on a radical body kit, expecting sudden improvement! Use an incremental approach - making small changes one at a time, and documenting your results.

GeorgiaZ, I have similar problems on my 280Z, though I didn't get the exact measurements. Front left and front right camber settings differ by about 2 degrees, rear left and rear right also differ from one another by about two degrees, though in the opposite sense. And now that I look at it again, the rear tires have substantial toe-in. After some discussions when I posted about this last year, the consensus was that either the chassis was somehow bent or the steering crossmember was skewed off to one side. Then I disassembled the suspension on all 4 corners, and found that the McPherson strut assemblies on the front right and rear left corners had incorrect kingpin inclination angles (not exactly the correct term for a McPherson strut - I refer to the included angle between the strut housing axis, and the spindle axis). The problem is entirely with the strut assemblies, NOT the unibody. Since then, I have been looking for parts-cars from which to grab stock suspension pieces. To-date, I've seen that many, many Z's have similar problems - and I surprised that more folks on this board haven't reported such problems.

The causes of the Z’s aerodynamics problems (lift, high drag) are multiple and in my considered opinion, can not be entirely “fixed” unless you are willing to undertake extensive sheet metal modifications. In the front, the the g-nose does help somewhat, but its curvature was designed more for aesthetics than function. Your idea of smoothing underbody flow is conceptually a good one, but keep in mind that proper design of venturi-type ducts requires consideration of pressure recovery, crossflow inside the duct, entrance and exit conditions, transient effects, .... It can be done, but you need to think of the entire vehicle configuration – and that’s best done with a clean-sheet-of-paper design. I recommend following the original BRE-type approach: urethane air dam in the front, small upswept spoiler in the rear. Each sells for around $100 (for example, at Motorsport). Those two pieces are the 70% solution for street-driving purposes. For all-out racing, the modifications will be driven more by class rules than by optimal performance. For getting better steering feel in “exciting” street driving, seriously consider those two parts.

Alternative discussion: when the exhaust valve is fully open, the static pressure just downstream of the valve is some number larger than atmospheric pressure. At the exit of the exhaust pipe, the static pressure is atmospheric. The difference between the two numbers is the back pressure. That difference results from restrictions and friction losses in the cylinder head exhaust port, the headers, the exhaust pipe, muffler, etc. The issue of whether “some small amount of back pressure actually helps low-end torque” keeps going back and forth. David Vizard makes a convincing argument in his books that zero back pressure is the best back pressure. What helps low end torque is exhaust scavenging (pressure pulses in certain portions of the exhaust system dynamically assisting the emptying of some cylinders) – something that’s lacking in open headers. In other words, an exhaust tract with zero backpressure also has zero opportunity for exhaust scavenging, so tolerating some back pressure is a necessary evil in order to allow for exhaust scavenging.

I think that the best reasons that one may wish to deviate from the JTR mounting scheme are (1) to obtain even further engine setback, and (2) to mount the engine directly to the frame rails, rather than to the steering crossmember. The latter is especially useful if you plan to frequently mess with the front suspension, where you would no longer have to worry about the engine mounts if you remove the steering crossmember. As for further setback, well, some situations may not necessarily benefit, others could use all the rear weight bias they can get; for example, if the engine front accessories can’t clear the steering rack. If you’re willing to dent/cut/reshape the firewall to accommodate further setback, welding doubler plates to the frame rails and then welding mount bosses to the doubler plates is a natural solution. In my case, the setback is especially aggressive, and the mounts sit approximately at the location of the tension/compression rod inboard ends – that is, locations where the frame rails are already reinforced.

Johnc, Regarding my earlier post - the idea was that since engine power to displacement ratio decreases rather strongly with increasing engine size, the larger engines appear to be less “efficient”. In going towards larger displacement, engine power to weight ratio generally also decreases, but much more gradually. So when comparing power to displacement, the smaller engines look tremendously better, but when comparing power to engine weight, the smaller engines look only marginally better, and in some cases (such as for older cast-iron inline engines in compact sedans, vs. cast-iron V8s of the same era) no better at all. Since the car itself doesn’t care about engine displacement – it only cares about engine weight, support accessories’ weight, and hood space – one has to wonder why power-to-displacement has become the standard metric of efficiency. And of course these various comparisons are apples-to-oranges, because given the trends in manufacturers’ philosophies, the smaller engines will have technical innovation on their side. In the typical modern OEM street application where accessories such as air conditioning and power steering have come to be considered essential, the larger displacement engines have an additional advantage: big engines do have bigger and heavier accessories, but not by much. The starter, alternator, water pump etc. in my 454 aren’t much bigger than the corresponding stuff for the 2.2L L4 in my 1974 Toyota Corona, just to give one particular example. So the difference between “bare” and “fully dressed” – for the larger engines – is less that it is for the smaller ones. Wringing out high hp numbers from a small-displacement engine is impressive, but not necessarily meaningful, for street applications. I wish that OEMs such as Toyota and Honda would apply their prodigious engineering resources to design large-displacement, low-rpm, thinwall-casting aluminum V-block (not necessarily V8) engines. But that just won't happen, because such an approach would contradict these manufacturers design culture.

I’m with Petew and Drax240z: the lens is the heart of any camera (well, maybe not pinhole cameras), and a point and shoot can’t compare to an SLR. Lens interchangeability, through-the-lens metering and through-the-lens viewing (especially important for close-focus photography), provision for remote flash, depth of field preview (very useful for technical photography, such as documenting Z construction1),.... But digital SLRs are still too expensive. In the 35mm film world, you can get a decent SLR body and a single-focal length 50mm or 35mm lens for around $400 from one of the mail order stores based in New York City (look in magazines such as Popular Photography). But digital SLRs are still $1500+, from what I've seen. My experience with film point and shoots was that the single-focal length cameras are superior, such as the Yashica T4 or the Olympus Stylus Epic. The Epic has a max aperture of 1:2.8 – very nice! P&S zooms run into severe problems at the longer focal lengths – principally, very small aperture, and all sorts of aberrations. I have not, however, been able to find any single-focal length digital P&S cameras (I mean NO optical zoom at all). The other problem with most digital cameras is “latency” – press the shutter button, and the camera fires after a delay, instead of “almost immediately” (in my Nikon N90s, it’s something like 40 milliseconds, if I recall correctly; maybe even less). That makes it difficult to shoot action shots, or to shoot in low-light situations, where you relax your stance after you think that the shot is over, and allow the camera to move – but it hasn’t taken the picture yet, so the result is blurry.

This brings up an interesting point: we typically compare engine efficiency in terms of power produced vs. cylinder volume displaced, or overall vehicle efficiency in terms of miles per gallon. But we know that vehicle acceleration depends mainly on power to weight ratio, and that for performance cars, a large part of overall vehicle weight is the engine and its supporting systems. So why don’t we normally compare engines in terms of power to engine weight? Large-displacement engines are not necessarily very heavy, while small-displacement engines aren’t necessarily light. Broadly speaking, you get more cubic inches per pound, so to speak, from a huge V8 than from a tiny L4. A 400 cubic inch engine probably won’t be 4 times heavier than a 100 cubic inch engine – in fact, the ratio may be closer to 2:1. So in terms of engine power to weight ratio, that lumbering low-tech cast-iron V8 doesn’t look so bad any more. I’m baffled by the concept of taxing displacement in addition to (or instead of) taxing fuel. Is a temperamental, high-revving small-displacement engine – making 20 mpg in vehicle XYZ – any more environmentally friendly than an engine in a lower state of tune, that displaces another liter or two, but weighs the same and gets the same mpg? Taxing displacement drives manufacturers to more complex designs, raising costs and reducing reliability. I wonder how things would have been different if Toyota and Honda built cast-iron, pushrod V8’s with 4500 rpm redlines. Those things would run for maybe 2 million miles, and go 100,000 miles between oil changes.

I overlooked in the above post.... replace the missing side of the box with a diagonal tube....

A surface panel is not necessarily acting as a shear web. Consider again the box (cube) example: remove one of the six sides, and the formerly stiff box is now weak in torsion. Katman, I have no experience designing competative race cars, but I've had the opportunity to dabble a little in airplane design here and there ... just a little. Monocoque structures are always reinforced with judicious selection of stringers, ribs and bulkheads. A stress-bearing skin and a tube structure underneath are complementary partners; they do not obviate one another. It is unfortunate that in most amateur automotive racing classes, and many pro classes, the "body" is just a shell, carrying aerodynamic loads but not suspension or drivetrain loads. If, in a street-type car, the "body" is the stock metal unibody, then indeed the resulting "tube frame" chassis will probably weigh more than the original OEM product ... all else being equal etc. etc. But more careful design practice allows one to lighten the unibody while compensating for strength with tubes. Assuming that intrusion of the tubes into the cabin is acceptable. Regardless, let's not argue about what's a monocoque chassis.

I used to have a '87 MKIII turbo Supra. Yes, they do weigh around 3600 lbs, and yes, they are pigs. I took it to Pomona Raceway once. My time was 15.9 @ 86, but by that time the turbo boost was down to around 5 psi, maybe slightly less. And did I mention that these cars are unreliable, especially considering Toyota's overall reliability? Head gasket blew at 89K miles, was showing signs of incipient failure again at 115K miles, at which point I sold it. The Supra was trying to be both a luxury coupe and a sports car; it largely failed at both.

Spiirit, Are you planning on a big block for your Z? Hmm..., that would bring the BBC total on this list to around a half dozen - perhaps time for an additional forum?

Speaking of revolutionizing the industry – why don’t cam manufacturers alter their present practice, and start grinding the cam dot 180 degrees away from its current position?