zredbaron

First of all, wow, this is a wonderful thread Josh, thank you for the tremendous time and thought you've put into this, and to all who have contributed. I've come a long way over the years thanks to HybridZ, but I'm still learning, and like many of us have an insatiable thirst for maximum performance, both theoretically and practically. That said, I'm just stumbling on this thread now, and my big-picture conclusion with the mythical JDM 400hp dragsters is that they're more hype than hope. I don't doubt that they may edge more ultimate hp out than our own L6s, but agree our road racing and autocross engines are built for area under the curve. I would have to see their engine on the dyno right after I saw an established engine on the same dyno, same day in order to believe 400hp with gasoline @ 12:1. It's too good! That would be nearly 130 hp/L! The Ferrari Enzo produces 110 hp/L with similar fuel/compression at 7800rpm. I just don't see the VE of 2 valves per cylinder with carbs and premium gas going against an Enzo's VE. Need to see that one in person, or hear from those who have. I agree with others that have defended the reasons development goes in certain directions or doesn't. ZR8ED, had some great VE comments, concur. Ultimately I would never want a JDM motor for a bunch of reasons, but this isn't about that. Yet. For shared knowledge purposes, I'd like to point out how similar my Jim Thompson / Sunbelt head is to some of the JDM head info you compiled. We agree power is made in the head, so let's start there. To my knowledge Jim no longer does L6s but works on BMWs. Sunbelt no longer exists, but merged with Kinetic Motorsports. I feel no moral obligation against sharing my head's information; I bought the head, I bought the cam. I'm allowed to share what I know about it if I want to, maybe other members with fancy heads from shops other than Sunbelt feel the same way... Disclaimer: I'm someone who got incredibly lucky and fell in line about seven years ago behind JohnC, who paid for serious R&D for his N42. I'm not an engine builder, however I do have some data about the E31 head Jim built for me. Also, I know there are other L6s builders out there, and I nothing of how they build heads or cams. Just sharing the one I own. And a lot of hot air. HEAD: -early E31 in style of JohnC's N42 -37cc chambers -44mm/35mm valves -pictures of ports below, very different around valve guides -208/134cfm in/ex @ .565" lift (recently tested, no details on bench) -202/145cfm in/ex @ .525" lift (according to Sunbelt as shipped, Flow Prow bench) Also according to Sunbelt: "200cfm on a Flow Prow bench is 225cfm on a Super Flow bench." I know nothing! These pics are from 2004 when I received the head from Sunbelt. Note how different the combustion chamber shape is (E31 head) with similar cc numbers. Also note how different his valve guide approach is. I also add that this cam is designed with a single set of springs (outer only) whose length is between that of typical inner and outer springs. This cam is profiled specifically for these springs and uses 25% less seat pressure. Or so I'm told. So that's a variable. Also note the texture isn't shiny. It's my understanding that polished actually increases surface friction, and a slightly textured surface has less drag (head loss) along the surface of the ports (dimpled golf ball effect). I'm surprised the JDM heads are so shiny. (Seems to me the old SSS / Nissan Competition valves were "swirled" for this very reason.) Okay so obviously the main difference thus far is port profile, texture, valve size, valve guides and peak flow numbers. And seat pressure. Lol. Isn't that just about everything except the cam!? .530" lift isn't necessarily so small if your entire engine is tuned for it... JohnC had .534" lift, Dan Baldwin had .550" lift in respective posts in 2004. Both Sunbelt-built, both powerhouse NA L6s. It isn't size that always counts, it's what you do with it. Or so I hear! Definitely not true with my tires! Contrarily, I had .525" lift in a head built by Jim, and I only put down 195 whp at the time. Street performance intake and exhaust, street compression, poor fuel, etc. Rebuilt in '08 to 12:1, race cam, maxed-out 40 DCOEs, and race fuel and put down 264 whp. Still more out there. Same head all along. Tune, tune, tune. For *your* head, for *how* the car will be used. my 2nd Sunbelt cam: .565" gross lift (Arbitrary? Nope! More on lift vs. flow below.) seat duration is 326º/315º .050" duration is 290º/275º lobe separation angle 104º Torque from 3500-7000 Power above 4000 (up to 7700, outer spring advertised maximum). Asymmetrical lobe, 104º separation. Note that the exhaust lobes are more asymmetrical than the intake. Has nothing to do with minimizing overlap; it's just to sound cool. (Haha!) I really hope this doesn't upset anyone. There's so much more to cams than basic specs. Any attempt to replicate would be a fail as far as I know. I say 2nd cam because the head originally was originally delivered with a cam with .525" lift and 290º/275º total seat duration. Hmm. I also very recently had my head flow tested. Different numbers than what Sunbelt provided (more on that in a bit). Here's a graph from the numbers I have this go-around: Note that for Jim's port/polish, there is a diminishing lift performance between .550" and .600". Again, no coincidence, .565" lift peaks the flow chart. I'm not saying Jim Thompson is the only one who has built a head/cam this well tuned, but I am saying that it's been done on this side of the pond. Just not with their oversize++ valves and somewhat radical headers. I would LOVE to know more about Dave Rebello's heads. I'd love to see pics of the ports, cfm numbers vs. lift, cam selection, etc. Suspension knowledge isn't proprietary, why does engine-building have to be? People are still going to go to well-recognized shops and order race motors to be built. EXHAUST. I honestly don't see how exhaust can come anywhere near supersonic speeds, no matter what kind of nozzle you create. But damn, look at those headers! Haha! I mean look at the damn things, they look like a waterpark ride! Our race primaries are mandrel and equal length too, so what? When I saw the octopus headers my first thought is that they appear to have fairly equal angular-distanced primaries, too. (Total degrees of bending each pipe does, at the same radius even.) This allows about as equal / laminar flow as one could hope to achieve comparatively between six primaries. I'd like to have equal angular distance in my own headers, even if just for my own warm fuzzy, but I really don't see it making much difference except for WOT at higher RPMs. I have yet to read an in-depth explanation of *why* 3-2-1 has better scavenging/torque than a 6-1. While the 6-1 might theoretically out-flow a 3-2-1 (less friction / head loss), the 3-2-1 will out-scavenge the 6-1. The only in-the-weeds thought I have is that in the 3-2-1 design, only 3 cyls are shared for a given collector. As the pressure wave reaches the merge point of these primaries, it sees a junction; an big pipe turn going the same direction down a 2.5" pipe AND two sharp u-turns backwards up the other two primaries toward the head. As the wave propagates past the merge point, low pressure is felt behind it, which is felt upstream toward the two exhaust valves via the other two primaries. This low pressure is shared by the two primaries. In the 6-1 design, this low pressure is shared by 5 primaries. 5 primaries, 4 strokes, you do the math... sometimes two valves are open vice one. It can't possibly scavenge as well in my mind. (I totally admit that I'd have to track out the 4-stroke cycle for all 6 cyls for verify the 3-2-1 setup never feels a pulse with two exhaust valves open. Not going to think that hard.) Torque, not power, is affected most by scavenging, right? Then that's it. Drag racing doesn't care about torque as much as power. Ultimate peak flow potential. An octopus header is a work of art for WOT only. Road racing cares about torque. Autocross does even more. The street even more. These Stahl header photos are courtesy JohnC. I believe in this pic they are 1 3/4" primaries (equiv of 45mm) for road racing applications. They run 45-48mm out there, we run ~42-45mm here for autocross / road racing respectively. Again, trend respective to how the motor is used. Note the three dimensional reverse-coning on the left collector. Looks similar to cyclone shapes on some household vacuums. Not to be confused with cyclones, this air isn't spinning, but note the gradual coning / venturi effect. Very nice. You can see these deliver two 2.5" collectors. I don't have it in hand yet, but JohnC is sending me a custom merge collector that sounds pretty damn cool (there's still one more merge with a 3-2-1 design of course). If I recall correctly, I wanna say it's a 20-degree merge angle (pretty steep!) where both 2.5" collectors merge to a single 2.5" pipe. At this point in time a pressure wave will scavenge the other collector tube, alternating strokes. Smooth. Then I think JohnC said it will even nozzle slightly (to narrower than 2.5") then expand to 3". He was very specific that this will be exactly 36"-38" or whatever it was from the exhaust valve. No idea why it was so specific, but I would theorize that it's the distance that draw torque out the most and was discovered experimentally. Perhaps he'll chime in. From this point on (i.e. the middle of a 3" pipe), the 6-1 comes back strong. It's an exhaust race! Haha. No, seriously. [in terms of transmitting a change in throttle position to the drivetrain, the 3-2-1 wins. In terms of ultimate WOT flow, the 6-1 wins.] "And they're off!" In the lead we have 3-2-1 that just seems to have been sucked away at tremendous speed by the previous stroke! It's hit a sharp bottle neck at this "merge collector" and now it's home-free with nothing but 6' of 3" mandrel pipe! 6-1 is way behind, BUT at this point from the exhaust valve both are traveling at the same speed (both are in 3" diameter pipe, similar displacement, similar head flow). The pulsing motor's exhaust is less dense (less time allowed for flow), therefore at steady state WOT, once both motors are up to speed, THEN AND ONLY THEN does the 6-1 design win the race. It has fluid density. The exhaust is traveling at the same speed as the 3-2-1 at this point, and it nears the muffler then it accelerates out. I have a theory for their velocity nozzle muffler, but I admit it doesn't quite feel complete. The revolver-style merge collector induces a rotation to the exhaust, right? Slightly cyclonic? Whirlpools flow faster than pulsing bubbles. Watch your bathtub empty itself and you'll see a whirlpool. They're whirl-pooling their exhaust, and this effect only takes place at steady state WOT... any transitions in throttle input will disrupt the flow enough to temporarily cause the flow through that funnel to be turbulent and run like crap. This ONLY would be applicable to a cyclonic exhaust flow, which would only be created from a 6-1 header with a revolver style collector. Again, I'm thinking this results in piss poor driveability / throttle response. One might argue that the exhaust is going one-way (whereas with a whirlpool, water and air are trading places), and that a whirlpool would therefore be fruitless. However, it's pulsing don't forget, so the air in front of and behind the pressure waves do funny things, especially when narrow, and just might be happiest to swirl and not fight. Like the air and fluid in this picture. Idiot check: what does Formula 1 do? Not a swirl! After their graceful merge collector, they aren't swirling -- they're in the weeds fishing for aero crap (I would argue that hot gases will only piss off their wings -- but aero is another discussion!) Back to the point, they're doing aero stuff, NOT spiraling their exhaust and funneling it out some magical orifice. Neither is NHRA. That's all the common sense check I need... a magic exhaust tip will not make my car go faster. If it would, you would see spiraled headers on Top Fuel dragsters that look like Dyson vacuums! That kind of thinking (tips will make me go fast!) is what gives JDM / RICE a bad name in the first place. And no Josh, that wasn't aimed at your theory. Basically I'm suggesting we have a comparable level of tuned exhaust performance they have across the pond; they are tailoring to peak flow/power and we are tailoring to scavenge for usable torque. Whew! Man, that's about as much hot air as I've ever typed. By all means, please put me in my place if I'm out to lunch! Found this video. Shows how much of a pig it is down low, as predicted, but god, does it that motor sound MAD! It's the red motor in the red S30 we've seen a few times in these JDM threads. INTAKE: Not much discussion, rightfully so. Pick the right intake to match the flow / usage of your head, tune it on the dyno, the end. BOTTOM LINE, they are too far in the land of diminishing returns for my wallet. No one would dispute that our autocross and road race motors' area under the curve would have a tremendous advantage over the JDM dragster, which is how we use them. Put their motor in our cars for our events and we'd get beat for a lack of driveability! Reverse is also true of course, we would lose at the drag strip. Note that the Kameari $6500 head claims 320hp, not 400. That looks like it has the potential to actually be a get-what-you-pay-for item, unlike the hardware. I'd like to know what Kameari claims that head, the one pictured, actually flows when delivered. Okay fine, this thread is about the engine, not its use. They only use their best ~3000rpm power band at WOT and that *is* their purpose. Fine. On dyno day add up the *area* under each engine's best 3000rpm band and compare them (peak too, why not). I would claim that percentage-wise, on the same dyno on the same day, there would maybe be not more than 5% better numbers on the JDM best vs. our best, whatever L6 that would be. That's my claim, maybe that's me being an American and defending our ways, but it's also my honest assessment with what I think I know at the moment. One of us would have to skip the pond to find out. Hats off to them for their peak hp achievement, though! And God, I loved the sound in the video of the red Z on track! Most people aren't willing to pay twice as much for a proven part in the search for that last bit of power. But hey, some people have too much money to spend. Luckily most of them go for "Porsh's." For the rest of us, I agree Tony D, send the money to a shop like Rebello and wait for a crate. Best option I see at the moment. Anyways, I'm rambling at this point and have probably embarrassed myself enough. I like my autocross motor, it's awesome. The end.

EDIT - post removed; it wasn't a complete post. Was supposed to click on Preview.

Somewhat related question: are pipe area and dB levels are related? That is to say, I would think that a 3" pipe would be louder than a 2.5" pipe. Would a difference in dB levels or tone also follow suit with the area? (If so, roughly by how much?)

Awesome, I bet you can't wait to go test it out on a track! Let us know when you do.

HAHA! I meant 3" long. It's length is the same as the diameter of the "straight" sections. Okay maybe it's 4" long. hopefully that's not what *she* said.

you mean to imply that 3" muffler in the video is the only sound deadening you have with your headers and your car is still that quiet? am I missing something?

Thanks for updating us. The LCAs are an expensive while-I'm-at-it addition! Sigh, I'm totally jealous btw... please upload pics of the link you shortened and of your final setup when able!

Thanks for the BSP engine swap allowances clarification, John. Heck, I'd say a "winning" S30 in any of the classes would be in the big-budget category!

You really should download the SCCA rules and read up on how cars are classed. Look up the class definitions for "Stock," "Street Prepared," "Street Modified," and "Prepared." http://cms.scca.com/...olo%20Rules.pdf In descending order according to expected raw time (current PAX): ES - E Stock (.825) BSP - B Street Prepared (.859) FP - F Prepared (.872) SSM - Super Street Modified (.875) XP - X Prepared (.887) PAX-wise, SSM is actually expected to put down a faster time than FP is. SSM and XP are the "wrung whatcha brung" classes that pit all productions cars against each other regardless of letter class. You will fall into these classes if you exceed any class defintions as outlined in the .pdf above. You could also consider this the "ascending budget" list, too. FP and SSM are arguably comparable budgets, depending on what kind of car you create. Read the SCCA Solo Rules, and *THEN* make a class decision based on budget, personal desires, etc. It's expensive and competitively frustrating to do it the other way around like I did.

Haha, sort of! The reason we're talking about this other stuff is the racing variable, in which classing is law and therefore motor choice is crucial if you want to run in BSP or FP. And Jon, I agree with you about a purpose built S30 being able to dominate XP. My times are rather middle of the pack in XP (Wash DC). Mine will never dominate of course, because I won't cut the fenders. If I ever decide that competition is more important to me than "building my dream car," then I would make it my life's purpose to chase national S30s. In the back of my mind, I honestly don't know what's more appealing, a tuned FP, or an XP L6 monstrosity. That said, however, I'm also under the impression XP is fairly up for grabs right now. That is to say, the class is new enough that no one has truly built a car to the class' potential yet. I didn't go to nationals, though, just regionals. I agree with Gollum with everything he said about setup dial-in being most important with getting your car to handle, not weight distribution / balance. Engine weight is not a factor in my mind, I shared my numbers to further quell misplaced concerns. I would point out though, that swapping a non-model specific engine will automatically kick you to SSM or XP in autocross. Sure, you might have a cheap, reliable engine with plenty of power, but SSM and XP expect you to put down some very fast times, and therefore whatever money you saved under your hood will now have to go into getting a 40 year old car to keep up with a highly modified Z06 on slicks 345-385mm wide. Not gonna happen. Cheapest reasonably competitive setup would be a BSP L6 with SUs, headers, electronic ignition, coilovers, camber plates and call it a race car! Stock brakes are more than enough for autocross, especially at the BSP level. Either that or build your dream car and don't worry about it. Those are your choices with autocross!

off the top of my head, last time I checked official SCCA classing, 3000cc displacement is the magic detail. basically if you don't have a stroker, any Z engine combination is allowed up to 3.0L for both BSP and FP. basic [national] SCCA classing and allowable mods for S30s (other than stock): BSP - suspension, seats, camber plates, electronic ignition, etc SSM - BSP allowances plus > 3.0L engine, turbo, V-8, composite hood, etc. FP - full slicks, significant weight reduction, chassis stiffening, fender flares, etc. XP - FP allowances plus > 3.0L engine, turbo, V-8, etc. Well setup S30s dominate FP at the national level. They won't make the cut in any other class at the level. FWIW.

Good replies. As others have stated, the 240Z is fairly well balanced right out of the box. Any coilovers would allow you to corner balance the 240Z very easily. My autocrosser (early '71) has a 50.1% front weight bias and 50.0% corner balance @ 2300 lbs (including driver) with 5 gals in a stock fuel tank, composite hood and hatch, lightened seats and battery. Stock dash, R180 diff (slightly forward, in the early 240Z style). If you honestly believe you will want to autocross your Z, I highly suggest you familiarize yourself with SCCA classes if not already an autocrosser. It doesn't take many mods before you're in a "wrung whatcha brung" class (either the street legal SSM or dedicated racecar XP classes) and are expected to beat all production cars in your 197x Datsun, which would/should never happen. The 240Z isn't out of place in the BSP class, but won't quite keep up with the S2000s. The 240Z can dominate FP, but that is a very regulated race car class. My 2 cents, turbo cars are less than ideal for autocross. You'll have to end up leading your throttle inputs to keep the turbo spooled and torque at the standby, I don't care how minimal the turbo lag is. Power isn't everything, it will likely take years before you can keep pace with a 135hp miata driven well on DOTs. Around 200 whp, in my experience, the 240Z will have more power-to-weight than an autocross course will allow you to put down to the floor (on 225mm DOTs, anyway). The point of all this is if you are going to autocross your Z, then I suggest you accept very early on that you may never, ever dominate your class as you might hope. If that's the case (as it is for me!), then in the end you won't care what class you're in over your head in -- you will simply love your car and have a blast driving the piss out of it. If that's the case, then figure out what ultimate 'HybridZ' gets your blood boiling and work toward it!

logan1, How do you plan to use the car? For me, this is the most important question, one that experienced people have asked me, and I didn't quite take their tone literally enough (at the cost of my wallet). Daily driver? Sunday hot rod? Race car? Why the 240Z? I stuck with the L6 because I fell in love with the motor before I ever fell in love with the car. I've since been addicted to two things: the sound and feel of a powerful NA L6 under load, and the competitive thrill of autocross (motorsports in general). Sure, I would be more competitive if I chose a different vehicle or cut my car and put big tires on it. I love my Z and its motor enough to outweigh the desire to start over in a car more appropriate for its class, so I improve what I can and enjoy both addictions.

Too bad this thread can't be separated into both a triple carburetor theory thread and a triple carburetor tuning thread. (The forum is 21+ freaking pages long, haha! Hard to sift through that many pages for something you remember being in there.) Anyways, the following is posted in a performance thread and the discussion also belongs in this thread as well. Topic of discussion later shifts to various sizes of header primaries in an all-out autocross motor application: So although I don't yet have any data per se, I thought I might revive some of the theorists and offer that the plots "are coming." For what it's worth.

Reporting back on my findings: 1 5/8" header primaries are the consensus. 1 3/4" primaries are for road race motors -- for autox, drop the diameter 1/8" to gain some low[er] rpm torque at a slight cost of high rpm power. Encountered stern warnings that 1 1/2" primaries would severely restrict a ~300 hp (flywheel) motor's power output (my outgoing headers are rusty Monzas from 1999 - 1.5"?). JohnC was also able to set me up with a header merge collector, which evidently should also help mid-range torque a bit as well. In a related note, after reviewing Dan's recent comments on the A/F mix ratio, I wonder if I might be able to improve my A/F curve with a proper exhaust. I'm not expecting a cure of course, but I can't help but suspect a measurable improvement to the A/F dyno plot might result. Better flow out means less dirty gases remaining behind and therefore increased combustion as well, or so I'm thinking anyways. Hoping to slightly flatten the rich and lean peaks that will likely still occur. I'll be sure to post the dyno plots when the time comes. It will be interesting to note the exhaust improvement's effect on all three curves. Another year or two later of course, fuel injection. (Hey, this thread started 7 years ago, after all!) [ EDIT -- There will be one other improvement on the dyno plot (unfortunately for the AFR theory, but fortunately for performance). Remember the radical cam that was put in the motor in 2008? I've finally tracked down the springs the cam was profiled for (the outer springs only design, limited to 7700 rpm). Had to order the springs from Jim Wolf Racing, in case anyone ever has to track down outer springs for a Sunbelt/Jim Thompson cam, haha. Anyways, the proper pairing of springs to cams is of course crucial (probably even more so for aggressive cams), making the total of 2 dyno variables: exhaust AND springs. ] Also, my flywheel and clutch are toast. Going with the ArizonaZ 6-puck sprung disc setup. Seems to be a fair price for the quality, should be a good weight for autocross, too.

m1noel, your old rear sway bar mounts from behind your diff, right? would mounting it in front of the diff (like the early 240Z) be a viable solution? i've been eyeing those wolf creek cv kits myself. how do you like them? they look pretty stout. p.s. hi mark!

Thanks Dan. Makes sense to me! Going to stick with that theory until I make the jump to ITBs. Speaking of engine upgrades, I've got the engine out of the car again. Had a coolant leak (700 miles after rebuild in 2008), so I returned the whole block to the machine shop for investigation. I haven't seen it in person yet, but they found the coolant was leaking between cyls #1 and #2 and had to weld the head. Currently waiting for the head to return from another shop that has a flow bench set up for inline 6 cyl heads. (I wanted the numbers for future ITB diameter selection.) To the point, although I'm leaving the intake alone for this rebuild, I'm upgrading to the Stahl headers while its all apart. As previously discussed on this thread, two 2.5" collectors will merge into a 3" outlet, but Stahl offers a variety of runner diameters: 1 3/8", 1 1/2", 1 5/8", and 1 3/4". Any suggestions? Yes, the engine aspires maximum NA hp attainable, but let's face it, the car is a dedicated autocrosser at this point and drivability / low end torque are factors. I also want to keep in mind that fuel injection *is coming* and intake flow capability will match that of the head. I'd hate the exhaust to be a choke point down the road. Also, how do racers feel about header coatings? I'd love to hear everyone's thoughts!

guess i never finished this thread. got all busy with the car and forgot. so yeah, that laundry list of to-dos a few posts back? i got them all done, on time for once, amazingly. i was busy enough that i didn't really take any pics of the progress, either. oh, well. unfortunately the success came at the expense of my body. i literally was going to bed after 2-3am every night. the night before the car show, i stayed up all night. in the end it was worth it, the event was a lot of fun and my 71 was very, very well received. here are a few shots from the show (all the way back from May 1st!): i think this was a 260z. this 350 was the only other Z there that fancied itself a racecar. completely gutted. i liked the rear hatch braces. a couple more S30s the detail on some of these cars was tremendous! there were so many in immaculate condition. seriously, it was almost new. indoor car show lesson learned: don't place your car on the outskirts of the room. put it in the center, under all the lights. literally, if you stepped back and just looked at the show as a whole, you would never have guessed that my Z was just painted. (there weren't any lights behind it to show you the shiny.) here are a few shots from my entry: unfortunately the fluorescent lighting made it seem more like red-orange than just red. one of my favorite questions of the event: "THAT's your battery!?" thanks braille! this is one of the biggest eye sores on the car right now. one of the penalties of the car sitting in the body shop for 9 months was that the (brand new) block came back with rust coming through the paint for some reason. nowhere else. (the blue fades to rusty brown just to the left of the alternator in the above pic.) the event was a people's choice car show. i was hoping for the 'best paint' trophy, and didn't really think i was realistically in the running for anything else. my engine bay was filthy compared to show cars that have had frame-off restoration. my vent control panel and center console were worse off than most of the S30s there. my only other car show experience left me with the impression that blinged-to-the-max or 100% stock was the only thing people cared about at shows. this was somewhat true; very few people inquired about engine internals or any other performance upgrades. all preconceived notions were absolutely blown away when it came time for the awards. evidently there were a lot more silent approvals than i had any idea of -- i was absolutely stunned when they called me up for best of show. my only theory is that they liked that i made a car that actually gets raced almost as pretty as the 'real show cars.' literally, i was so unprepared for the possibility of winning that i regret not being more socially appreciative. next time. [assuming there isn't a race that day.] all tucked away back at home... after taking this pic, i went up to bed and passed out in the early evening. i think i was seriously starting to get a little delirious from the lack of sleep...

very nice. my searches thus far have found nothing, and this looks to be exactly what i was asking for. thanks john! looks like the price tag will also motivate me to finally get around to putting the previous parts up for sale somewhere.

really? mounts backwards? interesting. damn, i want one. i don't want to reduce my front ARB, that will will only exacerbate my roll issues...

ok, so i was looking for a skinnier rear bar, and was told that there was no OEM bar until late '73. that blew my mind!

...and i bet it runs a hell of a lot better! beautifully detailed engine bay. everything looks brand new! cool video, brings back memories...

if you keep upgrading your engine and neglect to also upgrade from your 40 dcoes, your jet selection will go odd directions. my overworked 36mm equipped 40 dcoes for example are fairly happy to be running 60f9 idles, 155 mains and 155 airs. in the colder months, it likes 165 mains and 145 airs. strange, but true. currently idles at 14.5 on the wide band, WOT varies from 12.5 to 13.5 from 2k to 7k, *assuming* i properly feather the throttle pedal below 4k. i consider this about as close as i'll ever get, so i call it done. (i won't ever again attempt to tune to WOT for all rpm bands. not possible in my application, it seems.) also, i found while tuning via wideband, i could actually tune to a specific gear. i theorize this was because the cold air intake w/box was actually receiving a small ram air effect. tuning for a higher gear (ie 4th) required a larger main than tuning for a lower gear. i thought that was pretty cool. since the car is a dedicated autocrosser, i tune it for 2nd gear. we all like to hear each others' triples get on it, this local autox video was taken just yesterday:

the "no matter what" part is just stupid. you can always select mains to match the venturis. you'd just inhibit the engine's flow (and therefore power) potential if your chokes are too small. case in point, your new engine out flows your old one. 40 dcoes in my opinion should only be used for entry level street performance L24s and L26s. any increased displacement / head flow upgrades require larger venturis to enable the increase in flow / performance. simply stated, your engine is CHOKING for air. there is minimal air, which calls for minimally sized mains to balance it. go to 34-36mm chokes and rejet. your mains will be more normal. if you want driveability, try the 34mm first. if you intend to compete with the car or just want the performance, go straight to the 36mm. the head you have probably can out-flow the 36mm chokes, but i don't remember what bottom end you have. if you have >= 2800cc block, with your new head i'd say go for the 36mm and call it a day. you have likely upgraded your engine into an under-carb'd condition. welcome to the club.

unfortunately, no. next event is an autox school in two weeks, and I hope to have either a skinny rear bar or a thinner front bar to play with that day since there will be no shortage of seat time. adjustable, of course. haven't had a chance to investigate into S30 droop limiting options, either.