Dan Baldwin

See Jmort's response. It's only at low rpm that you lose volumetric efficiency due to pushing intake charge back through the still-open intake valve. At higher rpm, "on the cam" as it were, the column of air has significant momentum and doesn't just stop and turn around past BDC, it continues filling the cylinder even as the piston is rising. You can actually get significant ram effect from this and with tuned intake tract lengths you can actually get over 100% volumetric efficiency over a small range of rpm. The specs I gave are at zero lash, I don't know what the specs are at .050". But yeah, it idles at 1000-1200rpm. Sounds pretty bad ass This is the only dyno chart I have for it, unfortunately the electronic 280Z distributor crapped out the night before the dyno, and I had to throw in my 240Z distributor, complete with POINTS. Breakup above 6000 is points bounce. Pertronix is in there now, pulls hard to 7200rpm rev-limiter

My original 3.1 build cost I believe on the order of $2500 for all parts and machine work. That was with stock head/cam/SU carbs, and made a killer street engine. The big hp builders were cam and head porting done by Sunbelt which I got a great deal on, and a used set of triple 45mm carbs. Total spent on those was also ~$2500.Random avoidable misadventures have cost me more over the years than the basic setup. I want to run as high a C.R. as possible while not having any issues with detonation running pump gas and being able to run at least ~35 degrees ignition advance. In *my* experience with the N42, I was able to run 10.25:1 with the stock (~.010 shaved) N42 and currently at 11.6:1 with further head shavage, porting, and minor bowl work and a pretty big cam.When the headwork was done ~9 years ago, the word from the guys who did it (probably about as knowledgable on extracting power from the L-series as anyone in the U.S. at the time) was that the N42 I had was as good (maybe better) a basis for a decent-hp N/A L-engine as the P-heads. The P79/P90 heads have been touted as allowing much higher compression ratios, and I have heard of people with N42/N47 heads running into detonation issues at lowish C.R.'s, but in my experience, I don't think the N42 is giving up much if anything in terms of C.R. vs the P-heads. Agree with running as high a compression ratio as you can get away with, adding that you still want to be able to run at least ~35* ignition advance. To me, though, you maximize c.r. *after* cam selection. You cam to get power in the desired rpm range, and *then* run as high a C.R. as you can with that cam. I.e., you don't run a big cam so you can run higher c.r., you run a big cam for the desired torque/power vs. rpm characteristics, then maximize c.r. for that setup.

Every biggish-cammed highish-hp carbed L6 build I've seen does that, it's due to reduced V.E. and multiple carburetion in that rpm range. I.e., air comes through venturi once, gets fuel, then some air gets pushed back through the venturi due to late intake valve closing and picks up more fuel, then gets drawn through again, picking up still more fuel, at the next cycle. With fuel injection you could improve the A/F ratio, but you'd still have a big torque dip there, as it simply doesn't breath well at that rpm. What works great at 6500+rpm doesn't necessarily work all that great at 3800rpm...

Tee hee, it's been a while... Must throw in my .02 regarding the N42 head's detonation-proneness (or, in my experience, the apparent lack thereof). It got long, so here's the short version of what I've run, all on pump gas (91-93 octane), with an N42 head: 3.1 liter, stock N42 head (shaved ~.10 from previous rebuild), stock N42 cam, unshaved KA24E pistons, 2mm gasket, 240Z carbs. 10.25:1 CR, 10* initial/35* total advance, no apparent pinging 290*/.490" Schneider cam, 2" Jag carbs, 10.25CR, timing bumped back up to 18* initial/43* total, 180rwhp 310*/.550" Sunbelt cam, Sunbelt porting and minor bowl work, 3x2 45mm carbs, ~10.8:1 CR, 217rwhp at 43* total advance, 235rwhp at 34* - 38* total advance Rebuild w/ eyebrowed 89.5mm KA pistons, 11.3:1 CR, 255rwhp at 35* Recent rebuild of middle 1/3, shaved head, 11.6:1 CR, not dyno'd, still running 35* on pump gas. My original 3.1 build was done way way back in ~1995. Totally stock N42 head with ~.010 taken off, stock N42 cam, N42 block bored 3mm over, KA24E pistons (not shaved), 240Z rods, 2mm head gasket, ~10.25:1 CR, stock 240Z carbs. I had previously been running ~15-18* static advance with the L24, and found that I had to back this to 10* to avoid pinging. Unbeknownst to me at the time, this was about where I wanted to be anyway, at ~35* with mechanical advance at elevated rpm. So, stock N42 head, stock cam, over 10:1 CR, no prob on 91 octane at 35* total advance. Ran it that way a few years, then put in a Schneider 290/.490 cam and 2" SU carbs, and was able to bump the advance back up to ~18*. Pulled 180rwhp at the dyno. Eventually Sunbelt ported and did modest bowl work on my N42 and installed a 310*/.550" cam that allowed use of lightweight valve springs, and Igot a used set of 45mm 3x2 OER Racing carbs. I used a 1.5mm gasket (2mm minus one of the .5mm sheaves), CR now pushing 11:1. I took this setup to the dyno to check a/f mixture. Pulled 217rwhp, nice... Then I decided to play with the timing using the dyno's adjustable timing light and found that I was running 43* initial + mechanical advance! Backing it off gave a big power bump although no pinging had been noted previously. Continued backing it off and found that it made the same 235rwhp between 34* and 38* initial+mech advance. So I run it at 35* to be on the safer side. Then I wasted the bottom end at VIR by running it low on oil (it had been living on borrowed time, as long as I'd been tracking it I'd lose pressure on extended right-handers). Oops... Abacus in Norfok VA did the rebuild, now with 89.5mm KA pistons, eyebrowed to allow a thinner head gasket, 1.16mm (2mm minus one .5mm and one .33mm layer). CR bumped to ~11.3:1. Pulled 255rwhp with 35* advance. Yee-haw... Then at the '05 Zconvention track day at Watkins Glen, the #6 intake was leaking in air and I burned that piston (chamber OK). Oops again... Then last year I detonated the middle two pistons/chambers by running with a partially stuck throttle on the middle carb (1,2,5,6 pistons and chambers showed zero evidence of detonation, those pistons were left in for the middle-1/3 rebuild). Oops yet again... Chambers #2 + #3 had to have welding done (THANKS, Brad!), which led to the deck having to be shaved, chambers now 42.0cc, current CR is 11.6:1, still running full advance on pump gas, no problemo. So, long/short, you can run full advance on a decently high-compression setup with the N42 head. But lean it out and there's not much margin (which may also be the case with the "better-chamber" P-heads for all I know). Again, this is just my 0.02...

Dunno how much power you're making, but generally "giving some throttle mid corner" induces understeer, not oversteer. If you wanted to tighten your line, in most cases you'd want to lift or feather the throttle to point the car. You have to get most of your turning done early in the corner so that as you apply throttle and your arc widens due to unloading the fronts and increasing speed, you asymptotically approach the edge of the track at track-out. The car may indeed be understeery, but it sounds to me like you might be turning in too early, at least for the current setup of the car. If the car turns in fine initially, but runs wide later in the corner, you hafta get more of your cornering/turning done earlier.

Not the Corvette

Yes, I have done that before, worked out the geometry and it worked like a charm. But of course I don't remember the relationship and figured I'd check here first before degrading myself to putting forth any real effort

Howdy all, been a while... Alignment shop set me to the wrong specs, .25* front toe-in per side. Just need to know how a turn of adjustment at the tie rods relates to toe change on a '71 240Z (stock tie rods, steering arms, etc), if anyone has that info handy... TNX!

I disagree about "less leverage" with a shorter rod. If you work out the geometry, the shorter rod gives GREATER mechanical advantage on the crank throw at maximum cylinder pressure. Greater sideloads, yes, but greater max leverage too! In the end, integrated over the power stroke, the "leverage" averages out about the same. Hence, r/s doesn't really affect how much torque you're making. I've got cylinder walls less than .100", but don't have stupid-crazy hp Agree with the approach of "if it costs the same, do it". Longer rods do reduce peak piston acceleration for a given rpm. But again, for *most* of us, it's more practical to do a build with stock parts. And if you're not displacement-limited for class rules, just maximize displacement (within practical reason) and don't worry about r/s.

FWIW, I have my 1.60 r/s LD-crank motor limited at 7200rpm as well and it "revs really nice" up there as well I'd rather have 5% more displacement than a "better" r/s ratio.

My take on it: For most of us, it's not going to be very cost- or labor-effective to go to great lengths to optimize rod/stroke ratio, when the actual increase in CR you can run is going to be pretty minor. FWIW, I'm running the standard stroker r/s of 1.60:1. Also running the dreaded open-chamber N42 head (Sunbelt ported and cammed). I've been running this setup for years, at 11.4-11.5:1 CR (I had *thought* it was more like 11.1:1), on 93-octane pump, with full ignition advance (made same power from 34 - 38deg, so I run it at 35). I will own up that it's pretty close to the edge. A few laps with the middle carb linkage stuck open recently cost me pistons #3 and 4 (doh). Some detonation damage to the head required some weld-up repair, and they took .006" off the head to clean it up, so now I'm at 11.63:1. I think I'm-a start running race gas at the track...

1981 = smack-dab in the middle of the era of SLOW cars!

Isn't hp loss more like 3% per 1000 ft? That'd be an 18% loss at 6000 ft. 120rwhp at 6000ft would "correct" to 146rwhp at sea level. WEAK! Damn, did anyone used to think these cars were even remotely fast?!

'78 280ZX? Personally, I'm a fan of staying with small-diameter wheels rather than having to deal with the higher ride-height and gearing associated with taller wheels. If I were to make a change, I think I'd go 255/40ZR13 Hoosier A6's Hmmm, I gotta look into that... Who makes a 13x9 wheel that weighs and costs next to nothing?!

200+ mph 2 liter Z? Cool thread! Ballast at the front gives more aerodynamic stability. If the back end is "moving around" as mentioned, greater aero stability margin should help.

Thin stock sheet metal might benefit from the reinforcement. But again, with the Bad Dog rails (twice as thick = 8x as stiff in bending), I don't think the incremental benefit would be noticeable. They're not anything like as bendable/deformable as stock!

Take no offense, I know it's a work in progress, but I got a good chuckle out of the above pics:D Good luck widdat!

With the stock rails, you might consider doing this. With the thick/stiff Bad Dog rails, there wouldn't be any benefit.

Heh heh, can't believe you remembered I did that, jmort! It's been a while... I added 9/16" to the front lower control arms by adding in a channel-section plug with a flat-plate overlapped and scarfed onto the inner and outer parts of the cut control arm. I don't think you can (or should anyway!) add enough to gain 2* camber! I think I got something like 1/2* out of it, for an expenditure of about $50 total. It was worth it in my book, but I'm still short on front camber (soon to be addressed). Curious that you only have 1/2* negative camber with slotted towers. I was at more like 1.5* with slotted towers before adding to the LCA length, 2.0* after. Are you lowered at all or stock ride height?

TC rod has to move around a bit more than the top of the strut does, no? Actual angular movement at the top of the strut must be pretty small even throughout the entire range of suspension travel. How 'bout if I leave out the inboard of the three nuts and only tighten the other two Seriously... I'd love to go the coilover route, but the price difference is pretty extreme even prior to factoring in the labor I'll have to pay to do the work. Sectioning and welding strut tubes is not in my repertoire. Actually I can cut things up pretty well, it's the getting things back together part that is beyond me...

http://www.thezstore.com/page/TZS/CTGY/PSDC08 I just replaced the 30+ year-old strut mounts/insulators in my 240Z with new ones from Nissan. Unfortunately, the new ones are SUPER-SQUISHY! And the old ones (which had elongated holes instead of "D" shaped holes for the struts) are, um, gone... At Watkins Glen last Tuesday, I couldn't believe the amount of shimmying (loose-ish inner tie rods didn't help in this regard). Turn in, and then saw back and forth at the wheel over undulations in the tarmac, a la Tazio Nuvolari... So, in the interests of eliminating compliance AND gaining some negative camber, I'm ordering the MSA kit above. Unless someone here talks me out of it... Looks like a good cost-effective solution to me, and should get me up to where I wanna be camber-wise (currently at 2.0-2.2 front, 1.8 - 2.0 rear, would like to be ~2.5-3.0 F/2.0-2.5 R).

Thanks, fellers! I plan to run the Z again this year (ran my stock S2000 in '07), so I should be spending a bit more time here. I am not a fan of "dynamic compression ratio". It *implies* a more accurate effective "compression ratio" for an engine that is actually running, but in fact it is only accurate at zero rpm. It gives the impression that with a big enough cam you can run much higher static CR because of this "bleeding off", which *is* ocurring at lower rpm, but it is NOT ocurring at higher rpm. Fortunately, at higher rpm the time available for detonation to occur is greatly reduced. That is the *real* reason a higher CR can be run. At low-rpm high load, the big cam does reduce effective compression ratio. That's why it's a piss-poor concept. The lower "dynamic compression ratio" is meaningless at rpm where the cam is designed to work. The engine is aspirating as well (better even) than a smaller cam in its rpm range. Better to find out what the top builders are able to run for CR for similar builds than to go by "DCR", which could get one into trouble IMO. You think you're calculating "effective compression ratio" at rpm, but that's not at all the case. At 13:1 with a big cam, you are STILL squishing the cylinder's displacement by ~13:1 in the cam's operating range, even if you are aspirating enough less than that to get away with it at lower rpm. Yup, all depends on intended usage. Unfortunately, most people get a cam just to "wake up" the engine a little, and end up disappointed that the engine doesn't make any more torque, and they have to rev it higher to get that! Har har har! Agree 100%. Though I gotta say I've always been impressed with what Norm has been able to do breathing through SU carbs. Me, I wasn't up to screwing around with them to maximize their performance, so I just bought 45mm 3x2's. Don't have them anything like optimized I'm sure, but less work required to get more power!

Been absent awhile, but I gotta say, I do not think big cams "bleed off compression at ALL rpms". My understanding is that volumetric efficiencies of greater than 100% are possible with big cams at elevated rpm. My 3.1 went from 189 lb-ft of torque with the stock cam (at 10.35:1 CR) to 210 lb-ft (same CR) with a 290/.490" Schneider cam, to 220 lb-ft with a Sunbelt 310/.550" cam (at 11:1). When you "get on the cam" with high lift cam profiles, you go from losing a ton of v.e. at lower rpm to GAINING v.e. at higher rpm. The engine will aspirate its actual displacement (even more!). Which means you are not "bleeding off compression" at higher rpm. The risk of detonation isn't as high at elevated rpm because detonation requires 1) load and 2) TIME. At high rpm, there simply isn't enough time for detonation to occur. This is not to say that high-rpm detonation (which is more difficult to detect) can't be a problem. It has wrecked plenty of engines! But I disagree with the idea that big cams in a well-developed engine build will "bleed off compression" at all rpm. They sacrifice low-rpm v.e. for high-rpm v.e. Which also allows for higher compression ratios. Win/win, if higher-rpm power is your goal!

FWIW, my 3.1 with stock 280Z N42 head and cam, and stock SU carbs made 177rwhp and 189rw lb-ft. IIRC...

At any kind of "reasonable" boost levels, the snap-through acceleration of the piston at TDC at redline between exhaust/intake is a more significant tensile (i.e., crack-inducing/growing) load on rods than the compressive forces from the big kersplosion shoving the piston down during power stroke. p.s.: late to the party, holy FRICK what an awesome build! My favorite post: $3200 spent plus a TON of work. OUTSTANDING