Guest DaneL24 Posted May 9, 2003 Share Posted May 9, 2003 You know, I never really understood this whole load on the engine making the turbo spool faster thing...I would think that turbo spool speed would be proportional to the rate of exhaust gases flowing through the turbo. The engine should still flow the same amount of air in and out, regardless of the gearing. Since the engine is flowing the same amount of exhaust gas in any gear, how is it that the turbo produces more boost in first gear than it does in second gear? Is it because the engine is revving more slowly in higher gears, and therefore can't consume the air as quickly as the turbo pressurizes it...increasing overall pressure? But then again, the engine will put out less exhaust at lower RPMs... Ther has to be a logical reason why turbos behave this way. Does anybody out there understand it? Quote Link to comment Share on other sites More sharing options...
Mudge Posted May 9, 2003 Share Posted May 9, 2003 Momentum, the longer the air is flowing past that wheel the better your chances for it SPOOLING or spinning quickly. Just as when you shift a stick car the airflow drops, and so does the boost. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted May 9, 2003 Share Posted May 9, 2003 Crazy? Do the math and I'd get a 200 RPM drop with a new trans. I am not sure your math is correct. According to the link I posted, i ran some combo's. Running your trans with 3.90's and I guessed a 215/60r14 tire, you turn approx 3731 Rpms at 80 mph. The same everything except the ZX trans bumps the speed up to 92 mph at the same rpm. Coming down the line I got 80 mph at 3234 rpms, which is approximately a 500 rpm drop. Yes I realize this is not spot on accurate, but it is close enough to make a point. I don't really want to flame you or anything,you appear to be a nice guy, but you seem to have an opinion on everything, but nothing to base it on. You don't have the trans, and you have never tried it, as I have. Same scenario about webers. You haven't run them, I have. You have never tried to tune them, I have tuned them. I have a basis for what I say, and as far as I can see, you don't. Run a ZX trans and then comment on whether you think 3.90's are to much gear. I always found that to be a very balanced combination, and so have a couple of my friends, one ran mid 12's and the other has run very low 13's, both in excess of 110 mph. Both 280Z turbo transplants with stock ZX turbo FI. My best friend who has been fooling with Z's for probably 20 years also agree's with my assessment, in fact he put me on the combo better then 12 years ago. Anyway, sorry to digress Dane, I would like to see you try the ZX tranny and 3.90's if you have them, and see what you think. I think you will be pleased. If you can find a set of 3.70's, I think that would be good too. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted May 9, 2003 Share Posted May 9, 2003 Street car with 11lb flywheel, L28 pulley(smaller than L28DET), 3.90 and early Z trans here No problem with spooling, I'm getting 7psi in first, 10psi after 2nd gear no problem. (I just got it back together yesterday)That's on my new turbo with StageIII turbine and 60-1. So personally, no complain with gearing in my car. Turbo is load sensitive. more TB is open more the turbo works. VE got something to do with it. lower numeric gear will let you stay in the boost without chasing the gear. but as long as your boost is coming up faster than your rpm, I don't see a problem. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted May 9, 2003 Share Posted May 9, 2003 Also, I'm running 225-60-15 on the rear, I think that brings my final drive to like 3.70. Quote Link to comment Share on other sites More sharing options...
Mudge Posted May 9, 2003 Share Posted May 9, 2003 http://www.geocities.com/z_design_studio/transmission.html Just did the calc again and by gosh your right, 515 RPM difference with my 195/60 15", now I know I really need to get that trans (first the car has to run ). First gear however is actually worse between the NA 5 and the old 5, and first gear sucks I had twice pipes on the car and felt like I was racing just to get to 15 MPH and shift, putting me around 2700 RPM at 15 MPH!!! Somehow my brain confused the trans swap with the rear swap (been awhile since I ran the calcs), so going from a 3.90 to a 3.54 is the least difference of the two if I had to do one or the other first. 294RPM difference between the two rears @ 80 with a late model NA 5 speed. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted May 9, 2003 Share Posted May 9, 2003 Thats why that transmission and 3.90s work like peanut butter and jelly, and thats why I always felt the thing was sluggish with 3.56s. I liked on the interstate in over drive while cruising, but I hated waiting for the boost with 3.56's. It is really one of the sweetest combo's out there for a Z, running the ZX tranny and 3.90s' it gives a really nice spacing between each gear. Check the gap between second and third, thats where the ZX tranny really shines. No big gap, like Z trans and T5. Quote Link to comment Share on other sites More sharing options...
Mudge Posted May 9, 2003 Share Posted May 9, 2003 Thats the truth, the early 5 has a really screwy ratio spread. As for the rest, you caught me with my pants down, I will nominate myself for assclown of the day My car came setup with the early 5/3.90 and were probably pulled from a single donor is my guess, the fluid looked like it had been in the trans all 20+ years I look forward to the NA 5 down the road, maybe I will keep the 3.90 for awhile and see how things go. Quote Link to comment Share on other sites More sharing options...
Guest DaneL24 Posted May 9, 2003 Share Posted May 9, 2003 I looked up some info on the Electromotive 280ZXT at: http://zhome.com/History/Electramotive/DevTrubo.htm and that car had a tranny with a 2.21:1 1st gear ratio and a 4.41:1 final drive ratio, giving an overall ratio of 9.75:1. A ZX 5 speed and a 3.90 diff will have an overall drive ratio of about 12:1 in 1st gear. Now look at the Electromotive car's 1st gear performance: At 8000 RPM in 1st gear, the car would go 66 MPH. Torque peaked at 5500 RPM and horsepower peaked at 7500 RPM. Common sense says that in straight out acceleration, they probably would have kept the engine in 1st gear to almost 8000 RPM to reach peak power, therefore about 60 MPH. The car could run 0-30 MPH in 1.8 seconds and 0-60 MPH in 3.8 seconds. All of this in 1st gear with a really low numerical drive ratio (9.75 vs. 12 of ZX tranny w/3.90). If you put the pieces together, you can see that the car had awesome 1st gear performance with those ratios. Of course, the Electromotive L28ET was putting out a lot more power than a standard L28ET, but it still says a lot about turbocharged performance with low numerical drive ratios... Quote Link to comment Share on other sites More sharing options...
Mudge Posted May 9, 2003 Share Posted May 9, 2003 That may not be too bad, what tires are they running though? I eventually want to run a 245 on a 17" wheel but that will be a ways off, and probably 25.6" tall. The Camaro could do 60 at the top of first @ 7000 RPM, and that was with 3.42 rear gears and most people run a 3.73/4.10. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 9, 2003 Share Posted May 9, 2003 Electromotive 280ZXT... and that car had a tranny with a 2.21:1 1st gear ratio and a 4.41:1 final drive ratio, giving an overall ratio of 9.75:1. A ZX 5 speed and a 3.90 diff will have an overall drive ratio of about 12:1 in 1st gear. Well... comparing a track car's first gear is really irrelevant. Most track cars use third, fourth and fifth only on a race track. First and second gears are for getting out of the pits and are generally geared to get the car going without hurting the clutch too much. You'll want to look at the last three gears to identify anything meaningful. Quote Link to comment Share on other sites More sharing options...
Guest DaneL24 Posted May 10, 2003 Share Posted May 10, 2003 Oops...I did forget to look at the tire size...but they weren't tiny. I think it said 16". And yes, I know that its a track car designed for sustained high speed, but considering the specs I just posted, its still pretty obvious that despite it being a track-car, it still had awesome acceleration in 1st gear with a low numerical drive-ratio...which is why it is relevant. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted May 10, 2003 Share Posted May 10, 2003 I ran the early 77 stock 5-speed w/ 3.70 LSD in the turbo Z until it "gave up the farm" a month or so ago. I felt that the RPM's were too high cruising on the interstate and first gear was extremely short, but had no quams regarding the performance of the car using this tranny as seen in my sig. I now have the later zx tranny in the car, like the highway cruise, but have not been able to get it to the track to see if there is any improvement over the early tranny. I have an extra early tranny in the garage, just in case I like it better... Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted May 10, 2003 Share Posted May 10, 2003 The more sick power your car makes, the numerically lower you can go and still have good acceleration. FWIW, they used similar transmissions on the 300 hp NA motors too. And check the curb weight on their car. That is what I have been saying, there are more variables then just the fact that the car is turbocharged. Quote Link to comment Share on other sites More sharing options...
Klmykvl Posted September 23, 2013 Share Posted September 23, 2013 What do you guys think of the L28et with the T5 down to a r180 Diff with 3.36 ratio? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted September 23, 2013 Share Posted September 23, 2013 I still like the 3.54 and T5 for street and strip. A road racing track is a different story, and depends on a lot more factors. A 3.36 / T5 would be great for very high speeds or optimizing fuel mileage at highway speeds. It's a highly desirable ratio, but I don't think it would work for me. I have a 2.88 in my Mercedes 240D. Quote Link to comment Share on other sites More sharing options...
Tony D Posted September 24, 2013 Share Posted September 24, 2013 3.70 gears... 2nd is 60 mph at the top of second. Anything after that is illegal anyway...and the car will double or triple the speed limits in most any state. My 3.36 ran 2K at 50mph in 5th... YEECH! Also the E-Motive numbers above are "published"--the actual numbers are quite different, it had a bit more than 750hp at 7500 and 21psi... Those were just enough to impress the mag writers of the day. Real competition the boost was higher as was the rpm ability of the engine. It's really not relevant to this discussion. Quote Link to comment Share on other sites More sharing options...
osirus9 Posted October 15, 2013 Share Posted October 15, 2013 I've got a 3.7 LSD with the early Z 5 speed and I have to agree, 1st is way too short, and 4th and 5th are almost the same gear. Highway cruising at 80mph is almost 4k rpms and I'm at 2500rpms in 5th going 55mph. I was always considering a trans swap, but not sure if the T5 or the ZX was right for me, especially since I am planning to turbo the car. Seems like the general consensus here is the ZX which seems odd to me since the T5 has taller gearing and is stronger, unless I'm horrifically mistaken. Quote Link to comment Share on other sites More sharing options...
johnc Posted October 15, 2013 Share Posted October 15, 2013 You gear the car to hit redline in the highest gear at the start of the braking zone at the end of the longest straight. Then adjust the lower gears to minimuize the rpm drop coming out of the three most important corners on the track. Quote Link to comment Share on other sites More sharing options...
spiff Posted October 16, 2013 Share Posted October 16, 2013 What do you guys think of the L28et with the T5 down to a r180 Diff with 3.36 ratio? I have a l28et with a T5 and a r200 with a 3.36... I like it much better over my old 4spd with a 3.5 final drive that was 3000rpms going 80kph(50mph). Now I'm at 1900rpms(5th)... For my driving the T5+3.36 is a nice combo. Quote Link to comment Share on other sites More sharing options...
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