proxlamus© Posted March 19, 2010 Share Posted March 19, 2010 I currently have a open R180 with a 3.54 gear ratio and I have been able to find good deals on a Subaru R180 LSD with a 3.9 gear ratio.. Anyone here running a 3.9 gearing with a turbocharged powerplant?! Im building up my L28 with the Z32 transmission and I wanted to hear some peoples feedback whether they like the 3.9 or if it's too high. Thanks!! Quote Link to comment Share on other sites More sharing options...
drzed Posted March 19, 2010 Share Posted March 19, 2010 I currently have a open R180 with a 3.54 gear ratio and I have been able to find good deals on a Subaru R180 LSD with a 3.9 gear ratio.. Anyone here running a 3.9 gearing with a turbocharged powerplant?! Im building up my L28 with the Z32 transmission and I wanted to hear some peoples feedback whether they like the 3.9 or if it's too high. Thanks!! I run 3.90 in the 260Z in my sig. below. It works perfect for the combo I was running but it is an auto and more drag than street. You might find that 1st gear with a stick would be pretty short. Also remember that the kind of power you will be putting down is a lot for an R180. If it was an open 2 pinion R180 I would say no way but if that is a 4 pinion setup it should work - at least for a while. Quote Link to comment Share on other sites More sharing options...
Skittle Posted March 19, 2010 Share Posted March 19, 2010 I'm running a 3.9 on my turbo Z. I'm not sure what the difference is since i have not yet driven anything else. Quote Link to comment Share on other sites More sharing options...
B00STDZ Posted March 19, 2010 Share Posted March 19, 2010 High gearing(3.15, 3.36, 3.54) is better for the l28et as 1st and 2nd gear wont go by so fast and your able to build full boost... Quote Link to comment Share on other sites More sharing options...
S130Z Posted March 19, 2010 Share Posted March 19, 2010 I am running the 3.90 in my Turbo setup and hate it. I have a larger than stock turbo and I can never get over 10psi in 1st gear. It's also my DD and I drive mainly on the highway(3.90 is terrible for the highway). I will soon be going to a 3.54 as the 3.90 is WAY too short. Also, if your using the stock turbo cam, the 3.90 tends to keep your RPMS above the power band. Quote Link to comment Share on other sites More sharing options...
BayAreaZT Posted March 19, 2010 Share Posted March 19, 2010 I'm running a 3.7 with a T-5 tranny. The Z32 tranny has a slightly taller 1st and 2nd gear so it may feel similar with the 3.9. I preferred the NA 5-speed with a 3.54 but the 3.7 / T-5 is livable. Quote Link to comment Share on other sites More sharing options...
piston Posted March 20, 2010 Share Posted March 20, 2010 thanks for your guys inputs even though someone else ask the question. i have a n/a 3.54 planning to run with boost. for the longest time i was leaning towards the 3.90 since all the 2jz guys run the shorter 3.90 plus gears. its also the transmission that plays a roll in the gearings right? Quote Link to comment Share on other sites More sharing options...
johnc Posted March 21, 2010 Share Posted March 21, 2010 High gearing(3.15, 3.36, 3.54) is better for the l28et as 1st and 2nd gear wont go by so fast and your able to build full boost... Is the goal building max boost in each gear or the shortest 1/4 mile time? Quote Link to comment Share on other sites More sharing options...
B00STDZ Posted March 22, 2010 Share Posted March 22, 2010 Remember the L6 is no v8. Building max boost will allow it a better 1/4 mile time. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted March 22, 2010 Share Posted March 22, 2010 since all the 2jz guys run the shorter 3.90 plus gears. Who are all these 2JZ guys you are referring to? 6-spd Supras have a 3.15:1 final drive, Z-Gad runs a 2.93;1 and I run a 3.08:1. Is the goal building max boost in each gear or the shortest 1/4 mile time? The goal is to build max boost in every gear to get the shortest 1/4-mile..........and the less gears, the better. Quote Link to comment Share on other sites More sharing options...
piston Posted March 22, 2010 Share Posted March 22, 2010 scottie, that makes me feel a whole lot better. i was referring to the supraforum guys. i knew zgad had a low gear he mentioned about on one of his post!!! i just couldnt remember what it was exactly. but arent you both on auto? Quote Link to comment Share on other sites More sharing options...
B00STDZ Posted March 22, 2010 Share Posted March 22, 2010 Who are all these 2JZ guys you are referring to? 6-spd Supras have a 3.15:1 final drive, Z-Gad runs a 2.93;1 and I run a 3.08:1. The supra guys that like the lower gears are usually just interested in drifting. If your putting down any kind of power it is next to impossible to get traction with a low gear (3.9, 4.11, 4.38) You want traction and full boost go for with a high gear. Quote Link to comment Share on other sites More sharing options...
piston Posted April 10, 2010 Share Posted April 10, 2010 hopefully my 3.54 does great with my r154 trans and a .82 a/r exhaust side snail. Quote Link to comment Share on other sites More sharing options...
Mayolives Posted April 10, 2010 Share Posted April 10, 2010 QUOTE:"The goal is to build max boost in every gear to get the shortest 1/4-mile..........and the less gears, the better." With a road race application, finding the best gear ratio is always dependant on the track you are running. Like most of us, you probably don't have crew of mechanics and a shelf full of differentials that your can play with. However, your solution is a little easier to find. Your track doesn't change. The obvious and only rock solid way to determine which ratio works best for you is to try the 3.9 and then compare the results with a 3.54 or whatever higher one you can try. Do you have a good friend with a higher ratio rear and who is willing to lend it to you for a few runs? The "proof is in the pudding." Quote Link to comment Share on other sites More sharing options...
woldson Posted April 10, 2010 Share Posted April 10, 2010 The goal is to build max boost in every gear to get the shortest 1/4-mile..........and the less gears, the better. Going to have to agree here. When my friend put an auto into his 351tt, he shaved seconds off his 1/4 mi time. He runs a 2.X in the rear now and runs out of rpm in forth before the end. The auto zaps power, however, he can stay under full boost after the middle of second till the end. Road race, I THINK I would like a stick, what gearing? I don't know, seems like that would depend on many things including the driver. Quote Link to comment Share on other sites More sharing options...
Brad-ManQ45 Posted April 11, 2010 Share Posted April 11, 2010 Don't forget that tire diameter is also a part of gearing and unless flared/tubbed we are dealing with shorter tires... Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted April 11, 2010 Share Posted April 11, 2010 That's a good point about the tire diameter and it's not quite as simple as just the rear-end ratio. What really matters is the overall ratio which is a combo of tranny ratio, rear-end ratio and tire diameter, especially when you are dealing with other than the 1:1 tranny ratio. It's made even more complicated if you are running an auto tranny with a racing converter as the converter slip affects the overall ratio. A converter slipping at 10% (assuming it is unlocked) is going to make a 3.90 act more like 4.29. Combine that with a 26" tire and an engine strong enough to trap 135mph and the engine is buzzing at 7600 thru the traps. Drop it down to a 3.27 and it traps at 6400 and if you don't want to go over 6000, you have to run a 3.08. Not a problem for a turbo car as the taller gear puts the engine under more load making more power/torque. A manual tranny has no slip so a 3.90 is still a 3.90. However, combined with the tranny's 1st gear ratio and a 24.5" tire, the engine revs too quick in 1st and does not put the engine under load and most likely the turbo will not make max boost in 1st. It is sometimes hard to remember, but you cannot apply the n/a gearing mindset to a F.I. car. Quote Link to comment Share on other sites More sharing options...
Wedge Posted April 18, 2010 Share Posted April 18, 2010 I really love this topic, but is their any calculation program or just a formula that could help me choose if a R180 STI 3,90 diff used on a RB26 with Z32 tranny would work or not ? Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted April 19, 2010 Share Posted April 19, 2010 I ran a 3.90 with stock sized tires and the T5 tranny for a few years, and I hated it on the drag strip. First gear was useless, and second seemed too tall to launch. And 4th gear redlined before the traps, so there was a drop in acceleration or an extra shift, both cost me time. I went back to a 3.54 and that works really nice on the street and strip - redline 4th is around 125mph, right where you want to be with 400hp or less, and cruising in 5th at 70-80 nets me 30mpg. Quote Link to comment Share on other sites More sharing options...
sbooth Posted April 20, 2010 Share Posted April 20, 2010 I like the 3.9 with a 25" tire and a 3.06 first (na 280zx). If I was running a lower first gear (3.5), no way or a shorter tire for that matter. Using taller rear gears will load the engine more and can cause more boost making traction problems. 10 psi max with a 3.9(can't build max boost due to lack of load) vs 17 psi with a 3.54 may be a blessing in disguise. This assumes street type tires, suspension and lauch technique ( playing throttle jockey) vs real drag racing. Quote Link to comment Share on other sites More sharing options...
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