5AT 3.5 final drive differential swap.

[verilath]

great info. thanx ism

[jerseymike68]

nice information here

[dsmith]

Very good thread! I am going to do a 4.08 in my wife's 5at. I would like to keep the cruise if you come up with a way to make it work.

[DaveB]

Originally Posted by dsmith

Very good thread! I am going to do a 4.08 in my wife's 5at. I would like to keep the cruise if you come up with a way to make it work.

That's WAY too much gear for a 5AT.

[dsmith]

Originally Posted by DaveB

That's WAY too much gear for a 5AT.

haha. You don't know me very well.

[DaveB]

Originally Posted by dsmith

haha. You don't know me very well.

What you'll end up doing is making her 5AT slower in the 1/4 than what I runs with the stock 3.36 gear. You can overgear a car.

I've been to the strip with a set of 225/50R15 BFG DRs. The overall height of the combo is 23.8" or 2.5" shorter than the OEM tire height. This combo gives the 5AT a 3.65 gear. When tested at the strip, same day as my OEM 17" combo, the car was .15 and 1mph slower? Why? Because it forced a shift into 4th which added time and the car was crossing the line at only 4600rpms. For ideal gearing, you want to be crossing the line right at in the meat of the HP peak or roughly 6200rpms or so. Unless you plan on adding a 4,500rpm stall and crazy cams (plus engine work) to let the VQ35 rev and make power to 8000rpms, 4.08s are overkill.

I'll be getting an ECU flash to increase the rev limiter to 7100rpms which will allow me to run the short DRs while holding 3rd the entire run.

I honestly don't know where ISMSOLUTIONS is getting his info regarding the gains from increased gearing. .5 to 1.3 seconds? He's smoking crack. These cars don't from the factory undergeared. There is very little to be found in the gearing. It will certainly feel faster, but put it under the timers and you'll see the truth. Maybe .1 to .2 seconds.

[Tollboothwilley]

Of course, that is on a stock engine. If you have modified the car at all, intake, exhaust, headers, cats, lighter pulleys, etc....it will change the torque and power curve where it could very well improve your time.

Most people with the 5AT think the 3.7 or 3.9 is the way to go.

[OCG35]

Dave's right (this time) - 4.0 for a first gen (5AT) is not the best idea... 3.9 is pushing it... 3.7 is a very good option.

for a 7 speed AT, it might be a good option

[DaveB]

Originally Posted by Tollboothwilley

Of course, that is on a stock engine. If you have modified the car at all, intake, exhaust, headers, cats, lighter pulleys, etc....it will change the torque and power curve where it could very well improve your time.

Most people with the 5AT think the 3.7 or 3.9 is the way to go.

All those mods you listed won't change the overall shape of the curve. The VQ35 will still have peak power occuring at around 6300rpms and then power will ever so slowly drop off as it approaches the 6600rpm limiter. If you've got an extended limiter, you'll see power continue to drop after 6600rpms, possibly severely after 6900rpms. The shape of the curve is basically dictated by the cams and by the intake manifold. Add better breathing cams and intake manifold and you'll get a VQ35 that will extend peak power into the 7000-7500rpm range. The limitation then becomes the heads.

We'll see how well the 3.7 gears fair. I did some calculations last night with the 23.8" BFG DRs (225/50R15 mounted on 11lb Mazda Millenia wheels, 34lb overall weight), and the DRs actually make the ratio a 3.67, not a ~3.55 like I had thought. When tested a few years back, the DRs actually slowed me down because of the forced shift into 4th. I'll be getting the TS ECU flash this winter and the extended limiter should allow me to hold 3rd just long enough thru the 1/4 mile or I'll be shifting a few feet short of the line. We'll see how it goes in the spring.

[verilath]

I agree with Dave. I never thought about the higher end drop off though. It almost makes the Kinetix SSV worth it... for us 5AT guys. lol. I could never justify $750 on a manifold that only gives gains after 6000rpm (practically outside our powerband). However, I just picked up a 3.5vlsd to replace my 5at (stock 3.3 open differential). I plan on dropping 3.7 gears in it, but it would be interesting to see how a high RPM intake like the SSV works in conjunction with shorter gears.

Maybe making that extra shift worth it?....

[Tollboothwilley]

Originally Posted by DaveB

All those mods you listed won't change the overall shape of the curve. The VQ35 will still have peak power occuring at around 6300rpms and then power will ever so slowly drop off as it approaches the 6600rpm limiter. If you've got an extended limiter, you'll see power continue to drop after 6600rpms, possibly severely after 6900rpms. The shape of the curve is basically dictated by the cams and by the intake manifold. Add better breathing cams and intake manifold and you'll get a VQ35 that will extend peak power into the 7000-7500rpm range. The limitation then becomes the heads.

Not true. My car gained power all the way to the rev-limiter after I tuned. Red line is 6600. Rev-limiter is 6800, which is where my peak HP was at. Now I need to extend the re-limiter. Oh, and the mods I did definetely changed the curve.

[OCG35]

VQDE with stock cams will always dropped peak power at (or around 6300)...

Tollbooth, you are a good guy and have good info - I'm certainly not starting a debate with you... but without more aggressive cams I'm baffled how you made peak power past the typical 6300.... I've dyno many times with stock cams and its always dropped off at 6300 (even with rev limiter to 7200)... not until I have JWT S-2 cams installed did it make (and hold) power a little past that... I think without head work it’s not gonna go too much past 6500