At what point can your 3.9 gearing out perform the 4.111?

[georryan]

I've wondered this for a while. Especially after whatching Hardy pull away from me with 6psi of boost on the stock exhaust with his 4.111 tranny. At the time I was getting 10 psi of boost on the vf11 and I had my CES exhaust. I could hang with him, but he was pulling away.

Last night three of us lined up at a light. I'm still breaking in my clutch so we didn't launch, but once we all were rolling we hit it. The other legacy next to me had the 4.111 gears, it had a divorced gate Downpipe and full redone exhaust, plus it was getting full boost out of the vf11 (I'd say somewhere between 8-10 since my boost went up with my CES exhaust).

I had my stock exhaust on (which slowed the car a bit compared to the CES exhaust), I have the vf8 and an AWIC. I also was getting about 10 psi of boost and I have the exeedy LW flywheel. My car was faster. It was REALLY close, but I was pulling away from the 4.111 car when we were full out. I'm not sure what you'd need to do with the vf11 to pull on a 4.111 geared car, but you'd need the equivalent flow of a vf8 with 10psi or a little more to pull away from a fairly stock legacy with the 4.111 gears. That says a lot for the 4.111 gearset.

-Ryan

[BAC5.2]

From a launch it's a lot different.

From a launch, a 3.90 car will build boost much more rapidly, and since you'll be shifting less you will gain ground while the 4.11 car is shifting.

In gear acceleration will usually go to the 4.11 gear though.

[georryan]

Yeah, I've always wondered where I'd have to be to be able to pull away from a 4.111 geared car from a roll by just using the gear acceleration.

[555BCTurbo]

I have the catless exhaust, VF8, 4.11 combo...

And yes, the 3.90's pulled a lot longer, but the 4.11's pull really hard in the top 3 gears...

[scuzzy]

I have the catless exhaust, VF8, 4.11 combo...

And yes, the 3.90's pulled a lot longer, but the 4.11's pull really hard in the top 3 gears...

REALLY hard.


I mean REALLY hard.


god, it feels good.

Just think, an old chevy V8 camaro usually has a 2.32:1 or a 2.83:1 rear end and they pull hard as hell. put a 4.10 in one and it won't keep traction at all.

4.111 gears and lots of power is beastly. They pull like a mfer - but you win against them up top, in the 130-150 range, where lower gearing nets you more speed.

[THAWA]

From a launch it's a lot different.

From a launch, a 3.90 car will build boost much more rapidly, and since you'll be shifting less you will gain ground while the 4.11 car is shifting.

In gear acceleration will usually go to the 4.11 gear though.

Negative. Because of the difference in each gear of a Legacy turbo tranny, and a first gen RS tranny, plus the final drive, the RS tranny car will be faster through first and second gear, after that the tall gears will come into play. Having more boost doesn't help that much.

[BAC5.2]

The gear ratios show that it'll travel through the gear quickly, but the higher final drive keeps you in gear longer, meaning more time making power and less time shifting.

I went from AWD with a 3.90, to RWD with a 4.29 final drive. The shorter final drive is kinda nice, but it's a lot laggier. With the 3.90 it was almost insta-boost. It's not about more boost, it's about spool.

3rd gear is where the 3.90 should really start to show it's guts. When you can pull, full boost, hard, all the way to 90+mph, you gain a lot of ground. Espically when the 4.11 car has to shift in the 80's. The 4.11 should get you off the start, but the 3.90 should build steam and pass before it's 3rd gear is over.

At the drag strip, when the 4.11 car makes 4 shifts to get down the track, a 3.90 car would only have to make 3. Less shifting, more time on-boost, and less lag on a larger turbo = faster times.

From a random, 3rd gear pull from a roll, I don't doubt that the higher final drive would be able to take off and win. The gearing does help off-boost "pickup".

Given identical mods and gear ratios (save the final drive), I'd bet that the 4.11 car would be a bit faster from a roll, and the 3.90 car would be faster off the line from a launch.

[greg donovan]

thing like this are what is keeping me from modding my car.

to make it just right you have to do so many other things.

certain turbos work better w/certain gear ratios and final drive ratios.

too bad the audi/vw and the old justy CVT transmissions havent caught on. that would be awesome in a turbo charged car.

i dont care about top speed. but i want a cruising friendly 5th gear that will keep the RPMs down when traveling on the highway. i also want a tall 1st w/2nd 3rd and 4th being close and a little shorter. all while not having any dead spots in the powerband throughout the gears.

4.11s w/a rear LSD paired with quick spooling turbo that makes good power at 10-12 psi tops and a nice TMIC 3" TBE w/a good flowing cat and a decent muffler that wont make the kids ears bleed.

that means that i have to change a lot of stuff and spend A LOT of money. and i am not even sure such a set up is even possible.

[scuzzy]

thing like this are what is keeping me from modding my car.

to make it just right you have to do so many other things.

certain turbos work better w/certain gear ratios and final drive ratios.

too bad the audi/vw and the old justy CVT transmissions havent caught on. that would be awesome in a turbo charged car.

i dont care about top speed. but i want a cruising friendly 5th gear that will keep the RPMs down when traveling on the highway. i also want a tall 1st w/2nd 3rd and 4th being close and a little shorter. all while not having any dead spots in the powerband throughout the gears.

4.11s w/a rear LSD paired with quick spooling turbo that makes good power at 10-12 psi tops and a nice TMIC 3" TBE w/a good flowing cat and a decent muffler that wont make the kids ears bleed.

that means that i have to change a lot of stuff and spend A LOT of money. and i am not even sure such a set up is even possible.

Ah you've just got to stick with it and hope what comes out is what you like.

Patience is the key to the door of success.

Personally, I favor the 4.111 final drive, it has higher rpms at highway speed, but off the line - in my opinion and from my experience with old GM vehicles, the higher rear end will beat the 3.9:1 off the line and probably lead him, assuming both cars weigh the same and have the same power, all the way through third gear. fourth and fifth is where it will come down to, and once the 4.111:1 car hits 4th, the 3.9 will pull away because he can stay in gear longer.

the trick is, if you know you'll lose out to a higher geared car on the highway in 4th, the trick is getting so much of a lead on them that when you change to 4th, you still have that lead and can get back in boost before they take the lead from you.

the 4.111:1 will accelerate faster and harder than the 3.9:1, and it will beat the 3.9 off the line in my experience, but it will lose out in the higher gears because of gear change and being able to stay in gears longer.


But anyway, this is all good stuff we need to get together and put to the test.

[BAC5.2]

But when you are trying to run 30psi, you run out of gear SO quickly with such a high final drive.

Here is the speed at 6500RPM with a 3.90 FD and my dogbox:

Code: Select all

38.98	63.90	91.16	129.14	167.98

At 6500RPM, same gear ratios, 4.11 FD:

Code: Select all

36.99	60.64	86.50	122.54	159.40

Now, it might not seem like a lot, but think of it in a realistic setting.

If the two cars launch next to eachother, the 3.90 car will shift near 40mph. The 4.11 car will shift at 37mph. The 4.11 car will get to the top of first gear sooner, but the top of first gear also comes 3mph sooner.

By the time you get to the end of 4th in the 3.90 car, the 4.11 car has shifted into 5th gear (7 mph ago), and the 3.90 car is still in 4th. That's a shift less.

The average "racing" shift takes, what, .3 seconds? When you have to shift 4 of those, vs. 3 of those, thats 1.2 seconds of decelerating for the 4.11 car, and only .9 seconds of decelerating in the 3.90 car.

When you think of 1/4 mile runs, 3 tenths of a second is an incredible amount of time.

Of course, it all depends on setup. Shorter gear ratios and a higher final drive, will reduce the load on the engine. Less load means less turbo spool speed.

Right now, with the 4.29 final drive I have, the car is NOTICIBLY laggier than it was with the 3.90.

It's all kind of bench racing, really. Setup is key.

We have a WRX running low 11's with a 3.90 final drive and a helical dogbox and a Deadbolt Superzilla. If we put a 4.11 or a 4.44 final drive in the car, it would run slower times.

[Project_Legacy]

yea this all seems very true. the longer gears with a big turbo is a really nice setup. i have 4.11 gearing and first gear goes by so fast within a second or two.

[THAWA]

I agree with most of what was written up there, but one thing that really needs to be noted is the effective gear ratio, that is the individual gear ratio and the final drive ratio. There's quite a difference between a Legacy Turbo tranny, and an RS tranny. Also, given equal mods an RS tranny'd car would be faster than a Legacy Turbo tranny'd car.

But anyway, this is all good stuff we need to get together and put to the test.

We have

It's all kind of bench racing, really. Setup is key.

So damn true.

[BAC5.2]

Hardy - I do believe that there is a point where the RS geared car would lose to the longer legged Legacy.

The problem with almost every Subaru, is first gear. This is espically true with turbo cars. The gear is SO short, you aren't in it long enough to shift out of it. You can't build full boost in 1st gear in an STi, and it's tough to do that on an EJ20 with a larger turbo.

[georryan]

I've run 4.111 alongside the 3.90 geared cars in just about stock for stock comparisons. I think if they are setup the same it would be very tough for a 3.9 to do it. I've never actually launched either of them from a 3k-4.5k rev, though.

The 4.111 geared stock NA can stay on the tail of a 3.9 geared turbo that is stock. Throw a turbo in the NA and it will fly by the turbo car. That's exactly what hardy did. Even when I had 4 more pounds of boost than he had, and a good exhaust, he would still eat me for lunch.

It wasn't until I had the vf8 and the lighter flywheel did I actually take him. Even that was close, but he was getting some more boost by then as well.

I can't speak from experience on the launch, as I've never dropped the clutch in my car, and with so many of our trannies grenading lately, I don't really feel inclined to.

Yes the shifting takes some time that is for sure, but honestly, the 4.111 could almost launch in second if done right.

[BAC5.2]

But on a launch, you wouldn't pull much better of a launch with the 4.11 tranny.

Given the same setup, the 4.11 will be faster. There IS a limit though, where the higher final drive will hurt spool time and you'll just be shifting TOO much.

I put the dogbox back in yesterday, with the 3.90. Spools a LOT faster than the 4.29 did.

[THAWA]

That's true, there's always a limit, but you would have a have a fairly large turbo for that to happen. You would also have to a have a greater tuning advantage for the extra boost to overcome the mechanical advantage of the shorter gears.