jt223539

I am soon going to be boosting a D15b that is in my 94 Civic hatch and i was wondering which transmission is the best for boost? Any suggestions would help.

Thanks

JT

thermal

EX or Si tranny...

jt223539

I don't know why i though it was a Dx tranny, but thanks

JT

audiophile24

the cx 5 speed tranny looooooooong ass gears good for boost. i speak from experience.

jt223539

Ight thanks, i thought that it wasn't the EX, or Si tranny

Yell88CRXsi

That "longer gear for staying in boost longer" is per crap!

Gear ratios are merely a way to trade torque for rpm. With a higher numerical gear ratio, you are putting more rpm at the wheel.
With closer gear ratios, you are able to stay at a higher rpm in between shift points. Something like the LS transmissions are suited more towards the broad torque curve/low reving LS engine. It keeps you in the peak torque area in between shifts. The ITR/SI/GSR transmissions keep the rpm's built up in between shifts, to stay in the more peaky powerband.

Having said that, for the track the itr/si tranny is the best hands down. Most high whp turbo engines are operating between 5.5-9k, and having their shift points in between. In combination with a tall slick size (24.5"+), and the high shift point (8.5-9k), you are able to keep the engine operating within the optimum torque curve.

With the LS transmission, between shifts it would possibly drop you out of the optimal powerband and therefore make you slower. Gearing simply put allows you to stay in the powerband of your engine in between shifts.

The myth that you stay in boost longer with the LS transmission makes you faster is purely false. Think about that statement for a second. Acceleration is the measure of velocity over a unit time. Watching the rpms climb on the tach during a 3rd/4th gear pull, they would be climbing slower than with the si/itr tranny. Looking at the definition of acceleration as a measure of velocity over a unit time, the engine would be getting to the same velocity over a slower time lapse. This would yield slower acceleration, and simply put make you slower.

Having said that, the gsr transmission is probably the best balance of a street/strip transmission. The gearing is a little less aggressive as the itr/si transmissions, which will yield a little more traction. For all out acceleration si/itr tranny wins hands down. For a slower car, go with the LS transmission.

If you are having problems with traction in 1st or 2nd...they make something called a "Boost Controler" and boost by gear.

Fabrik8

The best transmission for boost is the one that you respect and don't beat the shit out of.


Shorter gearing is much better for acceleration. The only place this would possibly be a downside is at a track when you're trying to minimize the time lost off of power during a shift. Less shifts equals less time lost, but now you're talking about picking specific gear ratios for that, not just choosing between stock transmission A or stock transmission B.

No, you just proved it's true. But only when "faster" means top speed, not acceleration, like you said.
You do stay on boost longer. It's because it takes longer to get to the same speed. So eventually, because of the taller gearing, when you do get to the top of the gear you are going at a higher speed. You just get to that point slower, like you said. Hahaha..

Yell88CRXsi

Wording will get you every time...lol, I stand corrected.

But you are also correct about the Transmission A/B bit. The thing to do would be to custom gear for what you needed.
I just hate hearing people spit out that LS's are better for boosting when they fully do not understand acceleration versus top speed.

B-Well

x2

you will not top out a cx tranny in any sense so they are out of the question in the performance standpoint unless you had enough power to make use of the cx ratios. You've stated you're using a b7 so an ex tranny would make the bank for "street power" or "street speed."

I've used dx, cx and ex (oem internals) on my boosted setup. Before i boosted i researched the trannys available and the gears available as well as the final drives for quite a while. There are many setups you can run combining gears from different honda trannys but as far as stock box trannys go here are my thoughts.

The cx never did any good (except gas mileage).
The dx was nice for autox as the final drive is 4.058 and gears were spread a little more so there were less shifts involved.
The ex tranny is has closer gears and a 4.25 final so the the rpm drop from gear to gear is lower and the gears will rev out quicker thus having the greatest acceleration. (if there is grip to be had)
All d series first gears are the same but will feel different due to the different final drives. I could go on for a while with d-tranny talk but just pm me if you have any questions.

Fabrik8

I totally agree with what you said, I just thought it was funny that you proved yourself wrong through your explanation because I totally understood what you were trying to get across.

I'll take a B16 tranny over an LS any day. Well, I would if I still drove Hondas..