Stock 5 Speed gearbox, max bhp recommendations?

everything else aside, lets talk gearboxes.


My understanding is that the 5 speed box is stronger than the 6 speed due to thicker gears.

I have done lots of research and would like to clarify...

From my research 550whp seems to be the sweet spot. Anything more you greatly risk blowing a gearbox. No one really comments if this is for 5 or 6 speeds. If the 5 speed is stronger then would you feel comfortable pushing a little more?

Now this does all depend on the intended use. launching (drag racing) is different use to track and street and probably more stress on the box than track and street. I'm thinking out loud here but surely it doesn't make a difference between track and street? Maybe argue that the box and oil will get warmer during track use?

So lets just break this down more.

Based on a 5 speed box you want to run as much bhp as you can without risking breakage too much for each given intended use.

Track - BHP
Street - BHP
Drag - BHP

With adjustable boost one could have a street and track setting.

Feel free to post bhp and gearbox config and reliability?

Original gear box. 104k miles. Boosted for 20k miles for 7 years ranging from 415whp-560whp. Torque around 410. I think it's the torque that kills but unsure.

Sduff@Composites said:

Original gear box. 104k miles. Boosted for 20k miles for 7 years ranging from 415whp-560whp. Torque around 410. I think it's the torque that kills but unsure.

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Yup; torque & lube/cooling (or lack of lube) are the biggies for long-term durability, as is identifying the weakest link (bearing, gear, case) once you start boosting power above an OEM configuration.

jaffaz32 said:

From my research 550whp seems to be the sweet spot. Anything more you greatly risk blowing a gearbox. No one really comments if this is for 5 or 6 speeds. If the 5 speed is stronger then would you feel comfortable pushing a little more?

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Fun post. I've always wanted to hear from owners with boosted NA1/NA2's and to learn more about their NSX's drivetrain durability with an otherwise stock engine & trans. Since so few are DD's, and since I've always assumed that by and large, most baby their boosted NSXs and only occasionally really get down on it, a true sense of NSX transmission durability with upgraded engines may never be gained.

Two comments from the peanut gallery: You'd probably not go too wrong using HP as a rough rule of thumb for what you're trying here, but with a high-revving engine like the na1/na2's, using HP #'s can be misleading for what you're trying to do unless you look at torque at the same time. An 8000 rpm redline NSX and a 5000 rpm redline V8 muscle car Camaro, for example, both rated at 270 HP, will be putting a much different bit of torque thru their respective transmissions. Muscle car would put out much higher max torque than the NSX here, so if it were possible to swap transmissions between the two, you might be safer putting the Camaro's into the NSX than the NSX's into the Camaro, and even then also only if the bearings/bushings/seals/etc in the Camaro transmission could handle the nearly 2x max RPM of the NSX. At any rate, my second and main comment was: from my experience as an automatic transmission engineer, qualifying a transmission for a given Hp/torque capacity was a very difficult task, due to the so many variables that came into play regarding not only max engine torque & speed but also the shape of the torque curve over various throttle positions and the expected duty cycle/usage by the eventual driver....in fact, determining a transmission's potential to live behind a particular engine (especially for the times that transmissions designed for 190-HP 2v-V6 minivans were attempted to be upgraded to live behind a high-revving 4v small V8) seemed to be 20% analysis/prediction, and 80% long-term durability testing.

Edit: the above 2-cents is talking about the gearbox. For the clutch, that's a whole other story and outside of any experience I have.

About 380rwhp [CTSC]. 275k+ miles, 200k of it boosted. Stock motor, short gears & 4.23. Rock solid [knock on wood]

If you know your X, you'll know that it isn't meant for drag racing on slicks. I think 500rwhp would be my max for a daily driver.

I think Coz has mentioned a few times that 450hp for track driven on sticky rubber is about the all the gearbox can take before you start braking things, street driven can handle a lot more

BHP is just one point of reference. It's also Tires and driving style.
[MENTION=4034]Coz[/MENTION] is your man. Maybe he'll chime in.

I'm on my 3rd trans on 380bHP but tracked on slicks when I broke the first 2 trannies. 3rd tranny has been holding strong so far.

Boost by gear is your friend...

Im on original stock 6sp. 105k miles. Maybe 8 or 10k track miles, 100% of those super or turbo charged. Of course I only have 675rwhp so maybe others with more power and more track miles can chime in on the durability.:biggrin:

Solid urethane mounts can break gearboxes at relatively low power levels.

RYU said:

BHP is just one point of reference. It's also Tires and driving style.
@Coz is your man. Maybe he'll chime in.

I'm on my 3rd trans on 380bHP but tracked on slicks when I broke the first 2 trannies. 3rd tranny has been holding strong so far.

Boost by gear is your friend...

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I think your on to something... My oemclutch with maybe 10,000 miles is starting to slip after just 1000 miles on PSS tires.