After running with the 4.10's I already had in the car for 2 years with the turbo, I finally broke the rearend and just got the car back with 3.55's installed. The car is a 96 Cobra convertible with 5-speed, Hellion single 62mm with about 10lbs boost (spools quick) on slicks. It dyno'd around 450rwhp at one time, but it's got a few more pounds of boost and tuned better now, so who knows...maybe 500ish?? It usually runs high 11's at around 120mph with a best of 11.7 @ 121.75mph.

So the question is how much can I hope to gain in the 1/4 mile, both e.t. and mph going from the 4.10's to the 3.55's?

 

You can't really make a prediction like that since you've also changed the amount of boost you're running.

Were you running out of gear before the end of the track with the 4.10s? If not, then at the same power level, you may not gain anything at all. Since you have more power now too though, it will probably be to your advantage, once you get going, to have the taller gear in it.

If you can put a 2 step on it, that will help you more than just changing the gears. Especially since it's going to be harder to get it off the line now with the taller gears. I dropped from 11.80s to 11.50s by doing nothing more than launching with boost from the 2 step.

 

1) It was running out of gear originally, but I put on 28" slicks, making the final gear ratio something close to a 3.73 and that took care of that problem. So I will run 26" tires with the 3.55 gears.

2) Sorry I didn't clarify, what I meant was that the original dyno was without a couple extra pounds of boost, but the listed e.t and mph are with the current boost and tune.

3) I do now have a N2MB 2-step, but haven't had a good run with it functional yet!!!

 

Without the 2 step, I wouldn't expect to see much, if any, gain. Yes, it's going to put more load on the engine, but if you end up with slower 60's, then that will probably negate the gain from the increased load. Like I said though, get that 2 step going and you'll be good to go. Plus its WAY more fun to launch with boost.

 

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