Flint78

Hi,

new guy on the forum. I've been a lurker for a looong time.

Got a huge problem deciding what my rear gear ratio should be. Need help with that, since there is a ton of calculators all over interweb but its much better to rely on real life experience.

A bit of info. I live in Poland - a land where we do not have a real dragracing tracks. We race on airfields and there is almost no prep of the surface. So traction is the main issue here. There are a few good tracks in Germany, England etc I will go there for sure. But my main experience is on a road like structure - pavement / concrete etc.

I've had a Z28 that was suppsed to be pro-touring car. In the middle of the project I decided that it will go drag racing route - all the way. From pro-touring days it has a chicane 9" floater from Speedtech with 3.73 in it.

First I tried to run on 17" wheels ( brake rotors are huge and only 17 and up can handle them ), so I got 335/35R17 Drag Radial from Hoosier.
They were so tiny that I could not get enough grip and was burning rubber for at least 1/8th of a mile.

Best time with that tire was 11.51 with 143 mph and a terrible 2.6s 60ft

My tranny is Lenco ST1200 4 speed that has 1:1 final gear ratio.

With that combo I was at top RPM way before finish line. That was bad.
I was shifting the gears like crazy at the start and then waited.

My engine redlines at 7500 rpm Rev limit is set to 7300. Its a 572 BBC with 8-71 on it.
Got my shiftlight setup for 7000 so I guess I'm shifting around 7200 if I'll focus and do it right ( not always the case )

As for the peak HP and TQ of the engine - you can check out the curves at the end of the dyno test.


After few tests with that setup I decided to go up with the tire. Change the brakes in order to fit 15 inch rim and got 33's that are 14" wide.
They do have a bite and I have to say I got a lot more tracion now - so the main issue is fixed now.

But... with that big of a tire I finish the race and just at the line I finaly change to 4th gear. Entire race is done on 3 gears.

So the question is - what rearend gear ratio should I have that is optimal for best ET. Some calculators are telling me 4.5 some 5.1 - not a clue since I have no idea what my desired trap speed should be. I am planning to get a lot shorter Strange rearend with ratio that will be suited for that kind of tire.

I want to run at least next season on 33s.

So what are you thoughts on this one ?

Thanks in advnace
Flint