rear gear vs quater mile times

[ponchopwr70]

Well im going to be getting an over drive in the next month 90% sure its going to be the gear vendors over the 200r4. Since I'll be doing this I've though about changing the rear gears I have now (3.55) to either 3.90's or 4.11. With overdrive my 3.55 are like 2.76 with 3.90 like 3.08 and 4.11 like 3.20. First off I might just want to leave my gears alone but if I do decide to change them will I run faster in the quater? My 60ft times now are 1.78 and Im crossing the line at 5800 rather be crossing at 6200-6500 and would like a better 60ft. Any thoughts I cant really find any good test's anywhere.

[fishtail8]

Hey Frank, the only reason I put an O/D in my car was for the highway. I go through the top end in 3rd, but i'd rather keep the rpm's down for a bit longer engine life. I'd think more about what the car would RPM on the highway, seeing as it will probably spend more time there. Just my $0.02...

[The Stickman]

Well im going to be getting an over drive in the next month 90% sure its going to be the gear vendors over the 200r4. Since I'll be doing this I've though about changing the rear gears I have now (3.55) to either 3.90's or 4.11. With overdrive my 3.55 are like 2.76 with 3.90 like 3.08 and 4.11 like 3.20. First off I might just want to leave my gears alone but if I do decide to change them will I run faster in the quater? My 60ft times now are 1.78 and Im crossing the line at 5800 rather be crossing at 6200-6500 and would like a better 60ft. Any thoughts I cant really find any good test's anywhere.



Geez if there is that much difference I wonder what my 2.73's are like in OD.

[streetk14]

I'd say find a good rpm/speed calculator and figure out where the sweet spot is for your car. I set my car up to finish the quarter mile near peak power in 4th gear (T56 6 speed). For me that meant 3.70 gears as I'm hoping for 130 mph through the traps.

What MPH are you running at the end of the quarter? I'd think going to 3.73 or 3.90 gears would be where you should look. The 4.11's will probably be too much on the top end.

Here's the calculator I played around with to come up with these figures: http://www.car-videos.net/tools/speedrpm.asp?Car=Select&Num1=275&Num2=40&Num3=17&AxleRatio=4.11&Ratio1=2.52&Ratio2=1.52&Ratio3=1.00&Ratio4=1.088&Ratio5=0.78&Ratio6=&Ratio7=&Redline=6500&Increment=200&B1=Recalculate

[ponchopwr70]

My mph is 107 plus I have to factor in converter slippage. 3.90s might be the ticket since I wouldn't have a lock up conveter but will be able to keep up with traffic and pick up a tenth or two....

[ProdigyCustoms]

Deeper gears does not always equal better ET even if your motor makes power past the RPM your going through at now.

Perfect example, some years back when Michael and I built my street racer for the kids I did all the math and determined that the car could run 10.90s on motor and go through the traps at 125MPH at 6400RPMs. And it did, right off the trailer, did exactly what it was supposed to do.

2 years later the kids were bored with 10.90s and wanted nitrous, so we put 300HP of nitrous on and determined we would need 4.10s and a 29" tire to run 9,40s at 140MPH. Well it did exactly that. The nitrous and the gear / tire was the only change, never even touched the timing, jetting, nothing. We did add a retard box but that activated with the nitrous.

What I did not expect was it started going 10.70s on motor at 126MPH with the 4.10 gears and 29" tires, and was going through the traps at 6100RPM, even though it makes power to 6800RPM,

Morel of the story is sometimes the car like the lug a bit more, use the torque band better, and get there faster without being wound out.

With all that said, I have gone the other way with projects and picked up also.

So why don't you try your 3.90s and let us know what happens, LOL!

Confused now?

[ponchopwr70]

Frank as always you do help lol. What you just said I did read online or on the chevelle forums but it was someone else with the same results. Heres my rear wheel dyno graph after it was corrected with a bad exhaust and a junk converter ( I was 13.0 when I dyno'd it). I might throw the 3.90s in but If I like how it crusies with the 3.55's I might just leave it alone. Everytime I spend more to go faster it runs the same. My car went the same with street radials vs 26x11.50 et streets, I could deck the et streets off the line and dead hook, the radials I couldn't had to feather it. I think they grow, which in turn changes the gearing at the top end. I just bough drag radials I'll see what they do. Man winter sucks, I get bored and think about stuff that doesn't matter.