Okay guys IM going to have to change my rear gears pretty soon due to some highway traveling time. But I am wondering if this will effect my ET, well I know it will, but just how badly. I am currently runing a 4.1 rear with what looks like 26-27 inch tall tires. I plan to change to a 3.08 rear and some 28-29 inch tires if they will fit. My question is will this slow down, or quicken my ET. MY current best is 13.612 @ 103.44 with a 2.1 60 ft. time. I end up needing to shift into 5th right as I cross the line, but I just ride out 4th. So with the lower (numerically) gears, do you think I would be faster or slower?

 

Going from 4.10s down to 3.08 is going to kill you. Maybe run high 13s, who knows. What tranny do you have in your car? What is your motor combo? I want to see what you did to get your current time.

 

The current tranny is a Richmond 5-speed.

That's what I was thinking but some people have told me I might be quicker since I won't be shifting as much, and since I won't have such a hard time trying to get the tires to grip. Does that seem reasonable?

 

dropping a whole point off the rear gears will be about .6 sec of your time, plus if your going bigger an inch on tire size about, its like another .2 off your gear ratio so an effective 4.10 on 26-27" tires, a 3.08 with 28-29" inch tires will be like a 2.90 final effectively, over your old setup!! say hello to 14.20's believe it or not a rear gear ratio makes a huge difference on the performance on the car.

 

I'm not sure it would hurt. The Richmond has a 3.25 1st gear; with the current 4.1, that's way too much multiplication for a good launch on street tires.

Big slicks and a full on suspension would be needed to take advantage of a 13.325 launch ratio. That's the equivalent of a 6.05 gear with a close ratio Muncie!

If you do go to 3.08's, you would end up with a 10.01 launch ratio, same as a 4.55 gear with a close ratio Muncie. Still plenty of takeoff. Combine it with a high traction tall tire, that puts a bigger contact patch on the road, and you could easily see sub 2 second 60 ft's.

A 275-60-15 BFG Drag Radial (28" tall) will easily fit a 2nd gen. I borrowed a set when I was trying to decide which tires to put on my 71. They had plenty of clearance. Ended up going with 295-50-15's; I preferred how they filled up the wheel wells.

I hate the 3.08 1st gear in the TH700 in my 89 Formula 350.
Makes 1st gear borderline unusable with all the torque the L98 makes, especially around turns. And that's with a 3.27 gear out back. I would be much happier if the 700 had a 2.5 gear like TH350's and 400's. Driving in the rain is downright scary; I have to drive like I was on ice, unless I want to see the rear end swing around. Too much 1st gear can be a bad thing in a street car.

 

The 275/60 will fit nicely under the back end of a 2nd gen. I have 275/60's under the back of my '77 Z and they fit sweet. My car is also lowered with a drag suspension, and they still fit.

Dave

 

well I have some 29x11.5" slicks now, im not sure what that is in MM, but would they fit under the wheel well. I'm just afraid that I will loose all my competitviness, the car is a real top end car as it is, it runs out of gear long before it runs out of power. on the track, if they don't get a good 1-2 cars on the launch they won't win (usually) because my car will just real them in, but since if I just punch it in 1st it spins, and now 2nd is doing that to me. The other day I nailed it at about 2000 RPM in 2nd and the rear got a lil squirly till about the end of the gear. It wasn't swinging all over the place, but it wasn't catching full traction. And at the track I'm usually the only car to scratch 4th gear. PLus isn't it true that .1 of the 60 is .2 off the 1/4? So if I can nail a sub 2.0 60ft, shouldn't I run a 12?

but the basic question is still the same, will I be faster, or slower?

 

im glad you brought that up! just because your 60' goes down doesnt mean your 1/4 will, when you take away mech advantage, you hurt the cars ability to accelerate up top.

heres my own personal exp. i ran 13.5 on motor at 104mph with a 3000 stall and a th350. my tires are 27" tall with a 3.42 rear, i switched up to a 28.5x9 slick wich gave me an effective gear ratio of 3.10ish over my 27's. my 60' for the street tires was 2.15 and on slicks it was 1.87. but my 1/4 times were only 13.3 at 101. (note mph drop) this is because the taller tire caused a gear reduction causing me to pull the top end in the traps at about 4500rpm over 4700rpm. my motor was dynoed at 375hp and 400 lb ft! so just cuz your 60' drops doesnt mean your not hurting top end. now when i run my 4.10's ill be low 60' plus way lower et. id go to a 3.73 max with those new tires, anything lower and your shooting yourself in the foot.

 

What about going with 3.42 gears and the taller tires? That's what I run and it's a great gear.

 

Well im looking for 60-90 mph at 2000-3000 RPM, maybe 3500 pushing it, I have a richmond 5 speed which I have been told has a steep first gear.

 

whats your fifth gear ratio? cuz if you want gas milege, thats the only gear that counts. dont go too low on the rear gear+tire size unless you got 800lb ft of torque to move it fast lol

 

last gear is a solid 1:1, overdrive. I could easily fix the problem buy getting a 6-speed, but I don't exatly have 3k to spend.

 

Was your car a 4 speed car originally? How did the Trans bolt up to the BOP motor? I'd love to have a 5 speed....mmmm......Wishful thinking.