How much gear ?
Thread Starter
Drifting
Joined: Aug 2000
Posts: 1,805
Likes: 36
From: Annapolis MD
How much gear ?
I'd like to get some opions (actual experience is ok too :jester ) on how much total gearing is too much.
I've initially setup the rear ratio at 4.86 based on what I wanted the cruise RPM to be with a 200-4R overdrive trans (0.67:1 in OD). I've gotten some fairly strong opinions from one trans shop that the normal 2.78:1 first gear for the 200-4R would be too much to ever hook up with my current rear gears, and is suggesting an alternate trans (AOD based) with a 2.40:1 first gear.
Would the 2.78 "really" be too much? Would the 2.40 "really" be a lot better? I'd prefer not to change the trans mounts to accept the AOD, but it's not that big of a job since the car is still under construction.
Oh yea, the reason for the big gears compared to more normal Vette's is I'm running 30" tall rear tires. If you convert from my 30" tires to a more typical 25" tall tire the equivalent rear ratio would be 4.05. 4.05*2.78=11.25 total reduction in first, for a 3.73 and 700-R4 3.73*3.07=11.45.
Thanks - Greg
I've initially setup the rear ratio at 4.86 based on what I wanted the cruise RPM to be with a 200-4R overdrive trans (0.67:1 in OD). I've gotten some fairly strong opinions from one trans shop that the normal 2.78:1 first gear for the 200-4R would be too much to ever hook up with my current rear gears, and is suggesting an alternate trans (AOD based) with a 2.40:1 first gear.
Would the 2.78 "really" be too much? Would the 2.40 "really" be a lot better? I'd prefer not to change the trans mounts to accept the AOD, but it's not that big of a job since the car is still under construction.
Oh yea, the reason for the big gears compared to more normal Vette's is I'm running 30" tall rear tires. If you convert from my 30" tires to a more typical 25" tall tire the equivalent rear ratio would be 4.05. 4.05*2.78=11.25 total reduction in first, for a 3.73 and 700-R4 3.73*3.07=11.45.
Thanks - Greg
Race Director
Joined: Jan 2003
Posts: 15,175
Likes: 86
From: State of Confusion
Re: How much gear ? (GregP)
Just for reference purposes: I have a '79 Z28, weighing 3800+ lbs w/ driver. The 355" 10:1 SBC makes approx 420 HP @ 6200 RPM, running 12.80s with ease. I have an 8"-4500 stall torque converter in front of a THM400 w/ extra-low gears (2.75 1st, 1.57 2nd). The 12-bolt rear has nothing more than 'on-sale' traction bars added, and a 4.56:1 ring & pinion. I run 28" x 10" Goodyear Eagles on 8" wide wheels. The car hooks consistently enough to win MANY rounds and races; my typical 60' time is 1.88-1.92 (slow, but I deep-stage for quicker Reaction Times). My 'total' first gear ratio is 12.54:1 (2.75 x 4.56). GregP, you're THE first person I've known who considered the 'total' ratio! I can't say if your Corvette will 'hook' or not, but I think it boils down to four things: #1-'total' torque (don't forget, my SBC's torque is being multiplied MANY times over by the 4500-stall converter!); #2- 'total' first gear ratio; #3- the 'foot-print' of the rear tire (how 'WIDE' are your tires, GregP?); and #4- how well your chassis 'works'. If you have good weight transfer and a good 'foot-print', it 'should' work fine. Consult local racers and get their opinions. Let us know your findings! Just my $.02
Thread Starter
Drifting
Joined: Aug 2000
Posts: 1,805
Likes: 36
From: Annapolis MD
Re: How much gear ? (Glensgages)
Glensgages -
Thanks for the reply. Your setup (4.56 and 2.75 first) is sure close enough to say I'm not way out of range anyway.
The normal street tires are 15.50 x 29.5 Hoosiers. I could fit up to 17.50x32 slick, but doubt seriously I'd ever need that much tire. The chassis is essentially a back-half with 4-link and full cage, motor is moved aft about 10" and wheelbase is stretched a few inches just for fun. Weight "should" be under 2800# (I'm pushing for 2500 but who knows if I'll make it or not until I can get it on a scale).
The trans guy was so adament about it being too much gear I wanted to make sure I'm not misisng something, never too old (or stubborn) to learn something new.
-Greg
Thanks for the reply. Your setup (4.56 and 2.75 first) is sure close enough to say I'm not way out of range anyway.
The normal street tires are 15.50 x 29.5 Hoosiers. I could fit up to 17.50x32 slick, but doubt seriously I'd ever need that much tire. The chassis is essentially a back-half with 4-link and full cage, motor is moved aft about 10" and wheelbase is stretched a few inches just for fun. Weight "should" be under 2800# (I'm pushing for 2500 but who knows if I'll make it or not until I can get it on a scale).
The trans guy was so adament about it being too much gear I wanted to make sure I'm not misisng something, never too old (or stubborn) to learn something new.
-Greg
Race Director
Joined: Jan 2003
Posts: 15,175
Likes: 86
From: State of Confusion
Re: How much gear ? (GregP)
GregP, between the two of us, we STILL might be old enough or dumb enough to screw this up! :crazy: If your tranny-guy doesn't know of the tire size, chassis-function, etc., or been around racing, he is probably trying to 'do you a favor', in his mind. None-the-less, check w/ local racers; your local tracks will open long before mine!
Team Owner
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From: Former NCM Drag Racing coordinator, National director Corvette Challenge Spring Hill, Tennessee: Whiting, New Jersey
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Re: How much gear ? (GregP)
Glensgages -
15.50 x 29.5 Hoosiers. 17.50x32 slick Greg
15.50 x 29.5 Hoosiers. 17.50x32 slick Greg
:eek: :eek: :eek: :eek: :eek: :eek: :eek: :eek: :eek: :thumbs:
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From: Exit 89 GSP,Lakewood,NJ The Land Of Mojo
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Re: How much gear ? (GregP)
Greg, I'm no expert, but with the size of tire you are running, I think you'll be fine. That's going to be a huge contact patch, traction shouldn't be much trouble.
