3100 lb car, 421-670 hp, glide with 1.80s, running 5:13 gear, leaving at 3800 shifting at 7000 and crossing the 1/8 at 7300, car runs 6.10-6.20. I'm changing from a 28X10, 87 rollout to 33X17/16 103 rollout. The few calculators if found show 6.08 gear. Does that sound right ? I'd like to keep it crossing the line around the same rpm

IF USING WALLACE CALCULATORS they have one to show rpm using gear and tire size.

3.1459 x 32.73 = 102.97

3.1459 x 27.65 = 86.98

This message has been edited. Last edited by: Mike Rietow,

I hope you have good track prep. That's a big increase in torque multiplication to the tires.

I'd leave the 5.13 gears in it just to see what it would do first.

The 33 tire is a steam roller compared to the 28. Changing from M/T 28X10.5 89 rollout to the Hoosier 28X10 87 rollout picked the car up 6.15 to 6.10 so I know leaving the same 5.13 gear will kill the et. Maybe I’m looking at it wrong but the final ratio would be the same 5.13 28 as the 5.98 33 so what would be any different ? Not being a smart ass just trying to understand why you say the torque mutiplation would change so much.

The car 60’s 1.28 now and doesn’t MPH that great at high 108 for the ET compared to what I see most BBC do with 1.35-1.38 60s and high MPH so I don’t mind the torque as long as it’s the same as now.

5.43-5.67 Will be plenty

What’s the convertor stall at? It’s possible the engine spending more time at a lower rpm might produce same et with more mph. I agree with others that put the tires on and run with the gear you presently have. It’s free data.

Converter flash is 6300

I know it will work with the 5.13 but it will loose ET and that I'm not wanting

I have ran a near similar combo, as well as transmission customers of mine. It would help to loosen the converter a couple hundred more, but a 5.43 should be plenty. Are you on alky?

What it picked up with the shorter tire is telling ya the stall is a little too far above peak torque, same as the 7,000 rpm optimum performance shift point. That and the fact it crosses @ 7300 rpm slipping 5.5% at only 108mph.

Gonna be disappointed in et with the big tires. They're gonna slooow it down. If it were me I'd tighten the converter 300 rpm 5.83 Motive "performance" part # ring and pinion to lesson the disappointment. My guess it'll go 6.15 like that, maybe a little better w/big tires.

This message has been edited. Last edited by: Mike Rietow,

What are you trying to accomplish? More ET? More MPH? More traction? All of the above??

I looked back at your OP and think you have miscalculation in tire roll out. Those 33x17-16 will be over 105 when rimmed and aired @10psi. My recent set of 32x14-15 Hoosiers are 103.5 on 14” wide rims.

A smaller tire than you selected will produce better ET as another has said.I think your stall is fine and would want more if changing.

Converter was going 6000 and I had it loosened up 300 and the car did pick up 60'and ET. When ATI loosened the converter they said they couldn't tighten up to any so I went from 71 to 73/7400 at the strip. On the tire size there mounted aired to 10psi and measure 103. I'm not looking to gain any ET just not looking to loose a ton either. Car 60s deadly consistent all year but 330 moves in the hot summer more than I like. 60' 003 all day cold or hot, 330 may move .020 pass to pass so I'm looking at the wider tire fixing that issue.

And yes on alky

I would go with the 5.43 gear. That is going to help put some efficiency back into the converter. More gear than that, and you might run into inconsistencies caused by other issues. I would expect this car to wheelie more.

I ended up with 5.57 in my 3260# Chevelle but it had 14.5x32 on it.

quote:

Originally posted by C Hodge:
Converter was going 6000 and I had it loosened up 300 and the car did pick up 60'and ET. When ATI loosened the converter they said they couldn't tighten up to any so I went from 71 to 73/7400 at the strip. On the tire size there mounted aired to 10psi and measure 103. I'm not looking to gain any ET just not looking to loose a ton either. Car 60s deadly consistent all year but 330 moves in the hot summer more than I like. 60' 003 all day cold or hot, 330 may move .020 pass to pass so I'm looking at the wider tire fixing that issue.

Is your car spinning after the 60 foot? If the sixty is consistent, but the 330 isn't, unless you know its spinning, I highly doubt a bigger tire is going to correct the issue. My car was doing the same thing a while back. 60 would be within .003-.005 and the 60-300 increment would move .02-.04. Turned out to be issues in the transmission. I would be looking at what triggers the shift and how it shifts. When was the last time the transmission was freshened?

I've chased my tail for 3 years fighting the 330 issues. I changed from the heidts a arm front end to a Alston strut front end. It helped but didn't cure it. Added the grid to kill timing because I did norrowed it down to spinning when it shifts and that helped. Fixed it in cool weather but only made the summer better. I've added up to 150 lbs of weight. I've had the trans out added more high gear clutchs. I've moved 4-link bars in every hole and it boils down to just needing more tire. Trust me if I thought there was something that was causing it I've changed it. Good tracks it's deadly but not many of those left