Neil B

Hey Guys, I'm getting ready for the Texas Mile in a few weeks and I'm debating what to do about gearing. The car currently makes approx. 820 rwhp and has an MN6 transmission with 3.73 rear gears. I'm running a 345-35-18 Hoosier R6 which is 26.8 inches tall. Therefore, (if the stars align) in order to run 200 mph in 5th gear (.74 ratio), I will need to turn the motor 7,000 rpm.

I believe the motor's internals are up to the task with a Lunati crank, Oliver rods, Morel lifters and good valvesprings/pushrods. The cam makes peak hp in the 6,500-6,600 rpm range. So the question is, do I leave well enough alone and let it eat or do I look for a taller tire? I do not want to change transmission or rear end gearing at this point.

And if I go with a taller tire, what do you recommend? There aren't many options available in the 27-28" diameter range unless I go to a 19 or 20" wheel. And if I go with a taller tire will that mess with the TC/AH combined with my 275-35-18 front tires?

Also, I have run this car in the 1/2 Mile and it ran consistent 5,800-6,000 rpm (high 160's) in 5th gear on a 26.6" tall tire. That was with a larger pulley and about 3 lbs. less boost than I'm making now.

Opinions welcome. Thanks!

gotjuice?

Need more details. I assume this is a C5 coupe. The rear tire size, Is that a typo and a 19 inch rim? I think that is the same size that I ran in a 19 inch, 30 series. The gears are going to hurt you. How much torque, That is what you need at the Mile. I don't think you will make 200mph with a blower only car at that hp. Good luck and prove me wrong. I will be there to watch this time as I did not finish either of my vehicles.

Peter pan ran his C5, Same gears with 325 30 19 tires 3.42 gears with 750 hp. He was able to run 190.?. Not sure what rpm he ended up at.

I ran with 3.42 and same trans ratio, 345 19's. Went thru the traps at a little over 7k rpm, 215 mph. This was in a C6 Z06. I had more power than you are making.

Neil B

The car is a 99 FRC. MN6 trans with .74 5th gear. 3.73 rear gears. The car is flared and has 18x13" wheels with 345-35-18 Hoosier R6 tires (26.8" tall). Torque is in the 700 lb/ft range. I'm ok if it doesn't run 200, but I don't want to run out of gear in 5th. It was pulling 6,000 rpm in 5th gear at a half mile event.

gotjuice?

Ed ran his 03 Z06 stock trans and rear. Taller rear tires, Not sure of the size. He ran 198.? going thru the traps at 7400 rpm. No blower just larger built engine and juice.

winters97gt

Add a 100 shot. I think you're going to low on the torque as well. DA and wind will have a big effect.

gotjuice?

I agree, But I think the gears are still too much. Horsepower does not mean too much compared to torque. I have proven it several times at the Texas Mile.

Neil B

'Too much' gear as in I need a lower numerical ratio (i.e. 3.42 instead of 3.73)?

winters97gt

I'm pretty sure that's what Got Juice meant. He's pretty much the go to guy on Texas Mile stuff. I had the exact same setup as you. 800+rwhp car, RPM Stage 5 T56 with 3.73's out back. I lifted a head and took out my motor last week. I just ordered a built 6.0 block that will be here Friday and my nitrous kit just arrived.

I plan on running the Mile again in the Spring. I plan on making around 900/800 on blower, and 1000/900 on the plate kit. I also plan on swapping the 3.73's back to 3.42's.

Just for reference, I ran 171.5 in the half mile in my C6 with 825-850hp, bouncing off the rev limiter on a 27.4 inch tire in 4th gear. Stock gearing. Probably had a 173 in it if I bumped the limiter. But the car made close to 800tq. Higher compression 402 with a Novi 1500. That torque really pulls when running past the 1/4 and in street races.

JoeyG

Racing in Ohio and Texas I found a 345/35/18 MT took about 75hp more of nitrous to go the same 192-195mph than using a 335/30/18 BFG drag radial. This was with my RPM stage 5 m6 and 3.42 geared C5 coupe. My new setup makes 300 more lb/ft of torque and 100+hp more going along with GotJuices reasoning.

Neil B

This is really good data. Assuming the MT tire is 27.5" tall, you were turning around 6,030 rpm at 195 mph. The BFG tire is around 25.7" tall which would put you at 6,452 rpm at 195 mph. I'm not sure what your power curves look like, but I'd guess you were making more torque at the end of the run on the taller MT tire. Seems like the extra gearing on the shorter tire outweighed being in the meatier part of the torque curve on the taller tires. Do you know your hp and torque peaks?

Thanks.

Neil B

I picked up a set of 28" tires and 19x12 wheels as spares for the event. These will drop my rpms through the traps by 300-400 rpm. I will run both rear tire combos and see which one yields the highest mph. With my shorter Hoosiers (26.8") I have the same effective gearing as a ZR1 in 5th gear:

ZR1: 3.42 rear x .81 5th gear x 26.6 tire x 6,900 rpm = 200 mph
My car: 3.73 rear x .74 5th x 26.8 tire x 6,900 rpm = 200 mph

JoeyG

This was the dyno run of my old 416 single stage setup. I would run a 10# bottle and see pretty big pressure drops toward the end of the run.

Neil B

It's pretty interesting that the better gearing with the smaller tires went faster even though it pushed you further past the hp and torque peaks.

JoeyG

Rpm pickup on dyno was off by about 1000rpm. Thats why #'s happen so low in powerband

robert miller

with you on the TQ. Also to run good in any type of racing the full car has or needs to be set up for that one type of run what ever that is. You have one nice car man.. Robert