th350 and 4.30's
 

I've used all these different sites that tell you how to figure max mph and it says I should run a max mph of 124mph @ 6400rpm with a th350/4000stall/4.30's/28" tires. But, I am maxing out well before the finish line and it's no where even close to 124mph. What gives? Can these calculators be that far off?

Its due to converter slip. Your running out of RPM

So if I step down to around 3600 will that make it any better? Sorry if these are dumb questions but I am a 6 speed guy. :)

I'd drop gear not converter dude. I dropped from my T56 gear(4.22) to a 3.90 when i went to a TH350. It seems to be working very well.

I might throw in a set of 3.73's. We have a complete setup ready to go. Also have some 4.11's I can put back in there

From a 4.11 to 4.30 is like only 150rpm. 4.11 to 4.56 is like 325rpm. I just went threw all this. And im running a glide with a 1.76 gear, 9in, 3.50 gear, and 28w tires and im crossing at 6100 off the nos. With the 4.30 im crossing at 6800 off the nos. In the old car i had a th400, 4000, 4.56, and 26" tire. I was crossing at around 6850. With my 315's on, it would not finish the 1/4. Hitting rev. Thos were 25". Anyway, hope this help ya.

Your setup would be good for 1/8th mile.

With a th350, 3.70 gears, 27" tire, 6300 rev limiter my car will tag the rev limiter right before the line in the 1/4. Can fix that two ways. Run a 28" tire or bump the rev limiter up a little.

Have seen several people do this combo for the 1/4. th350, 4.10 gears, 28" tire, 6700 rev limiter.

Thats why you'll see cars at the track with 4.56/5.xx gears running 30+" tires.

Thanks for the input guys. I took it back to the track tonight to run the 1/8th mile jackpot race and it run a best pass of 7.41@92mph with a 1.58 60ft foot braking it from 3000rpm.
I did make a couple of passes all out and it would make it almost exactly to the 1000ft at 65-6600rpm where I was getting out of it and coasting to a 11.71@92mph. I'm thinking 3.89's would be about right.