I don't have tons of race experience but that ratio change will increase your RPM at 112mph to over 8000

5 ÷ 4.11 = 1.219

1.219 x 6800 = 8,292

The reality is that there is a bunch of converter slip at the 1/8 with the current combo(about 2000rpm worth……..+/- 30%).

That situation should improve noticeably with the lower gears.

Mathematically, the 5.0 gear would still have the drive shaft rpm under 6k @112mph.

5 ÷ 4.11 = 1.219

1.219 x 6800 = 8,292

This would be true with a manual trans as long as the clutch wasn't slipping. The problem with the OP setup is that it appears that his torque converter is slipping a ton at the 1/8 mile mark. As far as we can tell from the numbers he posted, his driveshaft is turning about 4400 rpm while his engine is turning 6700 rpm. Could be a bad converter, could be the wrong gears, could be something else.

Apologies, I should probably keep my mouth shut lol.

My goal was to accelerate out of the launch harder or faster. If that was to give up a little MPH at the 1/8 I was ok with it. I’m confused some on the converter slipping a “ton”. I told BTE/abruzzi what they flash at, what I shift at and what RPM is at the 1/8 and they both run about the same/setup similar.

The car will accelerate out of the hole harder as long as you have traction. You have huge rear tires so I assume you have plenty of traction but I guess you'll find out. A simple data logger would answer a lot of your questions but if you don't have access to one you can get a lot sorted out by just using simple math. The math right now shows your converter is slipping about 35% at the 1/8 mark. That isn't a huge surprise if the car is still accelerating hard at that point. Cars set up for the 1/4 mile are often slipping the converter a bunch at the 1/8 mile, especially if they have just shifted into high gear.

How fast should your car go in the 1/8th based on weight and power? That number should be your "guide". Once you know that number you can figure out what your gear ratio should be. It really helps if you know what the power curves for your engine are. If you don't have any dyno data then you have to work off how the car feels. Is the car laying over at 6700 rpm or is it still pulling?

When do you pull into high gear? Pretty close to the finish line or halfway down the track? With the 5.0 gears you might be pulling into high gear pretty soon after you leave the line.

That is enough info to put into Wallace Racing calculator. The 1/8th mile calculator at Wallace says 650 hp and 2900 lbs will run 6.09 in the 1/8th at 109 MPH and the ideal gear ratio for 6700 rpm and a 32 inch tire is 5.83

A starting line ratio of 9/1 is very close to optimum, maybe a tad high. 4.88 x 1.8 would be 8.78, not too much unless you have very large stroker motor. I get away with 11.17 due to using a soft launch (low rpm) and 33 inch tall tires.

I’m interested in what you are trying to say here. It’s a 500ci Indy maxx aluminum block, just 4.15 stroke.