Car is 2985 lbs. Current gears are 4,56 and goodyears 32x14.5 (32.8) 103 rollout. Powerglide has a 1,80 straight cut gears. 8 inch converter that when I tried by pushing the transbreak and flooring it and then letting go of transbreak and gas it went to 6150. What do you think of gears would you keep them or go to 4.30. Will be racing both 1/4 and1/8 mile. Will be loosing some weight in the near future. I bought fiberglass doors and complete front end. Will be running e85. Dyno sheet is the second one for e85. Did only one pull on e-85 and after outing in the engine in car it didn't want to start. We found out one of the rocker arms was not torqued right so the pushrods came off the rocker arms. Lucky nothing happened. Torqued down and everything sound good. Suspect it made less hp because it was getting loose.

I don't really understand the question

If you was testing the convertor and it went to 6150 and you shift at 6700-6800 then it will be fine

I would think 4.56 and 32 tire should run the 1/4 mile at 6800 rpm or so
Hope this helps

Try the 4.56 gears and see how they do. They should be close enough to make some passes. My guess is that you'll eventually need to swap in the 4.30 gears as you get used to the car and the power. You have enough power there to run high 8's at over 150 mph so depending on the converter slip you'll be spinning the motor pretty hard in the lights with the 4.56 gears. Depending on how well the chassis works and how good you are at tuning the engine you might eventually need to drop down to a 4.10 gear. You'll just have to work the process and see where you end up.

Up to 150 mph at the stripe, you should be fine, about 7400 rpm. That is figuring on decent lockup of the converter. You might want to call the converter builder and ask them . I suspect though that you will be told to try it. More gear with the glide will help, so if you have faith your motor can trap as high as 7600, i would run the 4.56. what track are you going to run at? I may be in your area right now.

I think you are going to end up with the 4:30s with that short 103 circumference. Where do you want to be RPM wise? Looking at those sheets I would say low to mid 7000s at the least.

My car is similar to yours with less power and with a glide, 4.30s, 106-107 circ. slick and a 6200 stall 8 inch converter I was over 7000 when I was running 1/4.

I only run 1/8 mile now so I run 4.88s. Shift at 6900 and cross at 71-7200. If you were only running 1/8th the 56s would be perfect I bet.

I loved my 4.30 gear in my Daytona with a stock 1.76 low gear powerglide, and a 16-32 slick. We ran lots of 1/4 mile races and running 5.40’s@160mph it was about perfect.

Your combination is very close to my old S/P car, similar weight, HP and tire size. Shifting it at 7000 RPM in the 1/4 mile that car ran 8.862 at 148.6 MPH, moving the shift RPM up to 7300 RPM the car went 8.866 at 150.4 MPH
That surprised the heck out of me, shifting it 300 RPM later out of 1st gear made the car pickup 2.+ MPH in the last 300 feet All the other times, 60Ft,330, 660 and 1000 Ft times and 1/8 mile MPH were identical
I did switch the rear tires later to a set of Goodyear 15x33x15 and that help hook the car up better over the Hoosiers and M/T
My new car will have 17x34x16 slicks on it due to having a lot more HP2300+ and in a smaller lighter weight car hopefully making north of 2500 HP

Depends on high you want to twist it. And how much power it actually puts down in the car. 890@2985 shows it's 156+ capable. Thats around 7850 with 5% converter slip, 4.56, and a 32" tire. A 4.30/7400, 4.10/7100. Now if you knock 10% Hp for loss you would run closer to 150. That would put you around 7550/4.56, 7100/4.30, 6800/4.10. Mine uses a 31 " tire (97" rollout), 4.30, 5% slip. It goes thru just over 7300@150 .
Doug

Gear the rearend for top end RPM. Trans gear for SLR.

Brackets, consistency, be conservative. Make it ET, make it 60', even if it's on the chip the last 100' of the track.

1.80 that heavy should be OK.

Since you already have the 4.56 gear in the car, I would run it at the 1/4 mile and see where the finish line rpm ends up. I would not worry about 7400-7600 for less than a second. Just have the valve springs for it....
If it ends up needing 4.30, then change them.

I'll be trying the 4.56 gears as recommended. In my previous engine which was a 499 that made 764 hp on the dyno at 6400 and shifted at 6600 car would go through the stripes at 7350 in excellent weather. When it would get hot (100f) which was most of the time it would trap at 7100. It is the same converter and same gear ratio and transmission. I will probably shift this one at 7000. Just don't want to trap at 7600 or more. I'd rather trap at 7400.

So what gears and transmission did you run with the old combo and at what altitude?

I'll be racing in Monterrey Nuevo León, Mexico. Elevation is 1400 but with the heat corrected altitude goes up to 5000+ in the summer. We were having and event today and tomorrow but it got canceled. We have rain int the forecast. It was going to be cold so altitude was going to be at around 1500 give or take. It would've been great to know the potential of the engine.

Converter company is Coan they told me that the converter would work fine no need for me to send it for adjustment. They said they could make it looser if it needed but not tighter. If wanted tighter I would need a 9 inch. They also said toctry out my gears. I suspect that it would need a 4.30.

You added 100 hp over your old combination so it is going to go faster. If nothing else has changed then you'll trap faster than 7400 rpm if you were going 7350 before. The same converter will slip more since the engine has more power so that will raise the engine speed too.

Track temperature and track prep down there may influence the low gear/SLR decision.

That car had 4:56 rear gears and a 1.80 low gear in the powerglide, I race it with four different sets of rear tires,14x32,15x33x15, 13.5x32 and finally 16x33x15.
The 1/4 mile track, Woodburn, OR is right at 180 Ft above sea level the best that car ran there was 8.862 ET with a best of 150,5 or so MPH. with a D.A. of around 1400 Ft. I raced that car mainly at the local 1/8 mile track at Madras ,OR airport which is right at 2500 Ft above sea level, the D.A. would vary there from 1400 FT to 4800 FT depending on the time of year and existing weather conditions Best ET their was 5.50 at 125.4 MPH in the fall just before I sold that car.
That car was real sensitive to track conditions on the starting line, the best 60 ft. was 1.23 in Yakima, WA which had great track prep

What was your trap rpm in 1/4 mile? 8 inch or 9 inch converter and what tires were you using?

I let all my logbooks go with the car when I sold it so I may not have the exact numbers correct on the trap RPM in the 1/4 mile, I think it was near or a tiny bit under 7000 RPM with any of those tires shifting it out of low gear at 7000 RPM.
The converter was a 9.5 inch Powerglide that I had A1 work on to make it work for my bracket motor, it would flash and hold right at 5600 RPM at WOT on the trans brake before releasing, shifting it at 7000 RPM it would drop to betwen 5600 and 5800 RPM depending on the D.A..
I ran several different sets of and size tires, all bias ply slicks from 13.5x32x15 inch Hoosiers drag slicks, a set of M/T 14x32x15 drag slicks and then up to a set of Goodyear 16x33x15 slicks. The roll out was from 101.2 inches up to 105.5 inches on a 15 inch wide rim with rim screws
The last change I did to that car was change the tranny fluid from some trick aftermarket racing tranny fluid to some old Valvoline straight Type F, that picked that stupid car up .2 ET and 2.0 MPH in the 1/8 mile
Guess what I'm using from now on