rcdynamic88

In need some input as to what rear gear ratio is preferred for 1/4 mile drag racing when running a 455 Olds with a T400. I realize there are many variables to consider...but what do some of you use...what are your 1/4 mile ET's? What is your preferred way to launch, what RPM do you shift at?

My 455 has a 10.3:1 CR, Edelbrock Heads w/upgraded springs, Lunati hyd roller cam (236/242 @.050 .565/.565 lift), single plane intake, 780 cfm QFT carb. T400 has a manual valve body and a 2500 stall converter.

This is in a 65 Cutlass that has a Moser bolt-in Ford 9". I use a 3.50 gear for street driving. When I go out to our local "marked off" 1/4 mile, I seem to just get into 3rd/Drive and get to about 4300 rpm and I have reached the end. I think I should be winding it out to a higher rpm at the finish.

I was thinking of getting another third member with a 4.10 gear, But I don't want to go too far, or not go enough. I have 28" tall tires and was planning on getting some drag radials of the same size.

So...what gear do you guys run...what do you think would work best for me?

J-(Chicago)

I run 13 flat with small valve heads, a 3.23 gear and 9:1 compression.
Shift it around 4700. go through the traps in 3rd around 4 grand if i remember correctly. Stock 69 2 barrel rotating assembly.
I'd judge your shift points by the strength and weight of your oiling and rotating assembly.
Since it's not my engine, I could recommend you to spin it to the moon, but I'm not sure that is sound advice. What times are you looking to achieve?

Run to Rund

Tire diameter, rpm, and trap speed are important. With 30x9 bias ply Hoosier slicks, here are a couple examples: 6000 rpm, 111 miles per hour, 4.86 gears; 6000 rpm, 116 miles per hour, 4.57 gears. The rpm readings are approximate; could be plus or minus 100 or so rpm. Now, with the low revving 455, you may want to keep it down to 5500 rpm like the NHRA stockers do. Early 400 and 425 like more rpm. You will need to calculate the difference with 28" tires and remember the radials don't grow at the top end like bias ply tires do.

rcdynamic88

I spun it to the moon last year, and hit it N2O, not good results ...thats why I have a new build this year. I asked the Lunati rep to come up with a cam that would be strong to 5600 RPM, and I got rid of the N2O. I would like to get into the low to mid 12's. Is that out of the question?

507OLDS

You want to figure out where the engine makes its peak HP.Then gear the car so that it is right at that rpm when crossing the line.If you are under that rpm,your engine is still accelerating,& making power,and not achieved maximum potential.If you are past that rpm,you are past the potential,& actually starting to lose power,& possibly starting to slow down a bit,plus putting unwanted stress on the engine.
Based on what info you have supplied,I would try a 3:89 gear(for the Ford rear).I'm not sure if a 3:70 would quite make it,but would be close.Again,it depends on where you make peak power.
My engine peaks at 5800rpm,so there is no reason to go beyond that.I have 3:73's,with 28" tall drag radials,3200 stall converter,& shift at 5500.She crosses right at 5800,but it did take a few different converters to get it spot-on.

Kennybill

You didn't mention any "oiling system" modifications. I would try the 3:50 gears first. I would be on the conservitive side of RPM's. Give it a try and see what your times are with your current setup. Then when you spend the extra money you can judge if it was worth it. JMO, Ken

Run to Rund

I agree with 507olds. If you take the mph that easily gives mid 12s, 111, and convert: 4.86 x(5500/6000) x (28/30) you get 4.16 ratio. The tire diameter difference will actually be greater if you use non-growing drag radials in nominal 28" vs. the maximum diameter NHRA stocker Hoosier bias ply tires, so something in the range of 3.89 to 4.11 should be good.

rcdynamic88

Thanks for all the input! I'm going to try the ratio that "507Olds" and "Run to Rund" thought would be close. I'm will have my other pig set up with a spool and some 3.89 gears.

Run to Rund

Here's another thought. There isn't much difference between 3.50 and 3.89. I'd make a few passes with your 3.50s first and then you can get a closer look at what difference would be best among the 3.89, 4.11, and 4.29 ratios available to you. Some racers like to overrev somewhat in high gear; it depends on whether power falls off fast after the peak rpm.

MN71W30

Some 26" tires would help without a gear swap. Years ago we had a stock 69 455 Olds that ran slower with 3.90 gears than when it had 3.55 gears. It seemed like it couldn't rev fast enough to handle the steeper gears. The motors best atribute was it's torque. When we geared it for torque we made our best run. It may or may not make a difference with the gear swap. I'd be interested to see the results.

Run to Rund

By the way, an NHRA stock racer told me he runs 4.33 gears with his stick 455, 9x30 slicks, car runs mid to low 11s at 2100 feet elevation (Las Vegas).