I am working up the combonation with my new motor, and am unsure on what gears to run.


Specs,

Drag car, 1/8th mile

Engine .060" 427 big block. 14:1

Cam has 280/290 duration at .050" .780" .712" lift

Tranny, Pwerglide, with brake 8" converter should stall right around 5000

9" rear spool

Tires will be 28x10.5 slicks

Race weight, 3200lbs

Some of my race buddies have said to run a higher gear because of the small tires, no lower than 3.73

I was thinking something lower, like maybe 4.30's

Ideas?

 

at 3200 lbs and a glide, 1/8th mile only, 4.88. I run a 5.14 in mine with a very similar setup as you. I leave the line @ 3,400, shift around 6,750, and go through the lights around 7,000. thats with 28x10.5's, and a glide with a 1.76.

 

I was going to suggest something in the 4.10 to 4.56 range for those short tires and only 1/8 mile racing.

My current combination uses 29.5" tires and 4.56 gears. My converter stalls at 6000 and I launch at 4500. About 3 seconds out of the hole I'm shifting my PG from low to high. I'm more set up for 1/4 mile racing though.

With a 1.40 60' time and 1/8 mile is 6.24, you would have to figure I'm shifting between 100 and 200' from the starting line. With too much gear/converter, you might end up shifting by the 60' mark. It doesn't really matter where you really decide to shift. There are some drag cars with powerglides running high gear only so they never shift.

The key to a good tire/gear setup is to stuff the tallest tire possible under the fenders then adjust the gearing to best suit those tires. A tall tire gives a better footprint from front to back. This will give better traction than a short wide tire.

 

I shift my car at exactly 2.25 seconds after it leaves the line. that puts the shift point right below 6,800. then cross the line around 6.65 ish or so. I shifted at 2.50 with the 4.56 gear. My best 60ft with the 4.56 was a 1.46. The best 60ft with the 5.14 was last week, 1.423.

 

I've always thought my 4.56 gears were not enough. 4.86 would be better but all the software programs I've tried say my combination should actualy be using 4.30 gears. I have a set of 4.30's but they're not set up in a third member to do a simple swap.

When I make the switch from 29.5" tires to 32" tires, all the software programs say 4.56 gears would be best when I think something in the low 5.xx range would be better.

I guess it just depends if you want super low 60' times or the quickest run possible utilizing the best power band range of the engine.

Gear selection also depends on the weight of the car. Heavy cars need deeper gears for torque multiplication. Light cars don't need as much gear.

 

id say somewhere from a 4.56 to a 5.13