Aright, I see guys telling other people that, 'at that MPH you should be runnin 12's, you need to work on your short times' How do you know this? Wheres the chart....

 

There is no real chart. MPH is a relationship to HP. ET is a relationship to gearing and traction. You can have a great MPH but poor ET if you can't hook up off the line or have poor gearing to use the engine's power better.

Then I still had a 383 stroker and 3.27 gears in the diff I was running very high 11's at 117 mph. Normally 12.0 is around 108-110 mph and 117 mph should be close to mid 11's.

My problem was that the gearing was all wrong. Because of the 3.27 gears, I was shifting into 3rd somewhere between the 1/8 mile and 1000 foot mark. When I crossed the finish line my rpms were still way below my shift point of 6800. The car had MPH because it was just getting into it's powerband as I crossed the finish line.

The only way a MPH/ET relationship will work is if you're topped out as you cross the finish line.

 

Hey Stephen....does that go the same for A4's??

 

You don't want to use OD in a drag race. The gear is small and weak and takes away a lot of power. It's designed to bring the rpms down while cruising down the highway not for WOT operation.

If properly set up you should cross the finish line at the top end of your 1:1 gear.

 

I dont think OD is a problem because my car doesnt even shift into OD until like 130-135mph. I have 3:23 gears in right now.

 

I see what you're asking and I'll here's what I think about it.

If you run like a 12.5@108 it means you're getting off the line super quick and not really gaining that much more up top.

On my first run at this track I had never been to before, I spun bad TWICE after I left the tree and wound up with a 15.0@103. Tell me how many 15 sec. cars trap 103? I compensated for my screw up by my car having enough power to wind out a good MPH on an otherwise bad run.

This guy I was talking to with a Lightning was running high 12s@105-106, which means he must be getting off the line super quick if he's trapping the same as me, but with a better 1/4 mile time. See what I'm saying?

When I first started reading 1/4-mile times I didn't understand them at all, but after a while you'll catch on.

 

You guys are on the right track. There are formula and you can make a chart of the various ets for a given mph.

They are called the pro stock et formulas. This is because they are empirical formula derrived from the pro stock drag racing class.

For every MPH these formula determine the quickest et that a car can acheive. Again, all real world ets based on ets pro stock cars acheive.

Bear in mind there is a different formula for cars under 100mph and that the formula were based on naturally aspirated cars.

I've said it before and I'll say it again, If you can run the pro stock et for any given MPH you are doing an excellent job with your combination. All components would need to match: converter, transmission gearing, rear end gearing, tires, traction, etc.

You will find the formula all over the web. Prestage.com is a good place.

I wouldn't even think of making any changes to any car without using the formula as a yardstick to see where I'm at and where I need to go. They are truely an invaluable tuning tool.

 

Yea....what he said. Also...thanks for the answers guys

 

www.prestage.com

My first link.

 

my second try

http://www.prestage.com

 

www.prestage.com

 

Well I just don't know how to make the link. Seems like the second one should have worked. A real easy version of the formula looks like this:

Et=1353/speed.

I'll keep working on the link.

 

The horsepower calculations on that site seem way too high. Maybe by as much as 20 %.

Daren

 

Be careful the formulas use rear wheel hp. Not flywheel. They claim about a 15-20% difference. I use 10-11% for chevy and 17% for ford (the pinion gear is further offset from the ring gear center resulting in lower drivetrain efficiency).

I've gone 13.7 @ 100,

10.10 @ 135,

10.30 @ 133,

12.24 @ 108,

10.89 @ 125,

Just a few I can remember,all within a couple tenths, it's not the exact formula but close and better than guessing. If I remember, I'll look tonight for the actual formula.

 

I run 13.34 @ 99.7 with a 1.84 60' on street tires. What does that say to you? From what I have read in this post I must have traction but not much HP? That was in a 3800lb car.