Drag Strip Gear Question

[tall69]

So, I need help understanding something.  If I lower my gear ratio, from 4.11 to say 4.56 to improve my starting line ratio, but increase my tire diameter (from 27 to 29) to keep my big end RPM in check, would I actually be improving the mechanical advantage at the starting line or would the changes cancel each other out?  Let's assume I'd have no traction problems with either tire and gear setup.  I understand the physics behind it, but I'm wondering if any of you have tested this at the track.

[Rory428]

Well, if you are having no traction issues, I don/t think you would gain much, if anything. Years ago, my buddy had a street/strip 70 Chevelle SS454 LS6, with a TH 400 and 4.10 gears. It was running low 12s at 116 MPH on 8 1/2x26-15 M/T slicks, with a best of 12.10. He hated the way his Chevelle looked with such short tires, so he went to a set of 4.88 gears, and 29 1/2 tall slicks. The car did look much cooler, but the net result was about zero. He did get a best of 12.09 out of it

[ericwevans]

Your gearing change is just over 10% while you're enlarging the tire diameter by  about 8%.  This will leave you with a change on the starting line of about 2%.  It would be like having a 4.19 gear with your current 27" tire.  So yes, they would largely cancel each other out, while still leaving a minor change.

[BattlestarGalactic]

So is the car bogging off the line, is that the reason you want a deeper gear?  Yes, putting a bigger tire and equally more gear is not going to help, likely make it a bit worse.  You need some tire rotation(spin) to help keep the motor up in the power.

[tall69]

So is the car bogging off the line, is that the reason you want a deeper gear?  Yes, putting a bigger tire and equally more gear is not going to help, likely make it a bit worse.  You need some tire rotation(spin) to help keep the motor up in the power.

Yes, it dead hooks and bogs.  I'm running 27x10.5 QTPs, with 18-22psi and a very mild burnout.  On one run last year, my clutch or tires slipped a little on the launch.  This resulted in a 1.71 60' and 11.90 ET, my best in both cases by a significant margin.  Do I try more air in the tire?  Smaller or different compound tires?  How do I get a controlled slip at launch?

[Falcon67]

It is setup dependent but I have not found any ET between a 4.11 and a 4.56, after removing other factors.  That's with a mild motor pushing a heavy car.  Sounds like your real problem is not enough starting line RPM.  My bitty 302 leaves with a 1.68 60' time, but the converter flashes to 4000 doing it.  If I put a 11" street converter in it, flash maybe 2200, it's leave like a bus even with the 4.56 spool in the back.

Drag radials usually work best in the 16 lb pressure range more or less.  Look at the wave pattern on the tire, it will tell you.

[My427stang]

You clearly need more power

Just teasing, but will your engine handle the additional RPM at the big end if you keep the same tire and go 4.56s?  If the answer is yes, add the gear but don't add the tire

If the answer is no, and its a CR 4 speed, I'd go wide ratio, if it's an AT, I'd add more converter, in fact, that may be the better answer in any case

[BattlestarGalactic]

My guess is the Close ratio toploader is causing all the problems.  They were fine if you have 4.88 gears in the back and slicks from the 60's that spin real easy.

What for shocks are you running?  Traction devices?  You need to tighten things up to not allow so much bite.  Tighten the front end so it doesn't rise, tighten the rear so it doesn't plant the tire. 

How about no burn out?  Skip the water, just stage and go.  A heavy clutch and no gear ratio is hard to get moving.

[Rory428]

I agree with Larry, if you still have a close ratio toploader, changing to a wide ratio gear set will make a major improvement in getting a heavy car off the line. Your current 4.11s with a CR 2.32 low gear gives you a starting line ratio of 9.53, leaving the 4.11s, and using a WR 2.78 low gear will give you a starting line ratio of 11.42. Even if you went to 4.88 gears, with the 2.32 low, your starting line ratio be a bit less than that (11.32). There really is no downside to using the wide ratio gearing on a street/strip car, or on the dragstrip. Maybe on a road race course, but you are not doing that, right? Back in the 80s, I had a 70 428CJ 4 speed Mach 1, with 4.30s and a Detroit Locker. With Goodyear 10x28" slicks, I could not get the car to leave as hard as I wanted to, plus I had to replace the clutch every other year. A buddy lent me a big spline (input and tail) crashbox Toploader that had been converted to wide ratio, out of his drag car.  This was back before 60 foot times were recorded, but the differance in how the car left the line was huge. Unfortunately,on the first pass, the mainshaft broke on the 2-3 shift, so I never did get a full 1/4 mile pass with it, but between how much harder the car pulled off the line, and a Friday night  "test cruise" made it apparent that the car was gonna pick up noticabely.  In talking with a couple of other guys who had done the same thing, they figured .15 ET improvement was typical. If I still had that car, I would have loved to have tried my 3.19 low gear Jerico in it!

[tall69]

My guess is the Close ratio toploader is causing all the problems.  They were fine if you have 4.88 gears in the back and slicks from the 60's that spin real easy.

What for shocks are you running?  Traction devices?  You need to tighten things up to not allow so much bite.  Tighten the front end so it doesn't rise, tighten the rear so it doesn't plant the tire. 

How about no burn out?  Skip the water, just stage and go.  A heavy clutch and no gear ratio is hard to get moving.

I switched to wide ratio kit when I rebuilt my toploader two years ago.  I wish there was a better 1st gear option for toploaders.  2.78 is just not deep enough.  I heard bad things about the 2.90 first gear so I skipped it. 

I switched to 90\10 drag shocks, small block front springs, and roller perches last year.  Which might have me going the wrong way?  I have slapped bars on the back with an extra leaf on the passenger side.  I'm launching at 4k+ RPM.  I'm already worried about breakage.  Thus far, it's either bogged or the clutch has slipped.  I really need a soft-lok clutch, but I drive it mostly on the street and don't want to deal with those headaches. 

I could maybe go to 4.33's from 4.11's.  It would raise my big end RPM by a couple hundred which would put me just beyond my targeted RPM max of 6k.

[57 lima bean]

11.90 street car.....I'd leave it alone.At over two tons,you don't want it to turn into a parts wrecker.

[Falcon67]

I'll also add that you'd only want to go to a taller tire to increase your contact patch, as in having traction - spin - problems.  If you are not having spin issues, then go up a gear and leave the tires.

[tall69]

I'll also add that you'd only want to go to a taller tire to increase your contact patch, as in having traction - spin - problems.  If you are not having spin issues, then go up a gear and leave the tires.

Okay, so no to a bigger tire.  I need to introduce tire slippage into my program.  I was under the impression that increasing tire pressure should theoretically create less traction.  Is this not accurate?  I've tried 18-22 psi and it still dead hooks.

[57 lima bean]

Is there a harder compound tire available?   http://hoosiertire.com/assets/Drag-Racing-3-17-17.gif

[MRadke]

What about a narrower tire?