Tires and dimensions:

[Sumner]

What I do now have enough knowledge about is the torque properties with gear ratios versus tire diameter.  Dad always mentioned a 1:1 final gear ratio out the trans as being ideal.  Don't know if that is a myth or not. 

Our transmission is 1:1 in what is the normal 4th gear, but they can and did put a overdrive cluster where 3rd usually is, so the direct through gear (1:1) is now our 3rd gear.  True we are giving up some HP running the overdrive since it is now not direct (straight through).  The problem we have is that with the Ford rearend we are running we are geared as high as we can be in the rear with 2.47 gears so have to resort to the transmission to run faster at less RPM's where our motor makes it's power.

A cam change or a switch to one of Sparky's GM rears would solve that problem, but as always time and money can rear it's ugly head.  If Hooley sells this car and builds a new one like he has talked about it would probably have a land speed racing type quick change with the low number ring/pinion in it.  Then we could run the 1:1 gear like you mentioned and that would be the most ideal.

c ya,

Sum

[Rex Schimmer]

It really (always!) gets down to horsepower and how much you have at the engine speed that happens when you make the shift from 4th to 5th. Using your numbers: 3.67 rear end ratio, 1.13 4th gear and .91 5th gear and assuming three things: 1. You have enough horse power to reach your maximum velocity at your maximum horse power rpm.2. you are running 30 inch dia tires 3. Your maximum hp is at 8000 rpm. ( I don't know what you have for an engine), but using these numbers your maximum speed would be 213 mph and you would shift from 4th to 5th at 172 mph. When you shift from 4the @ 8000 rpm to 5th your engine rpm will drop to 6430 rpm. Now if you look at the horse power required at (I am looking at aero power only) 172 mph then to go 213 you will require 1.9 times as much horse power to go 213 as you need to go 172 ( Hp required is a function of the speed cubed.) so that says you need at least 52% of your maximum horse power at 6430 rpms to not have the engine stop pulling. So you need to know your horse power curve, not your torque curve. Again this is hp required to over come aero loads only and does not include rolling resistance and any other frictional drags that may be taking horse power.

This also shows you why big blocks  with power glides work at the salt. The gearing my not be optimum for maximum acceleration but neither are the traction conditions so maybe dropping the big block into high gear and letting it lug a little actually could help acceleration by not having to much power available to spin the tires.

Lots of combinations that work and some that don't, the trick is to be able to look at the "cause and effect" and be able to tell why the do or do not work.

Rex

[wolcottjl]

I am beginning to understand.  Now if you drop my max speed by 70mph we are getting there.  My torque curve is pretty flat, it varies about 10% from 2100RPM to redline at 7200.  So I am what I think is 60% of HP or better after the shift.  I do not have a numbers printout but a curve plot for one of my dyno runs from last year.  We are headed back to the dyno in a couple of weeks with the throttle bodies on my little 16V 4 cyl.  I just want some ideas for tires as we get closer to the first Maxton meet.  I have 2 options for rim sizes that allow me to tuck the wheels further inside.  Right now they stick out a touch (1/2-3/4") where the air-dam can't cover. I think I have an idea of what to use. THANKS!

[Rex Schimmer]

wolcottjl,
I guess I didn't understand that you are running at Maxton, in a case where you have a pretty limited distance to accelerate and also much better traction than at Bonneville, going with "optimum" gearing is pretty important and certainly with a small engine to get absolute maximum acceleration you need to have gearing that maximizes the " area under the curve" and that is done by using ratios that maximize the use of your engine horsepower thru the gears. Using something like Sum has described is probably what you need you be considering. If you have a dyno chart of your engines output from that you can optimize the gearing by plotting the speed thru each gear and making sure that the rpm drop does not drop below pike torque. By doing this you will maximumize your acceleration.

I see Maxton as a long drag strip as opposed to Bonneville where you have lots of room but pretty limited traction. One other note I would highly suggest that you run the litest and smallest diameter  flywheel and clutch combination you can find, it will have a pretty big effect in the lower gears.

Rex

[wolcottjl]

Thanks, that opens up another question.  Flywheel weight, I read somewhere that you did not want to take too much weight off of a flywheel for running at Bonneville.

[Rex Schimmer]

wolcotjl,
Clutch/flywheel weight is again different from Maxton to Bonneville. At Bonneville you don't need the quick engine acceleration response that a light clutch/flywheel provides you as it can cause traction loss I would not expect that to be the case at Maxton.

Rex

[wolcottjl]

Rex,
Thanks a bunch.
Joel