With gas mileage and highway RPMs not the issue --only ET and MPH--any recommendations?:

388 stroker
Turbo 400
28 inch tires.

I have both gears. Thanks

 

what kind of cam?? trans?? weight of the car??

 

CompCam xs290 flat tappet (specs:http://www.compcams.com/information/...ess/XTREME.PDF)
Sportsman II heads, ported, larger valves
Turbo TH400 (3 speed auto, reverse manual valve body)
car weight - 3500 with driver

 

drag race?? 4:56's but if you have the 11's go with them.

 

Thanks. I do have them

 

Use the 4.11`s, if you even want more red light fun, put the 4.56`s in.

 

REd LIGHT!!!! nooooooo!!! I'm talking the tree that is, but I do enjoy those 60ft. times. He's got a pretty snotty cam, and yes with the 3 speed and considering he's got the gears I'd agree.

 

With the turbo, use a 3500 stall converter if the engine is making good power.

 

Forgot to mention --I have 3500 stall

 

desired trap RPM x .9 (slippage in converter ) x .006 (factor ) x 1/2 TH (tire-height ) divided/by expected MPH = GR (gear-ratio )

 

I 'm running 456's in my 79, great kick in the pants from a dead stop. Just remember if you can't hook up to the pavement, wheel spin will defeat your gear set up. I love my 456's just hate the gas mileage and high RPM on the highway, so out they go over the winter and in go 3.70's for a try next summer which are the ones that came with my Vette on the build sheet.

 

370's

411's and 456's are too low IMO unless strictly strip use

traction lossed is less seat of the pants HP feel.........sounds and smells good though

Jim

 

All of you should just do the math. Then make a wise choice based on actual red line of the motor. You don't want to be maxed out going through the traps.

When I had a 383 with a 7500 rev limiter my 4.11's worked great.

1st: 2.48 2nd: 1.48 3rd: 1

Tire Diameter 1: 28 inches
Rear Gear Ratio 1: 4.11:1
MPH
RPM 1st 2nd 3rd 4th 5th 6th
1000 8 13 20 0 0 0
1500 12 20 30 0 0 0
2000 16 27 40 0 0 0
2500 20 34 50 0 0 0
3000 24 40 60 0 0 0
3500 28 47 70 0 0 0
4000 32 54 79 0 0 0
4500 36 60 89 0 0 0
5000 40 67 99 0 0 0
5500 44 74 109 0 0 0
6000 48 81 119 0 0 0
6500 52 87 129 0 0 0
7000 56 94 139 0 0 0
7500 60 101 149 0 0 0

 

With the original post declaring:


..... why wouldn't he want to be maxed-out in the speed traps?

Provided that traction isn't an issue, I'd think any RPM he wouldn't use-up in 1320' would be leaving ET on the table.

 

I'm basing my opinion from what I learned from others and personal experience while drag racing in vehicles that changed the gearing all the time to aquire the best ET's.

I was trying to find a web site that could explain it better than me.


Okay! First off lets picture a typical dyno read out of a given motor. The HP and TQ will rise up to high level and continue on to a peak and then taper off. Lets call that the "power band" of the motor. It might be 3000 or more rpm wide.

Before and after this "Power band" things drop off pretty fast even though you might not have hit the "Red Line" So to make the best ET for a given motor you want to operate in this power band with gear changes all the way down the track. It takes Prostock cars 5 gears in 7 seconds to do this.

We are not ProStock and only have a th400 with three speeds. Most cars will get a better ET if they are not driven to redline in every gear because they are so far beyond their power band that the acceleration rate drops off.

The starting end of the track is also very important. Lets say that you did gear the car to be into the rev limiter right at the end of the track. That also means that your first gear is lower and turning more rpm per MPH. Once you get into a motor of any power like the 388 ci the poster has, traction is a limiting factor also. So you launch and having a very quick 1-2 shift spinning into second gear. That is not what you want in a powerful car.


So from testing and changing gears at the track I have found that your much better off to start out in a higher gear so your also at a higher mph when you have to do the 1-2 shift. Then be just coming off the "Power Band" through the lights.

 

Well said

 

Many thanks. And by higher gear, can you clarify whether your mean higher gear ratio or higher in number (meaning 4.11 higher than 3.7)

 

I LOVE MY 3:73's

 

Makes alot of sense George !