Engine Help...

[Stephen & Horace Johnson]

Originally Posted by Freddie

Hey guys I am finishing my Mustang finally... except I was forced to buid a bracket motor for it to start with, I am trying to figure out how much power it should have... I used one of the desktop dynos and I dont think that is even close..

Here is what I have:
302 Ford block .030 over with TRW 10:1 pistons, light wieght steel rods, stock crank, Main Girdle, Heads and mains studded, Zero gap rings, Crane .710/.710 Mechanical roller, Pro Comp 210cc Aluminum heads gasket matched, 1.6 Crane Roller Rockers, Parker Funnel Web intake, and a Holley 750 double pumper, I still have the stock distributor in it for now, I plan on getting a MSD unit..

This is put with a P&A C-4 Trans brake trans, and a 4500 converter..

The car is the 90 Mustang hatch, with full 10 point cage, frame connectors, QA1 tubular front end with adj. struts, 8.8 rear with 31 spline moser axles and spool, 3.73 gear, rear suspension is all adjustable with strange rear shocks, I am running a 28x10 slick, car with me in it is 2950#..

Desktop programs show this setup should run low 11's high 10's...

What do you guys think?

I agree, get rid of the 3.73 gears, its not goin to run in the 10s with that gear. I would change it to a 430 or 4.56.

my mustang (street car) runs 10.90s on motor with a stickshift and with a 4.30 gear and 28x10s



Stephen Johnson #2162
Horace Johnson #2167
SS/D 427 Ford Fairlane NHRA-IHRA
Record Holder

[greg fulk]

Freddie you also forgot to say what headers you are using? & yea get rid of the 3.73 gear....put the 4.30 in it so ya don't blow the tires off it!

[Freddie]

Sorry: I am using full length BBK headers, they are 1 5/8 tube with a 3" collector... I am thinking of putting a pair of flowmasters on it and running a real short system..

Would I be better off jst putting a shorter tire on it rather than change the gear? I also have a pair of 26x10 drag radials..

[Moparteacher]

A shorter tire doesn't have the same effect as a gear change. The gears multiply torque. 3.73 to 1 multiplies the rotational force by 3.73 times. 4.30's multiply by 4.3 times. So lets say the the driveshaft is applying 400 ft.lbs of torque. (400x3.73) divided by two. Two tires right? this equals 1492/2=746ft.lbs at each wheel.
(400x4.3)/2=860 ft.lbs of torque applied to each wheel.

A shorter tire will not multiply torque. A taller tire will allow for a taller gear and a greater torque multiplication. The only time you would want to move to a shorter tire is when you are in-between optimum gear ratios. Even then the change is minor.

Run the 28x10 only if you can't fit an even taller tire, and then calculate the optimum gear for shift rpm and mph.

[greg fulk]

Freddie a shorter tire also has a smaller footprint! I think that's the last thing you need with a trans brake. Are you running Hoosiers or M/T ? I know with some playing you can get a 28x10.5 M/T under one of those cars........of course if ya already have the 26x10's give them a try......on Dad's 6 cyl nova stocker the 24x9 M&H's are good for about .05 in the 1/8th over 26x 8.5 M/T. good luck & don't forget to play with lots of differant air pressures.........

[Freddie]

Greg: I have a set of 26x10 M/T drag radials a little worn but still workable... the 28x10's are also M/T's but these are slicks..

alot of guys I know are running close to the same car, mine is a little lighter, they are using the 28x10's and most are running a 4.10 gear, but also they all run a glide instead of the 3 speed..

[greg fulk]

yea a glide wouldn't "hit" the tires like that 3 speed. my neighbor/buddy has an 86 Capri (with an 88 mustang frontend) he had a 306 roller motor that ran 10.40's . it has 29.5 x 12.5 slicks & he left the line @ 5200rpms! with a C4! good luck! oh p.s. he has a 347 in the car now (alum head motor) it runs 9.30's!