new to bracket racing

[cicero819]

You can find a positraction unit for your truck in most junk yard, look for a van with a posi. You will be surprise to find that many service trucks for large fleets came with posi unit(GM gave many fleet posi at no charge). You can find some as I did with ratio as high as 4.10:1. Try to relocate the battery to the back and add one air shock to the right side, leave the spare under the bed to help in weight distribution. Good luck

[bogger01]

thanks for the tips.i plan to move the battery to the ear.i think i have also found myself a rear with positive traction.as a side question are the larger carburetors less affected by temp and hunidity changes.i can only go but so big on my setup but was just curious.thanks

[Bill Baer]

Originally Posted by bogger01

thanks for the tips.i plan to move the battery to the ear.i think i have also found myself a rear with positive traction.as a side question are the larger carburetors less affected by temp and hunidity changes.i can only go but so big on my setup but was just curious.thanks

Yep your correct! The less the restriction in the intake track the less the pressure drop across the carb the less affected it will be by temp and humidity. Resultantly tunnel rams with two carbs set up correctly can actually be more consistent than one smaller carb.

[bogger01]

i see.but how big is too big.like i said i have a small block (357 c.i.) with reworked 040gm heads and a performance cam of an unkown make and size and a factory aluminum intake.i have been told 650 cfm was as big as i could go.any thoughts

[Phillip marvetz]

850 dp.

[Bill Baer]

Originally Posted by bogger01

i see.but how big is too big.like i said i have a small block (357 c.i.) with reworked 040gm heads and a performance cam of an unkown make and size and a factory aluminum intake.i have been told 650 cfm was as big as i could go.any thoughts

There is a formula :Racing carb cfm = rpm x displacement / 3456 x 1.1 so it depends on how high your going to twist it @ 7000 RPM it comes out 795CFM so I would use a 750 the vacumn secondary (3310) being the easist to live with on a street car of the double pumper for race use only.
Now if you do the math an spin it 10000 RPm you need about 1136 CFM and in that case a tunnel ram and two carbs would be the ticket.
Note there are a lot of other varibles to be considered cam size ignition timing (intial lead and curve speed) collector length and torque converter stall and keep in mind that formula is for a dedicated race car.
The street formula is Street carb cfm = rpm x displacement / 3456 x 0.85.
Hope this helps.

[Phillip marvetz]

Originally Posted by Bill Baer

There is a formula :Racing carb cfm = rpm x displacement / 3456 x 1.1 so it depends on how high your going to twist it @ 7000 RPM it comes out 795CFM so I would use a 750 the vacumn secondary (3310) being the easist to live with on a street car of the double pumper for race use only.
Now if you do the math an spin it 10000 RPm you need about 1136 CFM and in that case a tunnel ram and two carbs would be the ticket.
Note there are a lot of other varibles to be considered cam size ignition timing (intial lead and curve speed) collector length and torque converter stall and keep in mind that formula is for a dedicated race car.
The street formula is Street carb cfm = rpm x displacement / 3456 x 0.85.
Hope this helps.

That is fine for a street car, If you want a bracket car that will repeat the 850dp is the way to go.