carb help
 

Alright guys some of you know i have been in the process of buiding a blown 460 for my truck. I am in need of some help now.

First off few years ago i got a awesome deal on a bbc stock bore, ran good, so i just pull the small block and slapped a cam in the bbc and ran it for about a year. Then i found out i was being paid wrong for a year or so and got a good chunk of money, so i decided to slap a 177 weiand supercharger on it. At that time i just ordered a 750 edelbrock. It ran pretty good. Then i dropped a valve and screwed the motor up. Took it to the machine shop bored it and put a full scat forged rotating assembly, a actual blower cam, and some ported polished 781s.

Well some point of building the motor and letting the carb sit around (it was drained and covered) the carb got something in it and when i went to start the motor it was flood horribly, I think i had soemthing in the needle and seat. Well the last few days i have been thinking, why should i take this carb apart and rebuild it when i already have alot of money in this motor, why not just buy a carb thats meant to run with a blower.

Anyway i slapped a 600 edelbrock on it to break in the cam and it runs alot better then my 750 thats currently crapped out. But i know 600 is not enough for the motor.

So the question on the table is ever cfm calculator i find asks for cid of engine, safe rpm, and Volumetric Efficiency.
on cid do i put 460 or 460 plus the 177 cid blower?
safe rpm is 5500 to 6000
how do i know volumetric effciency?

I really want to get this thing on the road and test drive it, but want to make sure i have enough carb and its running correctly also.

Any and all help is appreciated. any more info needed i can also supply that.

by the way it has a 3200-3400 stall, and a 4.10 posi unit.

Re: carb help
 

A BBC with a blower? I would say 850cfm- something like a Holley double pump.

Re: carb help
 

I would call holley tech support but I can tell you too small is better than too big.

Re: carb help
 

Barry Grant has a chart you can look at to help you choose a carb. it goes by cam specs, stall, gears, cubic inches, etc... it was dead on to help me choose the right size carb for my 505. Which was a 1000cfm speed Demon....

Re: carb help
 

Couple of things here. The one thing we don't know about is going to have the biggest part in your VE which is your heads. I think they use a default figure of around 80% or a little higher depending on your motor config. Careful not to go too big with the carb. The 177 is a small blower compared to the 6/71 + lungs. I'm too tired to look it up tonight but what you really need to look into is if you are going to need an external booster ref PV carb (a supercharger carb) on that style blower. I know it's a must for the 6/71 style but I'm not sure on the smaller ones. It's important for your carb's PV to get it's signal from BELOW the blower and not above it. It will have a big affect on it's streetability. You're probably going to need a little more fuel than a 600 but not sure about the 850. That 1 9/16th venturi is not the most streetable carb. A well built 750, which has 1 3/8th will feed a bunch of motor. You also don't have to spend the $$$ on a blower carb. You can have the PV area in the main body accessed for a port.

If you have no idea what I'm talking about, you need to get with someone local that understands blower carbs so this thing will see it's full potential!