noonstang

Im going for a new carb andI have a few questions regarding cfm, holley vs demon and double pump vs vac. secondary.

Bore .030
Pistons Forged T.R.W /Speed Pro
Rings Cromemolly
CrankshaftFactory Crank was undersized amount unsure
Compression11.2:1
Cam Lift.508
Duration 303 Intake
299 Exhaust
Valves 1.920 Intake
1.680 Exhaust
Heads Stock, Ported and polished
Headers Hooker Headers – Modified to fit
Intake Edelbrock Victor Semi-High Rise
Balance Crank rods and pistons balanced

The guy who built the engine said it would put out around 450hp. the car currently 1/4's in themid 11's. This car is not street driven, raced only. Currently sits with a burnt out 780 holley vac secondary which seemed to work well. I have been told this may be too much carb a 650double pump or 670 vac second would be perfect. I was just wondering what other people are running and what advice they could give me. Thankyou!

MadMan@TheWheel

For the interest of brevity, a 650dbl would work just fine with that engine, I don't really see how the 780 was considered too big, perhaps a little overkill but maybe the compression is what pushed it more towards the 780. I have had a lot of experience with the 750dbl pumpers and there is a guy locally that converted them to dominators to handle the high rev. motors and radical cam with high compression. Personally I am not a huge fan of vac. secondaries strictly because I have experience with the double pumpers and Dominator series carbs.

farseek1

HolleyR 4777-2, 650cfm Mechanical sec. Double Pumper, will do the job nicely.780 cfm too much for stock heads ported or not, guarantee you a 600cfm will outperform it. You cant stuff enough air through the stock heads to feed that size carb effectively.

my77stang

barry grant 650 > holley 650, its already got the goodies like clear sight plugs, billet base plates that dont have mounting ears that break off, billit metering blocks that arent warped and leaky, etc, etc, etc

noonstang

the complaints i hear against the demons is that they must be disassembled, cleaned, and reassembled before installation and can be very difficult and frustratingif warrenty is ever needed. As well as the tuning portion of the carb, grantedmany will argue nothing worksbetter then a well tuned barry grant carb, ive heard it taking hours upon hours to set up right, where the holley reached the same , maybe slightly less performance with a 1/4 of the tuning time. has anyone ran into those problems? or others?

my77stang

i had a 650 speed demon with vac. secondaries and when i went to sell it i pulled the bowls to make sure there was no residue from sitting for a few months. the inside of that carb was in 100% spotless condition and i didnt see a single spec of anything in there.

i was looking at 575 speed demons and 625 road demons, as well as 570 holley street avengers and i ended up with a 570 holley that was used on a dyno for a couple hours. picked it up for 200 bucks shipped (350+ retail new)

MadMan@TheWheel

Personally I think Barry Grant makes a far superior product, period. They are well thought out, simple to work on (once you get used to them) and if I was building another carb car it would be fueled via Barry Grant.

393Bird

I am using a Quickfuel carb on mine. I never had to touch it for 5 years. I just recently added a YSi supercharger, so had them convert it for blow through. Not a problem with it either. Set the idle a/f mixture and idle speed, and drive.

noonstang

Thanks for the help guys. i will be sure to keep allyour advise in mind when i hit the local performance shop this afternoon. thankyou!

WhiteWindsor

Look into the Holley Race HP 750, i have one and i like it.