taps

found a formula to figure cfm on blown motors,when i did the numbers on my combo i came up with 2318 cfm for 509 running 7800 rpm at 15 psi boost.

OneBadGMC

[(CIDxMax RPM)/3456] x [(Boost/14.7)+1]=CFM Required

That formula?

Didn't you say you had two 1090s? 1090 x 2 = 2180?

As long as you keep it at or below 7300 @ 15 PSI you won't starve it for air. Thats the point at which those carbs become your power restrictor.

taps

the carbs are king demon rs i am going to change to the 1195 venturi and recalibrate.that is the formula i used.any thoughts on jetting and timing,what about a boost timing master?

OneBadGMC

Jets, no clue. Maybe 80 square in both carbs?

Timing, start at 30 and read the annealing mark on the ground strap. Closer to the plug base, the safer the tune and less fuel required. The closer to the end of the strap the more timing and more fuel required. The closer it is to the end of the ground strap, the closer you are to burning stuff up.

Timing retard isn't needed with race gas. Taking timing out will simply kill power.

ashbros

OneBad

You are hitting the NAIL on the HEAD...........

I have seen so may blower motors choke on the dyno because of the limited capability of air intake when using the incorrect sizing of carbs..

When you fire them up you can actually hear the motor trying to breath & it just can't.

I can't tell you how may blower motors I have worked on that have incorrect carbs on them. Its amazing. Its my opinion that a lot of guys, by the time they are ready to purchase carbs are so tapped out of capital to finish their build that they purchase what they consider a reasonably priced set of carbs for their build based off the information from an inexperienced sales rep on the other end of the phone line...

In the back of their mind they are thinking I still have to buy plumbing, regulators, fuel pressure guages, braided line and fuel pumps. It's quite a heavy burden for the budget builder who's looking to tear up the streets or have thier day at the track...

Bottom line is; "Most guys just don't know", but thier ride looks bad as all get out with dual carbs & that massive blower sticking out of the hood.....

I had a similar build on a 515 BBC on Pump Gas 8/71 and only 5 lbs boost. With a healthy set of Jimmie Evans blower carbs on the motor I produced 789 hp @ 7400 rpm, I jerked the carbs off and swithced the motor over to injection , 851 hp at 7200 rpm. Go Figure...

OneBadGMC

Ya know, looking at the original parts list again...

If he ditched the gas carbs, got a good blower, mechanical injection, and added more boost, the HP numbers could go from 700-800 up to double or more.