I have noticed Holleys usually have their jetting squared ..like a stock 850 usually has 4-80's. Barry grants use different staggered jetting. For instance a 750 Speed Demon has 76's in front 83's in the rear. Could you go even higher in the rear jets ONLY or will that equate to the rear cylinders getting more fuel than the fronts and be a bad situation ? Or is that irrelevant as the centering of the carb is such that the front cylinders see just as much jetting as the rears do even though the rear cylinders are closer to the rear jets ? Thanks J
My preference is to run the primaries just on the rich side of a lean stumble. To make up for lean primaries, I run the secondaries on the rich side for a good overall WOT mixture. This might not allow a perfect mixture distribution at WOT, but the big plenum of the SP1 helps things out. Devon
Run the primary jets LEAN enough for optimum CRUISE air/fuel ratio, use the POWER VALVE to richen the mixture for WFO use. Which will probably mean you should be drilling the power valve channel restrictions to get the WFO mixture rich enough. Much better fuel mileage, longer plug life this way. Too many people use the JETS to correct the primary WFO mixture. That's not correct--the cruise air/fuel ratio is then too rich.
Many run no power valve on the secondaries. Then you must run 8 to 10 sizes bigger to make up for no power valve.
In as delivered condition from the factory Holley uses a secondary power valve (on most models) where as Barry Grant does not, at least in the mighty demon. I have not looked at a speed demon. So the jetting would be as you described.
I have a 455 with performer intake and a kenne bell c118 cam (stock 72 heads) i have hi comp pistons an zero deck hight. My speed demon 750 vacuum are jetted 76/83 and i am having trouble with hot engine and some detonation. (I have ordered a alu radiator, but not tried it in the car yet, i also use a fan shroud) Can someone recommend me to install bigger jets ? like 80/87 ?
Please see my reply in your new topic: http://www.v8buick.com/showthread.php?t=216464 Soe more input please before you focus on the carburetor. Devon
believe Devon,,,,, :Smarty: if you jet the primarys down to the point that the engine surges at a steady speed and then back up untill it doesnt,,,, that is where it will get mileage,,,,, and then add to the rear jets what you took away from the front + a size or two to give you the right ratio at wot.... the plus amount is because a carb tends to lean out at high speeds..... and leave the power valve alone....it will take care of its self....dont eliminate it and dont drill the passages in the plate,,, because if you over drill it ,,, it cannot be reversed......
