Carb Size

[rdorman]

The problem with most of the charts is you really need to know the volumetric efficiency of the engine to use them effectively. The only way you are going to get that information is on a very good dyno. Recently I ran accross this equation:

Volumetric Efficiency = 5,600 x HP x 100% / (RPM x CID)

Don't know how valid it is....... HP is at the fly wheel.

Second the opinion on the little air clean. Those Stellings OEM style cleaners may look nice but they are too small. I have a 15x3 k&n set up that fits nicely under the hood. I am even going to one of their air filter lids and a stub stack. You can hook a vacuum gauge to the air cleaner if you want and just see how restrictive it really it.

The carburator operates on pressure differential. So every thing from a restrictive air cleaner, undersize, oversize carb, tempature, barometric pressure, humidity and quiet possibly the phase of the moon will effect not only the CFM that you see but power valve, vacuum secondary operation etc. It is my understanding the HP series is jetted a bit rich because of its intended application. This on top of the DP generally being a bit rich. This all adds to what was said about the vacuum etc.

So what is the right size? That is one BIG depends. I can run everything from a 600 CFM vacuum secondary to a 850 double pumper and each one has its benefits(on a cleveland). Max HP, go towards the large size. Best drivability towards the low side.

There is a ton of info on sizing your jets. An aftermarket O2 sensor is about the best. Aside from that a new set of plugs and a very good magnifying glass like the one that doctors look in your ear with. Or just take the thing to a good tuner. Tuning a Holley takes a lot of patience but you will be rewarded in tuner heaven!

What would I do if I where you? Change my air cleaner and tune what you have. 2 cents.