[shommel]

what are the sizes and what is the power difference? and will a K code carb fit on an A and will you get more horse from it, and vice cersa(how much horse do you lose?)?which is the better to use holly or edelbrock? but from what i understand you cant add a paxton supercharger to a motor with and edelbrock,is this true?

[Veronica]

Hello. The 'A' codes had a 480cfm carburetor with the thermostatically actuated choke, while the 'K' codes had a 600cfm, manual choke carburetor. The 'K' codes were rated at about 50hp more than the 'A' codes, but the difference was actually more striking than that. The hp ratings back then were taken on a motor without having any belt-driven accessories on it, and, since you could get things like power steering, A/C, etc... on an 'A' code, the hp would always be a little lower than the rating, but, the 'K' codes didn't have any belt-driven accessories. The only belt was the one that ran the alternator and water pump, so, the 271 was a lot closer to accurate by today's standards. Personally, I prefer the old Holleys over an Edelbrock, but, that's just an opinion. The Autolite 4100 is a far better carb than either one of them. Hope that helps.

[Ivy66GT]

As usual, I can't disagree with much that Veronica said except to comment that the advertised CFM numbers may be a bit high. But that isn't uncommon as most makers, then and now, tend to be a bit optimistic on their specs. Pony Carburetors has some decent words on the subject and if you digest what they say the main difference in the CFM ratings is that the A code engine limit is near 6K rpm while the K code 600 CFM is for a 289 approaching 8k RPM. The ratio of RPMs is nearly the same as the ratio of CFM which is as it should be.

The Holley carb design is actually based on the Autolite/Ford 4100 and supposedly Ford sold Holley the design rights when they quit making them. Pony Carbs much prefers the Ford version but that is what you would expect since that is what they sell.

The specs for the '66 A-code (C6ZF-A) and K-code (C6ZF-C) carb are similar. The throttle bore sizes, front and rear, are 1.437" for the A and 1.563" for the K so the K can breathe slightly better. Even the A code manifold has the 1 9/16" bore size so either carb physcially fits either engine. The K also has a slightly larger primary venturi at 1.12" instead of 1.08" for the A. The secondary (rear) venturis are the same 1.19" in both. The primary venturi size difference is the main reason the primary jets are larger for a K. With a larger venturi, the air velocity is slower and a larger jet is required to supply the same amount of fuel. So the A with a 1.08" primay venturi and 0.049" jet isn't a whole lot different than the K with a 1.12" primary venturi and a 0.052" jet except that the extra 1/8" bore will allow a little more air to pass. There is a bigger difference in the secondaries where the K uses a 0.068" jet and the A uses a 0.058". The K is more concerned about power than fuel economy at higher RPM.

The main difference in CFM rating is the RPM difference in the two engines although there are some differences in the carbs. At low RPM you probably couldn't tell the difference between the two carbs. Most of the difference only comes into affect with your right foot firmly planted which is what you expect. And even then, the extra power has more do with the other engine mods that allow higher RPM, not particularly the carb.

[Veronica]

Hi again. I was kind of in a hurry this morning, so I didn't really have time to get into all of that, but, everything that Ivy66GT said is correct. My last K code had the 'correct' carb on it, but the one that I had before that one actually had an 'A' code carb on it, and, if anything, it ran a little better than it did with a 600cfm Holley. The A codes and K codes had the same intake manifold. The difference was the engine internals. The heads breathed a bit better, and had design features that made them able to hold much higher rpms, along with the beefier main caps, extra counterweight on the crank, beefier rod caps, higher volume fuel pump starting in like august of 64, etc... The slightly better air flow on the primaries did make a little difference, but not anything close to 50 hp worth of difference. It was the way that the K code motor was designed to be a screamer.