Thanks Charlie. Looks  like same carb, one new and one remanufactured which is probably good as new.


Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's

Hey Charlie, Im going to pull the plug and order the Summit Carb Part # SUM-M08600VS or the Edelbrock 500 performer for my 272 (Daily driver stock engine). Im having a hard time making up my mind which way to go. Anyone else who can offer some guidance, please chime in. 

Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's

I have no experience with the summit carb but based on what others have experienced, I would not hesitate to try it.
I find the Edelbrocks to be a pita to tune and they just are not generally as tunable. Pita doesn't mean hard.  It's just that metering rods only get you so far and when it gets to the point that you need to swap jets, there is a lot of screws and clips and little things that get lost easily to be removed and it is made less pleasant when the tuning is being done on a hot engine - I'd rather have a Holley style carb when it comes to tuning - much faster jet changes, fewer parts to loose and less time handling hot parts. I also had an issue with my 600 Edelbrock where the secondary air valve did not work correctly with my combo. That can also be worked around by grinding on a counter weight but on a Holley you just swap a spring and you're good.  Most of the time there does not seem to be a problem with that, however. Of course Edelbrock now have the AVS with the adjustable secondary air valve but it costs more.

Of the two options I'd go with Summit simply because I haven't used one yet.



Lawrenceville, GA

I run an Edelbrock 1405 on my F code. Seems to work pretty well. Very consistent at the strip, but not legal for pure stock. I'd disagree with Charlie about the tuning, with the instruction manual they provide it's a piece of cake. But then so are the Holleys. Be careful buying a used Holley, many of the older ones had Quality problems.



Frank/Rebop

Bristol, In ( by Elkhart) 

I have not ruled out a Holley 600, just have no experience with them. But I would still consider it with the two previous options. I see some factory rebuilt holleys on ebay (refurbished returns) but I dont know where to look as far as model numbers or carbs that would fit my manifold. I swapped my stock manifold out with an ECZ9425B to work with a new carb and get away from the "dizzy" distributer. dI just want a new or refurbished carberator (electric choke) that will run good and give me good performance. There are too many model numbers on Holleys, I dont even know where to start looking.

Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's

If you were to buy a "Factory" unit from holley, you probably be good. It's the Fly by night operators on Ebay that you'd want to be careful with. I've heard good things about the Summit carbs as well, IO would not be afraid to try one of them.  

Frank/Rebop

Bristol, In ( by Elkhart) 

If you go Holley, 570 Street Avenger,



Lawrenceville, GA

Another concern is over carbing my 272. If I remember correctly, Ted said the 600 cfm series would be fine. I will be sure if I get anything off ebay its Holley direct. Will also add the Holley 570 Street Evenger to my list of options. Thanks!

Darrell Howard Whitefish, MT Outlaw 56 Ford F-100's

I know I'm new here, but I'd like to add some insight based on experience:

The old formula for carburetor sizing was displacement x RPM x volumetric efficiency / 3456 = design CFM flow rate. Stock motors usually have a volumetric efficiency of .75, and 5000 RPM is a good default value. Using these variables, a stocker 272 will flow about 300 CFM. On the other end of the scale, a hotted up 312 spinning north of 6000 RPM will flow about double that with a VE approaching 100%, or 1.

Now here's where it gets tricky. 2 bbl carbs are flow rated at 3 inches of mercury, and 4 barrel units are rated at 1.5 inches. On top of that, stock carburetors rarely flow at rated value - it's usually less than that. To overcome these variables, I typically take the as-calculated design air flow and add 25%, multiplying by 1.25. Take that number and select the next higher carburetor size and you'll be fine - or you can go down one size and have better streetability.

As Ted said, a vacuum secondary carburetor is the way to go in the selection process. The vac secondaries will maintain a consistent vacuum signal - which is the power source for the analog computer that is a carburetor. A mild 272 will run very nicely on a Holley 390, whereas a 292 would favor a slightly larger carb, especially if it has dual exhaust or a mild cam.

If you go too far in the carburetor sizing process, you run into a characterization issue, which is a fancy way of saying the carburetor loses the ability to control the air fuel ratio as the throttle plates are opened. The vacuum signal drops to near zero along with flow through the venturis. At this point, fuel drops out of suspension and puddles in the manifold - making for very erratic operation. There are work-arounds for this, but they're either band-aids or part of and expensive custom carburetor build. By the time the carb is 75-80% larger than design flow - it's too big, in my opinion.

Hope you guys find this helpful.

A 390 to 465 cfm holley is plenty for a 272 even when warmed up a bit with a better cam and intake these two carbs should work fine but the 390 may need to be jetted up a few numbers from stock. These carbs as Charlie said are easy to tune and run great. A 570 avenger should work well but don't won't to go too big and start losing the bottom end torque from take off to 4500 or so RPMs.

-Gary Burnette-