Ron Pope Motorsports                California Custom Roadsters               

Yet another carb question

kgrimm

Supporting Member
Supporting Member
Here's another carburetor question. My car currently has a Holley 650 which is a bit leaky and has choke problems. The guy I bought the car from threw in a brand-new Summit carb that he never got around to installing (600 cfm vacuum secondary with electric choke)-the Summit carb is similar to a Holley but has a few improvements: no gaskets below the fuel line, windows for the float bowl level, etc. I also have a used 600 cfm Edelbrock Performer #1405 (similar to a Carter AFB) to which I added an electric choke kit. The question-which would be the one to use? The engine is a Ford 302 with an unknown cam (slightly lopey idle), a single-plane intake, and headers.
 
My gut says go with the Edelbrock. My head says run the Summit just to see how it runs. The Holley - rebuild it and try it out (is it a double pumper?). The Holley would be a bit of a gas hog if it is a double pumper. So there you are. Put the Summit on first. Then the Edelbrock. Last the Holley. Hell, run the Edelbrock and have the other two as "play" carbs. Thats my final answer. :shrug2:


For now.

John
 
I would put on the 600 cfm the 650 is a little large.Here is a great calculator cfm for cubes at rpm's. It is a good formula I have seen on other sites.600 is about right.
ebay cfm chart
 
There is also a formula for determining carburetor requirements located right here in our Tech Library.

That Summit carb is based on the discontinued 4010 Holley carbs, which was modeled after the 4100 Autolite carb. No actual improvements over the Autolite version, just another copy. All companies have R & D. To some, that is Research & Development. To others, it is Rob & Duplicate. :shrug:

John, it's actually a myth that a mechanical secondary Holley will use a lot more fuel than anything else. The boosters are only going to introduce as much gasoline into the air stream as the air quality and air speed dictates. And, depending on the carb and whether it has a 30 cc or 50 cc secondary accelerator pump, going from idle to full throttle will only introduce an additional 3 to 5 cc's of fuel. Holley rates their pumps on 10, full pump strokes. 5 cc's amounts to one teaspoon. So additional fuel usage is pretty negligible.
 
There is also a formula for determining carburetor requirements located right here in our Tech Library.

That Summit carb is based on the discontinued 4010 Holley carbs, which was modeled after the 4100 Autolite carb. No actual improvements over the Autolite version, just another copy. All companies have R & D. To some, that is Research & Development. To others, it is Rob & Duplicate. :shrug:

John, it's actually a myth that a mechanical secondary Holley will use a lot more fuel than anything else. The boosters are only going to introduce as much gasoline into the air stream as the air quality and air speed dictates. And, depending on the carb and whether it has a 30 cc or 50 cc secondary accelerator pump, going from idle to full throttle will only introduce an additional 3 to 5 cc's of fuel. Holley rates their pumps on 10, full pump strokes. 5 cc's amounts to one teaspoon. So additional fuel usage is pretty negligible.
Mike , what I was refering to was the "fun factor" of a mechanical doublepumper. If the carb is properly sized and if there is a sufficient additional "thrill" to appreciate when depressing the accelerator pedal completely, then the pedal will be depressed more often and fuel mileage will suffer. I think that all these formulas for carb sizes really are useful for racing applications or Weber type carbs that can be individually tailored to a specific engine size and application. But in general, street carbs can not be tailored to the application so you wind up with a generic small engine small carb combo. I would like to see more 450 Holleys or even 350 cfm 4 barrels used in multiple applications but then you get into complexity and overkill. Some people like to play with multiple carburetors and some just want one carb for simplicity. I prefer multiple.
 
If the carb is properly sized and if there is a sufficient additional "thrill" to appreciate when depressing the accelerator pedal completely, then the pedal will be depressed more often and fuel mileage will suffer.
I see your point. Although you seem to have missed my own. What I was pointing out is a secondary accelerator pump does not pump as much fuel as one might think.

First of all, proper or improper carb sizing has absolutely nothing to do with accelerator pump volume. Pump volume is constant for a given carb, no matter its air flow capabilities. If a mechanical secondary carb has a 50 cc secondary pump, it will require a total of 757.08236 full pump strokes to expend an additional gallon of fuel. If that carb has a 30 cc secondary pump, it will require 1261.803933333 full pump strokes to expend that additional gallon of fuel. A secondary accelerator pump will add additional fuel, but that additional amount is negligible.

As for single or multiple carb installations, to each his own. If you like running multiple carbs, I say go for it. Where there is a will, there is a way. There is no question a pair of small carbs can be made to work on a street-driver. There's no question a pair of smaller carbs on a tunnel ram will have more "wow factor" than a single carb. But even those small carbs will need more tweaking to perform as well as a single carb. And we both know those smaller carbs will never flow at full capacity, even at wide open throttle. And when push comes to shove, someone running multiple carbs on a street-driven car isn't giving a second thought to fuel mileage. :winkn:

Just a couple weeks back I managed to get a 3-circuit 1050 Holley working (not as well as I would have liked, but working nonetheless) on a 406 SBC a buddy put in a first-generation Camaro Super Stocker he's re-purposed as a pro street car. He's got himself a smart-looking pro street car, no two ways about it. And he was more than willing to admit that wasn't the best carb for the job, but he wanted "the look". So I banged on it for a couple hours and got it working for him. Like I said, to each his own. I've another pal who restored a '68 Z-28. This car is a real Z-28 and he spared no expense in the restoration. I hate to imagine what it cost him, but a couple years after he got it all back together, he came up with a complete cross ram intake/carbs/air cleaner set-up for it. Talk about "wow factor", that combination has really got it. It's an absolute tuning nightmare, compared to the single carb combination, but who cares what it runs like, when all you have to do to drop people's jaws is open the hood.

Heck, back in the mid-70's, I used to help a local guy with an E/MP Camaro. There were some serious street racers in the area, so we rigged up a couple pieces of aluminum round stock to make it look like the car had windshield wipers on it, hung some exhaust tubing and a pair of truck mufflers on the header collectors, so we could take the car out to hunt down a mark or two. Compression ratio in the 14:1 range, a pair of 660 center-squirters on a tunnel ram, 1.750" primary headers, a Doug Nash five-speed and a 6.17 ring and pinion. Hardly what anyone would want in a street-driver, but we were still driving it on the street. It had the front end tied down and a four link rear suspension, so it would beat you to death trying to drive it. And it always got more than its fair share of legal attention. Yes, it was really stupid, but it bears out my earlier point of where there's a will, there's a way.
 
Here's another carburetor question. My car currently has a Holley 650 which is a bit leaky and has choke problems. The guy I bought the car from threw in a brand-new Summit carb that he never got around to installing (600 cfm vacuum secondary with electric choke)-the Summit carb is similar to a Holley but has a few improvements: no gaskets below the fuel line, windows for the float bowl level, etc. I also have a used 600 cfm Edelbrock Performer #1405 (similar to a Carter AFB) to which I added an electric choke kit. The question-which would be the one to use? The engine is a Ford 302 with an unknown cam (slightly lopey idle), a single-plane intake, and headers.
I have the same engine ... 302 with mild cam ... I run the Edlebrock 1405 on mine and it works\performs just fine.
 
Thanks for the info everybody! I'm going to put the Edelbrock on and see what happens.
 

     Ron Pope Motorsports                Advertise with Us!     
Back
Top