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  #1 (permalink)  
Old 08-05-2017, 07:03 PM
snakesaway's Avatar
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Join Date: Jun 2014
Location: Melbourne, Vic
Cobra Make, Engine: Evans and Wooley, 302 Windsor, Supra turbo 5sp
Posts: 92
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Default Mild 302 carby size and fuel consumption

Hi all,

I currently have a mild 302 windsor that runs the following configuration.
30 thou over bore
Edelbrock Performer RPM manifold
Scorcher distributor
Cam is TRW TP205 (intake lift .472 duration 290) (exhaust .406 lift & 300 duration)
Holley 600 or 650 CFM carby

I have couple of issues

Not sure what CFM the carby is. As some highly intelligent individual in the past has filed off the model number on the choke tower The size comes from talking to AFD and using the numbers from the primary and secondary butterflies as a guide to CFM size.

I am getting about 20lt per 100 km which I feel is probably a bit high. I was speaking to my uncle who over the years has owned a wide and weird collection of vehicles, he too feels it is high.

I have a vacuum whistle that is coming from the carby once it is heated up.

Therefore with these to issues in mind I guess I have 2 options.

A carby rebuild. Hopefully to find out more info as to the carby size, jet size and accelerator pump size. Fix the whistle (gaskets) and perhaps armed with current jet size and accelerator pump size if these are wrong put the correct ones in and possibly improve fuel economy not that I ever expect it to great.

Or a new carby if so what are peoples recommendations I have looked at Holleys website and it recommends a carby between 570 and 650 CFM. They have various model Street Avernger, Brawler, Classic, Quickfuel and Slayer. I went through them all and are suitably confused as to what CFM or type to use. So if people some experience with any of the above your thoughts would be appreciated.


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  #2 (permalink)  
Old 08-06-2017, 06:40 AM
LoBelly's Avatar
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Cobra Make, Engine: RMC, carb 347 TopLoader and Jag running gear ~ so old school I time it with an hour-glass :D
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Hello Andrew

In very round figures, at 6000 rpm the 302ci is pumping about 525cfm, about 612cfm @ 7000rpm.
(1 cfm = 1728cim)

The Holley recommendation therefore appears to correct (as you'd expect).

When it came time to replace my aged and wobbly 700 double pumper I looked at the cost of refurbishing myself against a factory refurbished carburetor and decided that with the state of my carburetor and the number of things I wanted replaced - getting a refurbished carburetor was cheaper.

Holley has an ebay store where they sell factory refurbished carbs, I bought one, it arrived looking new and it has worked very well after a bit of tuning.


Your main choice will be between vacuum secondaries or a double pumper.

There are some nice 600 double pumpers or vac secondary 4 barrels currently listed that I think would suit nicely.

Personally I would keep it simple and get something like this:
Holley 0-4776S 600CFM Shiny Double Pumper Factory Refurbished 4bbl

If you're worried about the fuel economy then maybe look at the vac secondary equivalent.

Come to the AGM and talk carburetors - you'll get plenty of input.

Apologies to all the carburetor gurus for the forgoing massive over-simplifications.

Good luck Andrew.

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