[acr]

How does E-brock rate their CFM? According to their published specs. the Performer 500 & 600 CFM carbs all have the same air horn size, venturi size, & throttle bore size but they're 100 CFM apart?

[cool rockin daddy]

Errrr, you could call the toll free number to Edelbrock and ask them.

[acr]

I did, here is the answer I got."..the actual booster in the 500 carbs is a lot larger which contributes to the 100 CFM loss." What booster? Is he talking about the venturis? They're the same as a 600 in an Eddy.carb. In the older Carter Comp. Series the 500 CFM, had smaller 1-1/4 in. sec. venturis. I'm no mechanic, far from it, but neither their rating or explanation makes sense to me. I was hoping someone here could enlighten me.

[oldbogie]

Originally Posted by acr

I did, here is the answer I got."..the actual booster in the 500 carbs is a lot larger which contributes to the 100 CFM loss." What booster? Is he talking about the venturis? They're the same as a 600 in an Eddy.carb. In the older Carter Comp. Series the 500 CFM, had smaller 1-1/4 in. sec. venturis. I'm no mechanic, far from it, but neither their rating or explanation makes sense to me. I was hoping someone here could enlighten me.

There's a circular thing hanging in the center of each venturi, it delivers the fuel into the air stream. Generally the larger the booster the better the low to mid RPM fuel distribution, the smaller being less effective at low to mid RPMs but does better in the upper rev ranges.

This gets to be quite important with cam selection. If you over cam the engine and it's also tied to a heavier vehicle with a high ratio rear end so that the engine turns slowly and is loaded highly the carb with the bigger booster is the way to go. Conversely if the cam is mild or the vehicle is fairly light say under 3500 pounds with stiff gears like 3.5s and up, then the engine will rev more and the smaller booster, larger CFM flowing carb would be the better choice.

This ain't the half of it but ought to give you some ideas.

Bogie

[Mez]

You guy are not thinking this correctly if you held the booster in your hand you would understand exactly how it works its very simple. the BOOSTER on and edelbrock is the center booster and a ring around the outside which is what determins the size of the venturi. the venturi of the body of the carb doesnt change the ring does and its part of the booster itself. The ventury in the body is larger than the ring built into the booster so the ring is what desides the venturi size. so the 500 and 625 carb have the same size pri and secondary ventury as far as the body is concerned but the secondary booster is different because the ring around the outside of the booster is larger. its all one piece unlike a holley which the booster is only the booster itself. so yes you can change a 500 to a 625 by changing the rear booster but a 750 has a larger front venturi and the fron venturi cannot be changed the same way the front booster is like a holley. the body desides the venturi size.