I am need a new carb and I have checked with the local speed shops and it seems that everyone has different ideas as to what the CFM's it should be. I was told that the Q-jet is a stock 700cfm. If I was to get a Holley, that I should use a 600cfm, and then another shop would say that it should be 650cfm. AAAHHHH......!!!!! Which is it?


P.S. I don't have the feedback carb setup anymore. The owner before me butchered it

P.S.S. Would there be enough clearance with a spacer plate between the stock air cleaner and the hood?

 

To determine the proper CFM required, you need to state your engine displacement and cam overlap.

For the record- Rochester Q-Jets will deliver anything from 650CFM to 780CFM depending on the secondary throttle bore size and how far the secondary throttle plates will open- what this means is that the 650CFM units have an issue with throttle plate opening and this can be adjusted to get a full 750CFM out of the carb. The 780CFM units were typically used on big block trucks and had a slightly larger throttle bore.

 

Well,I guess I'll have to look into this a little more closely. I have a 305 and as far as the cam, I have no idea. Is there a way to check the overlap?

 

Don't worry about it- a relatively stock 305 can't move enough air to worry about it anyways. Anything from 600cfm up to about 750cfm would work A-Ok as long as you have vacuum secondaries (i.e. not mechanical) on the carb (Q-Jet and some models of Holley- check before you buy). If you decide you want to go with a Holley, keep in mind that they're harder to set up for good low speed and idling properties and tend to use up more gas than Q-Jets at low engine speeds.

 

My mechanic recommended an Edelbrock, only because the Holley is a little trickier to set up. I guess I have a decision to make. I can get a remanufactured Holley 650 for $275, or a new one for $425 with the adapter plate. Thanks,I appreciate the info, it clears up some confusion.

 

Get the Edelbrock 1405... Its a 600cfm and its sweet... Never had a problem with it and u can find them everywhere.. They have em at PartSource even for like 250 brand new...

 

Hey buddy. If you have a relatively stock 305, go with a Carter/Edelbrock. 600 cfm is the max i would do.

Very fool-proof carb.

As far as performance issues, stick with a Holley. More parts readily available, easier to work on & generally in my opnion a much better carb. Good Luck....

Post engine specs for a more detailed reply

 

Thanks for the info. My 305 is relatively stock, minus the feedback carb and distributor. I plan on some upgrades in the near future. I would like to get a few more ponies out of it. I plan on putting an Accel supercoil, cap and wires, TranGo shift kit PN #700,a K&N airfilter system and someday, when I can get the money together, a set of Hedman headers. Until then I must get a carb.The carb is toast. It was an old one that my mechanic had. He rebuilt it,but it still isn't right.

 

Definetly go with the 600 then. It will be good for you and will be even better when you open up that exhaust some.

Good Luck.