Swapped Carbs, have ?

[softballnrd27]

I took the Holley that I had on the 305 off and put a quadrajet back on it. I pulled the Qjet off of a stock 454, are there different sizes of qjets between the 305 and 454? If there is can someone tell me the sizes of them(cfm wise)?

[bhunt31]

yes there is. Most were 750cfm, but some were 850cfm that were put on motorhomes and some Big Blocks.

[James McClure]

Softball: Behunt is correct about the cfm rateings. Rule of thumb, if the donor vehicle is 1 ton or bigger it's an 850. If it's below 1 ton it's a 750. The cfm rate here isn't going to be a real big issue, what will be an issue is the metering rods and jet sizes, not to mention base carb settings like float level. If you leave it "as is" you fuel ecomony is going to, in a word, suck. Playing with metering rods isn't for the faint of heart, it's a pain in the ass. Go to NAPA and get the right Q jet from them for the application. DON'T tell them the core carb isn't the right one, just bring it back later, take your money and run. jim

[Ivan D.]

Alternatively just make a poll as to what jets/rods/hangers combo everyone is running in their stock or mildly-built 305s, then use that as a reference and buy a some pairs of jets and rods and a hanger or two.

[softballnrd27]

Put the holley back on, saving the Qjet for the BBC build.

[Ivan D.]

why you yanked the Holley to begin with, was it not running right?

[bigtruck81]

its a holley. do they ever run right?

[Ivan D.]

Well, you tell me - summertime I get near 20mpg freeway out of a double-pumper Holley, in my truck that is. I drive also at 1/4 throttle, and I usually I drive barefoot cause that's the only way I feel the gas pedal good enough to maintain a steady speed, that's how sensitive the thing is. I was in TX for the whole last month, came back to a truck buried under a huge pile of snow, dug truck out, engine fired right up. Never had a no-start situation, never had it stall on me, even when offroading (my carb ain't mean to go at crazey angles). Tis all about how you adjust it man, I'd only swap mine out for a badass-tuned Q-jet.

[Billla]

Originally Posted by bigtruck81

its a holley. do they ever run right?

If it's a vacuum secondary model then yes, they run perfect...if working properly and properly tuned, which is exactly the same process you'll need to go through for the carb swap you just did.

Holley "Performance" carbs (vs. their Street Avengers) almost always come out of the box with too early secondary opening and jetted way to rich for a near-stock engine. Edelbrock's Performers are generally pretty close, although they also typically need a secondary spring change. QJets need the same type of tuning when swapping one...so bottom line is that you're at the same point you were when you started - and with a lot less tunability.

[Billla]

Originally Posted by bhunt31

yes there is. Most were 750cfm, but some were 850cfm that were put on motorhomes and some Big Blocks.

Quadrajets came with two primary venturi sizes:

1-3/32, 750 CFM
1-7/32, 800 CFM

Both of these are way too much for a mild small block, but given the unique vacuum secondary approach (air valve) they work on just about anything

4G's (later models) have more variation, and range from 486 to 692.