I plan on using the original Q-Jet ( after rebuild ) that came on my 403 for the 455 I am building .... does anyone know what the CFM is on that Q-Jet ?
I am under the impression it's 800 CFM , but not sure .

 

Yes the 78 quadrajets are 800 CFM with a fully adjustable part throttle. With a proper rebuild and some minor mods it should work well with your 455. I have a similar one for a 77 403 that I plan to build eventually for my 455. I spoke with Cliff over at http://Cliffshighperformance.com He said with my carb number and engine specs he can give me a kit with the correct jets, rods and idle tubes for my application.

 

At the minimum, it’s capable of 750 cfm. Some of the later Q-Jets on smaller engines are mechanically limited to less than 750.

Some of the later Q-Jets are capable of 800 cfm, thru were used on Buick’s and Cadillac. I don’t recall how to identify those.

If you have a Q-jet on the 403, it can almost certainly be built to work with your application.

 

Here's the easy way to tell the 750 CFM Qjets from the 800 CFM versions. Look in the primary venturies. The 750 has a ring that goes all the way around the bore. The 800 only has a bump in one location and a larger venturi diameter everywhere else. in the photo, 750 on the left, 800 on the right.

 

Cliff is good no doubt but it won’t be totally correct. Buy a wideband O2 and tune it right.

 

Ok thanks for the input

 

X2 on the wideband O2 sensor for tuning. You’ll see the AFR mixture or Lambda at all parts of the use cycle - idle, cruise and WOT and can really dial the tuning in.

Chris