need to change carb, from qjet on a j intake, would like to install a new holley 4150 or road demon either way square bore. the adapter from square to spread bore is .850" thick, will this still allow the air cleaner and top hat to work under the hood scoop. the carbs are the same height. with the original gasket being about .250 inches, which i believe it was original, and the new gaskets with the adapter are paper thin, im thinkig it olny going to be about .600" higher the oem.

 

IMO - that's a big mistake!
Having owned a '69 442, and the only difference being the factory installed 3:42's, a Holley or Road Demon would be futile and a waste of time and money!!
Get a rebuilt factory numbers matching Quadrajet, and save your time and money, which, more than likely will obtain more performance and mileage than either of those other carbs!
I was getting 16+ MPG, overall, and although never at the strip, impressed more than a few people with it's accelleration!
Stayed ahead of a '70 442 [455!] from 0 to 60, and a BB El Camino from 55 to 110!
[Just a couple I remember]
GM designed that carb for that application - the others are 'generic' - tuned for general purpose applications - to get them exactly right, you'll spend hours!
Get a good factory carb, change the rear ratio, and let the fun begin!!

P.S. Somewhere I've a brand new Holley spread bore that I haven't sold because I don't believe it's the answer to 'bad-running' Q-jets. I've been able to correct their problems, cheaper!

 

... Or, to put it another way: Why do you want to change your carb?

- Eric

 

Do yu have a 69 "top hat" or a 70 ? You should be able to see how the foam is being mashed down and tell if you have the room to add the spacer or not .
the other thing do you run the hot air tube from the manifold? if so that might not fit ((short)) due to the carb lift. If you have a inch or two over the hard parts than it should work. If you have the 69 top then you will want to remove the foam and cut it off so you are not pancaking it when hood is closed . Let us know what you doo.

 

I've got a Holley 6497 650 spreadbore with mechanical secondaries that works great with my 455. It was an aftermarket replacement carb for the Q-Jet. If I had the original Q-jet I probably would have rebuilt it. I don't know much about carbs but I rebuilt the Holley and it runs well

 

I have 69 top hat, the qjet i have is a 70's carb and ran ok when the motor was tore down but has set for 2 years while motor project was being done and now the motor is complete, i hate to spend the money on a rebuild on non correct carb, especially since i have a new barry grant 750 that i ran on a 454 for a few months and was super. i stroked the 454 for my sons monte carlo and it was a little small for that motor and rpm range so i want to use the barry grant on my car but it appears its not going to work with my hood. I picked up the carb adapter today at summit its slightly over 3/4" thick and if the original did have a 1/4" insulator under the carb ?????? than im only 1/2" higher. Im going to use the barry grat for cam break in on the motor stand, when i put the motor in i will have to make the call then, I will keep you posted.

 

You could probably find a rebuild kit for the carb under $50. About the same price as a holley jet kit.
They're not too complicated and rebuild nicely unless the shaft holes leak.

 

I bought a "regular old" kit, without float, at Advance for $18.

- Eric

 

the 69 carb is common you can find them on ebay. Is the top a steel 69 or a
fiberglass one? If you get a flat top or flip the stock air cleaner lid You gain
some clearance to trim the lower edge on the top to lower it . I have looked at also cutting the drop hat in the center of the air cleaner adding a 1/4 ring to lower it some too should be able to soak up that adaptor plat with out to mch effort