350 swapped for 454 - what carb changes required?

[hwcoop]

I had rebuilt the carb using Cliffs Recipie #2 when i was running my 350, 4speed.
I have just swapped in a 454 bored .030 over, 10.5 compression, 305CC Aluminum heads, 119cc chambers, Performer intake, Crane 272 cam, 2" Headman headers 4 speed with 3.70 rear end.

Carb is 17054919, primary jets are 74, secondary rod=43, hanger U and as said above using cliffs Recepie #2
Timing set 16 initial, 36 total

Seem to be getting like a lean backfire /popping
What upgrades are recommended to bring it up to 454 specs?

Thanks,
Howard

[429bbf]

id try it like it is and tune accordingly. you never know it might be pretty close. fwiw

[Cliff Ruggles]

The big block Chevy engines aren't nearly as efficient as the small blocks.  The factory ALWAYS installed much richer calibrations in them, with TONS of idle bypass air.

It will like more fuel at part throttle on the primary side, so I'd go up a couple of jet sizes.  For the later large MAB carbs, the standard jets for the big block applications were often 77's or even 78's.

I usually install smaller MAB's in builds like yours, so we can bring in more fuel across the load/speed range without so much emulsion air leaning it out.....Cliff

[hwcoop]

Thanks Cliff!.

I'm going to reread "The Book" and order up some parts..
On a side note., i was cruising the auto wreckers the other day and saw a number of late 70's 500Ci Caddy's. any benefit to grabbing one of those Qjets and working with them? . Electric choke would be nice.

Howard

[Cliff Ruggles]

Any of the 1975 or later Chevy hot air choke carburetors will convert to electric in seconds.  No real advantage using a Caddy unit over a Chevy, anything you use should be set up exactly for the application.....Cliff