What changes do i need to make when replacing a 301 with a 400 in my 79 Firebird?

Asked by Derrek Sep 07, 2015 at 09:57 PM about the 1979 Pontiac Firebird

Question type: Car Customization

I was told the 400 came out of a 75-76
Bonneville. It has 2bbl. carb & intake. I
wanna change to 4bbl. & keep my TA
hood & shaker on my bird. Please
help!!

2 Answers
189,395

Paul answered 9 years ago

Besides some wiring modifications, new motor mounts and maybe heavy front springs, new exhaust there not much more that I can think of for the change over, good luck with her...

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1WikdWagon answered 9 years ago

Actually from first hand experience this should be a basic bolt in swap. Almost nothing from the 301 will interchange with the 400 though. Will have to locate an intake from a 350, 400, 428 or 455. 326 may be the same also but not positive. Edlebrock performer is an option over stick that will work with the shaker. Depending where you are I have three extra stock intakes. Including a good 68 intake. The 301 mounts should also work with no real issue as long as you have a post 70 block. Will have either 5 or three bolt holes for the mounts on the block. If it only has two bolt holes it's pre 70 and you are gonna have issues with mounts. Speaking from experience with that also.

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