qjet

[AlohaMonte]

i have a 72 350 ci with the stock 2 barrel. I'm switching it out for a rochester qjet (from a chevelle hahaha).

 

i know from the factory the compression for a 2brrl and a 4brrl are different on the MCs. Will switching to a bigger carb get me the factory stated 300hp or will the compression difference water that down?

[Guest]

On a 70 model it was different but from 71 on the compression was the same as was cam and most times the heads are of the same chamber,runner and valve size between 2bbl and 4bbl. A 70 4bbl was 10.25 to 1 on a four barrel and 9.1 on a 2 bbl. 71 and up all SB's were 8.5 to 1 except the LT1(71/72) in the z28's was 9.1 and the L82 vette engines from 73 to 80 were also 9.1.

Gm was the first auto maker to give in to pressure from the fed's and insurance companies to drop compression and power outputs! Ford and Chrysler held out, 71 on chrysler and 72 for ford. Then in 73 the first of many clean air acts was enacted and went down hill till EFI became the norm.

Some old motors type manuals incorrectly list comps for 71 and 72. If you pull the heads you will find 76 cc chambers and dished pistons in 99% of SB's after 70. They were 8.5 with a .015 steel shim head gasket, and like 7.7 with a .041 thick felpro head gasket.

Don

[AndyBill402]

Rice Racing,

Outstanding primer on compression ratios for the early Monte heads. I switched out the 2bbl on my 71 Monte small block for a Q'jet and an Edelbrok intake. I also have a 72 Monte small block with a factory Q'jet. I am 99% certain the heads and cam are the same for both cars. The engine now looks better with the upgraded carb and intake, and it runs better in the upper rpm ranges. Surprisingly, the gas mileage is about the same as it was with the 2bbl.