Carburetor education _ LT-1 cam

[Steve D.]

From the Corvette Black Book I see the LT-1 RPO# for 1970 (370 HP), 1971 (330 HP) & 1972 (255 HP). Question: are the LT-1 cam specs the same for all three years; more generally, is there only one set of LT-1 cam specs?

Four separate carburetor numbers are listed (2 for 1970, one each for 1971 and 1972). From the Holley web site numerical listing, the specs appear to be the same for 1970 and 1971, but the power valve and pri & sec jets change for 1972. All of these are shown to be Holley 4150 carburetors.

I apologize if thread fatigue is setting in, but I have a 327 with an LT-1 cam and an Edelbrock 1406 carburetor. At idle, the carburetor does not handle the cam . Assuming that there are one set of specs for the cam and that my cam meets those specs, can I assume (perhaps naively) that if I install a current equivalent of the original application Holley, that I can expect to get the engine to idle properly on the idle circuit alone, without modifications to the carburetor ? (that is modifications such as drilling holes in the primary throttle plates and opening the secondary throttle plates)

Steve

[Joe L.]

Re: Carburetor education _ LT-1 cam

From the Corvette Black Book I see the LT-1 RPO# for 1970 (370 HP), 1971 (330 HP) & 1972 (255 HP). Question: are the LT-1 cam specs the same for all three years; more generally, is there only one set of LT-1 cam specs?

Four separate carburetor numbers are listed (2 for 1970, one each for 1971 and 1972). From the Holley web site numerical listing, the specs appear to be the same for 1970 and 1971, but the power valve and pri & sec jets change for 1972. All of these are shown to be Holley 4150 carburetors.

I apologize if thread fatigue is setting in, but I have a 327 with an LT-1 cam and an Edelbrock 1406 carburetor. At idle, the carburetor does not handle the cam . Assuming that there are one set of specs for the cam and that my cam meets those specs, can I assume (perhaps naively) that if I install a current equivalent of the original application Holley, that I can expect to get the engine to idle properly on the idle circuit alone, without modifications to the carburetor ? (that is modifications such as drilling holes in the primary throttle plates and opening the secondary throttle plates)

Steve

Steve-------


There is only one cam and one set of specs for the 1970-72 LT-1. The camshaft was GM part #3972178 and the specs for it never changed to my knowledge. This camshaft also replaced the 1964-65 "30-30" camshaft for SERVICE.

[Duke W.]

Re: Carburetor education _ LT-1 cam

As Joe said the ...178 camshaft never changed from it's original release and the current Federal Mogul CS-1145R is an exact duplicate manufactured to the GM print.

However, depending on the source you may see different "specs". That's because there are different methods to measure high level data and the method used is often not specified. For example. the LT-1 specs are different in the AMA Specs and Chevrolet Power Manuals, which are different that what Federal Mogul states for the CS-1145R, the it's the exact same camshaft.

Carburetor calibrations often vary through the production run of a given engine configuration as the engineers strive to achieve better cold and hot driveabililty, fuel economy, and emissions. For example the 327/300 engine used five different AFB calibrations from '62 to '64.

Buying an off-the-shelf one-size-fits-all carburetor can lead to problems, especially if the engine has a long duration, high overlap camshaft. As I suggested in your previous thread the 1405 may have been a better choice. The last AFB, 3721SB, may also be a better choice, and they are not that uncommon or expensive since they were the service replacement part for all previous AFBs for many years.

The Holley 4150 from the 365 HP engine may also work. I don't recall you stating what manifold you have, and given the different bolt patterns of the AFB and Holley, one might require and adapter and differences in air horn diameter will require different air cleaners.

Duke