[AJ-]

I have a Pontiac 350 with unknown history. It looks to have been gone through as it was all clean, new gaskets, etc. Pulled the heads of and it has some miles on it but not a lot. Measuring valve lift it looks to have a classic mild .420/.440 type cam in it. I rigged up a stand and ran it for a bit, it runs smooth and had great oil pressure but a compression test afterwards shows 105-110psi across the board. It’s a 73 with the original 46 heads on it so it must be like the original 7.6:1 ratio or less with composite gaskets on it. Is this just a result of a super low compression motor and a slighter bigger cam, or is this motor tired?

I do have some 62 heads not doing anything right now I could throw on to make it a little more interesting, and even a car to throw it in if I want to have some fun with it but it’s not worth it if the ring seal is already not great.

[PunchT37]

If it doesn`t smoke, I`d throw the 62`s on.

Maybe check the ICL [degree] of the cam to see where it is.

[Stan Weiss]

You really need to find the IVC ABDC.

As an example. A Pontiac 350 with 7.1:1 CR and a 290 seat-to-seat intake duration @ 110 ICL should produce 110 PSI during a cranking compression test @ sea level.

Stan

[steve25]

I would pull the cover to advance the cam 2 degrees and take a look at the chain, and then slap on the 62 castings if they have been gone thru at least with new valve stem O ring seals and valve springs .

You may need the right intake gasket also since the exh crossover in the 62 castings is likely different then in your intake from the 350.

[Formulabruce]

Originally Posted by AJ-

I have a Pontiac 350 with unknown history. It looks to have been gone through as it was all clean, new gaskets, etc. Pulled the heads of and it has some miles on it but not a lot. Measuring valve lift it looks to have a classic mild .420/.440 type cam in it. I rigged up a stand and ran it for a bit, it runs smooth and had great oil pressure but a compression test afterwards shows 105-110psi across the board. It’s a 73 with the original 46 heads on it so it must be like the original 7.6:1 ratio or less with composite gaskets on it. Is this just a result of a super low compression motor and a slighter bigger cam, or is this motor tired?

I do have some 62 heads not doing anything right now I could throw on to make it a little more interesting, and even a car to throw it in if I want to have some fun with it but it’s not worth it if the ring seal is already not great.

Its stock, have one. Amazing how different the 1970 350 is, BUT both have enough torque to move ya!

[Shiny]

FYI, my 70 350, #11 heads, Summit 2800 cam, had cold compression between 120 and 130 psi at sea level.

Perhaps the cam is different or the 70 CR is actually higher, but I think the #11 heads are 88-92 cc despite the claimed 8.8:1.

[AJ-]

Thanks for all the responses. Sounds like my #'s make sense. Shiny thanks for your your #'s. I think the compression ratio must be a bit lower than the '70.. It's crazy how low it is, really. I'm hearing the pro move is to measure the duration and valve events but I don't have a degree set so it's not worth it trying to go into that level of detail in this situation.

The 62's are set up for positive valve seals so I just need to replace those and put some stock replacement type springs on and they should be good to go.

[steve25]

Get yourself a set of Crower 68407 springs and 87048 retainers.

[Formulabruce]

Originally Posted by Shiny

FYI, my 70 350, #11 heads, Summit 2800 cam, had cold compression between 120 and 130 psi at sea level.

Perhaps the cam is different or the 70 CR is actually higher, but I think the #11 heads are 88-92 cc despite the claimed 8.8:1.

120-130 psi fits right in with a 8.8 CR. Remember thats a Static CR.
What is amazing is that that 70 350 has 355 ft pounds of Torque
at only 2800 rpm ! That is Stout! >> and 2 bbl carb...... !!