Hey fellas, How much compression should my L79 327ci 350hp have? Currently measuring about 120fp. Tanks.
Google is helpful. This says the compression ratio was 11:1, but that doesn't have a lot to do with cranking pressure in a compression test. http://superchevy.automotive.com/71252/sucs-0732-chevy-l79-engine/index.html I'll add anything I find on cranking pressure.
Hi, thanks but not my question. Not the compression ratio, but the actuall compression value during a compression test, i.e., 120 pounds or ???
If they are all about the same you can get by BUT seems low to me. 150 160 would nice!You really need to do a leak down test to see where it's all going. You don't say if thats a wet or dry test............. JMO
Found one reference on another forum to something on order of 170-180 psi, but no details. Nothing official. Lots of variables. How wet are the cylinders? How hot is the battery? What rpm did you achieve while cranking? Plugs out of other cylinders?
Hi Fellas, Thanks, I thought it was low. IT was a wet test and the engine was holding really good oil pressure (65lbs). Not sure of the rpm, but it was a fully charging battery running a good starter, so whatever that would be. Guessing 100 rpm or more. I think I will to the leak test and see what that tells me. maybe guides if I'm lucky.
It has to get passed the valves before the guides come into play. You can have good oil presure and bad comp. Sounds like your heading for a re-ring and valve job at the least. They are nice running motors when they have compression. A wet test would be when you squirt oil into the cyl. not buy trying to splash oil up at cranking............... JMO again!
I did not actually spray oil in, I started it, ran it to warmed temp and then did the compression. I also was told by the guy I bought it from that it was rebuilt about 10 years ago. Maybe they did not put the correct pistons in if they bored it out. Is this a possible explanation?
Most of the cammed up stock Chevys had low reading due to the overlap ... if it don't smoke or use a lot of oil, don't worry about it.
Well, it does have a flat lobe! Luv that chevy cam engineering. So I do have to change out the cam. Been thinking of a Duntov 30/30 cam. Would like that "retro" rump te rump it would get.
How much variation in cranking pressure between cylinders? That's a good indicator of condition. Shouldn't vary more than 5% to 10%. Bob
Had a new 68 Vette with a 350-327 ,warm engine open throttle all pulgs out 180 PSI. Still had that at 50K miles when I sold it.
Has a bit of a sputter so I took off the valve cover and you can see the rocker is not moving as far as the others. It's adjusted correctly too, so that's how I came to the conclusion. Am I missing another possibility?
This IS NOT what you're looking for, but since it was already said that the compression ratio was 11:1, it is actually 10.35:1 with the .125 dome pistons. Butch/56sedandelivery.
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