360 compression
- Thread starter spstacman
- Start date
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fishy68
Tyr Fryr's Inc.
Not positive but I think they were all the same. And don't expect it to be as advertised. every one I've pulled apart had the pistons so far down in the hole it'd be amazing if it were even 8 to 1.
you won't know what compression is until you know how far the pistons are down in the bore...
then you can adjust the deck height and head gasket thickness to get what compression you want...
what pistons are you looking to use? flat tops or dish?
fishy68
Tyr Fryr's Inc.
Is this something you've measured or what the book says it is supposed to be? I have to ask because I've taken apart several 360's (LA's only) and every one was lower than advertised. Some were much lower. The very first one I did opened my eyes to this as it figured out at 7.6 to 1 and it was rated at 8.4 to 1... That's a huge difference.
fishy68
Tyr Fryr's Inc.
They were all old used engines. But how would being used affect anything anyway? The piston will still be the same depth in the hole and the head chamber size doesn't change. If anything a used engine will be a ever so slightly higher compression ratio due to carbon build up on top of the piston and in the chambers.
The problem with going by the original books is their not all that accurate due to manufacturing tolerances.
Maybe your right. I agree with the book, the information was gathered by the chrysler corp., so I believe it is pretty accurate to go by for a new one.But maybe you are right, you never know, im a learning mechanic, but I would like to know what the mathematical solution is to figuring out the compression ratio.
c
it is a mathematical calculation based on known facts....
as I said several post ago....tear the engine down and take measurements...
find out what your deck height is...find out what the pistons compression height is...
find out what your cylinder head cc are....head gasket cc....
then you find out what your compression ratio is...otherwise you are guessing...
He asked what the compression ratio for a new stock 1976 360 with a 2 barrel carb that he was putting together...I found that exact engine in my book, posted what the engineers at the Chrysler corporation figured out it was for and thats the end of that.
Good Night
Good Night
They're just trying say that the books are not always right when it comes to those things, even when they were new. Talk to any head pro and they will tell you,find a bunch of untouched factory heads of the same casting # and most likely they will be various cc chambers which it turn affects compression. Also talking to many that have rebuilt many motors and they will also tell you that the pistons are not always to factory specs as far as how far in the hole they sit.
So you would think that the factory would be dead on, but apparently thats far from the truth, with core shift and so-so quality control, the only way you know for sure is to measure everything yourself.
Butch
you need to talk to your machine shop and find out the part number/specs on the pistons...what deck height he is cutting the block to....what heads and their cc ...what head gasket he plans on using....
talking to us is not going to help you with your compression ratio...we are not doing the work...
talking to us is not going to help you with your compression ratio...we are not doing the work...
An engine's compression ratio goes down over time, especially older engines without stellete faced valves. That's every engine made before about 1984. Here's why. Valve seat recession. As the engine ages, the valves sink into their seats as they wear the seat face and the valve face itself. Valve seat recession can significantly lower the physical static compression ratio over time. This is one reason it's so important not to do your machine work "Chevy style". Chevy builders usually ignore valve seat recession and just grind new faces on the valves and seats, because they think it's ok to do that since they have adjustable rocker arms. The rocker geometry is by far not the only thing to consider here. There are specs on valve stem heigth, and valve face depth into the combustion chamber, measured off the deck surface of the head. If the valves are found to be out of spec as for depth, either the valves or seats or both need to be replaced, to regain that lost height into the combustion chamber, and raise the compression ratio back to where it is supposed to be. That's why it's very important to find a machine shop that's not Chevy oriented. I take all my stuff to Cassidy Machine shop in Macon. It is more geared toward industrial machine work, but they have the equipment to do anything and their work is second to none. A shop like that is what I recommend, because they HAVE to get it RIGHT when they are working on a set of $25,000 detroit diesel heads. Just some machine work FYI.
You got that dead right and that makes it even more important not to just slap somethin together. It all depended on the Monday/Friday thing.....whether the wife was willin the night before.......whether Jose had too much taquila tha night before.......too many variables there! LOL
Actually, it looks like all 360 production pistons have a 1.59 pin height, so the differences in CR should only be gasket thickness, deck height, and combustion chamber volume, maybe valve notches. CR also increases as bore size increases to a small degree. Looking at the chart in the Racing Manual, a 65cc chamber, .070 down in the hole, with a .020 head gasket in a +.020 over bore 360 gives 9.89 CR. This is actually less because they do not include valve notches. Soooo as these guys are suggesting, you better start measuring and using real numbers from your block. Zero deck height does not look good if you are running on pump gas. My 383 Block was .012 higher on one side than the other, as an example of Production Tolerance. As an aside, Chrysler introduced Induction hardened Exhaust seats in 1973 and up. Which should be good news. Magnum heads cc about 64.5 with stock valves.
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