92lt1

i was just curious if someone could give me a answer to the differrent compression ratios 350's have came with over the years, mainly 80's and 90's.

RB83L69

ALOT.

Everything from somewhat over 11:1 in the early LT1, to 8¼:1 in the 70s an early 80s, and back up to 9¼:1 in the L98 and over 10:1 in the LT1 of the 90s.

92lt1

do you know of any web sites that would give me the complete listing? ive searched and have come up dry.

RB83L69

I have no clue. That info, arranged that way, is pretty much useless. Not that uselessness keeps stuff off the Internet, but still.....

What is it you really are trying to find out? Maybe if you ask the right question, you can get the answer you're looking for.

Streetiron85

I don't know of any sites, but a Chiltons manual covering from 69> has some data.
In the early years they used 2 different head vols and 3 different piston dome sizes. and those combos gave anywhere from 8.5/1 to 11/1, roughly.
Then they introduced the 58cc alum heads later on. But I don't think they used those with anything except for flattop pistons.

You can figure it out mathematically with the above data.

92lt1

RB83L69, my cousin has around 15 or 16 350 blocks in his shed and he was curious as to what compression ratios they had and i told him to run the numbers and he said his quesiton about the compression was not answered.

RB83L69

If they're blocks, their compression ratio is undefined; blocks need pistons and heads and gaskets in order to have that attribute.

What is the sound of one hand clapping? This is in the same class of things.

92lt1

sorry, i should have said shortblocks.

92lt1

figuratively speeking with stock heads and gaskets.

Streetiron85

Shortblocks?

Still if it's a shortblock there's no way of telling what the CR is without the head.

You'll need to know the displacement of each one for starters.
Then the piston dome Vol
Then the head vol

RB83L69

Too many varieties of "stock" heads, too many different head gaskets over the years.

And on top of that, the question remains totally meaningless, in light of the fact that those things aren't there. Short blocks don't have compression ratios; any more than only children have sibling rivalry (well, most only children don't, anyway, only the real "special" ones).

Basically, there is no answer to the question. If there is, it's wrong. That's all there is to it.

92lt1

all i wanted is a complete list of gm 350 engines over the years with their specs. thanks for making me feel like a dumba@@. so does it make you feel good to run your mouth or what?

RB83L69

What we're trying to tell you, is that there is no such list; there are absolutely hundreds of different combinations of blocks, pistons, gaskets, and heads that have been available, most of which would end up being about 8¼:1, but many of which would have been slightly different; and even if there was such a list, it doesn't apply to what you've got, because you don't have motors, you have short blocks which by definition don't have a compression ratio. If you don't like that answer and just want to run your mouth and show that you don't understand much about motors, I'm terribly sorry, but that's just the way it is.

five7kid

iTrader: (14)

Don't blame RB for your feelings, he's just trying to get the information across. If you'd take a look at his post count, you'd understand that he doesn't continue to type for the sake of hearing himself talk. If he did, the mods & admins would have shut him up long ago. Obviously, he's still talking, so he's got something worth listening to (and when he's wrong, which is rare, he admits it).

Now, think about what you're trying to determine: What difference does it make what compression ratio an engine had when it was delivered, if the shortblock is now sitting in a shed? If they're all 350's, then you can tell by looking at the pistons what their relative compression ratios would be, assuming each had the same head on it. But, why would you care? If you've got a shortblock sitting in a shed, it must be there for a reason, because it's not out there moving some vehicle around right now. I might be willing to take a chance on what it would do if put back into a vehicle, but only if I wasn't too concerned about how it performed if I did it. Otherwise, since it's now sitting in a shed, I'd want to disassemble it and freshen up whatever is worn, which most likely would involve overboring the cylinders, which would require replacing the pistons, anyway, at which time you would choose replacements that would give you the desired compression ratio.

Any other use of the original compression ratio data would prompt us to either; a) protect you from yourself, or b) protect others from you.

Nobody's trying to be smart with you or make you look stupid, we're here to share technical data relevant to 3rd gen F-bodies and help each other out. If a lot of time has been spent on this thread trying to figure out why you're trying to figure this out, it's because it doesn't make a lot of sense to those who understand such things why you're trying to get this kind of data.

Streetiron85

http://www.mortec.com/castnum.htm
If a list is what you want, here's one.
I'm not sure if it has what you're looking for, but it's something anyhow

92lt1

yes that is close to what im looking for but with more detail like engine compression, hp, tq ect...

ME Leigh

There is no such list, you can start on for us though. It's kinda tough though considering over 50 millions SBC have been built, the majority of which are 350's.

You will have to look in a million different sources to find all of them. Good luck!!!

Streetiron85

I have a chiltons manual that has all thet stuff in it, but it's 60s-70s.
You might be able to get a later manual that has the info you're after.

ME Leigh

Yeah but you would have to have a chiltons manual for every year,make and model that came with a 350.

Dustin Mustangs

iTrader: (1)

Are you any good at math? If so, here's an idea for you, measure them. Start by measuring the bore and stroke. Here are some common stock values for those:

V8 Stock Bores and Strokes
SBC:
262 = 3.671" Bore x 3.100" Stroke
265 = 3.750" Bore x 3.000" Stroke
267 = 3.500" Bore x 3.480" Stroke
283 = 3.875" Bore x 3.000" Stroke
302 = 4.000" Bore x 3.000" Stroke
305 = 3.740" Bore x 3.480" Stroke
307 = 3.875" Bore x 3.250" Stroke
327 = 4.000" Bore x 3.250" Stroke
350 = 4.000" Bore x 3.480" Stroke
400 = 4.125" Bore x 3.750" Stroke
BBC:
366 = 3.935" Bore x 3.760" Stroke
396 = 4.094" Bore x 3.760" Stroke
402 = 4.125" Bore x 3.760" Stroke
427 = 4.250" Bore x 3.760" Stroke
454 = 4.250" Bore x 4.000" Stroke
502 = 4.468" Bore x 4.000" Stroke

Use this to get the swept volume of one of the cylinders. Then get something like this to measure your deck height volume. Add that to the volume of the head gasket you want to run and to the volume of your combustion chamber for whatever head you want to use. Make sure they're in the same units, divide the two, and blamo! That's a good ESTIMATE of your compression ratio. Like 57kid said though, if you plan on rebuilding those before you use them the compression ratio could change unless you get the exact same parts, which isn't very likely to happen.

92lt1

thanks iron, me leigh and dustin, that helps

Streetiron85

https://www.thirdgen.org/newdesign/tech/techdb.shtml

And of course there's this
But it's F bodys only AFAIK