What are the compression specs on 350 Chevy

[Fahra]

Can anyone out their give me the specs for the cylinder compression on a 350 Chevy, keep in mind Boys I am female in training. Oh one more thing what is the best V-Drive prop shaft to get and where can I get the best bang for my buck. Thank you all for your help my husband apperciate's it.

Fahra:)

[Wannabe]

Well, the specs are really varried. GM made them for so long, and so many applications, there have been many. Most of them ranged between 8 1/2 to 1 to the high side of 9 to 1. But that is for stock production line stuff. Boats have very different applications as they pick up cool water rather than a hot radiator. So you can run as much as 10 to 1 with standard premium pump gas. If you want to go with an aviation gas or racing fuel you can go as high as you want.
Next, we would need to know the application of the boat. The more power you have, the better the material of the pop shaft you need to stay safe. But the good stuff costs a pretty penny. a $500 prop shaft is not uncommon for a race boat. We also need to know how big of a prop shaft. (Not long, but big around.)
This is a pretty friendly board. The more direct the question, and the more background, the better the answers that you will get.

[RiverRacer]

Can anyone out their give me the specs for the cylinder compression on a 350 Chevy, keep in mind Boys I am female in training. Oh one more thing what is the best V-Drive prop shaft to get and where can I get the best bang for my buck. Thank you all for your help my husband apperciate's it.
Fahra:)

Welcome aboard you came to the right place!.. Compression ratios vary depending on what you're using the boat for, we need a little info on the boat and what it will be used for, and what is wrong with the prop shaft you have now???!..

[gfinishline]

"At this point I'm into BANG FOR THE BUCK, what is being offered?" Nice vague questions. No real facts involved. Please try to get down to basics as far as YOUR MOTOR GOES. Please keep in mind that we are all in training and your husband needs to try and get a little more specific on his facts. Otherwise this is all just BS.

[Fahra]

"At this point I'm into BANG FOR THE BUCK, what is being offered?" Nice vague questions. No real facts involved. Please try to get down to basics as far as YOUR MOTOR GOES. Please keep in mind that we are all in training and your husband needs to try and get a little more specific on his facts. Otherwise this is all just BS.


Funny, I thought the question is pretty straight to the point for those who know about the basics of a stock 350 Chevy. I checked the compression on each cyclinder to see if I have a blown head gasket. So my question is; Does anyone know the specs per the book?? Not too vague is it?? I would not want all of this just to be BS. (QUOTE) Hey but thanks for providing me with absolutley nothing.

Fahra

[hydroguy]

Which stock 350 engine? there were numnerous ones with different compression. If I remember correctly they went up to 375HP from the factory. So what compression did you find when you checked it? do you have HIPO heads on it and are they stock? Did you check the casting numbers so you could get an idea of the engine you have? there are many factors that enter into this. If you think you have a blown hed gasket that will show up as a discrepancy and you don't need to know the compression ratio it came with + you should be looking at the oil also for water in it.

[FC-Pilot]

Fahra, (this is in my nicest voice so don't think I am saying this to be nasty:)) the 350 Chevy came in a wide variety of compression ratios. That being said the readings could be vastly different depending on what it was built with originally (which often times can't be know without tearing it apart). Now being that you did a compression test you should have an idea as to the condition of the cylinder performance (or how well the rings, valves, and head gasket are sealing). The rule of thumb (as I remember it) is you want the compression of all the cylinders to be all within a 10% margin (the best and worst cylinders to be within that percent of each other). There are a few tattle tale signs of head gasket issues, if two adjacent cylinders are both very low while the rest are high, that can sometimes give you your answer. You can see if the rings are toast by squirting a little oil in the cylinders and redoing the compression test. If the numbers jump radically then that helps point to tired rings. The next thing I might try is putting compressed air into "suspect" cylinders. Then listen where the air is coming out. If you hear it in the exhaust then chances are good you have and exhaust valve problem. If you hear it coming through the carb then and intake valve problem. If you hear it coming through a breather (and hence out of the crankcase) then the rings or piston is toast. And last but not least, if you hear it coming out of the water dump then you have a head gasket problem.

Well there we have some ideas as to identifying the problem. Remember the actual compression numbers are not the most important issues but more important is the fact that they are close together.

Now, to explain where the comments were coming from, I can think of six or seven different compression ratios for the 350 engines over the years, and on top of that every different camshaft that came in them over the years (which may even be close to the hundred mark) will change what the compression test will read. That having been said asking for a figure for your compression test was vague. I hope you don't get offended, but with the info given to us our hands are tied as to giving you specific numbers. On top of that, the numbers will drop as the miles or hours increases, so that also puts us in a predicament. Anyway, let us know how close the numbers are and what you find with some of the other test ideas and we can try and help yo from there.:D

Paul Miller

[63Stevens]

if you are looking to see if you have a head gasket problem. take your compression testor and check the compression in all cylinders. If all cylinders are within 10-15% of each other everything is good. A bad head gasket will definately show on the compression testor. the reading will be down compared to the rest of the cylinders.

[Terrible toy]

I'll go out on a limb and guess you are talking about a v-drive ski boat. My recommendation is not to go over 9.5 to 1. You can run regular gas and still make decent power.

I've tried a few different prop shafts and the best was 17-4 PH stainless. K monel is a common alloy for shafts. Some of the others on here might have sources for you. Having not bought one in while I hope I don't have to for a long time $$$.LOL

Nice to see another lady hanging around here.

[canam10]

[QUOTE=Fahra;9424]Can anyone out their give me the specs for the cylinder compression on a 350 Chevy

If your just looking for a compression test number, most stock engines will be somewhere between 140 to 160 psi in each cylinder. Here are a few rule of thumb numbers
8:1~8.5:1 150-170 psi
8.5:1~9.5:1 170-210 psi
9.5:1~11.5:1 210-275 psi
11.5:1 & higher 250+ psi depending on cam and other variables as the other guys were talking about.

[SonnyGlide]

Mam, FC's post may B a lill long, but He's 100% correct on the step by step method in doing a Compression test to determine internal eng. problems.
and all the post below FC R as well.
Take the casting NO# on the block, and go to Super Chevy Site, and they can tell U what the cam specs were/are, C/R ( Compression Ratio ) etc. for a stock motor, this could help U find out what eng. U have w/out too much bench work.;)

Hope this helps