vince Posted September 21, 2007 Share Posted September 21, 2007 Ok! Let me start by saying that I am a rookie when it comes to the internal parts if the engine. The other day I was asked if I had ever done a compression on my stock 350. Today I decided to do one and came up with these numbers 1=135psi, 3=120psi, 5=120psi, 7=110psi, 2=110psi, 4=120psi, 6=110 psi and 8=135psi. So do these numbers mean to tell me anything? Link to comment Share on other sites More sharing options...
Guest ADGTRUNKLID Posted September 21, 2007 Share Posted September 21, 2007 Usually you do not want more then 15 pounds variation, considering the age of the car I would say it looked fine. Some people like to do the test with the throttle wide open to get air in. Link to comment Share on other sites More sharing options...
wallaby Posted September 21, 2007 Share Posted September 21, 2007 I was tought to have all the spark plugs out, and the throttle held fully open before cranking the engine to test a cylinder. It's not that critical...you'd be looking for a cylinder that has noticeably less pressure and that would be a sign of some mechanical problem. I'd say your numbers look pretty good. Link to comment Share on other sites More sharing options...
vince Posted September 21, 2007 Author Share Posted September 21, 2007 Should I try it again with the throttle opened to see if there is a difference? Or should I call it all good? One more thing, will this test give me any indication how solid the motor is? Link to comment Share on other sites More sharing options...
footballubet Posted September 21, 2007 Share Posted September 21, 2007 Those numbers look good. If you try it again with the throttle wide open, those numbers may jump up a little bit. Just make sure you get the same number of "puffs" as you crank the engine over. Usually 5 is enough. Link to comment Share on other sites More sharing options...
Guest Rice Racing1 Posted September 21, 2007 Share Posted September 21, 2007 Vince the rule is 10% variation not 15 psi. The biggest problem here are the 3 cyl's at 110 psi. 90 psi is the threshold of being able to work. Below 90 psi the cly dose not produce any power. Yes, those #'s mean the engine is weak powerwise. Either the ring seal is bad or the valve seat seal is bad. A stock low comp SB is in need of a rebuild once the comp drops below 135 psi. Don Link to comment Share on other sites More sharing options...
vince Posted September 21, 2007 Author Share Posted September 21, 2007 This is all good information. With these numbers do you think it would be ok to do a cam, lifter and spring change? or should I have a total rebuild done? Link to comment Share on other sites More sharing options...
MonteAZBB70 Posted September 21, 2007 Share Posted September 21, 2007 It sounds like more testing is in order. As Don said, you need to find out why those three cylinders are low. It could be as simple as a valve job. You might try running the same test again "wet". Squirt a small amount of oil into each spark plug hole before doing the test to see if the numbers come up. If they do, rings are suspect. Other than that, a leak-down test will give you the best idea of what's going on inside. Mike Link to comment Share on other sites More sharing options...
vince Posted September 21, 2007 Author Share Posted September 21, 2007 I ran the test again only this time with all plugs removed , full throttle, engine cold, and I gave at least 5 puffs for each cylinder. The results were much better. 1=165psi, 3=160 psi, 5=160psi, 7=160psi, 2=170psi, 4=165psi, 6=170 psi and 8=160psi. The first test was done by pulling one plug at a time, no throttle, and one or two puff's. Link to comment Share on other sites More sharing options...
Heckeng Posted September 22, 2007 Share Posted September 22, 2007 What are the "puffs" you are talking about? Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 22, 2007 Share Posted September 22, 2007 compression strokes, come-on Scott, get with it Link to comment Share on other sites More sharing options...
vince Posted September 22, 2007 Author Share Posted September 22, 2007 Sam, thanks for clearing things up for me. Scott thats the best I could describe the sound when cranking. I Told you guy I was a rookie! Link to comment Share on other sites More sharing options...
Heckeng Posted September 22, 2007 Share Posted September 22, 2007 I guess you're talking about counting the other cylinders firing since the comp tester is in the cyl you're testing then. I've never counted them when I've checked, I just crank it and have somebody watch the gauge and quit once it doesn't move! I sound like the newbie now! Link to comment Share on other sites More sharing options...
Sam (Bones) Posted September 22, 2007 Share Posted September 22, 2007 you can feel each compression stroke while holding/watching the gauge Link to comment Share on other sites More sharing options...
vince Posted September 22, 2007 Author Share Posted September 22, 2007 back to the numbers. Do you think it will be safe to change the cam, lifters and springs? I am trying to get a little more HP. Link to comment Share on other sites More sharing options...
wallaby Posted September 22, 2007 Share Posted September 22, 2007 The puffs are the compression strokes. You can watch the pressure continue to build each time a compression stroke comes along...until it seems to level off, and that's when you read the gauge. I'm thinking your engine should be sound enough to benifit from a new camshaft package. Now you just need to decide between the cam you want, and the cam you can use! Link to comment Share on other sites More sharing options...
vince Posted September 22, 2007 Author Share Posted September 22, 2007 Cool!! I have my eye on the Comp high energy 260 or 265 cam. Would that be a good mild upgrade? or do I need to go bigger? Link to comment Share on other sites More sharing options...
montefrazer Posted September 23, 2007 Share Posted September 23, 2007 Compression strokes to pump up the gauge. With a high of 170 and a low of 160, your engine seems to be in good shape. Link to comment Share on other sites More sharing options...
vince Posted September 23, 2007 Author Share Posted September 23, 2007 Thanks everyone for your help. I learned something new, more question to follow when I begin to put in the new cam. Link to comment Share on other sites More sharing options...
Guest K.J Parker Posted September 24, 2007 Share Posted September 24, 2007 I found that to have a accurate compression test I needed to have the battery charged up. I think the removal of the plugs is for the ease of engine turnover. I didn't find a huge difference between open throttle and not open. I normally took 4or5 engine revolutions in order to attain the highest numbers. Link to comment Share on other sites More sharing options...
vince Posted September 25, 2007 Author Share Posted September 25, 2007 KJ I was a little concerned about the battery when I was doing the last 2 cylinders. I think the key is the 4-5 compression strokes. It made a big difference in the second test. Link to comment Share on other sites More sharing options...
Guest 72yellowmc Posted September 25, 2007 Share Posted September 25, 2007 Vince you have a PM. Link to comment Share on other sites More sharing options...
Guest ADGTRUNKLID Posted September 26, 2007 Share Posted September 26, 2007 With the new cam and lifters you might also think about spring height and bind. As well as geometry on the valve stems. Any good head shop could test your heads for spring height and that. Although you nay want to get the recommended springs with the set up. Link to comment Share on other sites More sharing options...
vince Posted September 26, 2007 Author Share Posted September 26, 2007 Thanks Lloyd I will keep that in mind. I was planning on changing the rods and springs, I will make sue that all components work with each other. Link to comment Share on other sites More sharing options...
vince Posted September 26, 2007 Author Share Posted September 26, 2007 Robyn, Thanks for your help. Link to comment Share on other sites More sharing options...
Recommended Posts