What's your compression?

[carmangary]

Just curious what your readings are? How much should a healthy/worn engine be putting out? I know that the important thing is that they are close but I am still curious. Also, what's your engine size?

My 4.3L is putting out around 110psi.

 

[FE3X CLONE]

My compression is 11.3:1.

My cylinder pressure is around 200-204psi.

 

[gto78]

Just curious what your readings are? How much should a healthy/worn engine be putting out? I know that the important thing is that they are close but I am still curious. Also, what's your engine size?

My 4.3L is putting out around 110psi.

when you check do you hold the accelerator to the floor? Mine will go up another 25 psi when I hold the throttle open. I'm around 180 psi

 

[carmangary]

Wow, your compressions are a lot higher than mine. Makes me wonder if my engine is just worn slam out or something. Are your engines stock or are you running performance parts?

I propped open the choke and held the pedal down when I checked mine and had all the plugs out. I'm going to check them again probably this weekend since I should have my engine all back together and running (hopefully today!).

 

[Minion1186]

I have 11:77.1 compression 😀

 

[adumb]

I have 11:77.1 compression 😀

wouldnt 11 to 77.1 be vacuum???

lol jk, im sure you meant 11.77:1

😀

 

[86Cutlass383SR]

I'm not sure what a stock engine with stock cam should run.

You can have 12-1 compression but if the cam has a lot of overlap, say 250* @ .050" duration, then the cranking compression will be fairly low. Reason: the cam opens the valve earlier (to let in more intake charge) so the combustion pressure can't build up as high. At high rpm where these cams were designed to run, you have less time for this to occur. That is also the reason you need to run higher compression such as 12 or 14-1.

If you swap the cam to a stock type profile, say a 210* duration, since the valve opens much later the cranking compression will be MUCH higher.

That's why it's not so much the acutal number but the same for every cylinder. Yeah, a stock engine would have a specefic range but every engine wears differantly.

Again, I'm not sure what the numbers on a fresh stock cammed engine should be. HTH If you already knew this, sorry, some of our other readers may not.

 

[Bonnewagon]

As 86cutlass383sr said, look for each cylinder to be the same, no more than 10 % difference. If you think one or more are low, squirt some oil into the spark plug hole. If the pressure jumps a lot, it indicates worn rings.

 

[86Cutlass383SR]

And if the oil in the cylinder doesn't increase the compression, then you have bad valves. Compression is leaking past the vale seat and valves.