Low Compression Cylinder 1

[beeronz]

Hey everyone,
Long story short - raced at the track, blue smoke out the exhaust, cylinder 1 compression test 40 and the rest were at 150.

Now, onto trying to figure what exactly is the problem, and how to track it down.
I'm thinking rings but wouldnt know until tearing it apart. But is it possible for it to be valve seals? If so, how could I narrow it down to it being, or not being it? Any other factors that I am not thinking of, or which I am not aware of? Not the most experienced individual when it comes to motor builds, but I have the basics and what to look for.

Any input would be greatly appreciated!
Thanks!

[soryu]

A leak down test should help
40psi ??
Check your fluids for mixture.
Did you add oil to your comp test?

[beeronz]

A leak down test should help
40psi ??
Check your fluids for mixture.
Did you add oil to your comp test?

Ahh, the leak down. I forgot about that. I dont have the gauge to perform a leak down test at the moment. I'll give a friend a call tomorrow and see if i can borrow one and report findings on that.

40psi with a few drips down the cylinder lol. I know, I was shocked AF too.

Fluids did not have any mixture, oil is still beautifully tanned lol, and coolant levels have not changed or have any change of color.

Thanks for the input!

[Prok0]

Most likely damaged that piston, you could pull the plug out and use a bore scope to look in and you'll probably see the edge of the piston melted down.

It would not be valve seals, as even if they are bad they should not cause the cylinder to lose compression since the valve itself should sit flush on the seat and no air should get past it to even enter the port to then push between the valve and guide and up past the seal. The seal is more to keep oil that lubricates the head out of the port.

At any rate the motor is going to have to come apart to get repaired unfortunately.

[gptoyz]

Ahh, the leak down. I forgot about that. I dont have the gauge to perform a leak down test at the moment. I'll give a friend a call tomorrow and see if i can borrow one and report findings on that.



40psi with a few drips down the cylinder lol. I know, I was shocked AF too.



Fluids did not have any mixture, oil is still beautifully tanned lol, and coolant levels have not changed or have any change of color.



Thanks for the input!


You can also shove compressed air into the offending cylinder and then you can listen for the air leaking. It can only leak into the following:
Manifold/throttle body
Exhaust manifold
Oil dipstick
Radiator
Adjacent cylinder


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[beeronz]

Most likely damaged that piston, you could pull the plug out and use a bore scope to look in and you'll probably see the edge of the piston melted down.

It would not be valve seals, as even if they are bad they should not cause the cylinder to lose compression since the valve itself should sit flush on the seat and no air should get past it to even enter the port to then push between the valve and guide and up past the seal. The seal is more to keep oil that lubricates the head out of the port.

At any rate the motor is going to have to come apart to get repaired unfortunately.

Ahh okay. At least it narrows it down to the block. Like you said, not gonna know till I tear it apart. Unfortunately that won't happen for another week. I don't have the tools at home to do it and the shop is busy till then.
I've been looking at your bottom end rebuild packages on your website. Prolly order that once I know for sure what direction I'm going, and how bad the damage is.
Any input on the options to buy? Should I keep factory compression ratio if possible? Or do you recommend something else? I figured since I'm going in there and things need to come out, I might as well beef it up to handle at least 400hp. I'm sticking with my t28 in the meantime (since funds will be short after the motor build) but in a few years I'm thinking top mount manifold with a bigger snail with supporting fuel mods and such.

[Prok0]

My SR and a lot of our old race motors we went with 9.0:1 compression, IMO it helps keep the motor a little peppier out of boost but the compression isnt soo high that it warrants running race gas all the time or very low boost to avoid detonation.

On my old setup I ran an S14 T28, aftermarket manifold/o2 elbow/intercooler/exhaust, 740cc injectors, Z32 MAF, Enthalpy Tune, and on 18psi and pump gas I trapped 117mph in the quarter mile so its definitely a pretty quick setup.

I ran CP pistons on stock rods with ARP hardware but have built a new motor with another set of CP's and some Manley rods.