Interesting result of low compression, no further detonation

douglas vincent · Post by **douglas vincent** » Thu May 05, 2005 3:22 am

OK, I havent actually compression tested the cylinders yet but since the bad night at the track, and all the xtra oil coming in throught the crankcase breather lines, I am pretty darned sure I damaged something somewhere. Also, I have less power (not sure HOW much less, just less) off boost, and presumably less while on boost.

However, I still have plenty of power when on boost. And most importanly, the motor hasn't had a single instance of knock since then.

So lets say I broke a ringland or something, which allows some compression loss in the piston(s) that were susceptable to detonation. Is this similar to lower compression pistons IF the damage remains static?

I will rebuild eventually, but since I don't have the money right now, I might as well keep running it until something serios happens (I have an extra block and extra engine if something horribly catastrophic were to happen to the actual block). I will be running it in the next rallycross for sure.

If it stands up to the abuse from the rallycross without damage AND more importantly, knock, I will spring for the next larger pulley I can install and attempt the 10 plus psi I have been trying for for so long.

-K- · Post by **-K-** » Thu May 05, 2005 3:42 am

LMAO........
Look for some turbo pistons and you could run it up above 10 easy. Good to hear it's still running.

Water injection maybe? I think it would work well for your setup.

douglas vincent · Post by **douglas vincent** » Thu May 05, 2005 3:51 am

Yeah, the turbo pistons are on the table, as well as possible water/alchohol injection for the rebuild. But until then, boost away!

evolutionmovement · Post by **evolutionmovement** » Thu May 05, 2005 5:01 am

With a broken ring land, you'd get more blow by. There's a greater risk of developing hot spots, too.

Steve

douglas vincent · Post by **douglas vincent** » Thu May 05, 2005 5:16 am

Yeah, that what I suspect due to the high oil content in the intake cause I have no oil catch can.

But since I am not suffering detonation, I can handle a hot spot because a hot spot will melt something replaceable, like a valve or piston. Detonation will break something which can damage a cylinder. So I will just go until it won't go no more.

-K- · Post by **-K-** » Thu May 05, 2005 10:16 am

I wouldn't use turbo pistons and water injection. Seems like a bit much for 10psi.

Post by **Legacy777** » Thu May 05, 2005 3:28 pm

Is the oil coming directly from the breather lines on the heads or the main one at the back of the crank case? Or do you not know?

Rod G had a boosted n/a legacy. Was running around 10 psi with alcohol injection, and had a similar issue as what you seem to be going through. He thought it was the bottom end. After taking it apart, what he found was issues with the valves, not the pistons.

douglas vincent · Post by **douglas vincent** » Thu May 05, 2005 5:01 pm

Now that you mention it Josh, I had been having a horrid time with valve train noise. It would come and go like flicking a switch.

Since Friday night, it hasnt happened once. So a valve problem(s) could be what has happened.

I am not 100% sure where the oil is coming from, but I am pretty sure it is from the breather lines on the heads that then go into the intake.

Post by **Legacy777** » Thu May 05, 2005 6:15 pm

It'd be worth looking into before tearing into the block itself.

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Interesting result of low compression, no further detonation

Interesting result of low compression, no further detonation