Jack

iTrader: (2)

This a quote from the Rotory Resurrection site "115+ is like new, 100-115 is healthy, 90-100 is getting weak(1 year or less in most cases) below 90 could blow at any moment".

My FD had low compression 85psi on all six faces and recently let go. I think went lean (40 degree evening, 15psi, 105 knock peak recorded peak on PFC) My question, what contributes to low compression / "90 could blow at any minute". I would would think you would have problems with hot starting, low end power and maybe blowby.
Is there chamber to chamber blowby of hot gases creating detonation? Engine builders/ tuners please feel free to comment.

GoodfellaFD3S

iTrader: (213)

Low compression occurs when your apex seals and/or rotor housing surfaces are worn down. On a boosted application it's more likely to blow b/c the apex seals are older/hear cycled/weaker. On most n/a engines, the seals don't let go, they just keep wearing until one day they stop sealing so the engine won't start.

85 psi isn't insanely low compression. I think given some more time you would have experienced hot starting issues. Your turbo is so responsive that I don't think you'd ever notice a large loss of low end power due to low compression.

C. Ludwig

iTrader: (27)

Cranking compression not a good indicator of whether an engine "could blow at any time". An engine with outstanding compression can pop just as easily as one with poor compression if it's detonated. Just as easily an engine with poor compression can run for years. Cranking compression is simply that and nothing else.