hustler Posted October 3, 2011 Share Posted October 3, 2011 I have a turbo Miata with an engine that's about 3-years old. I was trying to get a baseline compression test for another car and then I was shocked to find: compression: 60, 60, 90, 120psi Leak: 60, 60, 60, 3% Now the strange part, the car still idles great with a steady 21" of vacuum, drives great in traffic, and still spins the tires in 3rd gear. I don't get it. There is no smoke, zero blow by, total confusion. When I leaked it, I heard tons of air going through the exhaust, I'm also fairly certain I was at TDC on each cylinder. I have another TT day this weekend and then I'm pulling the head off. What do you guys think? Would an engine with numbers that bad drive perfectly? Quote Link to comment Share on other sites More sharing options...
kbrew8991 Posted October 3, 2011 Share Posted October 3, 2011 Would an engine with numbers that bad drive perfectly? extremely doubtful Quote Link to comment Share on other sites More sharing options...
sperkins Posted October 4, 2011 Share Posted October 4, 2011 When I leaked it, I heard tons of air going through the exhaust, I'm also fairly certain I was at TDC on each cylinder. I'd pull the rocker arms off just to make sure the valves are completely closed and test it again. Quote Link to comment Share on other sites More sharing options...
hustler Posted October 4, 2011 Author Share Posted October 4, 2011 When I leaked it, I heard tons of air going through the exhaust, I'm also fairly certain I was at TDC on each cylinder. I'd pull the rocker arms off just to make sure the valves are completely closed and test it again. This engine has "shim under bucket" lifters and I have .009" of lash on the exhaust side. Some think it should be looser, some don't. I'm really confused. I also notices a leak at #4's exhaust manifold runner at the head when recently running Sea Foam through it, but that's the good cylinder in regards to the test. I'm just curious, if a valve is open (decompression stroke) will it show 100% leak or something around 60%? Quote Link to comment Share on other sites More sharing options...
hustler Posted October 13, 2011 Author Share Posted October 13, 2011 This engine has about 20-25k miles on it and about 70 hours of track time in my turbo Miata that runs about 245whp/235wtq. This is an 8.6:1 compression engine. I had serious leak down and compression issues and not sure what's going on. I'm guessing the valves are burnt at the seal. I'm also not exactly certain the head-gasket sealed properly between 1,2,3. #1 #2 and 3 #4 #1 #2 #3 #4 Uninformed assumptions: The pistons look great, I guess I know what I'm doing on dyno tuning. I don't like the carbon, but that's probably the nature of the best at 11.5:1 AFR. The intake valve in #3 looks like it melted, and there are some pieces of it fused to the dome next to it. I guess #2 and 3 are lean due to feeding fuel on both ends of the rail? What do you pros think about the color on the valves? Why do my intake valves look fried and the exhaust valves look healthy? I heard nasty leak through the exhaust when we leaked it. Should I switch to SS valves or even Inconel exhaust valve with heavier springs? My goal is reliability, not output. Quote Link to comment Share on other sites More sharing options...
hustler Posted November 1, 2011 Author Share Posted November 1, 2011 This just in: Intake valves were bent. Fail fail fail. Quote Link to comment Share on other sites More sharing options...
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