New 2.7 is in and were going to get it tuned this weekend. Wont be going past 25psi for now till we swap in the 2.8 forged stroker. Ill be rolling around on wastegate (10psi) for normal driving, with a highboost button for 25psi.
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Found the limits of a stock M20B25 Bottom End
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First thing I was gonna say was it's your spark cut that probably caused it. M20s are safer to use fuel cut instead. or raise your limiter a bit so you don't have to stand on it.
likely what happened is you broke a rocker, then had piston/valve contact, which caused the bottom end to fail since it was under so much stress. The pictures of the valves pretty much tell the same story.
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Originally posted by nando View PostFirst thing I was gonna say was it's your spark cut that probably caused it. M20s are safer to use fuel cut instead. or raise your limiter a bit so you don't have to stand on it.
likely what happened is you broke a rocker, then had piston/valve contact, which caused the bottom end to fail since it was under so much stress. The pictures of the valves pretty much tell the same story.
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Hard to tell from your pics.....does offending cylinder walls have lower carbon line than other cylinders? Kind of looks like that in the picture. If so, was your con. rod already bent for a while when this happened?
Also, any pictures of the crank thrust bearing? too much trust will twist/flex the rod and can crack the rod or cause a mess in the wrist pin area.
Could be something as simple as too much heat in that cyl (not enough fuel) and as a result locked piston?
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Originally posted by SLEEPYDUB View PostI also am running 20* of timing at max torque and up top so that could very well have a lot to do with it
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Originally posted by nando View Post20 degrees really isn't much for a 2v engine though.
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Originally posted by ForcedFirebird View PostYou don't want to see my timing maps then lol. A few of our builds have 23° @ 190kpa and 4300rpm...stock rebuilt bottom ends, 56-62mm compressors, 93 octane (which is actually e10 here). E85 still isn't widespread down here yet.
Originally posted by nando View Post20 degrees really isn't much for a 2v engine though.
Originally posted by ForcedFirebird View PostAt peak TQ and decent boost levels? I often see people pulling too much timing, but 20+ is healthy with a turbo. Go check out the maps thread ;)
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I was pointing that comment more towards Chris, people with supposed dyno tunes, even have awful timing maps. Stick to the age old rule and pull 1-2° for every 10kpa (just over 1psi) as a base, then go up from there.
For several reasons, I would rather not post my maps, specially an aggressive dyno tune.
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I found detonation occurs somewhere around 20-23 degrees on my 9.5:1 CR under boost when IATs approach 100 F.
It was safe up to 25 degrees when IATs were below 50 or 60 F.318iS Track Rat :nice: www.drive4corners.com
'86 325iX 3.1 Stroker Turbo '86 S38B36 325
No one makes this car anymore. The government won't allow them, normal people won't buy them. So it's up to us: the freaks, the weirdos, the informed. To buy them, to appreciate them, and most importantly, to drive them.
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Originally posted by downforce22 View PostI found detonation occurs somewhere around 20-23 degrees on my 9.5:1 CR under boost when IATs approach 100 F.
It was safe up to 25 degrees when IATs were below 50 or 60 F.
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