I went out for a rather large little shindig on friday night in the turbo 528e. Ended up running a twin turbo C4 corvette and a big turbo SRT-4. I beat the turbo vette from a slow roll, but the SRT got me on the top end. The guy in the skittle insisted on a 3rd gear roll at 60 miles an hour, because his tranny was dicked up, and apparently he couldnt shift into 3rd under power. I think it would have been different from a standing start or off the line. So whatever. I would hold him off until he shifted into 4th, then he'd get away.
As usual, I was observing what appeared to be a contrail behind my car while running. Its been doing that for months though.
I popped the oil filler cap off this morning to find just a wee bit of milkshake present. I'd been itching to pull the head for qite a while, so I thought this was a good reason to finally do so. It only took three hours, which I'm pretty proud of. The head came off the block so easily it was as if it had never been torqued down at all. Usually they're kinda stuck on there, and you need to pry a corner up to break that stiction. This time it just lifted right off.
The gasket looked fine. It was slighty pushed outward on the exhaust side of cylinder #5, which is also where it showed signs of external leakage several months ago. Theres a soft, white flaky film present on the gasket in some places, which is presumably just dried up coolant. The pistons and head show detonation occuring on the far side of the cumbustion chamber, opposite the spark plug near the exhaust valve. This slight pitting is only evident in cylinders 5 and 6, though cylinders 4-6 show a different pattern of carbon deposits than 1-3.
If the problem was ignition timing and/or fuel mixture, the detonation would be present in all cylinders. I realize 5 and 6 are the hottest, but the detonation should not be so much more evident there than 1-4. This makes me wonder why these cylinders are getting more air than the others, which seems to be the case.
The one thing thats apparent is that the throttle body opens slightly past 90 degrees. Against the stop, its open to the point that you cant see the throttle shaft on the side of the throttle that feeds cylinders 1-3 while looking straight into the throttle. It looks like its directing the majority of the air coming into the manifold towards 4-6, which would explain the detonation occuring primarily in those cylinders. I dont think this would make a difference when the manifold is under vacuum and drawing in a certain amount of air. I think it might be significant to have the throttle opening past 90 degrees when theres more than 30 pounds of air a minute blasting through.
Judging by the condition of the head gasket, I plan on installing another stock gasket. With studs strong enough to keep the head firmly attached to the block, it should hold up just fine. The head bolts seem to be the source of the failure in this case.
What are your thoughts on this?
Head came off today.
I think we should race in taking heads off lol. I'll definitely beat you with my 2002. Last eta head I pulled was probably only a few hours, but then again it didn't have any turbo stuff...
Under boost I definitely think an angled throttle would send air in that way, but I would say it would be more that 1-3 are getting less air from a lack of flow, rather than 4-6 getting more air from more flow if you get what I'm saying.
detonation isn't that good, you should probably fix it. in case you didn't know.
Under boost I definitely think an angled throttle would send air in that way, but I would say it would be more that 1-3 are getting less air from a lack of flow, rather than 4-6 getting more air from more flow if you get what I'm saying.
detonation isn't that good, you should probably fix it. in case you didn't know.
I would like to get all six pots on the same page. That seems to be the problem right now. I can take a bunch of timing out so 5 and 6 wont be pinging but 1-4 will be far from their detonation threshold. Thats not right. Its tuned for power right now, by the butt dyno. It seems like I've got the two cylinders running too hot for whatever reason, with the other four making good, clean power.
The throttle angle is easy enough to fix. I'll do that for sure, and I'll see what I can do as far as port work inside the plenum to help things distribute more evenly. At 30 lbs/min there is a half pound of air a second moving through the manifold. Thats a considerable mass of air, and the stock manifold has it blowing straight into the other side of the plenum. I'm thinking about a 666 fabrication intake manifold. That would solve this problem...
The throttle angle is easy enough to fix. I'll do that for sure, and I'll see what I can do as far as port work inside the plenum to help things distribute more evenly. At 30 lbs/min there is a half pound of air a second moving through the manifold. Thats a considerable mass of air, and the stock manifold has it blowing straight into the other side of the plenum. I'm thinking about a 666 fabrication intake manifold. That would solve this problem...
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M. Holtmeier
- Posts: 3025
- Joined: Mar 11, 2007 3:06 AM
- Location: Dallas, Texas
It's probably because you're pulling so hard the air is getting pushed back to 5 and 6! 
Have you thought about an imbalance in power cylinder condition? Maybe those 2 holes are sealing a little better than the rest. The head gasket sealing rings didn't have any dark spots on either side did it? If the head gasket comp rings are good, I'd want to see the piston rings.
Have you thought about an imbalance in power cylinder condition? Maybe those 2 holes are sealing a little better than the rest. The head gasket sealing rings didn't have any dark spots on either side did it? If the head gasket comp rings are good, I'd want to see the piston rings.The throttle plate rotating past 90 degrees won't steer the air like a rudder. It will create more turbulence... just like when it hasn't opened fully. 10 degrees before WOT would have the same effect as 10 degrees past WOT.
Slight differences in the casting of the combustion chamber can result in one cylinder detonating and not another along with variances in fuel delivery, spark plug orientation, carbon deposits, etc.
Slight differences in the casting of the combustion chamber can result in one cylinder detonating and not another along with variances in fuel delivery, spark plug orientation, carbon deposits, etc.
I'll take a closer look at the sealing rings. I dont remember.
The rings should be just fine. The motor uses absolutely no oil, and the last compression test was good. It just uses coolant when under boost, and it has for the last few months. I figured it was, as the coolant level would drop slightly with no external leaks. And the smoke it emitted while under hard accel had to be due to something. If it were oil that would show on the plugs and the dipstick. Looking at the carbon deposits on the pistons, I'd say most of the coolant was burning in #6, a little in #5 and barely any if at all in #4. 1-3 were normal.
It seems like it really blew the head gasket back when I was running the open downpipe. I guess I wasnt hearing the detonation over all that noise. Its been holding on until now, despite the external leaks, when coolant finally got into the oil. Thats either a blown HG or a cracked head. I'm not too worried about the rings or head. The bottom end looks very good. The head could have come off of any m20. The exhaust valves have that light brown/pink color. It looks good, other than the pitting in the head from detonation. Even thats not too bad.
The rings should be just fine. The motor uses absolutely no oil, and the last compression test was good. It just uses coolant when under boost, and it has for the last few months. I figured it was, as the coolant level would drop slightly with no external leaks. And the smoke it emitted while under hard accel had to be due to something. If it were oil that would show on the plugs and the dipstick. Looking at the carbon deposits on the pistons, I'd say most of the coolant was burning in #6, a little in #5 and barely any if at all in #4. 1-3 were normal.
It seems like it really blew the head gasket back when I was running the open downpipe. I guess I wasnt hearing the detonation over all that noise. Its been holding on until now, despite the external leaks, when coolant finally got into the oil. Thats either a blown HG or a cracked head. I'm not too worried about the rings or head. The bottom end looks very good. The head could have come off of any m20. The exhaust valves have that light brown/pink color. It looks good, other than the pitting in the head from detonation. Even thats not too bad.
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M. Holtmeier
- Posts: 3025
- Joined: Mar 11, 2007 3:06 AM
- Location: Dallas, Texas
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Das_Prachtstrasse
- Posts: 5616
- Joined: Sep 10, 2006 7:06 AM
- Location: Melbourne, Doooown Under
http://en.wikipedia.org/wiki/Stiction
I believe its a real word. And no, I didnt just write that wikipedia article to help my case. I wouldnt do that...
I believe its a real word. And no, I didnt just write that wikipedia article to help my case. I wouldnt do that...
What kind of gaskets are available.
I remember that to be an issue when I was rockin' the tii.
I had it down so I could crack a six pack with halogens in the middle of the night and replace that head, take a nap and go to work in the a.m.
Come to find out it was a hairline fracture in the block, but at any rate when I got the new engine I remember a lot of talk about gaskets, those that cut into the block a bit and those that don't, and then I know my SAAB buddies with big boost go copper. So maybe something there could assure you good uniform compression and whatnot if that's what yer lacking.
Just my, um, $.02
I had it down so I could crack a six pack with halogens in the middle of the night and replace that head, take a nap and go to work in the a.m.
Come to find out it was a hairline fracture in the block, but at any rate when I got the new engine I remember a lot of talk about gaskets, those that cut into the block a bit and those that don't, and then I know my SAAB buddies with big boost go copper. So maybe something there could assure you good uniform compression and whatnot if that's what yer lacking.
Just my, um, $.02
I'm going to try another stock HG with some better hardware. The gasket itself was in great shape, and for all the things I've read about Cometic's MLS gasket, I cant justify the massive price difference. The stock gasket did not deform or fail in any way, so I dont think the gasket itself is the problem. I just need to keep the head on the block, then I should be alright. I think.
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M. Holtmeier
- Posts: 3025
- Joined: Mar 11, 2007 3:06 AM
- Location: Dallas, Texas
Re: Head came off today.
I have a question for the 'OP'......how did you manage to beat the TT vette and not the SRT4? Just curious....turbodan wrote:I went out for a rather large little shindig on friday night in the turbo 528e. Ended up running a twin turbo C4 corvette and a big turbo SRT-4. I beat the turbo vette from a slow roll, but the SRT got me on the top end. The guy in the skittle insisted on a 3rd gear roll at 60 miles an hour, because his tranny was dicked up, and apparently he couldnt shift into 3rd under power. I think it would have been different from a standing start or off the line. So whatever. I would hold him off until he shifted into 4th, then he'd get away.
As usual, I was observing what appeared to be a contrail behind my car while running. Its been doing that for months though.
