olie05 Posted April 12, 2005 Share Posted April 12, 2005 This sucks. I was on the freeway, and I pulled up next to a 350z with some nice deep dish wheels and he looked over at me and we started racing. Downshifted to 4th and then got into 5th. At around 4000 rpm it sounded like my exhaust manifold fell off of one of the cylinders. So, I limped the car home, cus it still ran, and now I have a head gasket to replace. Now, I know I'm not going to avoid the "while I'm in there" disease, so what should I replace while i'm in there? I already ordered a felpro headgasket, and i got a new felpro intake/exhaust gasket. I'm also planning on replacing the cam with one from my spare head, because that one has matched rocker arms and lashpads, as opposed to what the machine shop guy did with mine, which was to NOT match them, so maybe I can save adjusting my valves as often as I do. Oh yeah, I think I know why that cylinder blew. If anyone remembers, I posted a while back about my compression test results, and all of them read 210psi's except for the 5th cylinder which read 235psi. I got a rough calculation that if 10.03:1 cr yeilds a 210psi reading, then a 235psi reading must mean i'm running 11.22:1 on that cylinder. (rough calculations based on 10.03/210*235) I'm hoping when I pull the head off I see something obvious that I missed when I was building the engine on the 5th cylinder. -Oliver Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted April 12, 2005 Share Posted April 12, 2005 nowthat you got the springs in i am sorry you have something else to fix.something i do when i assemble l28 motors.i have a tap for the head bolt holes.i run the tap through and clean out the holes with brake clean and compressed air.use NEW headbolts.any pitting on the bolt shanks will be a weak spot and i had a bolt break while assembling an engine once.make sure the bolts will turn freely in the block-if it binds up it wont torque the head even.be clean. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 13, 2005 Share Posted April 13, 2005 might also have something to do with that persistent belief that the #5 cylinder tends to run leaner than the rest on EFI Z's, or is that just Turbo Z's? I think it has to do with the EFI intake manifold in general. Quote Link to comment Share on other sites More sharing options...
olie05 Posted April 13, 2005 Author Share Posted April 13, 2005 Randy, I have ARP head studs, and the part that gets me is that I rebuilt this engine about a year ago... bastaad525: You might be on to something with this lean condition thing. Is it totaly mysterious or is there some substantial evidnence to go along with the theory? Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted April 13, 2005 Share Posted April 13, 2005 Port the head and smooth the chambers while you're at it. Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted April 14, 2005 Share Posted April 14, 2005 what kind of head gaskit was in it?heard fel pro is not good?got a full felpro set because i am doing alot of motor work.the felpro gaskit in the set has steel in the middle and is 1.2 mm not compressed. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 14, 2005 Share Posted April 14, 2005 well the main evidence is that, in turbo cars in particular, it's MUCH more common for the gasket to blow on the #5 cylinder... this is from experiences of several owners including myself with one blown gasket under my own belt. I think there is also some measureable difference in the #5 intake runner, maybe it's a different length honestly I dont remember but I seem to remember someone mentioning the actual reason WHY it runs leaner. But ask around on the turbo forums and see how many people have blown that pesky #5 Quote Link to comment Share on other sites More sharing options...
olie05 Posted April 14, 2005 Author Share Posted April 14, 2005 I got the head off yesterday. The headgasket blew on the #4 cylinder on the drivers side. There is still an issue with the #5 cylinder, because on the head, the exhaust valve is starting to go white on that one, but the rest of the exhaust valves have the normal color of metal. Perhaps I have a crappy injector on that cylinder? I need help diagnosing what my engine is doing! -Oliver Quote Link to comment Share on other sites More sharing options...
Xander Posted April 14, 2005 Share Posted April 14, 2005 it's MUCH more common for the gasket to blow on the #5 cylinder Seeing that the #5 cylinder is closest to the turbo inlet it has more to do with the temperature than fuel mixture IMHO. I do not see how the #5 cylinder can get much more air than the rest of them. But than agian I flunked fluid dynamics in school Quote Link to comment Share on other sites More sharing options...
Guest vvillium3 Posted April 14, 2005 Share Posted April 14, 2005 I knoticed the white on my exhaust valves the other day when I pulled my head off. What does the mean??? Running too lean???? Too hot??? Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 15, 2005 Share Posted April 15, 2005 Seeing that the #5 cylinder is closest to the turbo inlet it has more to do with the temperature than fuel mixture IMHO. I do not see how the #5 cylinder can get much more air than the rest of them. But than agian I flunked fluid dynamics in school Xander - yeah that's as good a guess as any, I wont even pretend to have a clue as to WHY the #5 seems to be the one that has the problem, I seem to remember someone telling me it had something to do with the runner but really I'm not even sure of that. I just know it's common on Turbo L6's with stock manifolds. Quote Link to comment Share on other sites More sharing options...
olie05 Posted April 16, 2005 Author Share Posted April 16, 2005 I fixed it! hehe... The felpro gasket is much better quality than what I had in there. You can see it just by looking at it. I'm just having problems resetting the timing and re-tuning stuff that became knocked out of adjustment ...I'll fix it in the morning. I'll report how it runs later. -Oliver Quote Link to comment Share on other sites More sharing options...
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