) 241 heads. 
Carbon related knock?
Thread Starter
Joined: Oct 2004
Posts: 2,142
Likes: 9
From: South Windsor, CT
Carbon related knock? 2000 LS1 with 241 heads, wrong factory tune? I just got my 2000 Z28 a week or so ago, and right away I noticed it was pulling timing at part throttle (spirited part throttle though, like pushing kinda hard through corners on back roads)...it's a 100% stock car with a stock tune in it and 93 octane from Mobil (my other cars all run AWESOME on their gas up here).
I ran a can of GM Top End Cleaner (the old part number thats "discontinued" but still on some dealers shelves) and did exactly as the instructions say (which I've seen others do). It seems to be running a lot better...but it still isn't perfect. I changed the oil immediately when I was done, and I don't want to change the oil again within 3 days...just seems wasteful to me.
Should I try another can of top end cleaner right before the next oil change or should I be looking at something else as a source of what the knock sensor is picking up? It's pulling timing a LOT LESS often now...but still doing it every once in a while.
I ran a can of GM Top End Cleaner (the old part number thats "discontinued" but still on some dealers shelves) and did exactly as the instructions say (which I've seen others do). It seems to be running a lot better...but it still isn't perfect. I changed the oil immediately when I was done, and I don't want to change the oil again within 3 days...just seems wasteful to me.
Should I try another can of top end cleaner right before the next oil change or should I be looking at something else as a source of what the knock sensor is picking up? It's pulling timing a LOT LESS often now...but still doing it every once in a while.
Last edited by Mike454SS; Aug 16, 2007 at 10:15 PM. Reason: change title
Thread Starter
Joined: Oct 2004
Posts: 2,142
Likes: 9
From: South Windsor, CT
Update...it seems to be doing it less and less (running better and better)...but once this morning in 2nd gear around 2500 RPM at like half throttle it did it again. The engine is very quiet on a cold startup (at 87K miles it's quieter than the 52K mile LQ4 truck I just traded in) so I don't think it's a mechanical noise...valvetrain is quiet too.
try sea-foaming your top end. Undo your brake boost line and suck about a half a can through it. Shut the car off and let sit for 10 min then start it up and take her out for some spirited driving. Will smoke a lot but its normal. thats the carbon burning out. you can use the other half can of sea foam in your oil about 100 miles before you change it. Should make it really black.
Jeff
Jeff
Thread Starter
Joined: Oct 2004
Posts: 2,142
Likes: 9
From: South Windsor, CT
The GM Top End Cleaner is like Seafoam (I think it's actually stronger). The problem still isn't gone...I'm kinda confused about the 241 heads on the car too...it's a late model year 2000...but still, I thought 2000's got 853's and 2001/2002's for 241's? Maybe it just has the wrong spark tables for a car with 241 heads.
Originally Posted by Mike454SS
The GM Top End Cleaner is like Seafoam (I think it's actually stronger). The problem still isn't gone...I'm kinda confused about the 241 heads on the car too...it's a late model year 2000...but still, I thought 2000's got 853's and 2001/2002's for 241's? Maybe it just has the wrong spark tables for a car with 241 heads.
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Thread Starter
Joined: Oct 2004
Posts: 2,142
Likes: 9
From: South Windsor, CT
Yeah I did those.
I looked at the spark tables for 01/02 cars and 99/2000 (I think 98 is the same but I can't view one)...the 99/2000 tables have a LOT more spark than the 01/02 cars do...upwards of 15 degrees at times...and 7 degrees more at full throttle.
It would seem to me that when they switched to 241 heads, they should have changed the tune. I understand the 01/02 cars have a different cam and intake manifold too...but neither of those would affect the tune enough to result in a 7 degree change in spark...that HAS to be something to do with the heads...particularly the combustion chambers...which would lead me to believe that the 7 added degrees I have over a 2001/2002 car is just too much...anybody ever tried to add 7 degrees to a car at full throttle...even on 93 octane it's going to pull timing...let alone the 15 degrees extra that it has in some part throttle areas.
We were so shocked by the difference (it's that ridiculous) that we checked the stock tunes in a few other 99/2000 cars just to be SURE it wasn't a really bad "performance tune" from some nitwit.
I looked at the spark tables for 01/02 cars and 99/2000 (I think 98 is the same but I can't view one)...the 99/2000 tables have a LOT more spark than the 01/02 cars do...upwards of 15 degrees at times...and 7 degrees more at full throttle.
It would seem to me that when they switched to 241 heads, they should have changed the tune. I understand the 01/02 cars have a different cam and intake manifold too...but neither of those would affect the tune enough to result in a 7 degree change in spark...that HAS to be something to do with the heads...particularly the combustion chambers...which would lead me to believe that the 7 added degrees I have over a 2001/2002 car is just too much...anybody ever tried to add 7 degrees to a car at full throttle...even on 93 octane it's going to pull timing...let alone the 15 degrees extra that it has in some part throttle areas.
We were so shocked by the difference (it's that ridiculous) that we checked the stock tunes in a few other 99/2000 cars just to be SURE it wasn't a really bad "performance tune" from some nitwit.
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