Cylinders 8 and 6 run leaner, hotter, more prone to det
#1244470
06/02/12 08:59 PM
06/02/12 08:59 PM
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Joined: Feb 2004
Posts: 1,417 Chicago, IL
blownEFI
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Posts: 1,417
Chicago, IL
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Question for engine builders. On a Chrysler RB engine do cylinders 8 and 6 run leaner or hotter than the others? I have experienced problems with a few of my engines where these cylinders seemed to get heat/detonation damaged but the other six cylinders were fine. Just wondering.
"These go to eleven", Nigel Tufnel
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Re: Cylinders 8 and 6 run leaner, hotter, more prone to det
[Re: blownEFI]
#1244471
06/02/12 09:08 PM
06/02/12 09:08 PM
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Joined: Mar 2003
Posts: 4,848 Memphis
HemiRick
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Memphis
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They definitely run hotter as they get the poorest cooling. In any V engine the rear cylinders always run hotter IMHO.
Take care, Rick 68 Coronet R/T 440 & 68 Charger 528 Hemi,and 5 Challengers! 6 cyl, 318, 360, 383, 451
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Re: Cylinders 8 and 6 run leaner, hotter, more prone to det
[Re: Cab_Burge]
#1244479
06/04/12 01:17 AM
06/04/12 01:17 AM
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Joined: Feb 2004
Posts: 1,417 Chicago, IL
blownEFI
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Is this on a roots blown motor?If so maybe it is the intake manifold distribution I seem to remember that the roots blown motors do that, load up the rear cylinders on the passneger side bank
No, this is a turbo engine running electronic fuel injection. The manifold is dry. Each cylinder has a fuel injector that sprays fuel directly into the intake port at the back of the valve.
I think I would try rotating those two injectors to the other side and see if the problems follow those injectors or not
Thanks. I already tried two entirely different sets of injectors, same issue.
"These go to eleven", Nigel Tufnel
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Re: Cylinders 8 and 6 run leaner, hotter, more prone to det
[Re: blownEFI]
#1244481
06/04/12 08:36 AM
06/04/12 08:36 AM
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Joined: Jun 2003
Posts: 52,972 Romeo MI
MR_P_BODY
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Romeo MI
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Quote:
Question for engine builders. On a Chrysler RB engine do cylinders 8 and 6 run leaner or hotter than the others? I have experienced problems with a few of my engines where these cylinders seemed to get heat/detonation damaged but the other six cylinders were fine. Just wondering.
How are you measuring this problem.. are you running EGTs on the pipes or just looking at the plugs... I'm curious also.. I always thought it was the center cyl on each bank that got hotter
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Re: Cylinders 8 and 6 run leaner, hotter, more prone to det
[Re: MR_P_BODY]
#1244483
06/04/12 03:45 PM
06/04/12 03:45 PM
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Joined: Feb 2004
Posts: 1,417 Chicago, IL
blownEFI
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Quote:
Quote:
Question for engine builders. On a Chrysler RB engine do cylinders 8 and 6 run leaner or hotter than the others? I have experienced problems with a few of my engines where these cylinders seemed to get heat/detonation damaged but the other six cylinders were fine. Just wondering.
How are you measuring this problem.. are you running EGTs on the pipes or just looking at the plugs... I'm curious also.. I always thought it was the center cyl on each bank that got hotter
We didn't measure EGT's. I just have an O2 sensor but it is located after all exhaust has merged together. We were tuning based on the a/f ratio as measured by that O2 sensor. So I don't really have any data on what happened in those two cylinders individually but I do know they got damaged during a dyno session last Saturday because before the dyno session I had done both compression and leak down tests on the engine and all eight cylinders were healthy. Then immediately after the dyno session I did compression and leakdown tests and discovered that cylinders 6 and 8 were both significantly down on compression and leaking badly. Before the dyno session all eight cylinders had compression readings in the 180 to 190 psi range (most of them 185 psi). Before the dyno session the leakdown was between 6% and 8% leakage on all eight cylinders (the engine is brand new freshly built). After the dyno session the compression and leakdown readings were unchanged on all but two cylinders (6 and 8). After the dyno session cylinder 6 had 150 psi compression and cylinder 8 had 145 psi compression. After the dyno session cylinder 6 had 25% leakage and cylinder 8 had a whopping 60% leakage. The leakage was NOT coming past the valves but rather past the piston/rings into the crankcase. Next thing I did was put a video probe in through the spark plug holes to visually inspect both cylinders. In cylinder 6 the piston is missing a chunk of it's perimeter probably about 1.5 inches long. In cylinder 8 it looks like a bomb exploded... there is so much damage I can hardly make out the piston on the video image. I also probed the other six cylinders and they looked fine, which confirms the good compression and leakdown numbers I'm seeing for those. For some reason it was just cylinders 6 and 8 that got damaged.
We think the damage happened on the final dyno pull, which we only put 7 lbs of boost in the engine. Air/Fuel ratio was in the 11.5 range, but again that was measured for all eight cylinders. For all I know cylinder 8 could have been in the 14's a/f ratio on that pull.
My plan moving forward is to use the EGT bungs that I have in each header tube and the O2 bungs I also have in individual header tubes (especially 8 and 6) and then monitor those two cylinders individually for a/f and egt then trim ignition and fuel as necessary. Don't ask me why we weren't using the individual EGT and O2 bungs.... that was a mistake on my part which I won't repeat.
Last edited by blownEFI; 06/04/12 03:58 PM.
"These go to eleven", Nigel Tufnel
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