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Whats the correct timing and spark plugs

Old 06-07-2011, 04:18 PM
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Default Whats the correct timing and spark plugs

I recently built a Gen 6 468 with stock oval port heads and air gap intake that dyno'd at 450 hp and 511 ft/lbs torque. When we dyno'd the motor the timing was set at 37 degrees total. I am running a MSD distributor, coil, and 6 box. I mistakenly turned the timing up when I removed the distributor and when I checked the timing it was 39 degrees. I ended up dropping a valve seat and ate 5 pistons because I think it was detonating. Now I am back rebuilding the motor and using the same block, same roller cam, same type pistons which are forged 18cc small dome but I have bought a set of Merlin 320 cfm rect. heads that are 119 cc and a Performer RPM intake. My compression ratio should be about 9.5 which is close to what I had. My question is does the 37 total timing seem to high to begin with and what is everyones recommendations on timing for this motor? Also what would be the best plugs to run in this motor? I was running AC Delco marine but I can't remember the #'s. When we dyno'd the motor all readings on the pyrometer were within limits but we didn't hold it at full throttle for a long period of time so I don't know if the timing would have been a issue or not.
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Old 06-07-2011, 05:50 PM
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Im told 34 total timing..
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Old 06-07-2011, 09:17 PM
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39 degrees is waaaayyyy too much timing for a 9.5 CR motor unless you are running some serious high octane fuel. 9.5 is pretty high for a marine motor that is always running at a heavy load. I would go 9-1 myself.

You need to play it smart and start timing off conservative when breaking the motor in and then you can always advance it later.

For 92 octane fuel start with 34 degrees or so and make a run and check some plugs. If everything looks good bump it up slowly from there
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Old 06-08-2011, 12:53 AM
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37* total is pretty high. I would say 32-34* is more common.
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Old 06-08-2011, 07:26 AM
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[QUOTE=cdail28590;3422905]I recently built a Gen 6 468 with stock oval port heads and air gap intake that dyno'd at 450 hp and 511 ft/lbs torque. When we dyno'd the motor the timing was set at 37 degrees total. I am running a MSD distributor, coil, and 6 box. I mistakenly turned the timing up when I removed the distributor and when I checked the timing it was 39 degrees. I ended up dropping a valve seat and ate 5 pistons because I think it was detonating. Now I am back rebuilding the motor and using the same block, same roller cam, same type pistons which are forged 18cc small dome but I have bought a set of Merlin 320 cfm rect. heads that are 119 cc and a Performer RPM intake. My compression ratio should be about 9.5 which is close to what I had. My question is does the 37 total timing seem to high to begin with and what is everyones recommendations on timing for this motor? Also what would be the best plugs to run in this motor? I was running AC Delco marine but I can't remember the #'s. When we dyno'd the motor all readings on the pyrometer were within limits but we didn't hold it at full throttle for a long period of time so I don't know if the timing would have been a issue or not.[/QUOTE]

HUGE issue
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Old 06-08-2011, 04:00 PM
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I know the 39 that I mistakenly had it at was to high and thats what caused the issue. That was my mistake and I am paying for it. The 37 degrees was on the dyno with the pyrometers on the motors and everything was good on the numbers and the plugs were good. I had it dyno'd with 89 octane knowing I would use 91 so I could have a little bit of cushion for any bad gas. I just didn't know if continuous running with the timing at 37 would show a different effect than the quick dyno pulls. It looks like 34 is the consensus which is what I was planning on taking it down to. What about plugs? NGK or AC Delco?
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Old 06-08-2011, 11:39 PM
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Originally Posted by cdail28590
I know the 39 that I mistakenly had it at was to high and thats what caused the issue. That was my mistake and I am paying for it. The 37 degrees was on the dyno with the pyrometers on the motors and everything was good on the numbers and the plugs were good. I had it dyno'd with 89 octane knowing I would use 91 so I could have a little bit of cushion for any bad gas. I just didn't know if continuous running with the timing at 37 would show a different effect than the quick dyno pulls. It looks like 34 is the consensus which is what I was planning on taking it down to. What about plugs? NGK or AC Delco?
But like you said, It was not run long enough on the dyno to tell. It should have been run at WOT for at least 1-2 mins continuous to let all the numbers stabilize.

If it was ok with 89 at 37* then it should have been ok with 39* and 91. The heat range on the plugs could have also been a factor. I would run some NGK UR5 plugs. The are the same as an AC R41TS and on the cooler side.
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Old 06-10-2011, 10:09 AM
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I think mine were AC MR43LT. I will look at getting the NGK's.
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