GEN VI 502 MPI Timing
06-05-2019 | 10:04 AM
#1
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From: Virginia Beach
GEN VI 502 MPI Timing
Hey guys...
The 502 MPI specs timing at 8 degrees initial with the ECM controlling total timing. Any advantages to bumping the initial to 10 degrees? Any disadvantages? This would put total timing at 34 degrees. I tried some searches around this, but came up short. I have BUP's new injectors in both and they run just a little fatter up top. Might be nice to take advantage of it.
Yay or nay?
The 502 MPI specs timing at 8 degrees initial with the ECM controlling total timing. Any advantages to bumping the initial to 10 degrees? Any disadvantages? This would put total timing at 34 degrees. I tried some searches around this, but came up short. I have BUP's new injectors in both and they run just a little fatter up top. Might be nice to take advantage of it.
Yay or nay?
06-05-2019 | 10:13 AM
#2
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Joined: May 2019
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From: Florida
Tomz - I have read several forums on this as well. Your not going to hurt it by putting your initial at 10 degrees but, I don't think you will gain much from doing it.
Many have said to just leave it at 8 degrees.
Many have said to just leave it at 8 degrees.
06-07-2019 | 09:52 AM
#4
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From: frankenmuth michigan
I guess my question is how do you know it will put total timing at 34, was your ecu previously programmed? 502 mpis have a really crappy timing table stock. I want to say stock max timing at 5000 rpms and 100 map is 28 or something stupid, in comparison , a 500 efi has 35.9 BUT has bigger cam so less chance of detonation because running compression might be liwer due to extra cam duration fwiw
06-07-2019 | 10:04 AM
#5
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From: Virginia Beach
Smitty, good question and points. My ECM is completely stock to my knowledge, and when John (BUP) tested my original injectors, they were stock as well. The engines do have CMI ETops, but as far as I know, the ECMs are as stock as the day they came from GM. I just assumed that it would be 34 versus 32 (from what I've read anyway).
The 28 number... is that plus the initial? Why would Merc run it without any timing on the top-end? Most big block Chevy's seem to be really happy at 34-36.
Last thing I want to do is put a hole in something.
The 28 number... is that plus the initial? Why would Merc run it without any timing on the top-end? Most big block Chevy's seem to be really happy at 34-36.
Last thing I want to do is put a hole in something.
06-08-2019 | 01:04 AM
#7
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From: frankenmuth michigan
Falling reference angle in regards to next physical TDC:
8.1 degrees. So setting the timing at 8 degrees makes tables correct, if you change base timing to 10, then you have effectively made timing 2 degrees higher in every table . Now, at 90 map a 502 mefi3 DOES have 32 degrees of timing from 5000 up so if your running at 95 map, it would blend between 32 and 29.9 so 31
factory rev limiter is set at 5200 and "returns" at 5000 so youd have to be propped perfect to ever be there and NOT be on rev limiter!
8.1 degrees. So setting the timing at 8 degrees makes tables correct, if you change base timing to 10, then you have effectively made timing 2 degrees higher in every table . Now, at 90 map a 502 mefi3 DOES have 32 degrees of timing from 5000 up so if your running at 95 map, it would blend between 32 and 29.9 so 31
factory rev limiter is set at 5200 and "returns" at 5000 so youd have to be propped perfect to ever be there and NOT be on rev limiter!
