Factory PCM's RPM Limit:
12-31-2004, 02:05 PM
#5
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Originally Posted by NoseUp
I can't seem to find an answer...What is the factory PCM good to? Is there a loss of accuracy at any certain point?
12-31-2004, 06:33 PM
#6
after 8000 it just continues the last value in the pcm on the tables that are referenced by rpms.. so you lose your accuracy.. as for the other stuff like coil packs or maybe injectors i think they would be a failure before the 8000 mark.. that is a pretty fast spark event.. no time for the factory coils to recharge.. so they lose spark voltage..
12-31-2004, 07:12 PM
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Originally Posted by bickelfirebird
It will read rpms much higher than any motor you might build.
Originally Posted by wait4me
after 8000 it just continues the last value in the pcm on the tables that are referenced by rpms.. so you lose your accuracy.. as for the other stuff like coil packs or maybe injectors i think they would be a failure before the 8000 mark.. that is a pretty fast spark event.. no time for the factory coils to recharge.. so they lose spark voltage..
Last edited by NoseUp; 12-31-2004 at 07:29 PM.
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12-31-2004, 08:24 PM
#8
Originally Posted by NoseUp
That's a negative. Nice try though...Very informative contribution
The duty cycle of the injectors will be fine because of their size, but you certainly make a good point with the coil packs. Do you have any ideas? After digging into info. regarding the new LS2 coil packs, I'd be more confident in them @ 8k than the 5.3's I had planned to use. They supposedly require less to fire than factory 5.7's and 5.3's. I know MSD has a replacement, but I don't have specs on them.
The duty cycle of the injectors will be fine because of their size, but you certainly make a good point with the coil packs. Do you have any ideas? After digging into info. regarding the new LS2 coil packs, I'd be more confident in them @ 8k than the 5.3's I had planned to use. They supposedly require less to fire than factory 5.7's and 5.3's. I know MSD has a replacement, but I don't have specs on them.
Why would you care anyway and why would you want to rev a LS1 to 8K. According to MSD, the MSD's have the ability to fire a second spark and on the first spark will fire more than the LS2 coil.
12-31-2004, 10:18 PM
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Let's not worry about the why's. The project will be complete with details soon. However, I have a few details to work out first.
Thanks for the info. on the MSD's. I've contacted them for specs, but they have yet to return my call.
I was just informed that the factory 5.7L coils would do fine @ 8k w/o recharging issues. He said "for how long, I couldn't say, but they'll do it." The sorce is an electrical engineer with a backround in automotive ignition systems. He did recommend that I find a more performance oriented coil for longetivity reasons. Is MSD the only after-market coil currently available for the factory PCM? I could have something custom made, no problem. But, now reaching the end of the project, budget creek is running dry. Custom electronics mean big $$$.The last quote I was given almost triggered my gag reflex...Just about anything mechanical can be made in-house. Ignition electronics on the other hand are beyond my current capabilities
Thanks for the info. on the MSD's. I've contacted them for specs, but they have yet to return my call.
I was just informed that the factory 5.7L coils would do fine @ 8k w/o recharging issues. He said "for how long, I couldn't say, but they'll do it." The sorce is an electrical engineer with a backround in automotive ignition systems. He did recommend that I find a more performance oriented coil for longetivity reasons. Is MSD the only after-market coil currently available for the factory PCM? I could have something custom made, no problem. But, now reaching the end of the project, budget creek is running dry. Custom electronics mean big $$$.The last quote I was given almost triggered my gag reflex...Just about anything mechanical can be made in-house. Ignition electronics on the other hand are beyond my current capabilities
Last edited by NoseUp; 12-31-2004 at 10:24 PM.
01-01-2005, 07:55 AM
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Because each cylinder has 720* before each firing event the effective charge time for each coil is twice that of a wasted spark system. The LS1 coil needs .003 second to charge completely. The ECM uses the crank and cam sensor to detect which stroke is the compression stroke for each cylinder. A 4-stroke only fires every 2 revolutions of the crank.
12,000 RPM / 60 seconds = 200 revolutions per second
200 revolutions per second / 2 revolutions per firing event = 100 firing events per second.
1 second / 100 firing events = .01 second per event at 12,000 RPM. This is well over the time needed to charge the coil.
If you do the math on a old distributor type ignition you will NOT have enough time to properly charge the coil as it has to fire 4 times per revolution instead of once for every two revolutions of the crank.
Just my thoughts anyways.
12,000 RPM / 60 seconds = 200 revolutions per second
200 revolutions per second / 2 revolutions per firing event = 100 firing events per second.
1 second / 100 firing events = .01 second per event at 12,000 RPM. This is well over the time needed to charge the coil.
If you do the math on a old distributor type ignition you will NOT have enough time to properly charge the coil as it has to fire 4 times per revolution instead of once for every two revolutions of the crank.
Just my thoughts anyways.
01-01-2005, 11:26 AM
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That's good to hear! Your thoughts are appreciated 
The required .003 seconds is FAR less than I imagined. I wonder with the MSD being a multiple spark coil, if they'd require additional time to charge. Until they get back to me I'm sort of in the dark with them. What are your thoughts on current draw with sustained high rpm use? I imagine larger gage wiring for the +12v batt and +5v charge/fire would be in order. I'd prefer to hack into anything that could possibly be a weak link before finding out the hard way. This was a very expensive and time consuming build...
The required .003 seconds is FAR less than I imagined. I wonder with the MSD being a multiple spark coil, if they'd require additional time to charge. Until they get back to me I'm sort of in the dark with them. What are your thoughts on current draw with sustained high rpm use? I imagine larger gage wiring for the +12v batt and +5v charge/fire would be in order. I'd prefer to hack into anything that could possibly be a weak link before finding out the hard way. This was a very expensive and time consuming build... 
01-01-2005, 12:33 PM
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If I were trying to tackle something like this, I would go look up some info about how coils work on a motorcycle/crotch-rocket. They seem to handle revving to the moon with no problems.
01-01-2005, 01:04 PM
#14
the amount of spark that a motorcycle has to produce i dont think would be as a car coil? the displacment of the cyl is not as big, and has higher compression so the combustions happens easier. .. lol you could just make it a diesel and not even use sparkplugs or a coil 
j/k j
j/k j 
01-01-2005, 01:46 PM
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Originally Posted by NoseUp
I can't seem to find an answer...What is the factory PCM good to? Is there a loss of accuracy at any certain point?
01-01-2005, 04:58 PM
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"Reinventing the wheel"...Where did that come from? 
I inquired about the rpm cutoff of the PCM and how accurate it would be at that point. That hasn't a thing to do with 'reinventing'...We already have the answer 
I inquired about the rpm cutoff of the PCM and how accurate it would be at that point. That hasn't a thing to do with 'reinventing'...We already have the answer
01-01-2005, 05:15 PM
#18
i just brought up the posibilitys of problems that might happen, sorry if all this got out of hand, the limit of the pcm is 8000 to be accurate, anything more and you loose the ability to change what is going on in the pcm. it references that last point when it left the table.. so if it left at 60 gm/s then it would hold that value in that cell untill it reentered the table at under 8000 rpms. the coil issue i would think will cause you a problem, they arent designed to go to 8000 rpms, .. but thats just my own oppinion, recharge time aint the full ballgame i would think, and it seems kindof hard to think that they could fully put out a full charge that fast... seems odd that gm would go and put on a part that would go that far if they never intended to go there... ?? sorry guys.