MSD 8572 distributor vacuum adv question
03-15-2009, 01:22 PM
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MSD 8572 distributor vacuum adv question
Hey guys,
been doing some reading on vacuum advance and I was wondering if my engine/cam combo will provide enough vacuum to get full use of the advance feature of my MSD 8572 distributor. I will have app 14in hg of manifold vacuum available at idle.
My engine builder (race guy) built and tuned my engine without using vacuum advance - its currently plugged
Right now I am all mech adv with a total of 34 deg all in at 4500rpm.
I was wondering if I need to change the MSD vac can to something like the Echlin #VC-1810 to allow full vacuum adv at < 14in hg.
TIA, Ed
been doing some reading on vacuum advance and I was wondering if my engine/cam combo will provide enough vacuum to get full use of the advance feature of my MSD 8572 distributor. I will have app 14in hg of manifold vacuum available at idle.
My engine builder (race guy) built and tuned my engine without using vacuum advance - its currently plugged
Right now I am all mech adv with a total of 34 deg all in at 4500rpm.I was wondering if I need to change the MSD vac can to something like the Echlin #VC-1810 to allow full vacuum adv at < 14in hg.
TIA, Ed
03-15-2009, 02:15 PM
#2
Race Director
How is your car at idle? If it's fine, I wouldn't worry about it. Otherwise you can change to a can that fully activates at 14 inches of vacuum. Your third choise is to get a programmable controller for the MSD but that is some real coin.
Again, I think the real purpose of the vacuum can is at idle and low RPM. Cuts emmisions too.
Again, I think the real purpose of the vacuum can is at idle and low RPM. Cuts emmisions too.
03-15-2009, 02:36 PM
#3
Race Director
Your MSD vacuum can allows 10 degrees of advance at 15 in hg of vacuum. I don't think MSD sells an adjustable can and don't think the GM or aftermarket adjustable cans will fit. You can check though. I would set the initial (best initial is probably 16 to 18 with your build) and mechanical to 34 - 36 all in by 2500 to 2800 with the vacuum can plugged and then use the can as is. With the compression and cam you have you won't need as much vacuum advance anyway. The MSD is nice in that it comes with the springs and mechanical limit bushings to adjust your mechanical to run the best initial but the drawback is the vacuum can is one size fits all. Still, this will give you about 45 or 46 total which with your build specs should be fine. Way better off idle and throttle response than 34 total all in @ 4500 with no vacuum can. Best initial will be trial and error but start @ 16 with weights locked closed and adjust from there. If you get a ping at low rpm when you mash the gas you need to dial your initial back and add mechanical to maintain your 34 - 36. all in number. 
Them race engine builders always do this. My builder dynoed mine set up the same way. Vacuum can plugged, timing all in right under peak torque. Fine on the track not on the street. Would like feedback! Drive it as set up with can plugged then set it up the way I described and let us know how it goes. This will help other forum mermbers with similar issues!
Them race engine builders always do this. My builder dynoed mine set up the same way. Vacuum can plugged, timing all in right under peak torque. Fine on the track not on the street. Would like feedback! Drive it as set up with can plugged then set it up the way I described and let us know how it goes. This will help other forum mermbers with similar issues!
Last edited by 63mako; 03-15-2009 at 02:50 PM.
03-16-2009, 11:33 AM
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Your MSD vacuum can allows 10 degrees of advance at 15 in hg of vacuum. I don't think MSD sells an adjustable can and don't think the GM or aftermarket adjustable cans will fit. You can check though. I would set the initial (best initial is probably 16 to 18 with your build) and mechanical to 34 - 36 all in by 2500 to 2800 with the vacuum can plugged and then use the can as is. With the compression and cam you have you won't need as much vacuum advance anyway. The MSD is nice in that it comes with the springs and mechanical limit bushings to adjust your mechanical to run the best initial but the drawback is the vacuum can is one size fits all. Still, this will give you about 45 or 46 total which with your build specs should be fine. Way better off idle and throttle response than 34 total all in @ 4500 with no vacuum can. Best initial will be trial and error but start @ 16 with weights locked closed and adjust from there. If you get a ping at low rpm when you mash the gas you need to dial your initial back and add mechanical to maintain your 34 - 36. all in number. Them race engine builders always do this. My builder dynoed mine set up the same way. Vacuum can plugged, timing all in right under peak torque. Fine on the track not on the street. Would like feedback! Drive it as set up with can plugged then set it up the way I described and let us know how it goes. This will help other forum mermbers with similar issues!
Them race engine builders always do this. My builder dynoed mine set up the same way. Vacuum can plugged, timing all in right under peak torque. Fine on the track not on the street. Would like feedback! Drive it as set up with can plugged then set it up the way I described and let us know how it goes. This will help other forum mermbers with similar issues!That sounds like a good plan.
I will leave the initial at 16 and have 34 total all in by 2600rpm with the vac plugged as a starting point. Will run it like this as a baseline before hooking up the vac adv to get a good comparison.
I did a little reading and it looks like the Echlin VC-1810 vac can will fit on the MSD distributor - it allows full vac adv at around 8" Hg.
Gonna be at least another 60 days before she hits the road though - heres the holdup:
yea I know........its ugly but this car is gonna be right when I am done.
Thanks again for the help, Ed
03-16-2009, 04:46 PM
#5
Race Director
Probably be better off with the MSD can. Full advance with #8 of vacuum could cause detonation issues due to to much vac adv. It will somewhat be trial and error. That looks nasty! Lots of work but looks like your plan is a proper repair. Good luck.
