I want to make my hot cam idle smoothly (yes yes i know)
I have a 502s with a lot of cam 236/244. 610/632 lift. They are MPI target idle is 750 RPM.

The mixture was leaned out from 12.5 to 14.0 AFR which stopped the eye burning smell.
I have advanced idle timing to 25 degrees which really helped smooth things out.
I have 10.5" of vacuum now (63 kPa on MAP sensor)

When I started the engines were horrible to be around now they seem pretty docile. I wonder how far I can go?

So i am going to change the old spark wires and look for increased vacuum.
Elminating missfires obviously would help so I am wondering if a MSD would increase help up the vacuum at idle.

BTW I cant find info on this just video that say look i put it in, hear it run.. rather than a before/ after vacuum reading.

MSD may clean the idle up slightly, no on the vac, If you have the AFR where you say and timing at 25 and still low vac, as long as toy have no vac leaks, nothing short of cam or cam timing is going to change the vac as far as I know. Daytona makes a system that has a built in aid for idling in a situation like yours, my son just put 2 on his AT.

If you are running a mefi computer that also has idle spark control.

is your idle timing steady or jumping around,if jumping around,you have idle spark control on/working.

That's a Crane 741 cam which is not that extreme for a 502. Same as a 525EFI cam except the 741 is a 112 instead of 114 lob sep.
You sure you don't have rockers adjusted too tight?? It shouldn't be that hard to get a decent idle with it.

I'm running a cam with a bit more duration and I locked my timing. I'm running the MSD 6M with the HVC II coil and it idles all day long without any soot or spark plug fouling. It burns so clean you'd almost think I had Cats, I'm running a big carb as well. The new 6M 3 has start retard and other features and with the HVC II coil and the 20 degrees of spark below 3000 rpm it idles beautifully.

Timing is at the best point for vacuum. Idle is good. I just want better. what kPa are 500s running?

FWIW I bought a MSD Digital 2L to see if it improved idle response. Hooked up a scanner Pro to read kPa and put a bowl of water on top of the engine to visually see the vibrations at idle. I ran the MPI 502s with a lot of cam 236/244 .610/632 lift with and without the MSD.... and drumroll. It did zero. The kPa stayed the same and the smoothness stayed the same. No increase in idle quality at all. I know a MSD has a place on boost apps and on the older ignition that didnt have good power, but this engine with low compression and reason plug gap there was no improvement.

As far as idle: seeing a good difference of MSD type vs normaltype ignitions go to the non quench engines of yesteryear (or big hp turbo/supercharged enginesith reallarge quench distances) or those with such big domes for ultra compression that close off some of the combustion chamber at TDC......will benefit for the extra degrees of firing from the amt of multisparks.


Oh, a carb or EFi with out to lunch idle settings will benefit from a MSD type ignition at idle too. :