Originally Posted by HigherPower

I didn`t really get my question answered.

I know 25* total timing is too low.

The question:
Will bumping the timing to 34* give me an increase in top-end rpm ?

Originally Posted by Biggus

Don, your stock 420 does not need locked timing. Engine builders will lock timing on big cam blower motors to increase vacuum so they will idle. One of the best features of the MSD system is that you can pick the best advance curve for your application.

I've owned several 420's over the years and found they idle the best at about 12-14 deg and need no more than 34. So, if I were you, I'd get a bushing and spring kit from MSD and set up your distributors so they can advance. If I remember correctly, the black bushing will provide 18 or 20 degrees of advance. install the light springs so all the advance is out by 2500 and you should have @ 34 total.

What I did was hook up a vacuum Gage and increase the timing until it pulled the most vacuum at idle. This is where you want to start (as I said above, @ 14 deg or so) then choose the correct bushing to set total timing at 34 deg.

Good luck,

Kurt .. a big fan of the old 420