Compression readings on my 1974 cutlass 455 range from 115-127. As far as I know it’s stock. Does that sound low or the nature of the low compression engine?

 

Sounds pretty good. How many miles? Check for worn timing chain/gears.

Good luck!!!

 

Thanks, timing gear and chain are good. I tore front down because I suspected wear in there. I haven’t been able to get it to run right, timing mark jumping around. It had been converted to hei. I’m changing back to points and see if that works, suspecting bad hei distributor now🤷‍♂️

 

Mechanical spark scatter can be a few things.
1. worn timing gears and chain.
2. worn or incorrectly shimmed distributor shaft/gear.
3. worn out cam
4. compression imbalance due to ring wear or valve seat leaks.

Other things can cause it too. Vacuum leaks, bad A/F mixture, bad carb, shitty ignition components, bad negative wire to the points et al...
Is the HEi running a full keyed 12VDC source out of the fuse box?

 

After market HEIs(Chinesium) have crap electronics. Ive worked on a few cars with them, and timing was erratic

 

Would that be in the module or something else?

 

Most likely the module. But if it's chineasium all bets are off on all of it. Could just be a loose connection or terminal.

Call or google Davis Unified Ignitions...DUI distributors and try one of his modules with heat paste. Should always carry a spare module & paste.
Verify all the wiring in the distributor is sound. Pull it out put it in a vice and really examine the wiring, Look at the shaft up/down & side to side play. Zero side to side. Minimal climb...or up down. .006 -.010"

 

I had a MSD ignition module in my 455 powered 87 Cutlass for a year or so. When I built the car, I needed a module, I figured the rev limiter would be a nice “just in case” thing. While it ran good, it wasn’t right. It never misfired, but just didn’t run the way I expected it. Once I installed a 6AL ignition box the difference was night and day. My “butt-o-meter” predicted an easy 25hp improvement.

Maybe I got a bad module, but after that it’s either a factory GM module, or a MSD ignition box. I don’t trust the cheap parts store modules, or the Chinese aftermarket distributors.

 

Thanks for the reply’s, I always thought a module either works or doesn’t!