[boulonman]

Hi y'all,
I just got a 68 Chevelle that seems to have been built for week-end track racing. It's got a 383 stroker, brodix heads/roller cam & rockers, single plane hi-rise w/Demon 750, built 200/really H.D built rear-end w/posi .410, ladder-bars,boxed control arms.
The seller didn't pass on much info as to what he built it for. It has quite a lope & seems to like higher RPMs, it definitely is jetted too rich, anyways it pings under certain loads, diesels on shut-off. I always use good gas so I figured over-timing was the culprit. I checked & it was off the timing tab which goes to 18 degrees, I backed it all the way to 12 & it would sputter, die, back-fire but pinged less, I tried 14,16, 20+ degrees, but can't find a sweet spot! Its got a full MSD control, rev limiter, coil & pro-billet distributor. I'm not familiar w/this setup, can the control box be adjusted, or does it have pre-set curves? It runs strong, but I know its not close to what it could do. I thought those older MSD modules had a algorithm ability or is it only the newer generation? Eitherway, I sure would like to hear some thoughts about this...
thanx, Alan

 

[Dave Ray]

WHICH MSD 'box"? 6AL has rev limiter,. and uses a feed distributor, but only reads the tming sent by the distributor by mechanical/vacuum advances.

What have you got?

Also, MSD Blaster coils, JUNK.

What I would do for a 10.00:1 c/r, moderate roller 383, 12 initial, 20 mechanical for a total of 32, 8 vacuum advance degrees, full manifold vacuum.

Variations would be for differences in engine c /r, and cam duration, start/close points.

 

[boulonman]

Hi Dave,
It's a MSD 6AL w/external rev.limiter bolted to fenderwall, not too sure if its a blaster but it is a red MSD w/billet pro MSD distributor, 8mm MSD spark leads w/heatshield, Accel yellow short plugs. I tried 12 initial but she runs poorly, occasional backfire & pings under certain loads, back to 18 more power, but more ping & diesling. Relativity certain the seller mentioned 10:001 cr & I'm wondering if he built it for track using racing fuel??? Of course I only use premium & even added octane boost but no improvement. The carb may be over-jetted & not fine tuned, its a demon 750 which I heard require lots of tinkering, but heard the opposite as well, once you dial them in right they perform well for a long time. it's a single plane edelbroeck which I believe are better suited for hi-reving mills. Not knowing the cam specs is a bummer, it would give an idea of what profile would perform best. I figure I may have to pay a pro to play around w/mixture & check out if the vacuum & mechanical advance are functioning properly. If I can't get it to run smoothly & pull strong. I'm playing w/the idea of swapping everything for a EFI system, lowering the c/r & install a low-profile supercharger. Of course money is tight so I'll have to do with what I got. thanks for the tips!
Alan

 

[onovakind67]

Hi y'all,
I just got a 68 Chevelle that seems to have been built for week-end track racing. It's got a 383 stroker, brodix heads/roller cam & rockers, single plane hi-rise w/Demon 750, built 200/really H.D built rear-end w/posi .410, ladder-bars,boxed control arms.
The seller didn't pass on much info as to what he built it for. It has quite a lope & seems to like higher RPMs, it definitely is jetted too rich, anyways it pings under certain loads, diesels on shut-off. I always use good gas so I figured over-timing was the culprit. I checked & it was off the timing tab which goes to 18 degrees, I backed it all the way to 12 & it would sputter, die, back-fire but pinged less, I tried 14,16, 20+ degrees, but can't find a sweet spot! Its got a full MSD control, rev limiter, coil & pro-billet distributor. I'm not familiar w/this setup, can the control box be adjusted, or does it have pre-set curves? It runs strong, but I know its not close to what it could do. I thought those older MSD modules had a algorithm ability or is it only the newer generation? Eitherway, I sure would like to hear some thoughts about this...
thanx, Alan

Mark your balancer at 36° btdc ( 1/10 of the circumference ) and set your total timing to 34-36° for starters.

 

[jeff swisher]

or get a good timing light with the dial back knob..
Sounds like your light does not have this...

You may need to tweak it to get your 18 initial and like onovakind67 stated shoot for 34-36 total....
Diesel during shut off is too much throttle opening....You need to kill the air to the engine and it will die instantly.
The fix i use is a step up solenoid ..set base timing against that ..you may need to make a bracket...
Or you may try 22 initial and back the idle set screw off..and still shoot for the 34-36 total for starters.
Engine builds like this is where a welded up advance slot comes in handy.
Heck a welder comes in handy in all car builds...
I can't live without my welders...and torches..just saying.

 

[CharlieB53]

Pop the dist cap and check the mechanical advance. Make sure that it is free and not locked.

Measure the crank damper dia and buy a timing tape. Bar the motor over to TDC, install the tape. Now you can see where the mechanical timing begins and how much.

Does it have a vacuum advance?

As previously posted set your initial timing, then slowly bring the RPM up and see just how much mechanical timing is there.

You may need up to 16 or 18 degrees initial but find out how much mechanical there is, your total initial and mechanical should not be over 32 - 34