So I have a 75 Hurst Olds that has had all the pollution stuff removed. Took a run yesterday and it was running great until the 2nd leg and upon acceleration I noted (I think they call it a knock) which apparently would indicate - possibly- that the timing is off or maybe a vacuum leak? Anyway,...the tag on the fan shroud shows the timing should be 16 degrees BTDC! But, since the pollution stuff is all gone, would I want to set the timing of say a 71-72 Olds 455 which is between 12-16 degrees BTDC?

 

Dwell angle is the wrong term.

You can reduce the initial advance as said. Worst case is you lose a bit of power.

 

Isn't dwell angle ....the "degrees" you set the timing too ? i.e. 16 degrees BTDC?

 

Dwell is the amount of degrees/time for the coil to charge. Ignition timing is when the coil fires based on the position of the piston.

 

ok, thanks

 

And on a 75 with HEI the dwell is controlled by the ignition module, and is not adjustable as with points distributors.

 

So with that ignition module if that goes bad is there a part to replace? Given my description doesn't that seem more of a timing problem I should check and/or the vacuum leak?

 

Give the engine what it wants, not what you think it needs.

Before doing anything, make sure the weights in the distributor are clean and free to move and retract. Make sure the weight pivots aren’t worn out. You need to make sure the distributor timing is accurate and repeatable.

Do you have dial back timing light? If not, you need a timing tape on the balancer.

Start the engine, warm it up. Disconnect and plug the vacuum advance. Connect a timing light, see what your base timing is, then rev the engine to 1000, take a timing reading, then rev to 2000, record the reading, then 3000, 4000etc. Eventually you will get to a point where the timing stops advancing, that’s your distributor advance. Hopefully you end up with a reading of around 36ish at 3500rpm. I say hopefully, because mid 70s HEI was calibrated with more advance, and were lazy coming in. You will more than likely need to play around with different cans, weights, and springs.

 

Outstanding advice right here.

 

If it is pinging/knocking on high acceleration retard the timing a bit and try again. On custom engines with no specs I always started with a stock base timing, took it for a spin, giving it a moderate WOT run through when warmed up. If it ran good without issue I would add a small amount of advance and run again. Once it got to where it has any detonation/knock, I would retard timing back just enough to get rid of the knock.
As others mentioned there can be other factors but assuming the distributor is good this should work. Just don't over do it. If it knocks all the time, try what others mentioned to troubleshoot.

 

I have a pacemaker so I'm not supposed to be messing with the vehicle running! Anyway, taking to the mechanic tomorrow and it ONLY knocked after engine was warm after about a 40 mile run. Then 2nd issue was the hard starting when I stopped for gas after coming back from the run, stopped for 5 minutes to get gas and it was almost like the thing wasn't going to start! I put new autolite 85's in and set the points at .045 and will have the mechanic tomorrow retard the timing by maybe just 2 degrees and I'll see how it does after that.

 

Well that is interesting. I have worked in the implantable pacemaker / defibrillator industry for nearly 30 years and have never heard that. Can you elaborate on what you were told and by whom?

 

Put a Progression Ignition in it. Then you can adjust all the timing parameters from your phone away from the running engine, on the fly.........

 

electromagnetic interference (EMI)
I was blessed with a defibrillator about a year ago.
Not sure if a car's electrical system would be a problem but my cardiologist warned me about welding and considers that a BIG NO-NO.
DAMN

 

Yeah, welding has a lot more power and generates a lot more EMI than an ignition system. Stay away from RADAR systems, too.