55.2-59 1959 GMC V8 vacuum

[ses427]

Swapped the 6 cylinder in a 59 to a 337 V8 from a fire truck. Struggling to figure out the vacuum advance and timing. The fire truck had the vacuum above the throttle plates rather than at the manifold port. Anyone have a similar setup and can tell me where the vacuum is pulled from? Thanks.

[geezer#99]

What’s a 337?
Is it olds, pontiac, Buick or Chevy?
As for your vac advance, what does the motor like?
Does it idle smooth or rough.
Pics of your motor help.

[dsraven]

not familiar with a 337 engine, but ignition is ignition so I would think the basics would apply. if you have a pic of the set up that would help. I googled 337 just to see it and all that came up was ford flathead engines. is that what you have there?
in general, I would think that if you are asking the question that implies that you are having issues with the engine tuning. before you change anything it is a good idea to start from scratch and do a check of things. start with recording the values you have right now. engine vacuum at the manifold side and the ported side of the throttle plates, idle speed, timing at idle and max, spark plug gap and condition etc. then do an engine compression test-dry and wet. vacuum check, distributor check for shaft play, mechanical advance component wear and return spring condition, vacuum hose integrity, spark plug condition, carburetor throttle shaft wear and carb general condition, etc etc. keep track of the results. sometimes doing this you find an issue, like the distributor mechanical advance is not working freely, has worn out parts, etc also see if you can find some specs for the tune on that particular engine.
here is a decent link that shows how the vacuum advance works and actually has vacuum gauges connected while driving to show the differences etc. also talks about initial timing and how that factors in, and how throttle position factors in for cylinder pressures and how to check the throttle plate positions as to where the ported vacuum port is located in the venturi area. if you use ported vacuum you will likely need to increase mechanical advance, which also increases maximum mechanical advance and that can also have an effect on overall performance

https://www.youtube.com/watch?v=WD_bhDq_8tY

[mr48chev]

The 336 Pontiac/GMC V8 was closer to 337 and some call it a 337.

Have you checked the carb number to make sure that they didn't swap a later carb onto that engine? Ported vacuum to the distributor advance came along about the same time as PCV valves did. When emissions started being an issue.

Personally I'd just disconnect and plug the line, set the intitial timing where I thought it should be and hook the line back up and go drive it and not worry too much about it unless it just doesn't perform the way you want.