Hysteric,
With all due respect to Bruce, here is what I know [ not surmising ] from over 50 yrs of working on/building engines. And I don't think Bruce 'gets' it as far as idle timing goes. He is not alone...
When cam duration/overlap increases, idle timing [ I.T. ] needs to increase. Other factors that will require marginal increases in I.T. are low CR, large ports, sluggish intake manifold.
And I don't agree with Bruce that Chrys 'are a bit different to other US products'. They all have combustion chambers, cams, valves, etc. The only thing that will differ is the amount of I.T. for each engine/combo.
In my opinion, Bruce has made a simple scenario quite complicated. Simple, in the sense, that if you increase I.T. from 10* to 40* with no other changes, & idle rpm increases 300 rpm, then what you have is a winner. It is very obvious in this scenario that the engine is making more power with more timing & no downside. The engine also runs cooler, indicating efficient use of fuel, air & timing. I have done the above many times, although a 300 rpm increase is unusual, usually 50-200 rpm increase. Once optimum I.T. is determined & set, I can reduce the idle rpm, often to lower rpm than it had with less I.T., & it idles smoother with more vacuum. The tip in response is also always improved, & I have cured off idle flat spots just by getting the I.T. correct. There is a reason racers lock their dists for max timing...
It is most important to set I.T. first before drilling holes in t/blades for bypass air, & then finding the engine idles/responds a lot better with a heap more I.T., but now it idles too fast & you have to fill some holes that didn't need drilling...
Chrysler missed the boat on manifold sourced vac adv. Others did not like the GM divisions. Not sure about Ford.
Chevs I believe idled with about 24*, a combination of init + MVA.
Pontiacs until 1968 left showroom floors idling with 26*, 6* init + 20* MVA. These engines had 10.75:1 CR & mild cams, with intake duration under 200* @ 050. When you consider these parameters, suddenly 35-40* I.T. for a modified cammed engine doesn't sound that much...
My GTO with Webers idles with 48*.
With all due respect to Bruce, here is what I know [ not surmising ] from over 50 yrs of working on/building engines. And I don't think Bruce 'gets' it as far as idle timing goes. He is not alone...
When cam duration/overlap increases, idle timing [ I.T. ] needs to increase. Other factors that will require marginal increases in I.T. are low CR, large ports, sluggish intake manifold.
And I don't agree with Bruce that Chrys 'are a bit different to other US products'. They all have combustion chambers, cams, valves, etc. The only thing that will differ is the amount of I.T. for each engine/combo.
In my opinion, Bruce has made a simple scenario quite complicated. Simple, in the sense, that if you increase I.T. from 10* to 40* with no other changes, & idle rpm increases 300 rpm, then what you have is a winner. It is very obvious in this scenario that the engine is making more power with more timing & no downside. The engine also runs cooler, indicating efficient use of fuel, air & timing. I have done the above many times, although a 300 rpm increase is unusual, usually 50-200 rpm increase. Once optimum I.T. is determined & set, I can reduce the idle rpm, often to lower rpm than it had with less I.T., & it idles smoother with more vacuum. The tip in response is also always improved, & I have cured off idle flat spots just by getting the I.T. correct. There is a reason racers lock their dists for max timing...
It is most important to set I.T. first before drilling holes in t/blades for bypass air, & then finding the engine idles/responds a lot better with a heap more I.T., but now it idles too fast & you have to fill some holes that didn't need drilling...
Chrysler missed the boat on manifold sourced vac adv. Others did not like the GM divisions. Not sure about Ford.
Chevs I believe idled with about 24*, a combination of init + MVA.
Pontiacs until 1968 left showroom floors idling with 26*, 6* init + 20* MVA. These engines had 10.75:1 CR & mild cams, with intake duration under 200* @ 050. When you consider these parameters, suddenly 35-40* I.T. for a modified cammed engine doesn't sound that much...
My GTO with Webers idles with 48*.
