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Something to be aware of that I have struck a few times now, twice on Chrys engines, when using H beam rods. The indents for the rod bearing shells are narrower than the indents on factory rods. The tang on the brg shell is too wide to fully seat the shell in the rod. Result can be wiped brgs. I...

RB, The reason you are not posting anything is because there is nothing to post. Full of baloney as usual. You said in post #90, smart people build engines that do not need 30* of [ idle ] timing to run. When I asked in a subsequent post what the 'formula' was, you said 'Math' in post #98...

440 Mike Post #102. When my car was built, leaded fuel was in use which allowed higher comp ratios. Nothing needs to be done to the idle timing because the engine doesn't ping at idle! The centri curve &/or total timing at idle may need tweaking on a stock engine. On the LS1 engines, WOT timing...

RB, Post #104. And just which books have the magic formula?

RB, Post #105. Totally wrong, as usual. If it has been proven 'many times', it shouldn't be too hard to find just one example to prove it.

Mattax, Post #94 is correct & you continue to be wrong on the reason for the switch to PVA. So Chev used PVA on one engine. It could be because I believe PVA was used on some man trans cars, but later man & auto got MVA. What about the millions of others that used MVA? And then switched to PVA...

Post #88 & the reason for the change from MVA to PVA. It was for emission purposes, as I stated in a prior post. You will find the info HERE: www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html You may have to type in the full address. I believe the article was...

Give us the MATHS, give some examples.......

So what is your formula for cam timing/compression ratio so that we can all build that magical engine that needs.....how much idle timing?

RB, Post #90. Smart people give their engine the idle timing it wants, which can be as much as 50*. You only have to read this forum & others where people have advanced their idle timing & found the engine idled higher, smoother etc. It idled higher because the engine was making more HP from...

Mattax. Post #88, fact not myth. Do not know why the L-78 used PVA, but millions & millions of GM cars used MVA. The changeover year was 1967-68. My GTO was driven off the showroom floor, idling at 26*. 6* initial + 20* MVA. By 1968, the idle timing was 6*; the vac advance was now ported. Same...

RB, Post #56. Using MVA at idle is one way to give the engine the idle timing it WANTS. There are other ways such as locked timing. The problem with locked timing is that the timing.....is locked. Nowhere to go if you get detonation. MVA is load sensitive & can be adjusted to keep out of...

A lot of BS creeping in here. Post #58 claiming the switch to PVA had nothing to do with emissions is BS. It had everything to do with emissions. GM, who used MVA, could not meet the stricter HC emissions standards coming into effect in the late 60s & had to switch to PVA. Switching to PVA...

Mattax. Post #57. I am well aware that Chrys was not the only one using MVA as I described earlier. The major auto makers all used it. I specifically mentioned Chrys because there are some who think Chrys never used MVA.

RB, Post #52. More BS. The dyno tells you how much timing the engine wants, not a dist machine. And yes, more timing at idle with longer duration cams. Timing at idle with Chry engines is the initial timing, usually in the 8-12* range. A 220 @ 050 cam is not going to need 50* at idle & I...

RB, Post #51 realllllllllly shows how little you know about ign. Man VA is just one method of providing ectras timing at idle, when it is needed. It is particularly useful because it is load compensating, & can be adjusted to drop off if detonation occurs. Unlike fixed timing..

dmopower, You know some smart people!

Fishmen, It seems you might be unaware that Chrys used manifold connected VA to cool the engine? For 1973-78: ' When engine coolant temps at idle reaches 225*f, the valve opens automatically & applies manifold vacuum directly to the distributor.....This increases engine idle speed &...

440 Mike, Post #43. 60* of timing at cruise is probably too much for a high compression engine of the 60s. However, if the engine has a large duration cam, it might require that for cruise & up to 50* at idle, but 25-45* is more common.

RB, Pleeeeeeeeeeeease keep posting [ post #38 ]. It shows how ignorant & stupid you are. I never said everything needs 50* of timing at idle.

Post #36. Cooler running. If you want cooler running at idle, then the VA needs to be connected to manifold vacuum, as I posted in #37. Ported vac is inoperative at idle.

Nope, but VA should be connected to a manifold source if you want everything in the list.

Yup, VA is not understood. Not helped by ignorant magazine writers you talk about the 'feature' engine in their article, & mention the MSD or DUI dist they are using for free plug, but make no mention of VA.

There is a two part video on Unity Motor Sports you tube, on vac adv. D. Vizard appears in part one. Done about two years ago, sorry do not know how to link it. Before & after results/comments are provided, on a tunnel rammed Ford with two 660 Holleys! Worth watching. I use a different method to...

It is good info, but oversimplified. Setting up MVA takes time, but no special tools. As RustRatRod, found out [ post #8 ], MVA didn't work on his combo because of the low 6" of idle vacuum. MVA will never work with vac that low. At least RRR recognised what the problem was & didn't criticise...

Pontiac also used MVA.

Iron, At idle, if you can 'feel' suction with your finger on the port above the t/blades, then that is bad news. Blades open too far for proper transition from idle to main cct. What cam?

All the VA does is supply timing. The engine doesn't care how it gets the necessary timing to run as efficiently as possible.....as long as it gets it. If the engine has a dist that has the timing locked, ie it idles at 36*, has 36* at WOT & everywhere in between, then it is unlikely to benefit...

Thanks for posting, very interesting. Nearly all the early engines had single pattern cams, & the Poly had a reverse pattern [ less exh duration ] cam.

This is why I asked if anybody had a cct diagram. Don't think you can 'just bolt the transistor to the metal case'. The metal body of this type of transistor is the Collector, one of the three electrical connections of the transistor, & is part of the electrical cct. I am almost sure it is...