intermittent Miss at cruise rpm

[markm]

Light throttle at 2100rpm, with no vacuum advance I think your timing is retarded quite a bit, which will make your plugs run colder too. That's one of the reasons for vacuum advance to keep the plug tips hot at idle, and light throttle. Figured that out from 40 years ago running a 427 with no vac advance. Couldn't get a set of plugs to last a month in town.

Could you expand on this a little because I have never experienced this I have 3 cars running Mallory Unilites without vac advance on street. A couple have 10 years on plugs.

[Rick_L]

While vacuum advance is a good thing for a street engine, it really doesn't have much to do with fouling plugs.

[chevynut]

I suspect plug wires. Looking for sparks under the hood is different than when driving under a load where cylinder pressure is higher. Also you say they're old and nicked so it wouldn't hurt to replce them considering eveything else you've replaced.

[55 Rescue Dog]

Could you expand on this a little because I have never experienced this I have 3 cars running Mallory Unilites without vac advance on street. A couple have 10 years on plugs.

There is zero reason to run a mechanical only advance on the street. The vacuum advance has been around on everything since 1930 for good reason, that the computer does now. Mechanical advance is controlled strictly by RPM, whereas vacuum advance adjusts for engine load, adding advance during light loads, adding heat to the plugs to help save, and burn off excess fuel. Plug tips get hundreds of degrees hotter with every degree of advance, and last longer. If you drive WFO all the time, then that would be the only reason not to have vac advance, but it wouldn't hurt anyway, because there is no vac advance at full throttle. A computer controlled engine operates basically the same, but better.

[markm]

There is zero reason to run a mechanical advance on the street. The vacuum advance has been around on everything since 1930 for good reason, that the computer does now. Mechanical advance is controlled strictly by RPM, whereas vacuum advance adjusts for engine load, adding advance during light loads, adding heat to the plugs to help save, and burn off excess fuel. Plug tips get hundreds of degrees hotter with every degree of advance, and last longer.

I have to run these distributers to run my Jones/ Moroso mechanical tachs on my 55 & 67 Camaro. My BBC with a tunnel ram and two Holley 600 knocks down high teens in MPG on the highway. I doubt I can improve that much if at all. I have a Vac advance equipped Unilite I bought for my 56 that sits on the shelf. I probably have to remove the wiper motor and rear two barrel to install. I am not convinced that it worth the effort.

[55 Rescue Dog]

I have to run these distributers to run my Jones/ Moroso mechanical tachs on my 55 & 67 Camaro. My BBC with a tunnel ram and two Holley 600 knocks down high teens in MPG on the highway. I doubt I can improve that much if at all. I have a Vac advance equipped Unilite I bought for my 56 that sits on the shelf. I probably have to remove the wiper motor and rear two barrel to install. I am not convinced that it worth the effort.

I have an Accel dual point, mechanical tach drive with a SW, or Moroso mechanical tach I would love to sell! I'ts been in a box for 30 years. I love mechanical tachs, but only with vac advance. Other than the cable, I loved the old school mechanical tachs. You could see each cylinder firing at idle.

[markm]

There is no sound sweeter than SBC with headers, 2.5 exhaust and turbo mufflers idling with a 30-30 Diuntov. as long as the plug wires are fresh.

[Eds56]

I suspect plug wires. Looking for sparks under the hood is different than when driving under a load where cylinder pressure is higher. Also you say they're old and nicked so it wouldn't hurt to replace them considering everything else you've replaced.

Thanks for all the responses, New wires are now on order....should have them in a few days. When i pulled the old wires off, i also found a burnt place on #6 wire, which is routed underneath.....so i couldn't see it before.

Now for the spark plugs, I have read countless articles and honestly just came out more confused, as apparently there is no "specific best plug" and a TON of opinions going in all different directions. I do appreciate the input, but the thought of an Autolite (FORD to me) plug in a Chevy borders sacrilegious...lol -- If these are indeed the best plug...then YES I will run them. And i probably will not notice much difference between them and if not that's ok too. This may be FOOLISH of me but to help me determine what works best for ME.... i ordered a couple to try along with a couple more R45s & NGK's. The thing i liked about the NGK 3332 is they are about 1/8"-to-1/4" Shorter in length than the R45s i had and a couple of my Header tubes are VERY-VERY close to the SP boot, so this shorter plug seemed nice. NOW i know that's not much, but Hey every-little bit helps. And i refuse to pay ACCELLs ridiculous shorty price $$$

[markm]

Lets see Autplites a US company is problem and NGK is ok, I don't get it.

[Rick_L]

Autolite hasn't been part of Ford for 30 years or more. Motorcraft is their brand for that stuff now.

At one time I ran NGK plugs in my stuff because they gave them away. Then I got a whole case of them where 1 or 2 plugs in 10 was dead right out of the box. I switched to Autolite and never had a problem again. Prior to all that, I ran Champion and AC with no problems either.

The NGK debacle was fixed I'm sure, just left a bad taste. I would take them the bad plugs at the races, they would say that can't happen but they'd hand me another box of bad plugs as they said that. It was too much of a hassle to find the bad ones.

Spark plugs are not magic. There's no silver bullet.