cboyd

Hey Guys
Just a quick question. I've just build a 383, Edlerbrock 200cc heads 10:1 compression and a Comp Cam 274H camshaft. I am using the MSD 6AL box and my dist. has no vacuum advance. What should my plug gap be. MSD recommends .050 to .060 for 10:1 and below. The plug is Champion RC12YC. Does this sound right to you guys.

As always, any and all advice is appreciated.

SanDiegoPaul

stay away from Chump plugs & use Autolite. For gap, I use .045" and I am well over 10:1 with a Mallory billet dist. With MSD though let's hope you get some feedback from others using it.

73StreetRace

A larger spark plug gap will stress your ignition components much more.
I have tried everything between 0.040 and 0.065 and found that there was no power gain above 0.045.
I've got a MSD-6AL ignition box, Mallory 55000V coil, ACCEL Shorty plugs and MOROSO Blue Max Spiral Core 11mm diameter wires.
Cylinder heads are stock. Compression ratio is 9:1.

Ironcross

Performance engines are .035 points or electronic.....

anything else is whatever

larrywalk

Having run MSD-6 CD type ignitions for over 30 years, I concur with their recommendations. Even when I have found that the plug gaps have eroded over many, many tens of thousands of miles to as much as .070", the integrity of the system has been great, the engine ran great to well over 6,000 rpm and the economy was good.

With a smaller plug gap, I have found that the economy was not as good - a smaller spark does not hit as many molecules of fuel, especially under high vacuum conditions, so a larger gap with a longer spark really does help - and this ignition box has enough kick to jump the larger gaps. Just make sure the rest of your system is in good condition and you'll be fine!

__________________
1978 Corvette
406 SBC AFR heads Lunati roller Quadrajet TH-350 3.08
11.59 sec / 118.9 mph 1/4 mile

cboyd

Thanks Guys
As always, lots of opinions, all good, just some diffrent. I do appreciate your input. Guess I'll just have to da a little expirmenting.


Clyde

7T1vette

With an MSD box and other suitable ignition components, .050-.060" plug gap would be best, IMO. Take advantage of the higher spark energy that the system will produce which allows you to go to a wider gap/bigger spark.

69VetteAngel

If you go to the MSD Paperwork, it states recommended gap based on compression range. Take advantage of the hotter spark and run larger at .050". I do in my 10.6:1 motor and i runs increadible with absolutely no adverse effects. Go to MSD and check out the instruction papers of the 6A/6AL.
Greg.

Ironcross

those wide gaps are all right or OK for computer controlled 'emissions environmental 'tree hugger engines, not for high performance.....but i suppose there Ok for the wifes Olds or whatever

cboyd

keep it coming
Clyde

Solid LT1

Run big electrode gaps over 0.050 and you'll start frying your plug wires/distributor rotor/distributor cap. The high voltages required to jump a 0.050-0.060 plug gap will try to find any place to leak and ground before they try to jump across a big plug gap in a high pressure cylinder bore.

0.045" is about as wide as I would run a plug gap and expect my secondary ignition components to live a reasonable life.

73StreetRace

That's what I was talking about in post #3

7T1vette

Gosh!! I wonder how all the cars built in the last 20 years get by with those larger plug gaps without "frying their plug wires"??? [Perhaps they buy plug wires made for HEI systems...hmmmm]

Ironcross

Nope, there trying to comply with emission standards and went all the way to .080 before they backed off...that's where smog engines run. Performance engines run best at .035...But do whatever you want, its your piece and not everyone has a high performance engine.

zwede

The RC12YC plug is meant to be gapped at 0.035". If you want to run a wider gap (don't know why you would) you need a RC12YC5 plug.

BTW, for those who think wide gap = more power: My '05 BMW M3 came from the factory with 0.028" gaps...

I run my 454 at 0.035. I tried a wide gap (0.050), but got a mirsfire where the spark went down the center electrode and jumped to the shell instead of the ground electrode.

larrywalk

Ok, you can call my carbureted, 11.5:1, 406 SBC, running mid 11s with large plug gaps, a tree hugger motor I suppose...

__________________
1978 Corvette
406 SBC AFR heads Lunati roller Quadrajet TH-350 3.08
11.59 sec / 118.9 mph 1/4 mile

cboyd

Well, Larrywalk, 7T1vette, 69VetteAngle, agree with the larger gap.

zwede, Ironcross, SolidLT1,73StreetRace, & SanDiegoPaul, for the smaller gap.

I kinda thought the .050 - .060 was a little big, and with 5 members going with the smaller gap and 3 going with the larger gap, it just makes me more courious why MSD recomends the larger gap....

Clyde

Ironcross

That's a respectfu time.

Ive done a little racing myself and both Champion and Autolite representatives told me to run .035. And why doubt the engineers that make them. I know I dont make them, I just use them.

MotorHead

Try them all, I did, 35 to 50 settled on 40. The really weird thing is I think the .050" gap was making my exhaust stink real bad. When I went back to .040" it is much much better, still stinks a bit but doesn't stink up the whole neighborhood anymore.

Don't know if the smell has anything to do with the gaps or not but would be interesting to find someone else who had a similar experience.

I also found the idle sound a little louder and not quite as smooth with the wider gaps, would be interesting to do some chassis dyno runs to find out if you make any more power at different plug gaps

cboyd

Hey Motorhead, I have been on this forum for 4 years and it was not until yesterday when I visited the Canadian Forum, that I realized you were from our side of the border. Great #'s on the RWHP. pretty impressive.It's very easy to take advise from members who have to #'s.