Spark plug gap

-
75dartsport

75dartsport

Well-Known Member
Joined
Jan 17, 2008
Messages
631
Reaction score
8
I am running Autoolite 65 plugs in my 360. W2 heads around 10 to 1 compression. Mopar 284/480 hydraulic cam. My question is it seems to pull real hard to 5600 rpm, then falls flat on its face. Doesn't seem to gradually just all at once. I pulled a couple of the plugs, and they were gapped at .025. Would this do it? Im running a msd digital 6al. What would the proper gap be? And is this the right plug for my combo. And before too many people tell me, I know the W2 heads are too much for the cam that is in it. It was just an experiment to see what the heads would do without changing anything else.
 
I thought you could run MSD's to .060?! tmm
 
anyone i know that runs a msd runs between 0.40 to0.60 gap if this is your problem i dont know just what im told
 
Agree with tmm - also, your total adavance - may want to check this. Is your distributor locked since you have MSD6 or do you have a vacuum advance? After all that check and re-tune your carb, will probabley be a little lean at this point.
 
BTW, sounds like a cool setup, how do you feel about the experiment?
 
75dartsport said:
I am running Autoolite 65 plugs in my 360. W2 heads around 10 to 1 compression. Mopar 284/480 hydraulic cam. My question is it seems to pull real hard to 5600 rpm, then falls flat on its face. Doesn't seem to gradually just all at once. I pulled a couple of the plugs, and they were gapped at .025. Would this do it? Im running a msd digital 6al. What would the proper gap be? And is this the right plug for my combo. And before too many people tell me, I know the W2 heads are too much for the cam that is in it. It was just an experiment to see what the heads would do without changing anything else.
Click to expand...

I run the same plug in my Hemi gap is .30
 
A plug gap is not going to make it suddenly fall on it's face.
Way more likley a spark timing issue or carb as mentioned above.
 
I have the same cam in a 340 and that is about where it takes a nap.
That is with ported X heads , 1 5/8 " headers and a 750 d.p. .....I'd guess around the same compression , but I didn't build this motor so I can't say for sure.
As for plug gap ....... I run .045 with all my MSD ignitions ( a half dozen over the years ) and it seems to work fine.
Having too narrow a gap probably isn't causing it to run our of power , but it is affecting combustion and efficiency.
This stick isn't going to work much past 5,800 in a perfect combination.......... it will rev past there , but why bother ?
 
The higher the compression the smaller the gap. low compression motors can run bigger gaps. heat range is also important to. you dont want the motor having it pre ignite. Also over timing can make it fall back. even octan rating.
 
It's a hydraulic cam and the rocker gear is heavier. What springs are in the heads? Sounds more like the cam gives up a little eralier than "normal", but I'd callit behaving fine.
On the ignition - I always set my MSD driven plugs at .040.
 
Thanks for the replies. Im running my timing at 34 total. 750 holley 80 in the front 85 in the back. It doesnt seem to be leaning out. Doesnt pop or anything, just falls flat on its face. I have new valve springs on the W2 heads to match the cam. It fell flat at the same rpm with the 587 heads also, so must be the cam. Just wasnt sure if the plugs and plug gap were proper for this setup.
 
The car ran low 8's in the 1/8th with 587 heads, and edelbrock performer and 700 holley. 3.55 gear. I have switched to a4.56 gear, W2 heads, holley strip dominator, and 750 holley. Just looking for a couple of tenths. I will hopefully have it to the track this weekend to see what the changes did.
 
Anyone else have any opinions. The drivers side rear plug is a pain to get to. Would like some input before I put them back in.
 
I would run a colder plug then a autolite 65...

a holley 750 dp 4779 comes jetted around 71p- 80s....you gotta lot of jet in the primaries....Does the carb still have the power valve in the primary side?
 
Has power valve still. When i had the car running I had 75 front and 85 rear andthe plugs were white. Didnt show any lean condition except for the white plugs.
 
I know that, I'm going to start fat. When I get to the track im going to re jet. I guess I'm going with a.045 gap and 34 degree timing to start. With the digital 6a I can mess with timing pretty easy.
 
The carb is a 750 base with proform body, and aftermarket metering. Not sure what it flows? It had 75 front and 85 rear when I bought it. Should I jet it with stock 750 double pumper jets? I had a700 holley on it before.
 
70aarcuda said:
jet for mph ...not for color of plug....
Click to expand...

Exactly. If it's pump fuel a white plug isn't far removed from normal. Should just be a little bit of color down at the bottom of the insulator which you need a good magnifier light to see properly. I have a hard time seeing plug gap or the cam causing it to just drop dead at 5600. Yeah the performance may drop off but it still should pull to 6k even if it's not making good power. I'd think it's more likely running out of fuel, like when the fuel system isn't keeping up. It doesn't always pop when that happens. When I had my old 360 in the Cuda the fuel pump shot craps on me and it nose dove above 5000 and never popped a lick. I knew it was a fuel delivery issue cause I had a A/F gauge on it and right when it dropped off the gauge went max lean. New fuel pump did the job.

Either that or the MSD has a 5600 rpm pill in it and it's shutting it down.

The carb I have on my 408 sounds like the exact same build as yours and I have 76 jets in the front and 85 in the back so I'd think yours is probably pretty fat with 80's and 85's. What high speed air bleeds does it have?
 
I need to check the air bleeds, not sure of the size. I have the limiter set at 6800, so that shouldnt be it.
 
You must log in or register to reply here.
-

Back
Top