OK so here is the run down of parts.

A MSD digital 6 box, Blue Blaster coil, pro-billet dizzy. I am trying to run 35* total timing and mechanically advance from 17.

My motor has a HUGE cam (for the street) and idles with about 6". Dynamic compression is under around 9.5 and static is around 10.5.

With these stats, MSD wants me to start the gaps at 0.050-0.060 and work my way bigger/smaller from there. Oh and I run a nice hot plug, then motor seems to really like.

I got advice from a friend who has a 1000 HP chevelle and he says I should only run 0.040, maybe 0.045 max.



What do you guys think? Please any and all input. Thank you.

-Dennis

 

bump....

please gimme some input on this subject. I have some free time tonight and wanna gap the plugs so I can finally say that the ign. is DONE. (for now)

 

I have my 355, MSD 8.5/6AL/ProBillet/Blaster2, BG carb, 10.2:1 CR, Cam = .488/.510L at 1.5 rockers but I have 1.6s which increase that # and 234/244D. I have the plugs at 0.055 which was recommended by a few people including MSD. Now if i were at the track I would start there and test/tune run with a few different gaps to get the best average. Reading the plugs is important too. .060 is the highest I would assume to go and .045 would be the lowest. Thats my opinion. Hope this helps. Read the plugs after a few miles. If they are fouling or getting more sooty (pending you dont have any other issues) then close them up a little.

 

Yeah that helps a little. Only deal is that I run N20 so I have to take that into consideration, and the fact that this car will only see the track twice a year maybe.

 

then why are you running a "hot plug"??

 

Well its not hot, its just is hot compared to a stock plug. Thats all. It is a 3924 plug I think, where as the ones u can get at a parts store are 3923. The heads recomend the 3924. So ai am running them, they are not HOT for this motor.

Thats all I mean. Do you think they will be too hot if I spray it?

I guess I will do the first spray with them and pull 6* on the digi box, and see how it goes. Not gonna do this for about a week as I am waiting for my new plate.

 

that plug is recommended do to the AL heads... i would guess that .055 is wide and you might even find that .045 is a little to big depending on how much of a shot you will run

 

I put it all back down to 0.035 last night. I am gonna leave it there till further investigations can happen.

she drives STRONG now

 

MSD advised me to run the next coldest plug from factory spec and open it up to .055"! My cam is 217~223@.050" with 15" of vac, 23*base and 44*full and 9.5 compression. I also installed an air/fuel ratio guage...everyone should have one!!!!! Plugs look good... tan color!

 

1. If you're running "huge cam" you wantto run a lot lot of intial advance. To the point of locking out the mechanical curve and run full timing at idle.
All your ignition issues will be gone. If your cam is 245@.050 or more you might as well lock out the timing. If you're between 222 and 245@.050 you want around 24deg at idle with a short fast curve to 34-36deg at rpm.

2. wide spark plug gaps= a larger spark kurnel but tax the ignition system more.
Electricity always seeks the easiest path to ground. So if the spark plug gap (while under the pressure of combustion and compression) is effectively wider than the smallest secondary ignition path to ground. (thru a plug wire, jump along the cap or to another terminal or thru the rotor to the steel advacne mechanism) tham thats where the spark will go. N2O raises cylinder pressure making plug gap even more critical. Your ignition parts) (cap rotor wires etc) will last longer with a smaller gap. ( less carbon tracking.)
The biggest advantage of the MSD is its multi fire capability at low rpm to help keep your big cams motor clean at idle and enhance throttle responce.
Not the fact that the increased spark voltage allows a larger spark plug gap.
I would target the .035 to .045" area.

3. A high performance motor that makes a lot of power and runs at WOT needs a "cool plug" heat range , not a hot plug. A cool9er plug gets rid of the high heat of WOT combustion to avoid preignition. A hot(er) plug is for a motor than idles a lot, has low compression, tens to misfire from lean AFR's and or burns oil. (the plug will retain heat to burn off carbon and other fuel deposits but will tend to cause preignition. Preignition as opposed to detonation is what kills motors quick ( cuts holes in pistons) . Especially on Nitrous. Preignition is to be avoided.
Get your spark timing curve in order based on your camshaft duration and work from there. (with cooler plugs) For N2) use a cool(er) non-projected tip plug.