Technical SBC spark plugs, aftermarket heads questions

My '65 has a SBC with Edelbrock Performer RPM 60739 heads. The engine is a Chevy 350, has a performance cam (no cam card info, sorry), ram's horn exhaust manifolds, '69 z/28 intake, Holley 670cfm carb, side pipes which are actually restrictive compared to a good under car exhaust. It's not a race engine by any means.

According to their online info, Edelbrock recommends Champion RC-12YC or equivalent for "most" applications.

I just pulled out AC Delco plugs # R45XLS. That's a 13/16 hex, 'resistor, 14mm, Heat range 5 (~middle of range), wide gap, long reach, extended tip' how I read the plug specs.

RC-12YC is 5/8 hex, 'Resistor, 14mm, heat range 12 (~middle of range), standard projected core nose, copper plus design' from the ref I found.

I don't see that the RC-12YC is equivalent to R45XLS anywhere.

I don't see any reason to not use the recommended plug. Anyone have any light to shed on this disparity? Why would I not be using the recommend plug that covers "most" applications. I see nothing special about my engine. I figure the hot-rodders here know more than me on this subject!

 

Only thing I can add is from my parts counter days.Ofren if you cross reference from one brand to another its off by one heat range compared to looking it up by application. Start with the RC12YC,and see how they work.The same engine in a Chevy II VS a 2 ton truck can call for different plugs since the engine lives in a different world work wise.

 

I expect the main difference is the size of the hex, the Champion plug will give you more room to work on it because it takes a smaller socket.

So...who put the AC plugs in the engine?

 

The AC plug that came in the 350 was usually an R45TS. That's a taper seat, 14mm, short reach plug with a projected tip. I never liked Champion plugs in a Chevy but lots of other people love them.

 

That's what I'm thinking. I am wondering though if the AC plug was chosen to fight fouling.

 

I would put in an AC plug because it's a Chevy spark plug. Oh....wait...it used to be. Now they're made in china.

 

Oh, the 13/16 was a PITA

Either the previous owner or his buddy that built the engine installed them. No way to know. Previous owner is a great guy but I am out of touch with him, and he wouldn't know the reason. He couldn't even tell me the cam specs. His buddy who lives in another state did it all and he never asked. It would be speculation.

 

The AC plug that came in most GM V8s was an R45TS as far as I can tell, lol

my Poncho, Olds, and Buick engines called for them.

 

I thought AC meant "All Chinese"

 

Chevy switched from large, gasket type plugs to the smaller, taper seat plugs in 1970, big block and small block. With the gaskets, small blocks used short plugs, big blocks used long plugs. The taper seats were all short. The aftermarket heads are another story, of course.

 

Yeah, no taper in these heads, and light install torque too

 

Does Edelbrock recommend a plug to use? My Dart top end kit came with NGK plugs.

 

When I first went looking for a parts store that stocked the RC12YC for my old engine with Edelbrock heads in the Henry J it was difficult to find a store with 8.
I found an independent store in a smaller rural town and shot over to get them, the old counter guy says "you must have a lot of lawnmowers" I was a bit taken back and ask why he said that, he replied that those are lawnmower plugs and you're probably going to piss some guys off until I can restock them.
They quickly fouled out and I'll always know them as damn lawnmower plugs until the day I die lol
I switched to NGK and never had a problem again with fouling.

Edit : I'll add that I had a full MSD ignition setup with distributor, coil and 6al box, so there wasn't a lack of juice to keep those plugs clean.

 

Yes. According to their online info, Edelbrock recommends Champion RC-12YC or equivalent for "most" applications. Fromm what I read re: my ignition, .035 to .040" gap is appropriate.

When Edelbrock says "most applications" for these heads re: plugs, they have to mean "moderate performance, but we're not liable for your screwups".

 

In reading about the Champion plug, I wonder why they suggest them.
The previous owner of my car must have been fighting a fouling issue. He would drive in parades occasionally.

Honestly, I don't care if the plug I use is for VW Micro-buses painted pink and purple polka dots, so long as it runs right and my backfire is resolved.

 

This is the HAMB, not “Alice’s Restaurant”

 

just wait until I pull out the glossy photographs

 

You can have anything you want at... I'm not going there..

 

Only if they are 8x10.

 

Checking the info on the head, it does call for the RC12YC 14mm withthe gasket. What fits most Chevy 350's doesn't fly here.
I don't know if there is a viable heat range comparision chart anymore with the one size fits a large area of heat ranges that they have now plugs. That particular AC plug R45XLS Fits 250 Chevy sixes but isn't listed for any small block.
Outside of the larger hex and ?? heat range it does fit the head though.

 

Roger that. The heat ranges are similar, roughly in the middle of the ranges for each brand. I may need a hotter plug maybe not. I feel with the ACs with the extended nose the previous owner was fighting fouling, which was probably due to his driving habits. The plugs are generally good but two are fouled with carbon and two with gas, but not badly. These two smell of gas though. Better than oil! I have yet to check gap but .040" seems about right.

I'm ordering up the Champions and cleaning up these AC Delcos, just in case for spares. I'm also revisiting my idle speed afterwards. My gut says that the 950-1000 rpm I was using to get an even idle with OK vacuum was partly due to the plugs. With the recommended plugs i'm going to re-evaluate what I'm doing with my Holley carb, and I'm going to lower the fuel levels in the bowls too. They are just too high.

 

If you are fouling plugs, you have some investigation to do and tuning.

 

Ugh ..... can't believe you're ordering those Champions

 

I have been running NGK racing plugs for years, Blown SBC, full race, no issue with them and they last . However my tune is kept spot on.

 

I've only had luck running Champion plug's with a Magneto. Anything else will foul them. AC, Autolite, or NGK seem to work for anything. Just my 2 cents...

 

We'll see. There's a lot of unknowns with this engine and of course I have not provided a blow by blow account of every idle mixture screw I've turned. I want to start with a baseline instead of going with speculations and guesses.

 

I also was just at an auto parts store to pick up a cap and rotor. When I said I need a cap and rotor for an old Corvette the kid said, "Corvette's a Chevrolet, right?".

Right, right, correct.

 

The car in my avatar has a Holden six cylinder of 1954 vintage. They use the same plug as an early V8 Chev. When I tried Champion plugs in it you'd swear I had the brakes on when doing a run. Changed them out for NGK on that day and the difference was like chalk and cheese.

 

When guys that have used Champion plugs and had them foul and underperform give you advice on not to use them, that's certainly not "speculation" and "guesses", that's real world hard evidence.
We've already been where you are and learned a lesson, that's why we can give advice when you ask for advice, we're not just blowing smoke up your ass, but by all means you go do you don't let us hold you back from conquering the world.

 

Don't you feel you may be blowing this out of proportion a little? You just assigned to me the role of asshole. And you know what? The hell with it. I don't need the personal crap.

Thanks all. See you later.