[echristie]

Gents,

After searching the archives, I have not found the answers to the questions. I have a '70 454, automatic, 3.42 gears, 180 t-stat, dual plane intake, Edelbrock AVS 800 cfm carb, Accel HEI, 8 mm wires.

There are Accel plugs in the car, but I found one has a cracked external insulators and there are some light brown colored carbon build up, so it isn't running to bad.

I want to know:
How you know what heat range to use?
What things influence spark plug choice?
Do you always run the recommended gap?
If not, what affect does opening or closing the gap do?
Is there a better brand than Accel? I grew up using Champions for everything, but I know there are other options.

Thanks in advance,

E.

 

[p-hanny]

Well, thats alot but I take a stab. (i`m sure I ll get worked over on it though)
1.Manufactor has a recommended choice. (that was then this in now though)
and they took all things into consideration at that time.
2.from what Ive seen its all about choice,some guys sware to one plug some guys say that plug sucks. so good luck finding an exact brand to run. Or at least one all your buds will like.
3.I always run the rec. gap but alot of guys try and open them up a bit thinking they get a longer or maybe stronger burn. Not sure I would agree you could increase performance but maybe (get more feedback on that) .
4.a wider gap causes a longer spark line wave on an iscilloscope but the end of the burn seems to be about the same where the flame out is and the coil output one plug to the next is similiar,, so you would have to think it would cause a longer burn? But would also cause overheating of the plug if it was too wide which is no good if the electrode over heats and starts to glow you can have all sorts of firing problems. I once put in 4 plugs wider gap then normal and 4 plugs narrower gap the normal on the same 350 engine on a boring summer day and put it on an iscilliscope to see the difference. It Was really hard to tell one cylinder from the other except for the end of the burn, one was more ragged then the other but the coil output (per cylinder)and oscilations where the same. Which lead me to belive it didnt matter gap wise. But hey that was just on a machine right,,,lol.
Most guys go with a hotter heat range spark plug on stock engines and on my blown car Ive heard running colder helps heat running hotter helps performance so who knows. I run stock plugs and dont know that I would gain much from anything different. Delco plugs is all I use in gm. Ford-motrcraft, chrysler -champions. In hondas ngk. I used to work for firestone and they used Bosch(not the platinum though) and they worked well in all cars. Platinum plugs seem to "fuel fowl" easier then the rest and they dont clean up very well. Which is bad news for the carb.vehicles on this site.One thing about all plug manufactures. They all advertise HP improvement with there brand. Well, if you put any plug in your car that has alot of miles on it it will automatically gain HP. DUH. Another thing I dont like about champions. They use a spring in the center of the plug!! no doubt,,crack one open sometime and look. I read an article once that said that is how they change the heat range. I read it but that doesnt make it true but I still would rather have a solid core plug in my ride. For my own ride though I will always run ac delco for "what I think" is the best plug out there. But then again like I said before good luck getting two guys to agree on what is the "Best plug" out there. My guess is your car is missfiring on that cylinder or running the coil juice directly to ground (which wont feel like a missfire it will just kill that cylinder taking the path of least resistance) and you dont even feel it, because the enging is so strong anyway and seems to compinsate for a weak cylinder. Put new plugs in it and you will sware you gained 50 horsepower with whatever plug you choose. This is how stories about one plug being better then the other get started. good luck,,,Paul.

 

[Mr Chevelle]

AC's in my chevy's, nothing fancy. I've tried Motorcraft and Champions but AC seem to work the best.

I run the manufactures recommended plug, heat range and gap for the particular engine. I have only been able to get resistor type, maybe non-resistor can be special ordered.

If I convert to an HEI from points I use the same plug but gap it for the distributor. Non-computer GM HEI's use a .045" plug gap. AC plugs can be purchased with .045" gap already set but I check each one before installing them.

If the heads have been changed I make sure the plugs are correct for the new head. Some heads use a tapered seat plug and some use a washer type. I also the check the plug thread depth.

I think the heat range is a trial and error deal. If you run it hard, mainly drag racing, try a colder plug. I believe the recommended heat range is for general useage.

I use to think a tighter gap gave more RPM's but I haven't heard that lately.

My 2 cents!

 

[Bob West]

I just asked the parts guy what plug is recommended and I run one heat range colder ex. 74 454(thats what it BEGAN life as) rec. is r44t and I run r43t and I gap them at .035. In performance applications you want to go one range colder, nitrous a couple ranges colder, gap depends on intended use also, tighter for performance, out to spec for a cruiser. I like AC Delcos too, just don't get the life out of autolite plugs.

 

[echristie]

I just asked the parts guy what plug is recommended and snip...

want to go one range colder, nitrous a couple ranges colder, gap depends on intended use also, tighter for performance, out to spec for a cruiser. I like AC Delcos too, just don't get the life out of autolite plugs.

Thanks guys for the info. The plugs in the car are Accel 0576S, which cross references to a Delco CR45TS. I got a set of those and will gap them at .035.

I pulled two plugs yesterday to see what they looked like. Medium brown with some build up on the electrode and the ground. I cleaned both and got the build up off. I put them back in and drove the car today. At part throttle, now it surges. Sheesh, I can't seem to even check things without something else happening. It's a tad frustrating. When I had my first Chevelle, I had the 300hp 350, TH350, points distributor, etc. It's been a few years, but I don't remember these kind of issues. When it ran like crap, you had a pretty good idea why. With this one, it seems almost moody.

I'm just venting guys, I probably forgot half of the tuning stuff I used to know, so now I have to relearn it. I'm off next week, so I am picking up a new engine analyzer and I will go from there. I will start by changing plugs, tuning the new carb, and once that runs well, I will start making adjustments to the timing to get 'er running smoother. Maybe 454s aren't supposed to run smooth.

Anyway, thanks again for helping clear the spark plug fog.

Thanks,
E.