[Gach]

Originally Posted by blueghoast

I still have the box I'll check and let you know. This motor is iron headed too.

GT

What Autolite plugs running in SM heads

[blueghoast]

Originally Posted by Gach

What Autolite plugs running in SM heads

NGK-8's also run them in my E-heads too.

GT

[bob d]

I've tried all different plugs in my 1965 tripower and the NKG XP 5'S run the best so far.

[Gach]

Originally Posted by blueghoast

NGK-8's also run them in my E-heads too.

GT

Thanks yeah 8’s didn’t work out for me had to go to NGK-9’s. Cooler plug. As you know

[Dragncar]

Originally Posted by mgarblik

That is interesting. Not really familiar with the Champion plug number you mentioned but I am almost sure Accel spark plugs were made by Champion in Toledo , OH. They were the "Yellow Jacket" plugs they used to market. Personally, I have had about equal results with Autolite, Champion and NGK plugs. I like the way the NGK plugs are packaged with the little cardboard tube over the business end. I have found some Champion plugs with the center electrode crooked in relation to the shell and ground electrode. But they all functioned fine. If I had to pick a "brand" price no object, I do like NGK. Very few defects.

The Yellow Jacket plugs are Nippendenso U groove. Fantastic plugs, but they do not make the right plug for High Ports. So I have Autolight 3911s in there as per slowbirds recommendation. He would know.
The JCY18s were a 2 piece electrode and it was not a good feeling to look at a flopping around pug wire and a hollow insulator.
You could literally hear the difference when the Accel plugs were put in.
I did that comparison thread on race plugs awhile back. While the Champion was the least robust of the plugs, I found nothing wrong with it.
The NGK had the thickest electrode. Autolight was OK too.

[geeteeohguy]

Originally Posted by Formulabruce

AC 45's are TOO hot without Lead in the fuel.
One can say "but they had these in the 70's Without Unleaded fuel" They also had EGR which technically "cools"the combustion..
AC R44 would be highest I would run. I changed out a LOT of the 45's at my dealership due to changes in fuel.
Alcohol in todays fuel makes your car work harder than it did when new, so why heat it more>?

THIS. Have run 43 or 44 plugs for the past 45 years in all my first gen GTO's. No need for the hot 45 plugs. Not optimal, either.

[S.F.]

Hello!

I use a AC45 on my 9.2 comp 455" with Swedish 95 oktan.

On my 9.7 comp 455" and Swedish 98 oktan I use AC43.

Both pluggs acted similar to the engine.

Thank You fron S.F. in Sweden.

[track73]

I have AC 43s' in my signature .030 over 455 with zero problems.

[Formulas]

When these engines were initially built and released to the public we had higher octane and lead along with i believe dirtier fuel than now, so the engineers specified a plug with a heat range that would cook off deposits

Now fuel is cleaner no lead the plug does not need to be as hot to stay clean and combine that with lower octane the original heat specs are not as appropriate and can lead to detonation pre'ignition

[unruhjonny]

sorry if this is something of a small tangent from the last reply;

I believe that "45" was the heat range all Pontiac 400's used from 1971 through to 1979;
The plug changed with the cylinder head revisions, but the heat range stayed the same;

Originally Posted by Rocky Rotella

Cliff, the #13 shows a chamber volume of 75.7 cc and a real compression ratio of 9.4:1 on a 400.

The same compression should be expected for a 1969 engine with #62 heads.

When you add in thicker head gaskets, and multiple valve relief pistons, the compression tends to dip further yet...

So all 1969-1970 400's (except for the RAIII and 1970 engines with #12 heads) made 9.4:1 compression;
I believe that for 1971 & 1972 (I don't have the source handy) the compression for 400's was 8.4:1;
I believe that the compression for 400' s in 1973 & 1974 was 8.2:1;
It's been widely published that 1975 & 1976 engines all made 7.6:1 compression;
I believe also that all 400's made after 1976 (except for the W72) also made 7.6:1 compression.

Which is all to say that PMD used with 9.4:1, 8.4:1, 8.2:1, & 7.6:1 engines one version or another of the 45 heat range for spark plugs;
R45S, R45TS, R45TSX ect, ect...

This is why so many people use a 45.

What I have been trying to point out is that the (relatively) few engines from 67-70 that exceeded 9.4:1 used a step cooler plug...

Then GM confused matters by discontinuing the 44 heat range and superseded it with the 45 heat range;
Then all of a sudden (some of you might have to dig back into your memories for this) people were saying that these older engines couldn't run unleaded pump gas... which was probably because the compression and gasoline required a cooler plug than the commonly spec'd 45.

[chiphead]

When I run the nominal numbers (.020 deck, .039 gasket, 75CC chamber, 6CC piston dish) I get 9.64 compression for a '69 400. Take deck to .010" and compression goes to 9.85.

I'd bet the actual compression ratio of the early 400s was in the 9.55 to 9.8:1 range. The 10.5:1 was blueprint best case. I have been noticing that the R45S were almost bone white with AFRs in the 14.x-13.x during cruise. Which I thought was odd that the plugs would be that clean when running a double pumper with 70/79 jets and 64 PVCR.... E10 93 octane.

Looks like I'll be moving to the XR5s. Will moving to cooler plugs allow the curve to come in a bit quicker? I'm all in by 3500 RPM. Its an older build in a hot climate and I don't want to set the tune on kill.

[blueghoast]

Originally Posted by Gach

What Autolite plugs running in SM heads

I'm sorry my SM headed mot has autolite AR3933's
My iron heads are autolite AR133 AR134S can't remember without looking
at the car

GT

[Gach]

Thanks so the autolite 3933 where ok, for me. Before I made change to NGK 9.

[1968GTO421]

Not trying to hi-jack OP's thread but do have an NGK question. I got my NGK's from Butler for my 428 with 6X-4 heads. Gave them my engine specs and they sent me some NGK plugs UR45IX (iridium). Have not installed yet due to health issues being treated now. I was checking out these plugs online and found several sites showing the UR45 plugs being equivalent to AC R43, ACR44, AC R45, and ASC R46. That's a wide span of heat ranges. Anyone have a better idea of how hot or cold these plugs are? I have used the AC 44 heat range for most of the my cars and AC 43 for running local drag race tracks. I hope these NGK's are closer to the 43-44 heat ranges instead of closer to the 45-46 heat ranges. Thanks!

[Skip Fix]

Used R44 in my RAIV motor gapped 0.45 with my DUI HEI