High compression spark plug question...

[nickpohlaandp]

He just text me that he went and bought some Autolite 26's. I think... from what I can find on Google, that those will be too high of a heat range. Can anyone back up that thought?

[statsystems]

He just text me that he went and bought some Autolite 26's. I think... from what I can find on Google, that those will be too high of a heat range. Can anyone back up that thought?

I can't find my book so I used and online book and it comes out WAY too hot. The plug he is talking about is a 10:1 pump gas plug.

[nickpohlaandp]

He just text me that he went and bought some Autolite 26's. I think... from what I can find on Google, that those will be too high of a heat range. Can anyone back up that thought?

I can't find my book so I used and online book and it comes out WAY too hot. The plug he is talking about is a 10:1 pump gas plug.

That's what I was seeing too. I told him not to use them. Hopefully he'll listen.

[RCJ]

You really need to state the plug gasket or taper and reach length to get a good recommendation. You could be comparing different size plugs ,causing the confusion of heat ranges.

[nickpohlaandp]

You really need to state the plug gasket or taper and reach length to get a good recommendation. You could be comparing different size plugs ,causing the confusion of heat ranges.

.460 reach, tapered seat

[In-Tech]

Here's my "rule of thumb". Compression ratio has nothing to do with anything. It's all about HP per cylinder/plug. I only use NGK so my ranges are for that.

Your plug, .460" reach, tapered seat, non extended tip. R5673-x

-6 up to 75hp per cylinder
-7 up to 85hp per cylinder
-8 up to 100hp per cylinder
-9 up to 125hp per cylinder
-10 up to 185hp per cylinder

There are other things that matter, fuel type, endurance/extended EGT etc etc. These are good starting points.

Rockauto.com has these racing plugs for $1.36 each.

[Zmechanic]

I am more curious as to whether or not his buddy's claim of using a hotter plug due to it being a high CR engine has any merit. My first instinct would be the exact opposite. Seems a hotter plug would lead to the greater possibility of detonation.

Your buddy is exactly opposite! That guy is a hole in a piston waiting to happen. Start cold, work hotter. Too cold = fouled plugs. Too hot = detonation. Which would you rather have?

Heat range is all about keeping the plug porcelain at the right temp to cook off deposits, not affecting how well the plug can ignite the mixture (unless it fouls so bad the spark suffers, of course). That Depends on cylinder heat, which depends on load conditions, power output, compression, fuel, timing, etc. If you need a hotter spark, then you need different ignition components, not hotter plugs.

Even if you don't become an expert at reading plugs for mixture, at least learn what the early signs of detonation look like, which is much easier.

[nickpohlaandp]

Here's my "rule of thumb". Compression ratio has nothing to do with anything. It's all about HP per cylinder/plug. I only use NGK so my ranges are for that.

Your plug, .460" reach, tapered seat, non extended tip. R5673-x

-6 up to 75hp per cylinder
-7 up to 85hp per cylinder
-8 up to 100hp per cylinder
-9 up to 125hp per cylinder
-10 up to 185hp per cylinder

There are other things that matter, fuel type, endurance/extended EGT etc etc. These are good starting points.

Rockauto.com has these racing plugs for $1.36 each.

Good info! Thanks

[GARY C]

I just found something interesting while Googling for heat range comparisons between manufacturers in regard to Autolite plugs.

"The last digit in an Autolite part number represents the Heat Range within a plug family.

For example, take the 254x plug series. Autolite has 2544, 2545 and 2546 available. 2544 is the coldest plug in that plug family, and 2546 is the hottest.

However, according to an Autolite reference chart, Autolite 86 has the same heat range as 2244 and Autolite 303 is a hotter plug than 2974.

Therefore, it is impossible to chart an Autolite Heat Range hierarchy, let alone a standardized comparison to other spark plug brands."

Seems like you could easily get screwed up trying to change over from one brand to Autolite, or vice versa.

Yeah the chart will get you in the area you need to be, I never saw a big issue with plugs except fouling cold ones. The head manufacture usually has a base line plug recomendation, Her is a chart that may give you an idea.
Plugs I have run for racing NGK -8 and (-9 nitrous), Autolite 133 and AC Delco , 44...(43 and 42 nitrous)

[statsystems]

I just found something interesting while Googling for heat range comparisons between manufacturers in regard to Autolite plugs.

"The last digit in an Autolite part number represents the Heat Range within a plug family.

For example, take the 254x plug series. Autolite has 2544, 2545 and 2546 available. 2544 is the coldest plug in that plug kfamily, and 2546 is the hottest.

However, according to an Autolite reference chart, Autolite 86 has the same heat range as 2244 and Autolite 303 is a hotter plug than 2974.

Therefore, it is impossible to chart an Autolite Heat Range hierarchy, let alone a standardized comparison to other spark plug brands."

Seems like you could easily get screwed up trying to change over from one brand to Autolite, or vice versa.

Yeah the chart will get you in the area you need to be, I never saw a big issue with plugs except fouling cold ones. The head manufacture usually has a base line plug recomendation, Her is a chart that may give you an idea.
Plugs I have run for racing NGK -8 and (-9 nitrous), Autolite 133 and AC Delco , 44...(43 and 42 nitrous)

There is a big mistake on that chart. It's so simple that it should not happen. Makes me question what else is wrong.

[GARY C]

Maybe you could tell us what needs correcting instead of just making a statement!

[statsystems]

Maybe you could tell us what needs correcting instead of just making a statement!

There is no such thing as a Champion plug with a 3/4 reach, 5/8 hex and an N designation.

If they missed that, what else did they miss? It's too simple to be a typo.

[GARY C]

I don't know? I wouldn't use a NGK chart to confirm a Champion plug, I would refer to their chart to get an understanding and then I would contact tech as well as racers using them.. Thats why I only commented on the ones I and others around me have run...The Champions I ran were the V59c.

Do you know if they are wrong on the heat range of that plug?