Spark plug question

[84cutspreme]

I'm not sure if this is the right section to ask this, but I am trying to figure out what heat range spark plug I should be using. I am currently using accel shortie plugs with lower heat range. How can I tell if they are right or if I need higher heat range. chevy 355cid, 9.85:1 CR, Dart SHP180 Aluminum Heads, 1,500-5,500 RPM Range, Stock Style MSD HEI distributor(streetfire, no comp). If any more info is needed just let me know.

 

[Fox80]

You have to watch a colder plug in a motor with aluminum heads, the heads dissipate heat so well the actually don't transfer enough to the plug, your motor will "foul" a plug that is way to cold, it can run rough, or act loaded up after start up if the plugs are a little to cold, a plug that is to hot could pre-ignite if way to hot or even burn the electrode off in extreme cases, a lot of things factor in, fuel mixture, timing, thermostat temp, your best bet is to talk to the head manufacture and give them your specs, they will be able to tell you spot on probably what plug to run, otherwise it's a trial and error process. I would always error on the side if a hotter plug, so the car isn't a pain in colder weather

 

[pontiacgp]

The more power you have the hotter the combustion chamber and cooler plugs are required. I know guys with drag cars they drive on the street and use a cooler plug when they go racing and a warmer plug to cruise the streets. The only way to find out what plug you need is to try a few out and see what the plugs look like, if they are really wrong you'll find out quick but there will be some close and you find out which is best with track times or a dyno

 

[565bbchevy]

I run NGK plugs in my 565 BBC with a heat range of 6 which is a pretty warm plug but it works great for street driving and stays running consistent, I have a few sets of colder heat range plugs gapped and indexed for when I hit the nitrous which would be 7,8 and 9's ( the higher NGK number the colder they are).
I have driven on the street with colder plugs and they run fine for a while but eventually with extended idling etc. they would carbon up and need to be cleaned.

 

[84cutspreme]

I currently have 0414s plugs in mine. They are the colder set and the only other set available is the 0416s. I don't notice any drive ability issues but I find that my motor runs the same or hotter now with aluminum heads that it did with old 882 chevy's. The engine compartment seems hotter too. I don't know if the two are related

 

[Fox80]

I run NGK plugs in my 565 BBC with a heat range of 6 which is a pretty warm plug but it works great for street driving and stays running consistent, I have a few sets of colder heat range plugs gapped and indexed for when I hit the nitrous which would be 7,8 and 9's ( the higher NGK number the colder they are).
I have driven on the street with colder plugs and they run fine for a while but eventually with extended idling etc. they would carbon up and need to be cleaned.

Very well put, like I said I have always leaned towards the hotter plug, the overall daily drivability if the car will suffer on the colder range type plugs

 

[khan0165]

sparkplug reading is a great knowledge asset for tuning

here's a few things you need to know.

- things to read are the;
1. Base-circle of the plug: sutt or lots of black on the base circle means rich idle. This is not necessarily a bad thing, often big cam or aggressive engines require a slightly rich mixture to make up more performance higher in the rpms. Rich idle can be cured by adjusting your metering screws.

2. Porcelain center: the porcelain is a good indicator of heat and fuel mixture as well. You want to see a slightly brown/off-white color, no gunk. White color shows a lean fuel mixture, black or gunky shows rich or oil burning. If you see a white color, with small black dots, this is a dangerous scenario with too much heat, you are about to melt parts.

3. Ground strap: the strap is a key indicator in sparkplug reading. The strap indicates the heat "shedding" ability of the spark plug. On a clean burning mixture, look closely and you will see a color change halfway down the strap, ideally at the the bend before the base-circle. If the color is too far at the top of the strap, the combustion is too cold, try increasing timing. If the color is too far at the bottom near the base circle, the combustion is too hot, try retarding timing. You want the color change right at the bend, this indicates a perfect plug temperature range and timing mixture.

Basically, with the above information...
after you've played with your carb mixtures and timing, and your plug's base circle and porcelain show nice clean colors, but you are still seeing too much heat on the strap; it is time to move to a cooler heat range. Try one range at a time, make hard runs, adjust timing if necessary, and see if it's sufficient.


I have factory aluminum heads on my small block, running 10.7:1 compression. I was using factory spec NGK plugs (I believe V-Power part# FR4). After playing with carb mixtures and timing, I found I could not run the ideal timing without too much heat and knocking. I then moved to the next heat range (part# FR5) and tried those. I found my ideal mixture and performance with two heat ranges cooler (part# FR6); this combo showed the best performance at the track without excessive heat.

... that being said, with quick heat-shedding aluminum heads, I find better street performance from the regular #FR4 plug with the higher heat range.

 

[thrasher]

What khan0165 posted is a good information and it makes reading a NGK plug pretty easy.
Though Autolite is also good plug I find them a little harder to read because of the dark ground strap and base coloring.

 

[woody31]

i run autolite #25 in my 362 small block chevy,,,9.5 to 1 comp 280 roller and iron heads,,,

 

[GT_80]

I have never had good luck with Accel header plugs- used them in 3 different small blcok chevy's including the motor I built in my cutlass now, which is about 9.7:1 compression, 305 HO iron heads with mild port and polish. I run delco R44T (I think) plugs that are shorter than stock ones, and a mid heat range. They work awesome. Never had better luck with my 305 heads.