Spark plug ratings for high HP twink

[Evante]

Hi All,

Does anyone have any thoughts of what heat rating spark plug one would use for a 170 hp twink. I am assuming that more horsepower means more heat, and so one might have to go with a cooler spark plug than standard.

Your opinions are gladly welcomed!

JAS

[Billmack]

I would really talk with your engine builder/dyno guy about that. There are a lot of things done to your engine to get to that horsepiwer. It would be a shame to melt a piston.

[nmauduit]

I suppose this is a Weber head : have you tried NGK BP6ES or equivalent for normal road use, then possibly cooler plug for track day / race use like BP7ES or even cooler if you spend significant time above 5000 rpm ?
I would think checking the actual condition of your plugs will give you the best indication of suitable grade for your given build.

[rgh0]

Its depends on how you have got 170hp and how you intend to use the car. The range is normally NGK 6BPES to 8BPES.

High compression, race fuels and longer track day sessions and your into the BP8ES range. Lower compression, premium unleaded and hill climbs and your in the BP6ES range.

more data needed

cheers
Rohan

[Evante]

Rohan,

Here is more information. Please let me know if you would need anything else.

1720 CC engine
Stroked and bored
McCoy Stage 3 head
1.575 Intake
1.34 Exhaust
Head porting opened up at bend area
7 degree raise in Intake runners
.440 Lift Cams at 250 degree duration@ .050" intake/Exhaust
TTR Muffler
Compression 10.5
Steel rods and crank

The car will be used on the road with occasional track days.

Best,

JAS

[rgh0]

I presume youre running about 10.5 compression ratio and normal premium unleaded pump fuel


I would use BP6ES for the road and BP7ES for track days. If you dont want to change plugs then try BP7ES as they may work OK on the road without fouling depending on you're carb tune. Similarly BP6ES may not overheat on the track depending on you're tune and nature of youre track days but this can only be determined by experimentation and this experimentation has some risk of engine damage if overheating leads to pre-ignition on the track.

cheers
Rohan

[1owner69Elan]

I am running NGK BP7ES in my high output Twincam. As supplied by engine builder.

Very similar spec to your engine. 91 octane (R+M)/2 pump fuel. Occasionally I run Sunoco SS100 (100 octane (R+M)/2, street legal unleaded) through the car, but don't find any difference in performance.

My valves a little larger, SAS Weber head, but other specs almost identical.

My car is not tracked but does fine on the road with these plugs.

[Evante]

Thank you Rohan, 1owner69Elan, and others!

We have decided to go with the NGK BP7ES for now and see how things go.

Best to you all!

JAS