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914World.com _ 914World Garage _ Spark plugs and compression ratio

Posted by: Joe Ricard Mar 17 2008, 03:21 PM

Old motor I was running 7.8:1 compression and 87 octane. NGK 7bpes plug. ran pretty good

new motor 10.1:1 compression 93 octane same plug getting fouling in a gradual progression right on up to horrible preformance.

I am picking up some NGK 6bpes plugs tonight. I seen a 5 bpes available too. How do I calculate what or which is best?

Tried leaning out the carbs but it had little effect now that the plugs are fouled.

Oh and rings are now seated which during break in the plugs got a beating.

Hell of a way to fix my traction problem. just reduce my horsepower.

Posted by: J P Stein Mar 17 2008, 05:44 PM

Get a check on your AF ratio. Your compression raise is considerable and your jetting may well have to change. I jacked mine up bout half a point and now it looks richer.
I dunno dick bout T-4s, but BP6s seem hot for 10:1 compression. You do have a multi spark, big plug gap ignition in there, right?

Posted by: Joe Ricard Mar 18 2008, 05:13 AM

Yep, throwing some pretty big lighting bolts at the plug. Complete Mallory ignition.

from what the guys on the Club were saying I need to get a couple sets of plugs and change them regular. High compression and 7000 RPM is a bit more than the average plug will withstand these days. Compounded by the new motor that is breaking in.

Funny you are the only one replying to this here.

Posted by: J P Stein Mar 18 2008, 03:08 PM

Does that mean everyone else here is afraid of rednecks or just don't wanna have to deal with one?