Board index Flathead Power-Technical Questions, Answers, and Suggestions Big Twin Flatties BTSV spark plug "chamber"

BTSV spark plug "chamber"

Moderators: Curt!, Pa

Post Sat Dec 23, 2006 5:32 am

Posts: 33
Location: Borne, The Netherlands
All BTSV cylinder heads have a "chamber" in which the sparkplug is placed.
Does anybody know why the sparkplug is put in such a "chamber"?

If I'm correct, the WLDR and KR heads do not have such a chamber.

I am wondering if I could close the chamber and drill/tap a new sparkplug hole that does not have "the chamber" and is positioned 90 degrees and not angled as it is now. I believe this would have a positive effect on the combustion process.

My goal is to raise the compression ratio and to improve the combustion efficiency for my 91" stroker ULH.
Relieving and flowing is already finished and I have custom 0.56" and .508" cams.

All info is highly appreciated!


Post Tue Jan 16, 2007 12:03 pm

Posts: 530
Location: Ogden, Utah, USA
SuperSidevalve: Panic had some thoughts on the "chamber" around the spark plugs. If I got it right it had to do with the odd shape of the combustion chamber at top dead center and flame propogation. The Flat head has a very wierd shape at that point and some issues with the way the mixture burns. Not to mention the rich mix we have in most of our bikes just so they will run reliably. Look at the carbon on any motor that has been in service and you get an idea. I think the chamber helped keep the plug from fouling and also held some heat at the plug. The plug is over the intake and this is gonna cool it pretty fast. If I got this wrong, blame me not Panic. He has some very good ideas about this sort of stuff and I get mixed up rather easy. Send him a PM and he might have some information for you. :)
Steve H

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