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Reply to "Eye Candy"

So I guess the one thing to add here is this: the larger the bore, the greater the effect of the second plug in the combustion chamber. The problem with doing this on a Type-1 is that even a 94mm bore is not really big enough to maximize the effect. I would assume it’s the same with Willhoit’s 2.2L.

Jake is able to run another point of compression with his big twin-plugged Type-4s, but they almost all have at least 100 mm bores. With a 4 inch bore, there’s a long way for a flame front to travel, and a lot of hot surface area to precipitate preignition.

I’m running 10.6: 1 compression with an FK8 on pump gas. I got the best twin-plug heads (Revmaster 049s) I could find, after someone on theSamba who claimed to know what he was doing ruined a set of $1000 CB superpros. The heads have really clean castings, good cooling fins, and are beautiful to look at— but are pretty old-school in the shape of the combustion chambers, and the size of the porting (for the flow-numbers I’ve got). Even with thermal coatings in the combustion chambers, 911 squirters on the underside of the piston crowns, and a DTM cooling system, I think I’m about 1/2 high of optimal on compression.

In typical fashion, Dave has again blown me away with his ability to innovate with parts on hand. What I have for a distributor is a locked out and modified 009, and the single pick-up was due to the limitations of that distributor.

Danny is 100% correct, crank-fire is better by any measurable metric. If I were doing this again, and I wanted the look of the distributor— I would use a crank positioning sensor, probably one of Mario Velotta‘s cam-sync sensors, megasquirt or magajolt, and just use the distributor to send spark to the right wire. The slop in the distributor is just fine if you aren’t trying to use it to control the spark.

And yes, “Oscar”, Rich’s 2.6L Raby monster was twin-plugged. What an awesome engine.

Last edited by Stan Galat
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