I agree with Rich, 100%. Indexing is important in 2 litre and modified Alfa engine but not for any other reason. The position of the spark in the cylinder, the amount of projection, does have an influence on performance, according to our dyno runs and times on circuits so a projected nose plug obviously has advantages although there are clearance issues. If someone is going to go this route, it has to be thought out carefully and clearances measured.
I have a set of GTA race pistons (lying around somewhere) with 2 small indentations designed into the dome of each to give the necessary clearance between piston and spark plug. From memory, they are Alfa (Autodelta) designed 2 ring, HC versions. Ciao tutti. Les (Apologies for the extended signature in my last post automatically attached by my Windows Smartphone) Date: Mon, 12 Jul 2010 13:27:55 -0600 From: "Richard C. Wagner" <[email protected]> Subject: [alfa] Re: Spark plug indexing washers, how thick? Steven wrote: > One of the things I've heard mentioned, is that indexing allows you to > orient the electrode/gap so as to allow the best combustion. With all of my experience developing engine simulations and looking into research on combustion within piston engine cylinders, I'd be very surprised if plug gap orientation had any affect on performance whatsoever. Flame propagation in the cylinder is accomplished largely by fine grained turbulence that is generated as the piston rises on the compression stroke. And the presence of the ground electrode poses little resistance to that effect. If the spark plug will interfere with valve operation, indexing to avoid an impact is essential. Otherwise, I wouldn't spend too much time or effort worrying about it. Rich Wagner Montrose, CO, USA '82 GTV6 -- to be removed from alfa, see http://www.digest.net/bin/digest-subs.cgi or email "unsubscribe alfa" to [email protected]
