Wow a 72 year old mechanic building impressive motors! What is in the water down under. Send some up our way.
Have fun

John,

I wish that engine was in my car! It belongs to a guy who does a lot of tarmac rallies, and has won many.

John Gregory rebuilt my engine last year, which is a 911/83 with 11.3:1 JE pistons, GE-60 cams, single-plug ignition, EBS racing springs, titanium retainers, and SSIs.


Matt Holcomb
MFIWDP
<b>PRVC</b>
<b>BOHICA</b>
1974 911 Carrera 2.7 RoW<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank"></a>
1975 Mercedes-Benz 280SE
<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank">Dedicated Homepage</a>
<a href="http://www.holscope.com/74Carrera2.7/rebuild" TARGET="_blank">Engine Rebuild Homepage</a>
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Tinton:
Yes there is an old trick to keep detonation down.
Bill Elliot of NASCAR fame came up with a trick on the pistons many years ago.
The basic idea was to cut a series of saw tooth shaped cuts into the side of the piston in the land between the first and second rings.
What this did - as the piston moves up - it forms a rolling wavefront to sweep the gas/air mixture away from the side of the cylider wall.
Detonation is caused by the exploding wavefront hitting a flat or reeflecting surface.
Elliot's affect allowed him to run about 17:1 compression and beat the heck out of all competition for a 1/2 year.
I tried the idea on a formula Ford ...works...sort of....it gave us an edge...but not sure if the mod or the driver was the real cause (we ran 11.5:1 when everyone else was limited by fuel to 9:1)
Bob

Bob,

That's interesting. When John Gregory was rebuilding my engine he used a special tool to smoothen all the sharp edges on the pistons. But I don't think this was done to keep detonation down as we had to lower the distributor advance to 28 to prevent detonation, which it did -- completely.

Do you lose power by lowering the distributor advance?


Matt Holcomb
MFIWDP
<b>PRVC</b>
<b>BOHICA</b>
1974 911 Carrera 2.7 RoW<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank"></a>
1975 Mercedes-Benz 280SE
<a href="http://www.holscope.com/74Carrera2.7" TARGET="_blank">Dedicated Homepage</a>
<a href="http://www.holscope.com/74Carrera2.7/rebuild" TARGET="_blank">Engine Rebuild Homepage</a>
<a href="http://www.cheaterswayside.com/911/gallery.asp?sort=0&userid=127" TARGET="_blank">Porsche Owners Gallery Profile</a>
<a href="http://www.pelicanparts.com/cgi-bin/pmpre/pm.cgi?action=display&login=Matt_Holcomb" TARGET="_blank">Pelican Gallery Profile</a>

he used a special tool to smoothen all the sharp edges on the pistons.

Its important to chamfer all the sharp edges on the piston crown prior to assembling the engine. The sharp edges can become hotspots and contribute to detonation. A few minutes on each piston with a piece of emory or crocus cloth will eliminate the sharp edges.

"Do you lose power with less advance"

Yes, unless the lesser advance is because of twin plug (at least that is what I understand).

Cam

Bob, That's really interesting. Where can I read more?

Bobby