Thanks for the reply I made a mistake with my figures my factory comp height is 1.760 not 1.625. You say a flush deck height piston with a dish, that's a mighty big dish. The engine I'm using for rebuild is a RG 225 block and the piston are below deck .187 give or take a few thou. I intend to use a 7.005 C/Rod K1 or similar which is .306 longer centre to centre than the stock C/Rod of 6.699. Who makes these pistons to give a compression ratio of 8.5 to 1?

Ive actually been looking into this myself, nothing is available off the shelf, you have to get a custom piston made.

The route I took may not be the best but its working for me thus far. I'm using the off the shelf k1/weisco forged piston and rod combo with a very thick copper head gasket to bring down the compression to 8.6:1.


Kev

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It's an option, how thick it's not ideal from my experience with a stock 225 with the piston being down the hole 187in the engine is more likely to detonate. I've had limited success running up to 10psi boost, timings 18 deg initial another 8-10deg centrifical then knocking 10deg timing out using a dual vacuum advance & retard modual with the vacuum advance locked out.Its very torquey comes on boost 1800 2000 rpm will run up to 8lbs boost easterly on the primaries will run up to 10-12lbs boost on the secondaries any more and it pings even with 18-20 all up timing. I'm using a Holley 390 with mechanical secondaries on an Offy manifold turned side saddle with the primaries furtherest from the engine, off boost it drives very nice with 54 jets & a 10.5 power valve, it gets a bit hot on a longer drive most likely because no vacuum advance. What are you using timing carb etc etc

225s do not like much timing, especially on boost. I would stay below 20 total advance up to 6 psi and below 18 above that.

Lou

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