Engine and Transmission Tech

May be some gurus can help me.

Stock RV8 has an quench distance of 0.065" (0.040" piston deck height clearance + 0.025" head gasket thickness).
RV8 has been designed to run whith dished piston and wedge semi-hemispherical head combustion chamber.

In theory if I use flat top piston I increase quench arera which itself increase pression rise which itself modifies burning rate.

But if the rate of pression rise is too high it will be done with the detriment of power.

So any recommandation with flat top piston ? Which is the maximum piston deck height clearance ?

I just bought this forged pistons : [cgi.ebay.com]

I intend to use them with my 3.1496" stroke crank and 5.850" rods.

So with this combo I have at this time a piston deck height clearance of 0.047".

With 37cc heads I give me a CR of around 12:1.

Thanks.



Edited 1 time(s). Last edit at 11/14/2010 05:00AM by Wotland.

Wotland, not enough info. What compression are you after ? The "add" says 1.488" And 1.15" for compression height , which ? If actually 1.488", that leaves piston .047", down from deck,(standard 8.960"). How are you going to "seal" 12/1 compression ? Application ? Fuel ? You will need a very "short" cam to run with-out valve reliefs ! IMO, 065" on quench is realitively ineffective. .020" would be absolute minimum,(NOT aluminum rods).Any mod's to piston tops should be for valve clearance and to aid turbulence. Any mod's to the chambers,(more cc's),should first be to unshroud the valves,a big problem with these heads, as valves are not centered in the bores. Your "effective" compression, will vary considerably, with cam, head flow ,induction and lay-out of exhaust. Good Luck, roverman.



Edited 1 time(s). Last edit at 11/14/2010 04:19PM by roverman.

How much do you actually increase the squish area ? Dished pistons have a rim of about 5-6 mm wide at the edge of the piston and chamber size is quite big. So actually, the increase in AREA is not that big. As for the quench distance, I would aim for zero deck height (if possible) and set the quench distance with head gasket. Opinions differ but I believe figures around 1 mm or 0,040" are most common. You would get that with composite head gasket and zero deck height.

Like Art already mentioned, you need to pocket the valves and with zero deck you most likely need a shallow dish for reasonable CR.

Just my 2 cents (sorry no guru...)