Quote:
Originally Posted by MR III
So far I know the supercharger engine main casing/blok and crankshaft,.pistons etc is exactly the same as that of the Silvertop 20V.
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there are at least 4 or 5 different 4age/4agze rod types.
early bigport, late bigport, smallport, sivertop 20v, blacktop 20, early 4agze, and late 4agze ALL use different pistons......
early 3 rib vs 7 rib blocks use different cranks
blocks are cast different as well....
the 20V's #'s are a bit exaggerated, and has been proved time and again on the dyno. The blacktops do make considerable more power than the silvertops (probably around 20whp), but comparing a blacktop to a late model 4agze... the 4agze wins in torque and whp.
When talking 4 vs 5 valves per cylinder -- if you're going to start saying that one flows better over another you need to understand the technicalities of airflow into the combustion chamber -- if you don't understand them, then you shouldn't be assuming that 5 is better than 4.
when talking about 2 and 3 valves per cylinder and 4 valves per cylinder there is a different effect -- they each have different types of swirl and tumble effects as the air flows into the engine -- a large portion of the amount of air coming into the engine is this specific flow -- and the velocity of the air entering the headport.
adding a 5th valve (3rd intake) actually has been proved on flowbench tests that generally the characteristics don't change all that much, and the amount of airflow doesn't increase. Remember, that when you are increasing the number of valves, you have to decrease the size of the valve. The combustion chamber on the 20V's should have the CC size as the 16V's, and in order to fit that 3rd valve in, they have to decrease the size of the main 2 valves.
So, stating that the 20V has better flow because of an additional valve actually isn't correct. A large part of the 20V's having better flow is actually due to the VVT and/or the ITB's (and how those ITB's are set up will determing the velocity flowing into the engine).
When running forced induction, everything changes because of instead of making the engine pull air in, you are forcing air in. Physics show that fluid will flow in the path of least resistance from high to low pressure situations -- the air flow into your engine is the same way. When you are forcing air in there is a specific pushing and pulling direction -- the addition of the 5th valve really doesn't help much in terms of the air coming in.
Thinking about it, actually, I would be concerned that the 5th valve may actually cause a problem in forced induction (over a standard 16V head). This is due to the extra intake valve actually opening earlier than the other 2 -- in a forced induction setup you would be increasing the pressure in the cylinder, making the pressure differentials between behind the intake port and the combustion chamber actually closer to one another when the main 2 valves open.
I would say make a choice -- 20V or 4agze.