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hemi pistons? why it isnt a hemi engine... why would you want a hemi engine? tscc is what suzuki consideres the z400 to be equipped with, a twin swirl combustion chamber.. not hemispherical.
 

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as i know it, 'hemi' does refer to the head design. most modern overhead cam 4-stroke engines are basically 'hemi' design, especially those with 4+ valves per cylinder. the term 'hemi' came from the hemisperical shaped combustion chamber reqion found on chrysler 'hemi' engines...
the performance advantages of the hemi head were soon realized, and domed pistions that come out of the engine to fill this combustion chamber were used to increase compression for race use in these engines. now most race engines use a hemi design becase it helps focus the force of the combustion into the piston... producing more hp

i belive what preston is looking for is simply a domed high compression piston. i'm curious about it myself...
who makes a good domed high compression piston for the Z400?(....without having to put in a big bore kit) what is it's compression ratio in a stock motor?
 

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The cylinder base gasket on the Z is rather thick and a thinner gasket can be sued to increase compression for little $$$!
 

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Pistons are easy to get. Wiseco, J&E, Ross, Venolia... You don't necessarily need a 'domed' piston to get higher compression. If the stock piston has a recess in it, merely eliminating that will normally give you a nice increase in compression. Regarding, the base gasket -- it appears to be slightly thicker than the DRZ "E" gasket, so changing to one of those will help. But, I don't think that will get you to the E's 12.2:1 ratio (Z400 ratio is 11.3:1). Another option is to machine the bottom of the cylinder barrel. According to some calculations I did a while back, lowering the barrel in the block .025" (by using a thinner base gasket and/or machining the barrel) will raise the compression ratio to 12.5:1. However, when you make those changes, there is a danger of the piston hitting the cylinder head, so piston-to-deck height -- the distance from the top of the piston to the top of the barrel -- must be respected in your modifications.

I'll check with a DRZ racer I know and find out what the deck height is.
 

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Regarding the deck height, my acquiantance didn't know specifically, but they have run no gasket (silicone sealer instead) and had no problems until they competed on one-mile ovals (he's a flat-tracker). He said there was some evidence of piston-to-head contact when they tore the engine down after a race. He surmises that @ the continued max rpms they run at, they experienced some rod stretch. He thought there would be no problem for "normal" competition.

I bought a DRZ "E" gasket and it measures .015" (about half the thickness of ours). According to my calculations, no gasket should put you near 13:1. That's probably too high for pump gas, BTW.
 

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sounds like the 'E' base gasket is the way to get a few more ponies than stock without a ton of cash invested.... and no relibility loss at all. (i thought this was true for a while, but it was unconfirmed.)
doing this it will likely respond even better to a mild to medium performance cam, even without porting work done to the head.
 

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STAY WITH A FLAT TOP HI-COMP. PISTON.
BETTER, MORE EVAN BURN. FOR THOSE WHO KNOW CARS,
THINK QUENCH AREA
 

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on drz head gaskets

QUOTE
Regarding the deck height, my acquiantance didn't know specifically, but they have run no gasket (silicone sealer instead) and had no problems until they competed on one-mile ovals (he's a flat-tracker).  He said there was some evidence of piston-to-head contact when they tore the engine down after a race. He surmises that @ the continued max rpms they run at, they experienced some rod stretch.  He thought there would be no problem for "normal" competition.

I bought a DRZ "E" gasket and it measures .015" (about half the thickness of ours). According to my calculations, no gasket should put you near 13:1.  That's probably too high for pump gas, BTW.[/b]
hers yout onfo on the head gasket
 
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