Thread: Deck Height
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asphaltgambler asphaltgambler is offline
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Join Date: Nov 2004
Location: Nokesville, Va.
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Some people may disagree here. I've spoken with many experienced engine builders (non-Porsche) Suprisingly some have said that there is no extra HP in the basic short block other than doing spec clearances. All extra HP is in the top end.

I dis-agree. My experience is that exta HP is everywhere in the engine. Starting from the filter all the way down to the exhaust tip. Minimum deck height is one area that is often overlooked or set at "safe standard".

If that rotating assembly is done correctly and piston/ring measurement is where it shoud be why are people setting this @.035-.070?? -That is a huge 'dead space' and wasted HP.

For some reason .035" for deck height seems to be 'the magic number'. If you look at a performance builders spec for a small block Chevy that number is the same. A Harley Evo engine deck spec .035-.045 -See a pattern here? I think the majority of builders reccomend that because most people won't or don't take the time to properly set up the basic short block. So that minimum number is a safe spec.

Recently I've seen two street builds on this forum that were excellent in every single way except (IMO) comp ratio and deck height. In both cases I feel that some HP/TQ was just given away by not really optimizing the compression and the squish area to the fullest extent per their build plan.

I'm a European tech by trade and have built many non-P-car engines. Most of my late model engine experience is with Volkswagon. The 1.8 Turbo engines they use have the pistons hanging OUT of the block!!....slightly. They typically run less than .020" deck height (with compressed head gasket)! In this engine the stroke is longer than the Porsches' flat motors. They also run @200PSI cranking cylinder pressure -which is close to 11.8-1 static compression and 8-9lbs of boost on pump gas.

So how can they do this?? The answer is in the technology of the combination. And part of that equation is the close deck height. I mean .020" or less in a mass production engine? This engine is rated @190HP. I've seen chip/intake/exhaust mods easily take this to 250. I've also seen the stock short block reliably handle up to 350 HP.

BMW also sets their deck height on the late engines as close or closer. I believe that .035" is an out-dated spec in todays engine build. There has been significant improvement in tooling, piston design to allow closer pisiton side clearance to reduce noise and improve ring sealing and thermal expansion. Why not apply the rest of that technology in your Porsche build?
'07 Jeep SRT-8 - Hauls groceries and Hauls *ss
'85 Guards Red Targa - F@#king Money Pit
'95 Road King w/117ci - No time to ride, see above
'77 Sportster Pro-Street Drag Bike w/93ci - Sold to collector
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Old 11-20-2004, 09:56 AM
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