Stock gasket thickness is 0.030. All of the NSX techs I have ever spoken to have advised not to mess with the stock quench and deck height on the NSX engine. If you do change the deck height, you need to use these because the centerline of the cams will change relative to the crank and your timing will be off otherwise.
The NSX PGM-FI system has a knock sensor and adjusts total timing on the fly in real time. Factory timing is set at 15 deg (+/- 2 deg) BTDC at 800 rpm on a manual transmission NSX. Total timing is set at the factory and the adjuster screw is covered by a rivited block, meaning Honda does not want you touching the timing adjuster. There is a procedure to do so involving drilling out the rivets to remove the block and expose the adjustment screw, but only to get the timing back to OEM spec.
I am sure some people have had NSX heads on a flow bench, but no one has ever disclosed the numbers. Here is the bottom line: the stock heads flow extremely well from the factory. 3.0 and 3.2 engines with even modified cams show little gain with head work. You should PM member greenberet- he has a lot of info and insight on the breathing capability of the stock engine. The stock airbox provides far more CFM than the 3.0 or 3.2 need to run at max efficiency. In fact, the SPEED World Challenge NSX used the stock airbox with a supercharger.
The bottleneck in the intake is the bellows and throttle body, but at 3.0 liters there is no restriction and only a slight one (worth maybe 5 hp) at 3.2 liters. It's only when you add FI or increase displacement that you really start to see a problem. On stock engines, things like bored throttle bodies and extrude honed intakes add only small amounts of power. Honda designed this engine to flow well. The real "flow" bottleneck on a 3.0 is the exhaust. The manifolds are cast iron and restrictive and the exhaust is too. Headers and exhaust make a big difference on the 3.0 (20 whp or more). The 3.2 comes with OEM tube headers, so the gain is not as great.
Honda took everything they knew from Formula 1 and poured it into the NSX engine. The flow was designed and tested using Honda's F1 facilities. It has long been accepted that finding NA power on the NSX is very difficult and expensive. It's a big reason why Comptech ditched their NA engine program and started selling the supercharger. Bang for the buck. That's not to say NA power is impossible. The C32B used in the JGTC NSX race car is basically a stroked (3.5) verson of the stock NA2 engine with hot cams, ITB and Motec engine management. It makes 500+ hp. Closer to Earth, Vance's NA2 dynoed over 300 whp with just headers and exhaust. I personally think a NA NSX is the way to go and if you have the money, go for it!
