LittleCharger wrote:
The decompression feature of the 90"s block will give a false compression reading, no different then some of the v6 mercury motors on simple cranking so get your head cut by someone with some knowledge not just some local machine shop.
As noted above it does give a false (low) compression reading, the decompression feature is exactly what it is, it allows a small about of compression to escape into the exhaust port on start up allowing for easier cranking this is a feature on some of the omc two cylinder blocks as well as some of the mercury motors (small and large), in theory as the engine turns higher rpm's the feature does not come into play. On the top end performance it should not make any difference, bottom end yes but we are not doing Lemans starts (unless you hook! lol), it is hard to say where the impact of the feature drops off. All I know is the 92 block does not have the bottom end like the 86 block (seat of the pants testing here folks), my 92 block is not fresh and has the original pistons in it, so I'm not really comparing apples here, we only swapped out the crank as it was only going to be a back up block but who's a thunk I'd actually put more hrs on it then the 86 block.
I'm just an accountant so take my words with a grain of salt, anything I've accumulated has been from talking and asking alot of questions from people that are alot smarter then I at this game. There are alot of guys that are more then willing to help out if you simply ask and listen. There is tons of knowledge out there, one simply has to listen and be open minded, there are many ways to do things and challenging on the theory is great but do it in a constructive way and you will learn a hell of alot more then just trashing someone's thinking.