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You're not that far off, really. I ended up with a bit more compression than I wanted on my FJ, and found that when fully heat soaked on long summer rides, 6-7 psi was all it would tolerate on 93 octane. By adding a super cheap and simple single stage water injection unit I was able to run 10-11 psi. Then there's always good gas when you want to run more boost. Still, this only goes so far. The one advantage to actually doing a top-end specifically for turbocharging is that you have a few options you wouldn't otherwise have. For one, normally aspirated engines like a very tight squish band to improve mixture turbulence. The smaller the piston-to-head clearance at operating temperature the better. This is required because combustion pressure is low and flame front travel speed is low as well. In a turbocharged or nitrous application this is not the case. Since flame speed is proportional to combustion pressure, and the pressure, specifically the BMEP (Brake Mean Effective Pressure) is greater over the entire cycle in these cases, the added turbulence of the tight squish is not needed and is even detrimental to smooth combustion. Similarly the added peak combustion pressure of a high compression ratio is not needed either. The effects of these parameters becomes more significant as specific power levels rise. The point to all of this is that when you build the top end specifically for you turbo application, you can both reduce the overall compression ratio and open up the squish band by using a very thick base gasket. For extremely high performance applications you might even run the piston squish band 0.080" below the cylinder deck height at TDC. It's something to consider anyway. Doing a motor like that wouldn't necessarily mean you'd have to buy new pistons, although I would recommend good, hard chrome wrist pins with a heavy wall. I wouldn't think you'd want to change the rods, either, if it's just going to be street ridden at less than 15 psi. Wrist pin problems are often misdiagnosed as rod problems since wimpy pins seize in the small end and then throw the rod as a result. Regards, Bob "Bob Buehler" <ribicf@hotbot.com> on 10/01/99 12:04:30 AM To: "Turbo Bike Mailing List" <turbobike@natvideo.com> cc: (bcc: Bob Shammas/EQA/Nsk-Corp) Fax to: Subject: [turbobike] Water injection Hi Gang: I need some advice on water injection. I was told or read somewhere that water injection was relitively simple and inexpensive and would alow for the use compression ratios of 9 or 10 to 1 as is found with stock pistons. I believe it also was supposed to inhibit detonation using stock compression ratios even at boost pressures as high as 12 or 14 psi. This all sounds to good to be true. It it is true, it sounds like I could substitute low compression pistons and high dollar rods for a water injection system. This would also save a lot of motor disassembly work. Maybe I'm dreaming but could I go from low boost (5 to 8 psi) on a stock motor to 12 to 14 psi by just adding a water injection system. Any input is always greatly appreciated. Bob Buehler Twin Turbo CBX or Bust HotBot - Search smarter. http://www.hotbot.com