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Well put, Watson ! R Douglas Cutler -----Original Message----- From: firstname.lastname@example.org [mailto:email@example.com] Sent: Thursday, October 28, 1999 7:17 AM To: firstname.lastname@example.org Cc: email@example.com Subject: Re: [turbobike] Turbo horse power vs compression ratio << File: att1.html >> That's an interesting and often observed phenomenon. The real question is, is it an illusion? Often one's perception is so blinded by the big hit the turbo affords up top, that one believes the low end power has been sacrificed. We usually find that the power curve never drops below stock unless something is wrong. Maybe there is more tweaking in the carburetion that needs to be done. Do you have dyno curves before and after? Have you ridden a stock one again for comparison? This situation is a lot like when you put nitrous on something. After getting used to the big hit, it kind of feels like something's wrong with the bike when you twist it without nitrous. Then you realize it was that slow all along. You can generally make more peak power with less compression and more boost unless your compressor is maxed out or beyond its "good" efficiency range. Reducing the compression ratio (CR) reduces the peak cylinder pressure (PCP), helping to reduce preignition/detonation and reducing the maximum stress on all of the components. One might believe that this would reduce power, and this is theoretically correct, assuming all other things are equal. But PCP occurs at only one slice in time over the power stroke event. The Brake Mean Effective Pressure (BMEP) is a measure of what you really have to work with over the entire event. By using a reduced CR and packing more mixture into the cylinder (via more boost) you can increase the BMEP above what is was before you reduced the CR, and end up with a similar PCP. This way the maximum stress stays the same but you make more peak power. Of course, this is where you do lose low end (off boost) power since there is no additional charge when you're off boost. For true street use, less boost and more CR is usually better and results in a more linear power curve (if there is such a thing on a turbocharged engine). In practice, getting it right is a delicate balance between chamber shape/design, boost level, intake temperature, CR, squish, and ignition timing, not to mention matching the proper turbo to the application. More displacement will always help fill in the bottom and make boost sooner. Later, Bob firstname.lastname@example.org (RAW ANT) on 10/27/99 08:42:22 PM To: email@example.com cc: (bcc: Bob Shammas/EQA/Nsk-Corp) Fax to: Subject: [turbobike] Turbo horse power vs compression ratio This question is for anyone that can help. Well my turbo system is complete. I notice that I have a lot less low end power. Could this be do to the turbos back pressure. The second question is, if I lower my compression and run more boost will this actually afford me more horse power or is it just easier on the motor. THANX everyone.