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RE: [turbobike] Turbo horse power vs compression ratio

Bryan (bgoodwin@iquest.net)
Thu, 28 Oct 1999 19:41:46 -0500

Well put indeed!

At 11:53 AM 10/28/99 -0500, Doug Cutler wrote:
>Well put, Watson !
>R Douglas Cutler
> -----Original Message-----
>From: 	shammar@nsk-corp.com [mailto:shammar@nsk-corp.com] 
>Sent:	Thursday, October 28, 1999 7:17 AM
>To:	rawant@webtv.net
>Cc:	turbobike@natvideo.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
>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
>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
>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
>unless your compressor is maxed out or beyond its "good" efficiency
>Reducing the compression ratio (CR) reduces the peak cylinder pressure
>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
>Pressure (BMEP) is a measure of what you really have to work with over
>entire event.  By using a reduced CR and packing more mixture into the
>(via more boost) you can increase the BMEP above what is was before you
>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
>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
>In practice, getting it right is a delicate balance between chamber
>shape/design, boost level, intake temperature, CR, squish, and ignition
>not to mention matching the proper turbo to the application.  More
>will always help fill in the bottom and make boost sooner.
>rawant@webtv.net (RAW ANT) on 10/27/99 08:42:22 PM
>To:   turbobike@natvideo.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.
FZR1000 turbo EFI
(aka The Money Pit)