Compression boost for 550SX Standup?
Anthony Melucci
I'm running 106 psi with stock bore, several hours after a hone and new rings. Double checked my gauge against another and seems to be on track. Some members on the list thought my compression was way too low, since they were running 140 psi stock and 170 with aftermarket equip. I'm considering getting a performance head to get a little more pep. What types of compression are people safely running with this engine?
Clymer also says the 650SX range is: 125-192 psi
I don't think that upper limit is stock. I had an '89 650SX with
Mariner head at about 165 psi and was eating plug electrodes with predetonation.
Had to use higher octane fuel. Isn't 165 psi and above where it's
recommended to run 92 octane?
Well, back to the 550SX. So if the upper compression limit for the 650 isn't stock, then if Clymer is consistent (unlikely) the 550SX upper limit of 112 isn't stock either, but it's real close to what I'm getting, so maybe it is stock. Is there some shortcoming in the crank that can't support much more power on the 550? At what point does the stress exceedith the strength? I'm sure some of you have an idea of a safe limit for sport receational use on this boat. Only other mods are a Solas 15 degree and an R&D aquavein toploader grate.
Thanks,
Jono
m-cooper
pressure and ran fine on pump gas. My ported PJS cylinder on stock 650
bottom end has 150 psi cranking and detonates plugs out of the head on pump
gas. I say this to show the effect that porting has on cranking pressure.
You need to calculate the true compression ratio and squish for fuel
requirements. It
may be that the different port styles of the 550 vs 650 cause the cranking
pressure to vary so much from one motor style to the other.
Mike
Anthony Melucci wrote in message <381F9129...@ipass.net>...
MR-HPT
I'm great fool for man with brains.
Regards George HPT Sport USA
http://www.hpt-sport.com
duckm...@my-deja.com
Anthony Melucci <AVMe...@ipass.net> wrote:
>
> --------------F2E82FF05AFF1E864C4CE72F
> Content-Type: text/plain; charset=us-ascii
> Content-Transfer-Encoding: 7bit
> Content-Type: text/html; charset=us-ascii
> Content-Transfer-Encoding: 7bit
>
> <HTML>
> The sometimes erroneous Intertec Clymer Kawasaki Shop Jet Ski manual
(1976-1991)
> lists the 1985-1991 550cc engine compression like so: 78-112 psi.
>
> new rings. Double checked my gauge against another and seems to
be
> on track. Some members on the list thought my compression was
way
> too low, since they were running 140 psi stock and 170 with
aftermarket
little
> more pep. <B>What types of compression are people safely running
> with this engine?</B>
>
> <P>Clymer also says the 650SX range is: 125-192 psi
> <BR>I don't think that upper limit is stock. I had an '89 650SX
with
> Mariner head at about 165 psi and was eating plug electrodes with
> Had to use higher octane fuel. <B>Isn't 165 psi and above where
it's
> recommended to run 92 octane?</B>
>
> <P>Well, back to the 550SX. So if the upper compression limit
for
> the 650 isn't stock, then if Clymer is consistent (unlikely) the 550SX
> upper limit of 112 isn't stock either, but it's real close to what I'm
shortcoming
> in the crank that can't support much more power on the 550? At
what
> point does the stress exceedith the strength? </B>I'm sure some
of
> you have an idea of a safe limit for sport receational use on this
> Only other mods are a Solas 15 degree and an R&D aquavein
> toploader
> grate.
>
> <P>Thanks,
> <BR>Jono</HTML>
>
> --------------F2E82FF05AFF1E864C4CE72F--
> If you are only getting a 106 reading, you need to bore your
cylinders before bumping your compression up. You should be in at least
the 140 range. You can safely take it up to 170 with no problems,
however I strongly suggest spending the extra few cents a gallon, and
run 92 octane. When you get your cylinders bored, you might as well
send you head off to get it milled at the same time. By the way, I had
two 650's, fresh motors, one had 175psi, the other 145psi. It is due to
the port height on the cylinders! Oh yea, you need to use a snop-on
gauge for an accurate reading. Good luck, Steve
Sent via Deja.com http://www.deja.com/
Before you buy.
MR-HPT
cranking pressure reading? What will gage read when RAD is 95% in the
morning and drops down to 82% in the mid day? What will your gage read if
engine spins at 750 rpm versus 1500 rpm? Bed info is worst then no info.
GJG
Larrysperf
>cranking pressure reading? What will gage read when RAD is 95% in the
>morning and drops down to 82% in the mid day? What will your gage read if
>engine spins at 750 rpm versus 1500 rpm? Bed info is worst then no info.
>GJG
>
>duckm...@my-deja.com wrote:
>
>> In article <381F9129...@ipass.net>,
>> Anthony Melucci <AVMe...@ipass.net> wrote:
>> >
Plus if it is eating spark plugs squish is way off.Larry
duckm...@my-deja.com
MR-HPT <hpts...@apex.net> wrote:
> Steve you need to quit posting dark age information. Who sells fuel
based on
> cranking pressure reading? What will gage read when RAD is 95% in the
> morning and drops down to 82% in the mid day? What will your gage
read if
> engine spins at 750 rpm versus 1500 rpm? Bed info is worst then no
info.
> GJG
>
George, I never based the 92 octane statement on compression, I based
it on the basic need for decent fuel in any engine. It is better to use
92 than 87! I'm sure that you will agree, of course it depends on
several things. However in a stock, or near stock 550 engine I feel it
would be the ideal thing to do. As far as the compression gauge, it is
ONLY a GUIDELINE! Not for HPT! I was correcting the Clymer manual.
However it can be a GREAT GUIDELINE for STOCK engines, again I would
think that if you pulled that gerbil out of your ass, you would agree!
My best regards, Steve.
> duckm...@my-deja.com wrote:
>
> > In article <381F9129...@ipass.net>,
> > Anthony Melucci <AVMe...@ipass.net> wrote:
> > >