Hey guys, I've been doing a lot of reading and I'm curious if anyone wants to share first hand experience. I'm building a surf ski, nothing crazy (61x, b pipe, lightened flywheel, head, 9/15 hooker) i did a comp test with the stock head, 150psi per cyl. I installed a protec head i had, 160 per cyl. Has anyone run their ski, then swapped heads to run a back to back comparison? I want to run premium pump fuel. Is it worth it to invest in a head with higher compression? Thank you guys! Frank.
What are your thoughts on compression?
- Thread starter truth609
- Start date
DAG
Yes, my balls tickled from that landing
- Location
- Charlotte, NC
Absolutely 100% 180-185 psi can safely be ran on Pumpgas with most setups. Some can get by with more depending many other factors. Definitely worth it
long beach local
long beach local
- Location
- Az
I have been running a stock uncut head with an oem head gasket in salt water (surf) for many years and its more reliable than a an oring head head IMO. I have the same set up as you on my 61x surf motor with 44carb and it has proven to be bulletproof . I have 82.5mm pistons and get around 165psi (perfect) In my experiecnce the motor may run Slightly better on the edge but its just not worth the headaches I would keep it low and spend $ elsewhere
bored&stroked
Urban redneck
- Location
- AZ
I run a shaved factory head at 175psi. Why anyone with access to 91octane gas wouldn't is beyond me.
The bump from 150 to 185 psi is so so so so worth it. Just don't be stupid about it. The extra compression makes for a ton more fun. I was very impressed by the increase in throttle response. Makes it super snappy and a little violent 
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- Location
- Saskatoon,SK
Eric Gorr told me long ago that a 10% compression rise is worth 6% added horsepower.
- Location
- the jetski grave yard
I've been running 205-210 since 2009 and I use the worst garbage yellow terpintine smelling syphon gas you could ever imagine. if you don't hold it wide open for extended periods of time, excessive heat wont be an issue. riding surf is mostly blipping the throttle with short bursts, I'd run high comp all day long and not even think about buying 91.
- Location
- Lake Havasu City, AZ USA
Mmmm... bet that smells good when burning with walmart oil.
Vumad
Super Hero, with a cape!
- Location
- St. Pete, FL
Only up side to stock compression is wawas sells 89 octane ethanol free.
- Location
- the jetski grave yard
I make up for that stench when I fire up the XS1200 on AV gas
bored&stroked
Urban redneck
- Location
- AZ
I've never heard walmart given a nickname nor seen one selling gas so......what the hell is wawas?
- Location
- Lake Havasu City, AZ USA
Its a convenience store chain on the east coast...
Vumad
Super Hero, with a cape!
- Location
- St. Pete, FL
Vumad
Super Hero, with a cape!
- Location
- St. Pete, FL
As a side note, all of the Walmarts and Sams around here do sell gas.
I do a lot of business with Wawa, but I actually still buy the fuel for my Ski from Racetracks. Wawas premium is 92 instead of 93. The little place called Boligers can't get ethonal free 93 anymore. Sucks.
I do a lot of business with Wawa, but I actually still buy the fuel for my Ski from Racetracks. Wawas premium is 92 instead of 93. The little place called Boligers can't get ethonal free 93 anymore. Sucks.
Exactly my experience. If it is a surf/freestyle ski only, then you can run higher compression without issue. I have run 210+ on my surf ski for years without any detonation or reliability problems. However, I run 93oct gas only and limit WFO throttle, and give our parts skis' old gas to our local buzzards.
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It is also good to remember that compression is just 1 thing to consider when setting up your ski. It is the complete package of mods/setup along with ride style and maintenance that will determine overall reliability.
Compression is important to consider but so is other factors like squish and dome shape. Milling a stock head will increase compression, but the squish is still huge due to the thick stock head gasket and dome is still stock shape so performance is less than on a/m oringed head like ADA which have much a much tighter squish and different dome shape/design.
A stock style head gasket seals very well and can seal even a cylinder with issues. Dropped sleeves and uneven cylinder top castings are somewhat common and need to be considered/checked when switching to an Oringed head. If the cylinder is in good condition, reliability is very good.
Elevation, gas quality, ignition timing, pipe choice, etc. all factor into a package of mods. The ideal compression for reliabilty can be very different for different setups and is just one part of the mix.
Compression is important to consider but so is other factors like squish and dome shape. Milling a stock head will increase compression, but the squish is still huge due to the thick stock head gasket and dome is still stock shape so performance is less than on a/m oringed head like ADA which have much a much tighter squish and different dome shape/design.
A stock style head gasket seals very well and can seal even a cylinder with issues. Dropped sleeves and uneven cylinder top castings are somewhat common and need to be considered/checked when switching to an Oringed head. If the cylinder is in good condition, reliability is very good.
Elevation, gas quality, ignition timing, pipe choice, etc. all factor into a package of mods. The ideal compression for reliabilty can be very different for different setups and is just one part of the mix.
air blair
you are the reason
- Location
- thumb, mich again
I'm with buzz but havnt been riding as long as him. High compression is a no brainer mod to me, even with a stock pipe.
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