300 psi compression

the gman · Oct 26, 2014

I know all gauges are different and just trying to get a base line so my 300 has gores porting with the ktm Sx head and Eric tightened up my sqwish from last year and I have 225 psi. This setup is for 3-6000 feet and was setup to run on pump gas. This just seems high, anyone have any ideas....thank you. Garry

This test is at 1700 feet

Summitseeker · Oct 26, 2014

Following.... That seems really high. I have the same setup as you, I have not done a compression test but 225 PSI would be hard to kick over! I will do a compression test on mine this week and see what mine reads.

chumbilly1 · Oct 27, 2014

I have two different heads (300sx) modded by cycle playground and they are 225 and 230psi. I requested 50% 110 @ 2k and 5k elevation. This spring I tried to run the bike @ 2k with the 230# head and it literally would not rev at all. Switched heads and runs fine. I may use a thicker base gasket this winter to raise the exhaust port and lower compression # slightly. I feel this is the edge of too much compression.

the gman · Oct 27, 2014

Did you ever check your sqwish chumb? I checked mine before I sent in my jug and head for port work and after. I will check my records and post what eric set it at, just wondering if it's too much. Thanks

mtn-doo · Oct 27, 2014

Hey Garry, yes. too much compression will kill your top end. Zero over-rev. Try the .075 base gasket. I think you are currently running the .050.

mtn-doo · Oct 27, 2014

Better yet, buy the Slevens star head and domes. Use the AA dome for 6000'. Problem solved.

the gman · Oct 27, 2014

Talked to eric today and I had a sqwish of .072 and comp. of 185 before sending in my jug and head for porting. He did his work and tried to get my sqwish to .050-.055 which would of got me to 200-205 comp. Problem was my base gasket I did my sqwish with was .024 and the common base gasket is .020 which is what I used for my rebuild. My sqwish was .046 with the .020 base gasket which gave me 225 psi. Head is on its way back to eric to cut .005-.010 which with the common .020 base gasket should get me right at the .050-.055 sqwish he says is safe for pump gas at 3-6000 feet. I will post sqwish and psi when my head gets back. Thanks for the responses. Garry

the gman · Nov 7, 2014

Update on head work,got head back from forward motion and sqush is .054-.056. Psi is now a more reasonable 210. Hope it runs good on pump gas.

chumbilly1 · Nov 8, 2014

I have not gotten into checking sqish. I look at it like suspension valving. I am simply better off to let a professional do their work and I will go to the jobsite and do mine. Just not enough time in life for me to learn it all. Maybe I am a slow learner?? I am going to add some basegasket this year though as I feel my topend was being held back by the high compression. Another thing I have noticed about high comp engines is the carb signal is so much stronger they are more difficul to jet. It will be interesting to see what a SC does when you change port timing and head.

wwillf01 · Nov 8, 2014

chumbilly1 said:
I have not gotten into checking sqish. I look at it like suspension valving. I am simply better off to let a professional do their work and I will go to the jobsite and do mine. Just not enough time in life for me to learn it all. Maybe I am a slow learner?? I am going to add some basegasket this year though as I feel my topend was being held back by the high compression. Another thing I have noticed about high comp engines is the carb signal is so much stronger they are more difficul to jet. It will be interesting to see what a SC does when you change port timing and head.

I just had my 300 ported by Eric gore and I have a Lectron... I had to richen my rod .75 of a turn... This is a good bit richer and I turned the power jet a half turn richer. But once set your are good to go

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chumbilly1 · Nov 8, 2014

wwillf01 said:
I just had my 300 ported by Eric gore and I have a Lectron... I had to richen my rod .75 of a turn... This is a good bit richer and I turned the power jet a half turn richer. But once set your are good to go

Sent from my iPad using Tapatalk HD

That is interesting, with the Dick's modded Keihens I have been using, I end up using leaner brass across the spectrum. I always figured this was do to increased velocity and signal. Could also be that I am running more race fuel than is needed I guess.

wwillf01 · Nov 8, 2014

chumbilly1 said:
That is interesting, with the Dick's modded Keihens I have been using, I end up using leaner brass across the spectrum. I always figured this was do to increased velocity and signal. Could also be that I am running more race fuel than is needed I guess.

I know for mine the amount of race gas I use makes a huge difference.... I use 88 non ethanol 3 gallons with 2 gallons of 110... 40 to 1 with a good synthetic... I find if I go to high on the octane I loose power....

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wwillf01 · Nov 8, 2014

chumbilly1 said:
That is interesting, with the Dick's modded Keihens I have been using, I end up using leaner brass across the spectrum. I always figured this was do to increased velocity and signal. Could also be that I am running more race fuel than is needed I guess.

The other thing is to make sure to run a step colder plug... I found with the higher compression it seems to run smoother.

Sent from my iPad using Tapatalk HD

mtn-doo · Nov 8, 2014

chumbilly1 said:
I have not gotten into checking sqish. I look at it like suspension valving. I am simply better off to let a professional do their work and I will go to the jobsite and do mine. Just not enough time in life for me to learn it all. Maybe I am a slow learner?? I am going to add some basegasket this year though as I feel my topend was being held back by the high compression. Another thing I have noticed about high comp engines is the carb signal is so much stronger they are more difficul to jet. It will be interesting to see what a SC does when you change port timing and head.

Having run the Smart Carb with modded two strokes for some time now, I can report they simply respond to signal. Pretty cool. Port timing , ignition timing etc. The signal is responded to with zero changes in AFR or EGT. They don't have jets that only deliver one amount of fuel. They respond to signal, even load factor not throttle position. Pretty sweet

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300 psi compression

the gman

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