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Discussion Starter · #1 ·
Did a compression check on a buddys 925 with my craftsman gauge and read 235psi across the board. Couldn't believe it so we checked it with his snap-on gauge and read 240psi across. is there such a thing as too much compression? Only runnin 4-500ft with it.
 

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Did a compression check on a buddys 925 with my craftsman gauge and read 235psi across the board. Couldn't believe it so we checked it with his snap-on gauge and read 240psi across. is there such a thing as too much compression? Only runnin 4-500ft with it.
what gas are you running c14 ????? that is hight
 
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what gas are you running c14 ????? that is hight
that does not sound right at all...c16 sounds more like it...lol is there even a base gasket in this motor??
have you done a squish or cc the combustion chamber??? that is a very high number..
 

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Discussion Starter · #6 ·
he runs it on c-16. Looked like a 3 hole gasket when i pulled the cylinder off. I never rode it but it just seems like it should be faster than it is. Not even a challenge for my 800 improver. Thats why i was wondering if to much compression can hinder things. Never really looked into his motor but i might go check the squish and cr and see what the deal is. Oh yea and the thing is miserable to pull over. Almost gotta set the parking brake to do it haha
 

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Maybe she'll run on a diesel / race gas mix.


Bring that compression down about 30 points or so and it'l probably run a lil bit better.
 

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c14 is good for 230 psi or higher Recommended for naturally aspirated engines operating at over 8000 RPMs with CRs of 14:1 and over in drag race cars, 4-stroke drag race motorcycles, snowmobiles and PWCs (230 psi or higher). Spec fuel for NHRA Comp Eliminator.
Color: Yellow
Motor Octane 114
Specific Gravity: .696 at 60° F

http://www.vwparts.net/VPC14.html
c16 Used in turbocharged engines, blown engines and nitrous applications with CRs up to 17:1. Recommended by the top nitrous oxide companies. Spec Fuel for NHRA Comp Eliminator.
Color: Blue
Motor Octane 117
Specific Gravity: .735 at 60° F
 

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Cranking compression really does not mean much. You really need to figure out the compression ratio. For 500 foot in the heat of summer you can run a lot of compression. Have you checked the squish?
 

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Discussion Starter · #14 ·
Prolly have him try some c-14. Not sure who the engine builder is. Motor was bought second hand here on dootalk over year n a half ago from someone in utah.
 

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Prolly have him try some c-14. Not sure who the engine builder is. Motor was bought second hand here on dootalk over year n a half ago from someone in utah.
I just moved back from Utah. Wasn't mine but curious who you got it from.
 

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Its not my motor but im not sure who it was. Next time i see him ill ask him. Came with crankshop pipes and carbs and ignition and i think dyno sheets as well. My guess is that motor was build for high altitude where it wouldn't have this kinda compression up there but down here at 500ft elevation its got a ton of it.
 

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Its not my motor but im not sure who it was. Next time i see him ill ask him. Came with crankshop pipes and carbs and ignition and i think dyno sheets as well. My guess is that motor was build for high altitude where it wouldn't have this kinda compression up there but down here at 500ft elevation its got a ton of it.
is he jetted right 500ft elevation. how is the piston wash ???
 

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Prolly have him try some c-14. Not sure who the engine builder is. Motor was bought second hand here on dootalk over year n a half ago from someone in utah.
The engine was probably designed to run at 10,000 ft. Compression will be about 32 psig less up there, then it is down here.

Maybe needs new domes for low altitude running! If you cc the dome and clearance volume you will find it is about 15 + to 1...
 

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Generally in Utah you would ride anywhere from 7000 to just over 10,000 foot. But if it was used in there grass drag series then it was used more around 5000 feet in elevation. Might explain the high cylinder pressure down at or near sea level.

I wonder if the pipes were changed for the high elevation too???
 
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