Ideal Compression

[gregrob]

Ok guys, I had Kevin do a 4mil aggressive dune port engine for me at the beginning of the season. At the time I was running pump gas and T-5's.

 

I have since stepped it up to methanol and a set of shearers. The bike isn't even tuned because of the cold weather but it rips way frickin harder now.

 

Compression is still down at only 150lbs with 19cc 4mil domes.

 

I dont plan on switching back to gas, I love the way it runs on methanol so I want to change up the timing and domes and get the most potential out of it...

 

Maybe Kevin will chime in here but what would you guys recommend for timing and compression.

 

Bear in mind I DONT want to put undue stress on my crank or make it more unreliable, just want to get a little more power since I'm running meth.

 

I'm thinking maybe 8-9deg of timing and 180psi compression?

 

Discuss...

[locogato11283]

why dont you just call the guy that built your motor. 150 psi and 19cc domes seems awfully low to me.

 

i run my 10mm at about 175 psi and +7 timing. runs like a champ.

[bonbon]

why dont you just call the guy that built your motor. 150 psi and 19cc domes seems awfully low to me.

 

i run my 10mm at about 175 psi and +7 timing. runs like a champ.

150 psi is about right for those domes at ~6 - 7000 ft asl. I have 20 cc's that run 140 psi at 6400 ft asl. A lot of the good riding areas out here in wyoming and colorado are above 7000 ft.

 

EDIT: I just looked at the chart on Noss's website and his is actually a little higher than it says.

[locogato11283]

id run a smaller dome then.

[dajogejr]

JT ran his 4 mil on 155 to 160 PSI all day and it ripped. And I think he maxed the plate out.

 

However...this is a duner, not a strict drag bike.

 

Where is the squish at? I like a looser squish but smaller dome. I also run a LOT more timing.

 

For a duner, I would keep the compression below 180PSI...and timing at 7 or below.

 

For this particular motor....you can't go by NOSS's chart.

It is ported....and his chart only goes to 5000 feet.

[locogato11283]

id try to get it up to about 170. thats a good number thatll give you a little more on bottom but wont compromise your R's on top.

[KEVSWS6]

Run a 17cc dome and +7 on the timing if riding hard in the dunes. That should put you at 180 PSI and still be good and safe. Keep the squish at .045 to .050

[KEVSWS6]

bonbon that is a great picture you have in your sig!

[bonbon]

bonbon that is a great picture you have in your sig!

Thanks! That was before I tried to break my ankle later that day..........

[trex banshee]

i run my trex motor at 145ish psi and +10 timing on alcohol...it didn't like alot of compression, well i guess ive only tried two different sizes of domes. That trex shit is too expensive to have a lot of it. my exhaust duration is pretty high as well though.

[BigRed350x]

why dont you just call the guy that built your motor. 150 psi and 19cc domes seems awfully low to me.

 

i run my 10mm at about 175 psi and +7 timing. runs like a champ.

 

Uhh... remember where we and jamie ride... lol! Damn all you low-elevation bastards! I have to run 17 or 16cc domes to get decent meth compression.

[BigRed350x]

Thanks! That was before I tried to break my ankle later that day..........

 

Which time was that? LOL! I remember taking that pic for you. Then you ate shit and almost died like 10 times.

[bonbon]

Which time was that? LOL! I remember taking that pic for you. Then you ate shit and almost died like 10 times.

That would be with AJ and Michelle and we loaded up to leave a little early then Rick showed up. He went up on the poolaris and I went over the handlebars going down. Shouldn't have kicked down the ledge for him damnit!

[BigRed350x]

That would be with AJ and Michelle and we loaded up to leave a little early then Rick showed up. He went up on the poolaris and I went over the handlebars going down. Shouldn't have kicked down the ledge for him damnit!

 

ROFL! You feel a good 8 ft vertical and smacked into the ground and your banshee landed on you. Seriously jon, you have the worst luck with crashes.

[bonbon]

Just wait until I have a 4 mil cheetah w/powervalves so that I can get that power instantly climbing.........then I'll start the stupid shit. Either I will destroy sand mountain or sand mountain will destroy me (hopefully just the bike though if that's the case)