Double base gasket mod sled?

[Dragonalain]

Last year I built a different high boost mod sled. It only had 1.5 days on it till I broke off a shitty carbon fiber reed and hurt the engine. I knew the reeds were not gonna last long but figured I’d get atleast two test days in. Anyways I rebuilt the engine with some wisco slugs that I’ve had great luck with running boost on before. I took it out for a test day and I have a slight issue. My compression is 140psi which is too high for my liking. I have two options machine a set of high comp ssi domes to get down to 110-120 psi or try to do a double or triple base gaskets on the low comp domes and get it to my desired comp.

Has anyone ever done a double base gasket with a steel gasket?

Some Vertex cyl base gaskets have switched over from the steel compression type to a steel with a felt ish layer on it. I’m thinking of put on a couple steel felty gaskets together.


Did 17 pounds boost on it last year and it worked great till it ate a reed. I have not been on a sled as fast as this was since the 400 hp nypex days. For the doo guys who think nothing can beat a g5 I also have one of them and it feels like a 340 fanner compared to 17 pounds boost.

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[drew562]

Last year I built a different high boost mod sled. It only had 1.5 days on it till I broke off a shitty carbon fiber reed and hurt the engine. I knew the reeds were not gonna last long but figured I’d get atleast two test days in. Anyways I rebuilt the engine with some wisco slugs that I’ve had great luck with running boost on before. I took it out for a test day and I have a slight issue. My compression is 140psi which is too high for my liking. I have two options machine a set of high comp ssi domes to get down to 110-120 psi or try to do a double or triple base gaskets on the low comp domes and get it to my desired comp.

Has anyone ever done a double base gasket with a steel gasket?

Some Vertex cyl base gaskets have switched over from the steel compression type to a steel with a felt ish layer on it. I’m thinking of put on a couple steel felty gaskets together.


Did 17 pounds boost on it last year and it worked great till it ate a reed. I have not been on a sled as fast as this was since the 400 hp nypex days. For the doo guys who think nothing can beat a g5 I also have one of them and it feels like a 340 fanner compared to 17 pounds boost.

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Double base gaskets on big twin cats all the time

 

[rknight111]

What about an aluminum head shim like I did with my Nytro, Id run it by Tom at Motts.

 

[Dragonalain]

What about an aluminum head shim like I did with my Nytro, Id run it by Tom at Motts.

I was thinking of that, kinda like the fix kits. I’m not sure if I could get a thin enough piece of aluminum to only drop the comp psi by 20. I don’t have any personal experience with the old rotax and the different base gasket thickness to see how much the psi drops per .010 of a inch

 

[rknight111]

I was thinking of that, kinda like the fix kits. I’m not sure if I could get a thin enough piece of aluminum to only drop the comp psi by 20. I don’t have any personal experience with the old rotax and the different base gasket thickness to see how much the psi drops per .010 of a inch

That's why I am recommending you visit Tom at Motts.

 

[Dragonalain]

That's why I am recommending you visit Tom at Motts.

I’ll call him today.


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[sirkdev]

Can’t do more octane?

 

[DRD]

I ran double base gaskets on a NA sled, never a turbo though.. It will also change your port timing with a thicker base gasket...

 

[maxwell]

Can’t do more octane?

im wondering the same, i ran 15lbs on my race sled with 140psi.

 

[Bnorth]

I would lean toward a dome change just because the base gasket impacts port timing.

 

[Dragonalain]

Can’t do more octane?

I’m 90% sure I had 30L of 120 race and 10L of premium and it was det city. If I used The octane calculators properly it says that should have been about 113 octane. I’d like to run 10-12 pounds on av As it’s easy to get. If I want to use the upper 1/2 of the boost gauge I’ll run race.

Going up the trail the sled sure felt promising. Was building enough boost at 4800 rpm to have to dump it when I let off the gas. Got up top to open it up and my day was ruined.


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[ABMax24]

I’m 90% sure I had 30L of 120 race and 10L of premium and it was det city. If I used The octane calculators properly it says that should have been about 113 octane. I’d like to run 10-12 pounds on av As it’s easy to get. If I want to use the upper 1/2 of the boost gauge I’ll run race.

Going up the trail the sled sure felt promising. Was building enough boost at 4800 rpm to have to dump it when I let off the gas. Got up top to open it up and my day was ruined.


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What's the AFR when that's happening? These motors like some extra fuel to keep to DET at bay.

What turbo is in it? Spooling at 4800rpm seems like the turbine is pretty tight or clutching is keeping the rpm down.

I don't think you're going to get 10-12 lbs on just av gas, at least not without dropping compression a lot, and then the bottom end response will be awful. Could maybe trying pulling some timing.

 

[kovs]

How thick are the Polaris base gaskets with the steel/felt ?
What is your current squish with it being det city I wonder if it’s a bit tight then throw in boost on top
If you open squish up .015-.020 depending how big it is now would make quite a change in compression and take a lot of heat off edge of piston under boost

Curious what Tom had to say. He machined a set of domes for me many years ago



Back in the day I ran stacked gaskets on my skidoo and a modified dome. The port timing sure didn’t hurt anything but they would work out over time. They where just a paper type tho not stamped


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[Dragonalain]

Never had time to call Tom today.

This old 17 800 axy was always a star it started life as a 174 and would always over rev the factory clutch. Even when the sled was loaded heavy pushing headlight deep snow. We had several in the group and this one was quite a bit stronger than the others.

Couldn’t sell it for decent coin being a 174 so I decided to retire the old pro that I ran for a decade of heavy boost and chute climbing.

Turbo kit is a Frankenstein build.
-2874 billet wheel
-Turbo Oil tank delete
-A old redline g2 controller with a fuel knob.
-Custom build air box and silicon one piece charge pipe that has tremendous volume.
-Qap-5 daltons loaded at 81g it was reving higher than I like at 8450.
-32/46 helix (I think)
-Air box pulls from the factory location with extra fire and ice vents but that was not enough so I tied in a 2.875 id snorkel.
-turbosmart bov tied into the air box to blow the snow off the intakes.
-2.5 inch straight pipe tunnel dump.
- new this season - custom reed cages to accept reeds from a cfi-2 along with some reeds cut in 1/2 to double up the lower set.
-egt fast response
- races edge rear arm from god knows what with some ice age rails that I had to drill holes for my set up.
- custom fuel lines and a Napa efi fuel filter.



I’m running an old boost-it Yamaha rising rate fuel pressure regulator along with a fuel pressure gauge. I have 38psi at idle. I need to check fuel pressure with an air regulator.

Sled was running 1150 egt when it was det I added some fuel and was down around 1000 but it was on the boggy side. Never hit det with more fuel.

Sleds super clean as wires and hoses bother me a lot so everything is in a certain location to make the hoses/ wires as short as possible. I even moved the coils to the steering busing so the plug wires are short.

I climbed 2 chutes with it last year and when I got down from the second one the boys were friggin impressed and Their eyes were wide open. The sled was so fast it just floated on the snow only trenching about 8 -10 inches in waist deep chute show. I let off about 3 sled lengths from the top of the chute and still caught 5 ft of air.

But until I get this unit running like it was last year and some videos this is all hearsay lol.

I never checked squish as I never thought id have a problem. I also never checked the difference between the oem steel gasket and the steel felty gasket.

Sounds like I have a couple things to check before the next trip out but I have some other things taking up a lot of my time this winter. Hopefully it’s ready to rock for the end of Feb.


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