1996 Summit 670 Compression

[Broz]

Can anyone tell me the cranking compression of a 96 summit 670 at sea level?

Or what should we have in a fresh engine at 4200 feet?

We may mill the head or what about base gasket thickness and port height location? We have some room in the piston to head area as we are slightly over .065"

I know,,, we just got her running and now want more. It's a sickness right?

Jeff

 

[LBZ]

I would say anything above 110-120 would be good but would be looking for higher maybe on a fresh broke in engine.

 

[Broz]

Thanks LBZ, I think we are about at the 110 and feel it is low for a motor with 50 miles on it. But the good news is both cylinders are the same. I want to check the accuracy of my comp. gauge first. I just didnt know what to shoot for at our elevation of 4200 feet. I would expect it to be lower than a sea level test probably by 15%.

I want to stay with 87 to 91 octane fuel too so dont want to over do it.

Jeff

 

[JBDoo]

I just picked up a 97 Mach Z and it pulled 120 psi across the board. I think .050 is the minimum recommended squish, for pump gas anyway. I wouldn't go with a thinner base gasket, have the head milled instead. Do you still have the oil injection pump? There are a few horses to be gained with the shorty cover and a 501 spec rotary valve. I did that as well as matching my case to the base gasket and my 97 Summit 670 would run right with the 99 Summit Xs even with the HAC system functional. It is a sickness, every sled I've owned has been made faster....till it blew up. When I can afford a REV someday I've promised myself to put a can on it and leave the rest alone.......we'll see if that happens

 

[Broz]

Yes, the oil injection is still fuctional as well as the HAC. I have been looking for a 501 RV. Didn't know about the short cover? What were thay on? Also see that the 501 was used on a 96 Mach 1 along with vm 44 carbs. Might look for a deal on a set of those too.

Wonder what we need to mill off the head to get another 15 ~ 20 pounds of compression?

Another problem we have is hooking this thing up. It has a M-10 136"x2" under it and we have adjusted it with some improvment, but it really needs more hook.

Thanks
Jeff

Jeff

 

[JBDoo]

Actually if you can download the 99 Ski doo race manual it has lifesize pics of all the rotary valves. You can just lay yours over the picture and mark how much needs to be trimmed off and grind it down. Thats what I did on mine. The shorty cover was only used on the MXZX race sleds, but I've never seen a factory shorty cover. You should be able to find one from most sled shops. After re-reading your post, if all of your riding is done above 4200ft you can probably shave quite a bit off your cylinder head and as long as you never ride it down low you won't even need race fuel. I'd find the nearest sled shop that knows Doos and see what they recommend. I wouldn't waste your money on the 44s though, every test I've ever seen only showed a 2hp or less gain with them and that was with twin pipes. the rotary valve mod should end up being free and the shorty cover you may be able to find a used one for around a $100 or less.

 

[Broz]

I will look for the photos of the 501 RV and get to cuttin. I had fears that the 44's may not be the best choice. They would probably give up some throttle responce and low end to get that 2 hp at the very top. Probably not the best when you get in the deep stuff either.

So we will do the 501, and look for a short cover, I assume this cover supports an oil pump too?

Then I still need to know what a target PSI on compression is at 4200 ft alt.
Last night we tested my compression gauge to a good quality gauge I had and it tested fine. Then a re-test of compression confirmed we have 105 pounds per side with throttle open and 5 pulls on the rope. I am guessing ,, and this is just a gutinstinct guess, take .015" ~ .020" off the head (if piston to head clearence will allow) and shoot for 135 pounds of compression. ???

Thanks!!

Jeff

 

[Broz]

Update!!

I took a spare head we had and milled it down .020" this put me about .053" average piston to head when measured at both sides above the pin.

Compression came up frm 105 to 125 when pulled till the gauge stopped moving with carbs open.

We took the main jets up 10 on each side, this put us at 380 on the PTO side and 370 Mag side.

Our testing was done at 4200' at 31 degrees F. We ran it a bit farther each time at WOT and hit the kill while still WOT. All the tests showed it was right there as far as color. I feel it needs a bit of Fuel as the electrode insulator is more of a light brown with a slight red tint. But definatly not dark brown. So it will probably get a 380 / 390 and retest.

The clean kill at 1/2 throttle test showed the plugs about the same as WOT. Maybe a bit richer.

See the pligs here and let me know what you think?
https://www.snowandmud.com/forum/f396/take-look-these-plugs-please-41296.html

Next we will cut a 501 RV and see what that does.

Thanks.

Jeff