Compression?
- Thread starter gman086
- Start date
Seems REALLY low to me but my gauge may not exactly be calibrated that great either but I was expecting 140-150!Checked my 11 last year after the injectors went out, (worried it scored a cylinder at the same time)@ about 400 miles and had 115, cant remember if it was hot or cold though.(snap on gauge)
Well, at 12.1:1, it's not gonna be what you saw in 08/09 on the CFI4. There's a reason these things can run on 87, and high compression isn't it. Yeah, the CPU retarding is part of it, but not all of it. Sorry, not piling on, just triangulating on why we should anticipate lower numbers than we would normally expect.
That sounds about right G-ster....I just tested one at 350 ft altitude with my recent new $300 Snap-on Compression tester and got 120 lbs cold and 118 lbs hot. The 2010 and newer heads on the 800's really lowered compression. My 09 with a 2010 head is 125 lbs cold and 122 lb hot.
Aftermarket heads should wake these things up.
Aftermarket heads should wake these things up.
C
chunkysoup
Well-known member
That is low. My wifes sled has 115psi in both cylinders and its time for a rebuild! Granted its not a pro but 2 strokes in general like compression!
Well... Maybe.. But i kinda dont think so..
Piston to Cyl. Clearance.. is only .003 on my engine That a Tight one!
Plus thats only after 3 Hard Pulls..
I did get up to 120.. with stock head after 4 pulls..
I didn't sugar coat it..
I didn't try to get extra compression out of it by coating it with oil.. either..
Max with the new head.. was right a 125-128 psi..
i am happy.. It sure pulls over a little harder too..
and get to the psi Faster!
Piston to Cyl. Clearance.. is only .003 on my engine That a Tight one!
Plus thats only after 3 Hard Pulls..
I did get up to 120.. with stock head after 4 pulls..
I didn't sugar coat it..
I didn't try to get extra compression out of it by coating it with oil.. either..
Max with the new head.. was right a 125-128 psi..
i am happy.. It sure pulls over a little harder too..
and get to the psi Faster!
Well... Maybe.. But i kinda dont think so..
Piston to Cyl. Clearance.. is only .003 on my engine That a Tight one!
Plus thats only after 3 Hard Pulls..
I did get up to 120.. with stock head after 4 pulls..
I didn't sugar coat it..
I didn't try to get extra compression out of it by coating it with oil.. either..
Max with the new head.. was right a 125-128 psi..
i am happy.. It sure pulls over a little harder too..
and get to the psi Faster!
Piston to Cyl. Clearance.. is only .003 on my engine That a Tight one!
Plus thats only after 3 Hard Pulls..
I did get up to 120.. with stock head after 4 pulls..
I didn't sugar coat it..
I didn't try to get extra compression out of it by coating it with oil.. either..
Max with the new head.. was right a 125-128 psi..
i am happy.. It sure pulls over a little harder too..
and get to the psi Faster!
C
chunkysoup
Well-known member
sorry... i meant the stock head compression. 125 is a good number. At 115 the engine is underpowered and kinda sputters a bit in my situation anyway.
...Hmm U sure you got your Jetting Right.. Sputters.. is not going to come down to compression!!!
Sound like it needs a little tuning..
C
chunkysoup
Well-known member
i have double checked jetting. valves were clean. reeds were good. plugs were new. going to do a rebuild cuz it has quite a few miles on it and i will go through everything again.
Just for comparison sake-- not to start a brand bash...
Anyone know the compression on an Arctic Cat (Suzuki) M8 motor?
I think we can all agree that is a stout 800 motor, just curious what the compression is like in that motor.
Did Polaris really detune their 800 so much to relieve stress on engine internals?
Anyone know the compression on an Arctic Cat (Suzuki) M8 motor?
I think we can all agree that is a stout 800 motor, just curious what the compression is like in that motor.
Did Polaris really detune their 800 so much to relieve stress on engine internals?
Murph YES
It's built for the masses and to be safe and reliably used at all variances. If Polaris could be guaranteed that you guys would run consistent fuel at a given burn rate then they could sell the base line setup at higher compression and performance. BUT they can't be assured of that minimum standard so what you get stock is the average of the worst case scenario and that is that. Remember there is ONE setup sold to be used in a universal environment from sea level to the moon.
This is the reason why we can make a stock exhaust, stock ported sled 20-25% faster ie quicker with compression and a proper overall state of tune as we increase in altitude. (and it will live just like stock) Or if you want to run higher compression at sea level you have to compensate with a slowed burn rate IE higher octane fuel and you have to have experience to know what the requirements are.
Nothing has changed in the design of the pump. What has changed is how we feed the pump and tell it to POP. Octane burn rate v compression are absolutely critical performance factors for the Polaris system. If you know the ceiling of what they'll take and set your sled up within those parameters (and always stay there) you have an awesome high performance vehicle.
It's built for the masses and to be safe and reliably used at all variances. If Polaris could be guaranteed that you guys would run consistent fuel at a given burn rate then they could sell the base line setup at higher compression and performance. BUT they can't be assured of that minimum standard so what you get stock is the average of the worst case scenario and that is that. Remember there is ONE setup sold to be used in a universal environment from sea level to the moon.
This is the reason why we can make a stock exhaust, stock ported sled 20-25% faster ie quicker with compression and a proper overall state of tune as we increase in altitude. (and it will live just like stock) Or if you want to run higher compression at sea level you have to compensate with a slowed burn rate IE higher octane fuel and you have to have experience to know what the requirements are.
Nothing has changed in the design of the pump. What has changed is how we feed the pump and tell it to POP. Octane burn rate v compression are absolutely critical performance factors for the Polaris system. If you know the ceiling of what they'll take and set your sled up within those parameters (and always stay there) you have an awesome high performance vehicle.
