why wouldnt you just get a high compression piston, its such a pain to mill the head and have to deal with timing chain slack.

 

RZR is push rod Engine...What have seen of head every small ports. Flow is the killer here ... thinking extrude hone head..increase valve size...remap box ..cam. Anyone have manual on sportman 800 HO ? Have RZR dealership manual with cd...manual list part numbers. Then could cross check what parts have been changed on Sportman same engine...might be cheeper to change parts ? Just idea of old road racer here.. I could be all wet too on this thought .

 

I have checked with my dealer and the pistons in the new ho are the same as the valved are also the same as what I have but the head casting itself is different than mine as for as between the rzr and the sportsman 800 HO.

 

ford4442003...ok sounds like the head is better flowing then? If you know fords ..different flow on 351 c 2v ver 351c 4v heads. Port size and valve size on 351c...but like stated before ...RZR flow looks bad.. cost would be something to check ...is cams the same too ? If same valves...bare head ..change over upper system...easy..if cost of bear head isn't like everything else Polaris sells....over priced . might still check extrude hone head...if cost is less increase valve size. Then Check this site..High Performance Designs , Inc. They have porting stock head with stock valves 500.00 also + 2 mm over size valves porting 550.00 ..think must send in your head off RZR and it must be cleaned too. something polaris must have known for while....poor flow on 800 engine design. This company also has cams...but know nothing of thier work ? But remember increase flow...must redo control box on fuel...timing...ect . everything goes hand in hand . Ok i'll shut up....don't have Polaris dealer that is nice in area. Would like to know price on ho bare head ? enjoy Your RZR....

 

Yes I had a cleveland 351 4v and the valves and ports are much larger than the 2v but I do not want to go with much larger valves because as you know to much porting and valve work and you loose your low end and that would not be good for trail riding.

 

No timing chain in 800 polaris gear driven

 

Yep...Your right there ford4442003....that's why I like Extrude hone ...cleans intake and exhaust ports real nice ...no increase for the most part on size..just makes the air flow sooo much better. What do You think about just addding 800 ho head ? still think something different might be worth checking into if cheeper than extrude hone. Ford went to large on ports and the fuel started to deatomize and formed fuel droplets on intake runners on 429 boss at low intake velocity...LOL Can get carried away on size. Know that polish ports can cause same thing at times. Extrude hone will leave some fine rough texture to not cause problem of real high pollish. Ford used this on SVO Please let me know if You find out what really is different between heads. Know what dealer told You...but now You got me wanting to know more ! If You deck head ...think RZR has dish piston..might want to putty head with valves full open at top of cam lift to check for clearence ...then can figure how much to deck head . But figure that You already know this since there are some really smart folks on this forum. Thanks for the great post ..it made Me think today while working on getting shop up and running. smiles

 

being the head surface is alrady flat, decking won't be of any advantage. We changed from a stock RZR cam to the Sportsman 800 H.O. cam in the race car, Polaris says it gives an 8% increase in torque and horsepower. I don't have any numbers but it is definetly more rippy coming out of the corners. AAEN performance has some head and valve stuff. They also offer porting. I ported the cylinder head some. Compared to the Ranger head, the RZR head is alot better design and only needed some clean up and minor reshaping on the intake side. The exhaust side has one little bump to get out of the way and smoothing behind the valve seat. I haven't looked into higher compression pistons yet. I desert racing its all about survival so I don't want to jeapordize the reliability. If you start changing up RPM's though you will want to make sure that the second rod (closer to front of car) can receive enough oil to keep from seizing past 7k. Also there is a company that will taper bore the throttle body out to 44mm. That might help it breathe better in its own. Let me know if you find some higher compression pistons or a 7mm stroker crank somewhere.

 

Hello, I Have Not Found Any Highter Compression Pistons But The Manual At The Polaris Dealership Claims 11.0 To 1 For The H.o. Engine Compared To 9.5 To 1 But According To The Part Numbers The Only Things Different Are The Head, Valves And Cam And Lifters. So There Must Be A Smaller Chamber In The H.o. Head I Know This Does Not Make The Ratio Highter But The C.c. S That The Chamber Has Must Be Highter. To Get Mine Up To 11.0 To 1 I Think The Head Would Have To Be Shaved About 65 Thousands This Is More Than I Am Able To Sacrifice To Find Out That There Is No Longer Enought Valve Clearance.

 

a smaller cc head would raise the comp number when you check for compression you take the cc's of the head into account also...besides the area left in the cyl

 

first of all you dont want to shave the head because the rockers are non adjustable, and Todd if your looking for some pistons my dealer has a set of custom CP 12-1 pistons for around $300, i have a pair in mine along with ported head, efi controller, dragonfire exhaust, etc. it runs alittle better, but all of you thats planning to hop the 800 up your soon to find it will take a lot of $$ to make a noticable difference.

 

you wouldnt shave the head because for one you 'd have to shorten your pushrods, also theres not much there to shave.. rzr has coffee cup pistons so the combustion chamber is in the dome of the piston..
i just finished a mild port job and polishing on my head.
this head is a very good design. the casting is very clean and it looks like it would flow really well. i just ported for really really well ..
if you want to increase your compression you shouldnt get over about 12.5:1 there is no center bearing to support the center of the crank and i've heard at more than 12 and a half they start coming apart.
i'm hearing of good results from swapping cams. i've swapped my cam but i've apparently done something wrong because it's not running right.. getting ready to pop it back out and double check my work..

 

youll get it marty

 

just want to get this straight the only differece in the HO 800 is the head it's self and the cam and the valves. so clean up the intake and exhaust ports throw the HO 800 cam in with a little bit higher compression but not enough to blow the crank and you should have an awesome motor

 

i wonder if doing that would be better then just throwing the HO 800 head on the rzr and trying to make it work?

 

has anyone ever twisted or broke a crank?

 

You could shave heads or get a head gasket from a 02 700 same bore gasket is a 3rd the thickness of stock 800 cam head and injector is diffrent on 800HO also some clutch changes

 

Is it worth doing porting,cam and cdi? what is the gain(really?) Seems like alot of scatch for possibly a little return.

 

i am also curious as to the gains they are making. seems this post has died down recently maybe a bad sign ha ha

 

Hey, Greg You mite try bikeman performance they offer head porting service also cams. they have done this for a long time now and their good .have done some checking around and have decided to use them. will be sending head off next month. also getting throttle body ported along with cam.will post results when installed. still waiting on exhaust gasket as of today.installing looney tuned dual exhaust and fuel controller.
"LET THE BIG DOG EAT"