Thinking of going to the Big Bore but have one small problem. I have the Pro Design Cool Head and they do not make a Big Bore version. I was wondering since the stock head can be milled to match a Big Bore why can't the dome be done the same way. My Polaris dealer said it should bo OK to do but they are not 100% sure. Will not buy another cool head or use stock head.

Thanks
Ronnie

 

Ronnie, I think there is a couple of things you should think about when doing all this. First, a big bore wont actually make more HP according to Mike at HPD.If I can find a stock or .020 jug somewhere, I am going to go smaller actually. It is harder to fill the top end when it gets bigger when the bottom end stays the same. The other thing is heat. My fan runs more than it ever did before. I added an inline cooler and out some water wetter in it, and it seems to do fine now. And, of course, you have a much bigger slug going up and down now. You would have to send your head off to someone like HPD or someone real good to machine your present dome you have. Better stick with someone real good with big bore stuff,though. Personally, I would list that one on e-bay, then buy the setup from HPD along with the girdle kit and have your cylinder drilled for the extra strentgh. See if they will sell you the shell part of the head, and I will sell you my pump gas big bore chamber for 1/2 what I paid for it. I run the race gas version now, so I dont need it. All in all, if I knew now what I did before I would have bored out my cylinder to .040 over and saved some time and hassle. OH YEAH, HPD did not mark on the box what the clearance was supposed to be on the big bore piston, and it seized up after 3 min because it did not have enough clearance. A regular forged takes about .003, but the big bores take .004-.0045 clearance. That might save alot of headache for you. Dont get me wrong, the thing flies and runs hard. I just do all the work myself that I can, and the not enough clearance incident just kind of left a small bad taste for me, but I love my Polaris. Hope this helps,Bubba

 

Ronnie, you might want to gab with HPD, or the Bad Boyz crew, seems to me the big bores were hungry when it came to the reeds also...I think that was when the spacer was used. I've got two cylinders race-ported and .040...with everything dialed in, the only thing that might make me crave more hp, would be toying with alcohol. Have you seen the polished jugs yet?
To address the big bore head, like Bubba suggested stay with the pros. I know HPD's part #'s are different for the big bore billet heads. Not sure if they contracted Pro Design for the heads or not....don't know if the HPD domes would fit is what I'm getting at.

Ken

 

I did forget to mention the fact that what aken said is correct. I have already munched a set of reeds on my V-force cage. Luckily I caught them in the nick of time and nothing happened, but they werent in the motor but about 3/4 of ayear. another thing to watch out for.Bubba

 

I also went thru 2 sets of reeds,until i set them on the high tension setting.I am using the v force 2.That was with the FTR pipe.I now run the HPD race pipe,the reeds are holding up just fine.Later.

 

it is very possible,AAEN,RCR,HPD, should get it done,while aftermarket
head still better in performances,mine is .020 over and it won't be anymore,with a big bore you go trough some top end flat spot loss comparing to the stock bore,the torque gains and trottle response is always noticeable but at top end reductions,the exhaust ports (heights) still too low in stock form.

 

scramblered, you definitely have to re-port everything after boring one out more than one size over. I am pretty radical on transfer port duration and exhaust duration. I would like to know what HPD uses for their numbers on those, but I know they wont give up that info. Like I said before my wheeler pulls hard turning 7500rpms and I could still put more weight into the primary I'm sure. No more tuning right now until the alcohol gets put on. Bubba

 

I have Ritter mid to top end porting already.Just trying to get more torque out of. Do not realley care for a lot of top end. When I do get to race people it is only about 300ft if that. It is time for a bore and I wasjust looking at my options.

Ronnie

 

Ronnie, It all comes down to what you want. The term "no replacement for displacement" is certainly a true thing. If it's done right, I dont see any problems. I have been running the mess out of mine and no problems to date except reeds, but I am on the lighter setting. I would recommend a re-port, though if you big bore. That would correct the port timing and get things they way they should be. Done forget, HPD says a reed spacer is mandatory with big bores to correct primary compression. That played some havoc with the stock airbox fitting after that. But I still love it! Bubba

 

Ritter might be able to mod the coolhead to match a bigbore piston. Unless you have a mechanic in the know....I'd stay away from the dealer guys that aren't 100% sure.

Jay