Port and polish heads?

Okay you engine builders. I have be told by many that if you port and polish your head that it will take away form bottom end. However, I have a mechanic that works for one of my companies that informed me that if you add displacement you should port and polish your head along with bigger values. What do you guys think?

Depends on whos doing the P&P. If they get too happy with the grinder and raise the timing too much, it will hinder performance. It will be great on the bottom and suck on the top, or visa-versa, suck on the bottom and be wonderful on top. Bigger valves have nothing to do with it, if it's done wrong......Just a bigger hole in the piston...........

For polaris Ronnie, I have always trusted my mods with www.hpd-inc.com They have awesome customer service and love to talk shop on the phone during tech hours.

do it you will like it

Well, there is really a few things you need to know first when it breaths better it will increase the rpms ( make it build power up top faster ) and with bigger valves/porting you will get a quicker reving machine. But there is some truth to the losing the bottom end stuff. Your cams will affect power more than anything because it controls the valve duration. There is also something to say to the whole vortex flow in how it atomizes fuel/air mixture in the combustion chamber..Plus in some street bikes they will actually puddy up the intake side of the head to create more power.. So to sum it up you do lose bottom end but if your cams, exhaust and intake will support the flow you will gain it back plus some in mids and high rpm.

Just ......bottom line is this.....everything has to be blended together....matched for what you are trying to achieve.....very hard to build a "Stump" puller and a "Speed Demon" all in one engine.

KYWILDCATS74 wrote:

..... So to sum it up you do lose bottom end but if your cams, exhaust and intake will support the flow you will gain it back plus some in mids and high rpm.

That is my understanding (which is very little) of airflow and fuel. If I was to (and I have) add displacement a long with a cam I should port & polish, port throttle body and add a good exhaust.

Big R I would say yes. The only thing you have to watch is HP vs $$.. Once you get so far the HP per $ starts getting pretty high. Thats at least what I tell my customers. But if you have added displacment with a set of cams and exhaust if the price is right do the port and polish.. Make sure you have a fuel controller to map what you have done. Also look at your clutching. You will want your clutch to shift at a higher rpm to get the HP out of the headwork so you will actually see the HP at the ground.Have fun and enjoy!

KYWILDCATS74 wrote:

Big R I would say yes. The only thing you have to watch is HP vs $$.. Once you get so far the HP per $ starts getting pretty high. Thats at least what I tell my customers. But if you have added displacment with a set of cams and exhaust if the price is right do the port and polish.. Make sure you have a fuel controller to map what you have done. Also look at your clutching. You will want your clutch to shift at a higher rpm to get the HP out of the headwork so you will actually see the HP at the ground.Have fun and enjoy!

I am guessing you have not read my build thread? When you get time check it out and get back with me and give me your feed back.

https://southernsxsriders.forumakers.com/t6251-my-rzr-thread

I scanned through your build and by the way nice transformation on your bike. First off all I am no rzr expert I am one for the Kawi's and do know engine's. I will say that I have heard from multiple engine builders that you do not get the gains from the polaris engine as you would from the 750 vtwin as it pertains to big bore. That is why they trend to turbo's instead. But I cannot verify this claim because I havent witnessed this first hand. So what I can do is speak in general. If I was you and I had the extra resources I would do the head work. You have already gone this far. I think your fuel controler will be fine if it is adeqaute now. Just tune with a air/fuel gauge ( I got one if you need to borrow one for tuning). But mostly it is clutching... I have seen so many BAD AZZ engines ROBBED due to clutching. On your RZR you will have to raise stall and have it shift out at a higher RPM.. Maybe shim your primary spring or lighten your weights or a combination of both. THis will put the gains to the ground were you will feel it. Dont look for it to be huge HP gains. Probably talking 3to7 RWHP. But your engine sound will change and it will rev like it never has before. So IF you do it expect to have to manipulate your clutch to see the max gains but dont expect to much gains because you may dissapoint yourself. 3to7 RWHP you can feel in the seat of the pants and it will rev quicker and you mids to high should be a major impovement.

I ported/polished my head and added +1mm swirl-polished valves and I love mine.

On a Rhino 700, the throttle body was 42mm....I added a White Knuckle Racing 54mm Throttle body also. They say it adds 7 RWHP on a built motor, and 5 RWHP on a stock Rhino.

To do the job right you need a flow bench/machine.

Stakk wrote:

To do the job right you need a flow bench/machine.

Yep....the only way to know if you have gone to far or not far enough.

Stakk wrote:

To do the job right you need a flow bench/machine.

If I do it I was going to buy one from the same people that sold me the big bore kit. I would think it would be a good fit.

Stakk wrote:

To do the job right you need a flow bench/machine.

Bam. That's hitting the nail on the head. Not only do you need a flow-bench, you need to know how to read it...........I personally have no clue...You watch a little ball flyin around in a tube....