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650 heads on a 750?

11K views 20 replies 8 participants last post by  Evanrude 
#1 ·
I read the compression increase on the 2012 750 was most attributed to the use of 650 heads. Does anyone know if this a straight bolt-on? I am just curious since I have 4+ years remaining on my warranty and am not ready to start modifying things to that degree. But, if it is a straight bolt-on, it may be worth keeping an eye out for a set of used 650 heads to have ported/polished, etc for the future...
 
#2 ·
Yes 650I heads not 650 prairie heads,the prairie heads would fit and bolt on but intake design is different,the 650I Brute heads have same intake and carb setup,and these will do the compression help.
 
#3 ·
Yep. same heads that cams on the 650i since 2005. they are the new 2012 750 heads as well as the TERYX4 heads. these will also be on the 2 seat teryx heads.

the cam shafts are also much larger duration. this is where the mid-top gains are felt and why they like to rev to7200- 7400 vs the 05-11 models prefer 6800-7000


there will be new custom pistons ready for the new 750/650 heads in a few weeks. were shooting for 67-70 rwhp stock bore

John
 
#4 ·
Thanks for the information guys...I will keep an eye out from time to time.
 
#5 ·
Not looking to hijack a thread but, wouldn't just buying an after market camshaft give you the same results? If not, then can we get an explanation in details about the differences?

Thanks

Dave F.
 
#6 ·
It may (and I would have to dig into the details of the camshafts), but I was (for the future) considering increasing performance in stages with the first to be ported heads and if I am going to port/polish heads, I may as well increase the compression too and the head swap is an easy way to do that. I already run premium fuel so that is not an issue.

Speaking for me, I would not want to install too radical of a cam in the pursuit of more HP, I will assume they are similar to automotive engines and they begin to lope with increased duration and you have to dive into MAP/fuel curve (and possibly injector) changes. I am not quite ready to mess with that aspect of high performance, call me conservative, but I want more power but not at the expense of reliability or increased maintenance or "tinkering".

Make sense?
 
#7 ·
Buying an aftermarket cam be the same as 650I heads?? Yes and NO

go buy and install a "hotcam" you'll gain 2 rwhp. you can only install very small cams with stock pistons.

go install a builder cam (with correct valve pocket pistons) and you are talking 15+ rwhp gains. but to install these you need pistons and valve springs which account for the gains as more of a "package deal"

I see 650i heads making about 2-4 more HP than the 750 head. simply because there is a smaller cc combustion chamber.

this is why 650i machines often run just as well as the 750i machines. you are comparing a 633cc machine to a 749cc mahcine but power outputs are very similar.


now the 2012 brute uses the heads and larger cams. so the 2012 750 vs a 650i, the 750 will crush it.

John
 
#12 ·
Buying an aftermarket cam be the same as 650I heads?? Yes and NO

go install a builder cam (with correct valve pocket pistons) and you are talking 15+ rwhp gains. but to install these you need pistons and valve springs which account for the gains as more of a "package deal"

I see 650i heads making about 2-4 more HP than the 750 head. simply because there is a smaller cc combustion chamber.


John
Wouldn't this fall under the category of a stock bore kit and a stage 3 cam? Usual price?

I looked for 650i heads and even used they go around 800$ together. Going by price and gains I'de say the big bore kit would probably be the best bang for the buck?
 
#11 ·
You have to retune for anything. pipes, airbox mods, snorkels, pistons, cams. whatever. That's really not an issue.


Anyone that's been around motors will know a properly built motor will last just as long or longer than a stock counterpart.

I have 730 motors I built back in 2005 running the same today as they did when I built it 7 years ago and they are 60+ rwhp setups. I put NOS on a stock KFX back in 2004-4005 and there's a guy that still runs it and has never had a single issue.

tuning and setup account for reliability just as much as who put it together and what parts they used.

John
 
#13 ·
John, definitely not aimed at you or your work and there is merit to what you are saying, but I also know the issue I raised is valid too. If it were not, we would not see so many instances of "I just installed XYZ and now my BF does/does not do this" or "I just installed new cam or head or piston or <insert hipo part here> and the engine is doing XYZ" posted here on Kawieriders. The longevity of a properly built motor is directly related to how it is maintained and operated--"hot rods" are typically ran harder than a stock engine and therefore the tendency is for them not to last as long between repairs. In addition, many that modify their motors do so fairly quickly in the life of the car/truck/ATV and thus it is never known how long the stock engine would have ran versus the modified one.

I have built many automotive engines in my time and I know there is a trade-off between reliability and performance (no matter how good the parts are and how well the assembly is done). Speaking strictly for me, I do not want to constantly be working on my ATV, I want to enjoy it on the trails. So I want to be selective on what I do with my BF's powerplant and not create a situation that requires constant tuning/maintenance/work.
 
#16 ·
either way, whatever you do, your warrantys still shit. in my opinion its cheaper to leave the engine stock. not saying it will blow up or anything. but say you do something to the engine, and break an axel. you take it to the shop and they say "sorry but youve voided your warranty. i cant fix this under warranty. its gonna cost you $3453.32" thats just my opnion. which im cheap lol.
 
#17 ·
Which is why I stated in my original post that I had 4 years remaining and was not ready to make any major mods as yet...this was for the future but I wanted to know if the 650 heads would raise the compression. It was information only...
 
#18 ·
oh and hows your k&n on yours? ive got the exact same fourwheeler and i talked to a guy at the shop and he told me that the k&ns dont run right on a brute force. he said every time he sells one the person comes back buying a stock air filter.
 
#19 · (Edited)
I have not noticed any difference between the 2 filters--either positive or negative. The filter has not changed the way the engine runs, but I also have not seen any tangible horsepower improvements either. My primary concern is whether or not the K&N filters as well as the stock filter--more air flow usually equals less filtering capacity. I may have to invest in a pre-filter like a sock to go over the K&N in the event that I see dust in the intake.
 
#20 ·
hmm i might buy one. anyone have any suggestions on how to fix belt slippage? i was riding today and hit a hole that used to be pretty shallow. well not any more. i got half way through it and all of a sudden it sounded like i put it in neutral and was revving it. then it just caught i guess and started working again. but it did make some kind of screaching, squealing noise.
 
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