Yfm350 serious power build!!

['00 WO-YA!]

It nearly seems like an oxymoron right? Associating our engine with making good power, no way, that's for 2 stokes & more modern 4 strokes right? It sure does seem that way, search the web over & you'll find that the majority of people do the big 3 & beyond that suggest just getting a 450, kinda sad really Yup, the 450's are badass & have tons of power potential but how about this. Lets build one of these engines to make some good power, what would we do, it doesn't have to compete with 450's but has to have that, "WOW, THAT'S A WARRIOR!" effect. Can we make suggestions on different levels of displacement like say 350- 366cc's, up to 400cc's & then 400+? I have 2 engines, both in need of rebuild, I wanna do like a 362 or 366 with one engine with a good cam, simple head mods & stuff like that. Basically a budget performance upgrade, I'd like to get 26-28rwhp from it, the other engine I wanna go all out with, just make it as nasty as possible. I'll try to start......

 

['00 WO-YA!]

It was suggested to me from someone reputable in this business to do this, bore the cylinder til true, .040, .060 or .080 over, whatever clears the cylinder, use a quality 10.5:1 piston, referably JE in my case, a quality valve job & I will blend the rest of the port myself. It was also suggested to me to use a .450 lift cam with quality springs, new timing set (possibly adjustable cam gear) & chain guides & an upgrade carb, 38mm I believe, properly jetted ofcourse. I've left out exhausts & intake systems b/c most people already have suitable equiptment & don't change it. I was told that this setup would yield 26-28rwhp & run nicely & that I should bump my front sprocket to a 15 or 16t so the engine could "use" the powerband. I currently have a 14t & 20" holeshots btw. So what are some of the more serious mods that you guys have & what kind of results? This is to make finding good info & power combinations easier to find for those searching for options-thanks, James

 

[duneracerweston]

First off a .450 is way tomuch cam for a warrior a 415 or 430 is about as big as you are gonna wanna run and. A +1 intake valve and as for intakes go with a 38mm carb and a alum air box eathe cfm or um racing with a k&n with a outer wears and for exhausts a fmf. Power bomb header with a white bros e series or yosh pipe and I think id run 12:1 comp for max power if you don't mind running race fuel that should get you between 30-35hp and that about all you can do except cam timing and flywheel key

 

[bones]

well if your thinking outside side of the box for the 2nd motor there are a number of big bore and stroker kit out there of the warrior

JE has the 366cc kit

Powroll has a 365cc kit and a 430cc stroker kit

CWR has a 400cc and 410cc big bore kit as well as a 460cc stroker kit

FST has the 446cc stroker

Hotrods has a 379cc stroker and had (but you can still find on Ebay) a 396cc stroker

And if you wanna get real crazy there is parts list on here for a kit FST had but no longer offers 500cc stroker
http://www.yfm350.com/forums/showthread.php?t=15103

 

[Jebbysan]

Personally after riding again today...and getting a groove on how I ride....I would do a big bore....these things do not need anymore torque....I would like to do a 86 or 87mm motor...10.5 gas ported piston and big webcam..(.430/.430)
+1mm stainless valves...5 angle valve job...my port job....massaged chamber
Round this out with a big 39mm carb....
It would still have a good mid range hit...but it could rev out up top.....
Another thing I would do would to balance the crank/piston/rod assembly for smooth running at all rpm's....

Jebby

 

[duneracerweston]

A lightened flywheel aftermarket electronics and all the motor mods and it would run!

 

['00 WO-YA!]

Awesome! Now we're bench racing, lol! Weston, I personally thought that the.450 cam was gonna be a bit much as well & was thinking about the CWR .415 but again, the .450 is what was "Suggested". Now, Jebby, Web cams has 2 different .430 grinds right? Which of the 2 were you suggesting? As far as compression goes, I'd love to do a 12:1 but it's just a tad too inconvenient for me to find good fuel where I'm at. On to exhaust, rarely does anyone suggest changing the headpipe, what is the advantage here? I've cleaned up & smoothed the weld at the flange of my header & it's sweet! Also, I have an oldschool "Race" adjustable Supertrapp & it's a lil loud but has actually grown on me, I'd rather spend $500 on a real big bore than changing exhaust unless someone is gonna say that it's a total piece of junk. Next, what 39mm carb & what do I need to hook it up specifically, I'm talkin from cables to filter attachments etc. Remember, this is supposed to be an informative thread where people kind find complete info!

 

['00 WO-YA!]

Thanks guys, this thread is shaping up nicely! Oh, Weston, I think we can prolly both agree that the .450 would be quite a bit more tame @ larger displacement (430+) Not sure why it was suggested for a 362-366 build unless it was thought that I just wanted to drag race, I did mention needing to spank some Blasters, lol! Maybe there's where it comes from, idk.

 

[duneracerweston]

The .450 is built for top end power only

Th oem head pipe flows enough but not optimum the fmf flows a lot better on a all out motor then the stocker I changed mine because I broke my oem one and good lord it opened up I wasent suspecting that

As for carbd kehin makes the 39mm and makuni makes the 38mm and both should come as a comprete bolt on kit

 

[Jebbysan]

Now, Jebby, Web cams has 2 different .430 grinds right? Which of the 2 were you suggesting?

The .430 straight across....the other one is .430/.390....
I would fortify this with premium springs and titanium retainers....viton valve seals and stainless valves....At 87mm...I would also scribe the bore into the head and radius the chamber to the edge of the bore for optimal quench....
The Stainless valves would have a 15 degree back cut on them for Low Lift flow....like I said a 5 angle valve job and a nicely ported and blended
I and E port will make a screamer out of this.....I could see this going well over 8000 rpm and making good power....
The 10.25 and 10.5 pistons are just a number....A 12 to 1 piston with a radiused chamber and large cam would probably live on pump fuel....
The cranking pressure would not be so great with the big cam....
This could make an easy 35 horsepower in my eyes....

Jebby

 

[duneracerweston]

If you ar wanting a pump gass 12:1 your going to haveto do a tad of head shaving to get the compression down to around 11.5:1 or lower

 

['00 WO-YA!]

Weston, good to hear that you've had good results from the FMF, I've actually thought about it pretty seriously, hoping for a lil power & to quiet down the Trapp a tad, although I really like the Trapp, THUNDEROUS @ distance witha friend riding my junk! Jebby, for budget & simplicity, ya think the 12:1 JE 366 would work out ok? I'd love to do the 87mm with my spare engine but my goal is to get this thing running strong over the winter for next spring. Btw, who do you suggest for the valve job? Oh, any experience with those 2 carbs, is one preferable over the other or are they pretty par & where do I find them?

 

[duneracerweston]

I run a 38mm mukuni never run a kehin on mine before so I'm no help there

 

[beastlywarrior228]

id say a 37mm fcr would be good for a stock stroke motor but for a 446 the 39 would be best

 

['00 WO-YA!]

I run a 38mm mukuni never run a kehin on mine before so I'm no help there

Is that a takeoff carb from another quad or a kit from a retailer? Where'd ya get it if ya don't mind me asking?

 

[beastlywarrior228]

you can get it off ebay or duncan sells the 38mm keihin. a 37mm keihin fcr comes off a 250f bike and 450 quads like the trx450r use the 39mm fcr

 

['00 WO-YA!]

you can get it off ebay or duncan sells the 38mm keihin. a 37mm keihin fcr comes off a 250f bike and 450 quads like the trx450r use the 39mm fcr

Thanks guy, a lil bit of reading makes the FCR sound pretty good. What would I need to make it work & what are the chances of getting a good used carb from ebay ya know? Also, the Edelbrock is bragged upon, is it big enough to support good power or gonna be restrictive?

 

[87warrior917]

If you ar wanting a pump gass 12:1 your going to haveto do a tad of head shaving to get the compression down to around 11.5:1 or lower

If you shave the head it will up the compression.... Just go with a 10.5:1 JE piston. Your not gonna feel that much of a difference between the 2.

 

[beastlywarrior228]

Thanks guy, a lil bit of reading makes the FCR sound pretty good. What would I need to make it work & what are the chances of getting a good used carb from ebay ya know? Also, the Edelbrock is bragged upon, is it big enough to support good power or gonna be restrictive?

eh i dont see whats so good about the edel but with some carbs youll have to modify for a thumb throttle or use a twist

 

['00 WO-YA!]

If you shave the head it will up the compression.... Just go with a 10.5:1 JE piston. Your not gonna feel that much of a difference between the 2.

Haha, I knew what he meant, I just didn't wanna say anything, he was talking about relieving the chamber of some volume but it came out wrong, lol! Yeah, milling the head would increase compression for sure.