300ex help!!!

[scott58976]

I am new to this fourwheeling thing so bare with me but i need some serious help....ok i bought a 300ex off a kid his mods were alreeady A Wiseco .040 over 11:1 piston....Supertrapp Full Exhaust with carb jetted...well i went and got my head bored out .080 and bought a Wiseco 11:1 .080 high compression piston otherwords i had it bored to a 297cc...i also went and got a HMF slip on exhaust and will be using the stock 300ex header....and a UNI air filter..i also put on a motion pro twist throttle...14 tooth front sprocket...36tooth rear spocket. ok now i have my engine torn down still i havnt put it together yet..and i was reading through these posts and now im starting to wonder that if i put this thing together the way it is sometihng is gonna screw up... so here comes the questions......should my carb be rejetted since i changed from a supertrapp to a HMF or could i just get a 400ex carb.....should i get an oil cooler.....is it really gonna have that much more power......is it gonna be alot easier to blow up or seize the engine.....is there anything else i should prolly do with these kind of mods??? for example a better cam bigger valves head shaved??? what other ways to improve power with a low budget??? sorry for it bein so long u probably think im an idiot but i would rather be an idiot than put alot of money into a wheeler and have it ruined...so i appriciate it alot Thanks

[bradley300]

your going to have to ride it to figure out if it needs jetted, but chances are you will need to adjust down a tad since you went to the restictive stock header. you shouldnt need an oil cooler and it wont be much faster than a stocker. keep the oil fresh and last just as long as the stock motor did. the shaved head and bigger valves arent needed unless you just want every ounce of power, but before you do all that, i would send the head to be ported.

[scott58976]

Exactly what is porting........and how much would it set me back?

[fluxcapacitor]

Man, i wish i knew about this website when i was building my 300.....just stumbled on it tonight. Anyway, port and polishing is basically taking a grinder and taking out all the imperfections in the metal in the head of you motor. It makes every surface smoother so that the air and fuel can enter and leave faster. If you are doing port and polish work, make sure you are geting your valves angled too. With the 300ex, I would recomend gettin the oil cooler system with any over stock bore application. If all your work is done right, and the motor is re-assembled correctly you shouldn't have any major problems with reliablity. Now keep in mind, you are making the walls of your cylinder smaller everytime you bore it out. This will cause the motor to run harder. I would also recomend an after market CDI/Rev Box with all this work. Good luck, your getting more work done then i ever did to the 300. Oh, one more thing, get a K&N filter, they're only 10 bucks more than the UNI and a lot better performance wise.

Flux

[scott58976]

yea i knw i wish i knew about it too before i did that stuff it sure woulda made things alot easier.........another question with a stock rev box can u run it wide open? and what if i get a high rev cdi how will i knw when to stop openign the throttle up?

[fluxcapacitor]

With the stock rev box, you will hit the rev limit very easy. this happens when you wait too long to shift. All the aftermarket rev box/CDI's do is allow you to not hit the rev limit. This way you don't loose too much pwer between shifts. I don't know if Dyna makes one for the 300, but I'm def. gonna but one from Dyna on my Z. Good luck.

Flux

[scott58976]

oh alright i understand now.....i knw Big Gun has one.....around how many HP do u think it will produce with the mods i got now plus gettin a port and polish and aftermarket CDI with a k&N

[bradley300]

unless you have a high rev cam, your blowing your money on a cdi, becasue the motor will amek peak power well before the stock limiter will hurt you

also, stick with a uni or white brothers air filter. they dont make quite the power, but they filter a heck of alot better

[fluxcapacitor]

Ok, here in lies where opinions come in. I know from personal experience that after I put a CDI on my 300, I was able to beat a friend on a warrior consistently in a drag race. Before the CDI we would go back and forth. They are so cheap for this bike, its worth having the extra RPM's so that you don't loose power, that is just my opinion. Yes the UNI and White Bros. filters do filter the air better, because they are foam filters. The K&N is a much better performance filter and in order to have clean the air just as good, put an outerwear cover over it.

As for your horsepower #'s, it is hard to say. In the original post you said you bored out to 297cc....i'm pretty sure that stock is 298cc. If your going .080 over, now someone correct me if i'm wrong, i think you're around 370cc. I've seen 300ex's with 370cc, cam work, port and polish, and full system pipes handle up on piped Z400's in a drag race. So a GUESS on HP would be around 37-39ish.

[bwamos]

A new CDI with an increased rev limit is definatly a bonus on the 300ex.

It benefits the 300ex more than most other quads, in the fact that the 300ex rev limit is horribly low. I should be 1000rpm's higher off the factory floor.

Most quads you wont see an imediate benefit.. but with the 300ex.. the benifit is there right away.

However... the origional poster will benefit the most IMHO from getting rid of that tiny tiny stock header and getting a real header. FMF & White Bro's both make good headers for the 300ex and they should both hook right up to your HMF Slip-on.

The HMF silencer is a bit less restrictive than your prevoius one.. BUT as is.. the header is your restriction, not the silencer. Jetting should be close, if it was correct before. Replace the header, punch the lid (or get an outerwears lid), and you'll see a great improvement, everywhere.

The 300ex also benefits greatly from a goot port polish and valve job. But.. you can always do that later. It only takes a few minutes to get the head off. I wouldn't port the head yourself.. have a pro do it.

[bwamos]

Originally posted by fluxcapacitor
As for your horsepower #'s, it is hard to say. In the original post you said you bored out to 297cc....i'm pretty sure that stock is 298cc. If your going .080 over, now someone correct me if i'm wrong, i think you're around 370cc. I've seen 300ex's with 370cc, cam work, port and polish, and full system pipes handle up on piped Z400's in a drag race. So a GUESS on HP would be around 37-39ish.

300ex.. stock displacement is 282cc's 74mm x65.5mm and puts out about 15hp at the rear wheels (18 at crank).

0.080" over (2mm) = 76mm x 65.5mm = 297cc

With the mods he has (assuming he will replace the pipe), he'll probably get about 23-24hp tuned correctly. With the stock header, he's not going to break 20hp.

23-24hp may not sound like much.. but that's a HUGE improvement over a stock quad. 60% power increase.

[fluxcapacitor]

ok, thanks for the clarification bwamos. I just had a brain fart!:D

[scott58976]

thanks for all the help u guys sure do know a hell of alot more than me lol......why wouldnt wouldnt u do the head urself? i think i got the right tools and my dad owns a wood sop that has air tools that can probably do that...one more ? ..how fast u think it will top out with them mods including my 14/36 sprokets? would it keep up with a stock 400ex???

[elementryder]

acceleration will suck but top speed will be close

[scott58976]

I decided to port and polish it myself.....how much bigger do i go??? thanks and i was told i should only do the exhasut is that true ?????? what is the best way to do a port and polish job?

[Ryanwolfe911]

Be very careful. You can't add material back to the head. I have found that just match-porting the intake and exhaust ports makes a hell of a difference. And it's super easy. I don't think I have heard of anyone using Extrude-Honing on the head ports, but why don't you give it a shot. The stuff is all the rage on top fuel dragsters. They basically pressure feed this really abrasive clay through your head ports, and it polishes surfaces you couldn't even touch with a grinder.
check out they're website, and click on abrasive flow machining.

[300exrider25]

i would let the pros do it for you but if you do do it you need to to both the intake and exhuast if you want the most power out of it. all you want to do is smooth all the rough edges that might let more fuel or exhuast through if it was smooth. you are basically making the ports bigger so more can flow through and be careful so you dont make it worse than it already is.

[scott58976]

how much bigger should i make the intake port opening? ex: like .030 ....and the exhaust?

[scott58976]

i need some help

[300exrider25]

im not exactly sure how much bigger but you can call mickey dunlop at four stroke tech and ask him just go to 4stroketech.net to find the number and you have to call between 4 pm and 7pm eastern time

[humblesquirel21]

i dont mean to steal this thread or anytihng but you guys seem to know the 300's engine well and i have a question about honing if its not to much trouble


i just rebuilt my 300 stock bore with an 11:1 comp. weseco

its a 2003 with a substacncial amount of hours on it I wasnt aware of honing till this evening. how important is it my engine is completly rebuilt but still seting on my bench

should i tear it down and hone it then rebuild again


this is my under standing of how to hone take a wire bush to the inside of the cylinder carfuly and clean/refresh the walls then finish the honeing with a light sand paper like 280 grit this is what weseco instructions say is it the correct way to do it

[scott58976]

i would tear it back down and hone it out since it doesnt take it that long to do it....and if u are gonna hone it out i would have a pro do it

[humblesquirel21]

havein a pro do it is a problem theres no one in my area that can really do good engine work unless i drive an hour and 15 mins down to magic racing and chuck the engine guy down there is a master but hes allways really busy so i wont get my head back for awhile


if the inststructions are correct it sounds pretty simple but i dont know if their correct (by correct i simply mean that i intrpruted them correctly Im sure weseco knows what they are talkin about)

[kd5sfq]

Originally posted by bwamos
300ex.. stock displacement is 282cc's 74mm x65.5mm and puts out about 15hp at the rear wheels (18 at crank).

0.080" over (2mm) = 76mm x 65.5mm = 297cc

With the mods he has (assuming he will replace the pipe), he'll probably get about 23-24hp tuned correctly. With the stock header, he's not going to break 20hp.

23-24hp may not sound like much.. but that's a HUGE improvement over a stock quad. 60% power increase.

I agree, 23-24 HP is about what you will see on a dyno.

[Sjorge450R]

Originally posted by scott58976
I am new to this fourwheeling thing so bare with me but i need some serious help....ok i bought a 300ex off a kid his mods were alreeady A Wiseco .040 over 11:1 piston....Supertrapp Full Exhaust with carb jettedpiston

why would you get rid of the Supertrapp pipe????

[bwamos]

Probably looks.

But, I agree the Supertrapp full system is a much better setup than an HMF slip-on and stock header.

[Sjorge450R]

Originally posted by bwamos
Probably looks.

But, I agree the Supertrapp full system is a much better setup than an HMF slip-on and stock header.

I think the Supertrapp looks bad arss. Big polishable silencer with a flat black header??? Why does everyone hate Supertrapp?

[scott58976]

the hmf gives it alot more power and sounds alot better than mine......plus i got rear ended and it had a nasty rattle in it

[Sjorge450R]

Originally posted by scott58976
the hmf gives it alot more power and sounds alot better than mine......plus i got rear ended and it had a nasty rattle in it

how do you figure that a slip on gives better power than a full system. Another thing, how is a HMF, a non-adjustable exhaust going to be that much better then the IDS-2 which is adjustable for top end and bottom end???? Not trying to start anything here, just pointing out some facts.

[scott58976]

yea u do got a point but the pipe was junk anyways i couldnt reuse it

[exkid300]

If you want more power get the DG rcm head pipe it fits perfect...

[scott58976]

how much will that cost me?

[scott58976]

how much will that cost me?

[humblesquirel21]

i would estimate around a 150 give or take id personaly get an hmf header to match your hmf pipe

[scott58976]

do u think i will be able to keep up with a 400ex

[scott58976]

anyone?

[humblesquirel21]

its not likely if the riders are of equal skill a 300ex goes 56 stock and the 400ex goes 69 so with some modifications both quads can prolly squezes out another mile an hour 400ex=70 ish and the 300ex =57 ish thats jsut my estimate through educated guessing. My 300 might keep up with a stock 40 but if you look in my sig i have a crap load of stuff on it most importantly for top speed is my gearing being at 4/36 and my over rev box

just my .02 i chould be wrong

[scott58976]

yea mine aint stock either...Wiseco 11:1 piston bored.080 over...HMF Pipe...Jetted carb...Hot Shot CDI High Rev Box...Port and polish...the head shaved .020...14/36 gearing with 22 inch tires...............so u think that will keep up with a stock 400ex...........how fast does urs go?

[scott58976]

and the reason why i havnt tested it to see if it will is because my motor aint all the way back together

[scott58976]

anyone?

[bwamos]

Originally posted by scott58976
yea mine aint stock either...Wiseco 11:1 piston bored.080 over...HMF Pipe...Jetted carb...Hot Shot CDI High Rev Box...Port and polish...the head shaved .020...14/36 gearing with 22 inch tires...............so u think that will keep up with a stock 400ex...........how fast does urs go?

If you have an aftermarket filter (K&N or UNI style), have the airbox lid removed, and everything is tuned correctly (depends on what it was ported/cammed for) you should keep up with a stock 400ex.

I didn't read the entire thread... you did get a cam right? You really need one matched to your porting and compression, if you haven't. No need to answer the cam question due to my lazyness.. just a heads up.

[scott58976]

no i didnt get a cam yet u think it is really neccessarey with them mods??...and i got a K & n filter......what is the top speed of a stock 400ex

[scott58976]

no i didnt get a cam yet u think it is really neccessarey with them mods??...and i got a K & n filter......what is the top speed of a stock 400ex

[humblesquirel21]

400ex top speed (for the old one) 69mph
300ex=56mph

[scott58976]

ok i got a problem i dont know if it is a big problem or not though.....i just put together my engine andi fired it up to break it in and it sounds awsome except for a very load knocking noise. i have no idea what it is and my pipe got hot really fast like i didnt even run it for 30 seconds and it was too hot to even touch really quick.....and the knocking noise is coming right where the valves are... the only thing i can think of is that when i put the stock head gasket on i had it bored .080 over so it stuck over the edges a lil could the piston be hitting that metal gasket??? PLease help me! thanks alot

[Sjorge450R]

Originally posted by scott58976
ok i got a problem i dont know if it is a big problem or not though.....i just put together my engine andi fired it up to break it in and it sounds awsome except for a very load knocking noise. i have no idea what it is and my pipe got hot really fast like i didnt even run it for 30 seconds and it was too hot to even touch really quick.....and the knocking noise is coming right where the valves are... the only thing i can think of is that when i put the stock head gasket on i had it bored .080 over so it stuck over the edges a lil could the piston be hitting that metal gasket??? PLease help me! thanks alot

did you remeber to adjust your vavles?

[scott58976]

i adjusted the valve clearnece and it is still making the same sound

[scott58976]

also if u listen very closy there is like a pinging sound to it

[scott58976]

anyone????