Hey, i was just wondering if there are and easy inexpensive ways to raise the horse
power on a 300ex.
Is there a sprocket change that con be done to help.

I already have a White Bros. E-Series and a K&N air filter.

Also I'm courious to see wat you guys have done to your 300ex.
If you can post some pic's it would be helpful. [img]i/expressions/face-icon-small-smile.gif[/img]


Thanks Alot,
Jake

 

gear up to a 14t front sprocket if you are running 20 inch tires. Get a black box that raises the rev limit by at least 1000rpm. if you have a full e-series including the headpipe your ok if not get the head pipe. cut some one inch hole in your airbox lid if you don't ride in alot of water and make sure your jetted correctly. Get a higher compression piston (no more than 11:1 if you want to run 93 octane) and switch to a used 400ex carb from ebay. Also the airboot from a 350x trike is said to increase the air flow.

As far as the prices:

14t sprocket: $10
black box: $70 - $120
E-series head pipe: $120
Piston (including topend gasket): $110
400ex carb: $40 to ?????

with all of these mods you should be able to raise the HP from ~17(stock) to ~22HP

Add a more aggressive cam with the stronger valve springs and retainers and you might be able to push 24HP. That kit will set you back about $300 and will reduce the reliability by a little.

 

im runnin 22" Mud Lites is there any othere sprocket that would work well with them?
wat if i got a sprocket, black box, and 400ex carb?

also have you done all of this to your ex?


thanks

 

on mine (better say her's just in case[img]i/expressions/face-icon-small-wink.gif[/img] ) i run 14-38 gearing with 20 inch rear tires and 13 - 38 with 22 inch rear tires. The 13-38 with the 22's is actually geared higher than the 14 - 38 with the 20's. What are you looking for more top speed? Since i have a black box with the rev limiter removed completly i try to gear so i won't over rev in top gear. most black boxes have limiters that are simply set higher than factory so your aim would be to gear high enough so you aren't constantly hitting the rev limiter in top gear (if you are indeed looking for top speed).

As far as my other mods (only counting motor): i have an e-series headpipe with a pro circuit t4 slip on. I'm also running a k&n with an outerwear and 6 one inch holes in the air box lid. My pics will be back up soon, i just added some so i have to wait for the Mods to approve them.

I stopped there since it has enough power for my girl to get around right now. So i may be adding the cam, valves, high compression piston, and 400ex carb this winter depending on whether she want to keep the 300 or step up to a 400.

The first thing i would get would be the black box, just be sure to get one that still has a rev limiter built in (not mine). It will give you an extra 1000 RPM which will raise your top speed in each gear.

Then you can determine which sprocket you will need. I can give you much more details including fromulas for choosing a sprocket.

As far as the 400ex carb... this won't help too much unless you are modifying the internals of the engine. on a stock bore stock compression 300ex they will add a little noticable increase in top end power but will also remove some of the grunt right off of idle.

 

Ok, thanx alot i might be able to get that black Box somtime soon. I'm not really looking for top speed as I am loking folr quickness and throttle response and a little more spunk.

Right now i have the the stock header and a e-series slip-on. Does the header really make that much of a difference?

Also can u go ahead and give me those formulas for the sprocket.
I'm only goin into the algebra 2 advanced class so don't make it to complicated.LOL

I do a lot of trail riding, actually thats about all i do....if that helps you any. Also what is your favorite or most recomended tire for trail riding.

 

where do you find a black box at and how much do they cost? for a 250x im right beside the 400ex on drag and trails but i want to get the higher rpms out of the bike so where and do you half tto advance your timing?

 

My sons 300 has a White Bro's mild cam, 12:1 piston, (and yes we run 93 octain with no problems) Uni filter, rejetted, and Pro circut t4 pipe. We have the stock gearing with 22" tires. It runs good, and is a very trailable machine. It has enough pep to get the front end up in a moments notice, and yet it starts easy and seems to idle well. I don't know if someone has changed the rev box on ours, but I have never seen it hit the limiter while riding.

 

The header does make a noticable difference on the bikes ability to rev faster during midrange and top end. Since i put the slip on first and then the head pipe later i was able to notice a difference.

I also do alot of trail riding with the my/her 300ex. If your trails are really rocky and ground clearence to the swing arm skid plate is a concern stay with 22 inch tires, if ground clearence in not important 20's will work just fine. I prefer the 20's when i can get away with them since it lowers the bike's center of gravity making it handle quicker. I personally prefer holeshot XC's (6ply) but any good 6ply tire will hold up well on the trails. Also a tire with a flat profile (think razr's, holeshot's) will allow the rear end to slide easier while a tire with a curved profile will stick more in the turns promoting tipping. since your mud-lites aren' t in your pics i'm not sure but i think they have a flat profile (haven't looked at those tires latley).

Here are some simple formulas that will give you an idea of how gear and tire changes will affect your gear ratio and speed:

#1) first simple gear ratio: (# of teeth of rear sproket) / (# of teeth of front sproket ) = final drive ratio

some examples for the 300ex ( a lower ratio means you are geared higher)

front | rear | ratio
13 38 2.923
14 38 2.714

#2) Gear ratio vs tire size: (rear tire diameter in inches) / ( final drive ratio) = inches of rear wheel rotation for each revolution of the front sprocket

In other words each time your front sprocket makes one rpm you while travel this far...... the farther you travel the higher geared you are.

some examples using the gear ratio's from #1

tire diameter | ratio | inches traveled per revolution
20 2.923 6.84"
20 2.714 7.37"
22 2.923 7.53"
22 2.714 8.11"

These 2 formulas make it easy to determine top speed which i will give an example of below incase anybody needs it (i'm going to do it step by step for the benifit of others) but to gain the quickest acceleration to a given speed is much more difficult and will require you to try different gearing and tire combinations. at least with the help of these formulas once you find something close you'll know how what you change will affect the ratios.

In order to estimate top speed correctly you need you engine's top rpm, the top gear ratio (internal gears), the final drive ratio and the tire diameter.

top speed = ((((rpm / top gear ratio) / final drive ratio) * tire diameter in inches )/ inches in a mile) * minutes in an hour = mph

I'm going to go through this step by step using some made up rpm and top gear ratio numbers since i'm not sure on the 300ex's top gear ratio or stock top rpm.

1) top speed = (((( 8,300 / 0.98) / 2.923) * 22") / 63,360" ) * 60 (putting the numbers where they belong)
2) top speed = ((( 8,469.4 / 2.923 ) * 22") / 63,360" ) *60 ( in this case the front sprocket is rotating at 8,469.4 rpm's)
3) top speed = (( 2,897.5 * 22" ) / 63,360" ) * 60 ( the rear axle is rotating at 2,897.5 rpm's)
4) top speed = ( 63,745" / 63,360 ) * 60 ( with 22" tires the tire is covering 63,745 inches per minute)
5) top speed = 1.0061 * 60 ( or travelling 1.0061 miles per minute)
6) top speed = 60.366 MPH

this fomula can be used for any gear as long as you have the gear ratio .... the ratios are usally listed in the specifications section of your owner manual.

I hope these help you out, they won't tell you exactly what you need but will give you a very accurate idea of where you will be after you decide on your changes.

 

Is that a true 12:1 compression ratio you are running or is it just a 12:1 piston? I know a true 11:1 ratio will work fine with 93 octane but a true 12:1 has alway been hit or miss when it came to detonation running 93 octane at my elevation and summer temps.

If it never hit the rev limiter while riding, especially in 1st gear then i would be willing to bet yours might be modded or removed. the stock limiter was set very low and will easliy hit in 1st and 2nd.

 

thanks a ton Semms40oz that will really help a lot! But i have no clue how to find the top rpm can u help me there. how much will the black box let me go in rpm's?
also you can probably find a black box on e-bay for fairly cheap.