kx500 outlaw kart motor

[funkj]

first off; Great site, lots of really good solid info, hats off to those that provide it. Thanks so much. Thanks

I'm a long time kart racing dad, years of building  and racing two strokes on the national level. mostly IME 100cc, KT-100 cc yamaha, Cr-125's and a host of 200cc Yamaha motors for fun.

Recently, I've been "volunteered" to help a struggling 500cc  outlaw kart racer of a mutual good friend. I The only one in class running a bone stock kx-500 with a Sup pipe and a mid pack racer who I'm guessing is just outclassed by better prepped motors.

Un familiar with the kx-500 other than my week of lurking/reading self educating.ive never been a fan even in kartting for an all out top end motor and always been a fan of a motor with good mid range/ upper power. So saying that I think I have talked myself out of elimination of the power valve presently the stock motor has a good mid range/upper pipe by straight up performance.

My thoughts at this point right or wrong and certainly acceptable and open to to advice and critical opinion.


1. Raise cylinder to zero deck or deck to zero.
2. Like to shoot for 194 ex duration.
3. Clean widen transfers, possibly raise but like to keep a reasonable blow down number
4. remove exhaust sub port wall.( Not sure what to do with compression bump)
5. Clean / widen exhaust port.( Stay with 75% ish of bore possibly)
6. Open exhaust floor back up from raising cylinder.
7. Make modifications/clean power valves.
8. Raise booste port
9. Clean/port intake
10. Modify intake for v-force Reed cage.
11. port / clean transfer main/aux.
12. Cut head for :
        A. 1.3 to 1.5 squish clearance.
        B. 5 degree squish angle
        C. 35cc chamber installed.

Note: I've heard of several national guys running kx500 with out power valves but I'm not wanting to put this guy in a balls out top end motor with a bunch of piston maintenance.id like to shoot for so.ething in the 8600 rpm power range.

Flame away guys..

           

[billb]

He should be beheaded for removing it from the bike!

[funkj]

Oh boy, and I thought Ford blue loyalist were bad.

[umberto]

I think your project sounds fun.  I love it when people think outside the box with our favorite big two stroke.  We have a few guys on the site that are very well versed in modifying the 500.  Some of them don't get on very often, so it make take them a few days to comment.  Be patient though; there is a lot of knowledge on this site.

[funkj]

Umberto, thanks for the support.

Yea, this guy is in a field dominated by Honda CR-500's. Im not particulary brand loyal between Honda/Kaw but Ilike you I'm encouraged to help the guy outside the box. I'd like to see this guy in the front row, so I'm gonna give it my best, and a kinda of pay it forward effort to help out a racer.

[sandblaster]

Oh man.... I've been wanting to do a KX500 Kart engine for some time....
Jason Tanner who does all my builds for me has been doing several CR500 Kart motors but it seems in that game KX500's are far and few between.
In fact, his build won the local championship last year.

https://www.youtube.com/watch?v=wEC_voeVpws

Can you make the KX500 competitive?
Oh yes you can.... 
Most of what you said you would like to do is ok.
But there is some easier ways to do it.
Don't raise the transfers or ports... Lift the entire cylinder using a spacer and two base gaskets.
A good number to shoot for on the port timing is 191.
191 give a good all around power range...
Don't get me wrong, 194 will work but it will start making the engine a bit peaky.
You can get really close to 191 by lifting the cylinder approx .080".
That means you would need a .060" aluminum spacers available from Cometic, one .020" standard base gasket, and one modified .020" base gasket also available from Cometic.
But before I go further, is the engine pulled apart?
If not, watch this vid and get the info asked for.

https://www.youtube.com/watch?v=eTjceU2M7kw&t=110s

[funkj]

Sandblaster, thanks for the responce. After lurking for a week I was hoping you would would be one of those who offered advice.

Yes, I'm excited to do the project. Just watching him run mid pack with a bone stock kx5 eBay motor with who knows what kind of time on the motor against some well prepped pro build Cr's motors I hope is an indicator there is a ton of potential in a Kx5 equally prepped.

His present plan is to buy a used cylinder/head and make the proper modifications and continue to race his present motor and at some point change them  over and have the same modifications for a spare cylinder/head. Maybe even change the second cylinder/head up a bit depending  on the performance of  the first.

He located a in-expensive 85 cylinder (non Pv) that needs plating but I really didn't feel as if I had enough info/knowledge to pull the trigger on that and suggested we stay with the same year cylinder for simplicity.

[sandblaster]

What year engine is it?
What fuel do you plan to run?
What carb and intake is on it?
Does it still have all the gears in the trans or are you using only one gear? Usually 4th...

[funkj]

1.Not sure what year, he hasn't identified it yett but he thought it was 88 or 89.

2. I think right now he runs 93 pump

3. Stock carb/intake/reeds and cage.

4. No gear delete , yet.

5. I thought he ran a Sup pipe , but my buddy says he run's a stock  pipe.

[sandblaster]

Ok, well... there is plenty of room for improvement   

One thing to remember.. When you have the cylinder plated, be sure to add .001 inch of extra clearance.
Kart engines get ran on the cold side and I have seen a number of them cold seize.

There are some key differences in the cylinders by year,

Post a pic of the left side of the cylinder...

You don't want the 85 cylinder.

[1901306708]

My couple ideas. Take em or leave em.

Blowdown is way more important than transfer duration.

That center powervalve is a joke. You want a nice clean (as flat as you can get without catching a ring or piston) exhaust port edge to send a good pulse into the exhaust. That's the most important thing of the entire cylinder layout in my opinion.

Going to a bored kehin at 41 added a couple thru the powerband on a stockish engine. If you get a motor that flows, a 44 will add 3-4 on top of that.

The kx is not set up for making power. Need help to make it flow. Gotta do it all to get big gains, otherwise your just talking 1-2-3 hp here and there. Cylinder work, pipe, carb, compression, timing all need major help in my findings on the dyno.

[funkj]

My couple ideas. Take em or leave em.

Blowdown is way more important than transfer duration.

That center powervalve is a joke. You want a nice clean (as flat as you can get without catching a ring or piston) exhaust port edge to send a good pulse into the exhaust. That's the most important thing of the entire cylinder layout in my opinion.

Going to a bored kehin at 41 added a couple thru the powerband on a stockish engine. If you get a motor that flows, a 44 will add 3-4 on top of that.

The kx is not set up for making power. Need help to make it flow. Gotta do it all to get big gains, otherwise your just talking 1-2-3 hp here and there. Cylinder work, pipe, carb, compression, timing all need major help in my findings on the dyno.

I'm definitely open to suggestions..

1. I'm unclear on you center Pv comment if your suggesting it's removal I'm not sold completely on keeping it. However I'm apprehensive on its removal due to my inexperience. I don't want this a top end peaky narrow  band build with a bunch of piston maintenance.keeping in check he has a mid/upper pipe designed around a 8600 rpm and a track that doesn't have to have a top end 200 hp alky motor to win.

2. Also unclear of the blow down comment, maybe eluding to cut the ex-port to desired duration  rather than lifting the cylinder and keeping stock blowdpwn transfer numbers.

I appreciate the comments.

[funkj]

1901306708

Re read your comment and see where you where going and the importance of port shape and efficacy regarding blowdown and duration not being the only important factor.

It does raise the question if a guy left the center valve at what point can you modify it and know where you have achieved the most efficient usefulness on both ends. Good old fashion R&D.lol

[sandblaster]

Here is food for thought...
You are driving very small diameter tires.
Yes, they are wide but you can only apply so much power to the dirt and drive forward and not spin the tires.
From what we learned on the championship kart is that smooth usable power is where it's at.
It's a learning curve based on your track size and conditions.
Sometimes you have to go slower to go faster.
That is why you can go to 10 different tracks with the same set up and some you will do good, others you will get destroyed.
Kart set up and engine tuning will play a huge part in winning and loosing.
Don't over build is my suggestion... it's tempting to do but will hurt you far more then help you.

On your Kart are you using fourth only or are you shifting?

[funkj]

Here is food for thought...
You are driving very small diameter tires.
Yes, they are wide but you can only apply so much power to the dirt and drive forward and not spin the tires.
From what we learned on the championship kart is that smooth usable power is where it's at.
It's a learning curve based on your track size and conditions.
Sometimes you have to go slower to go faster.
That is why you can go to 10 different tracks with the same set up and some you will do good, others you will get destroyed.
Kart set up and engine tuning will play a huge part in winning and loosing.
Don't over build is my suggestion... it's tempting to do but will hurt you far more then help you.

On your Kart are you using fourth only or are you shifting?

I think that track the locals use 3rd/4th.

It's a hard lessons but the simple fact is you can't win with a great motor, poor driving and poor chassis, nor can you win with a great chassis, poor motor and driver or a great driver and poor motor and chassis. But you can win consistently with a good driver, good motor and good chassis.

As far as smooth on dirt in outlaw class it just isn't as critical as other classes and other kart venues that don't have the power to re-cover. I've seen   both in outlaw the smooth driver who drives radial preserving corner speed to the guy who pitches his kart and clutches for a big hit off every corner.

I prefer not to put the driver in a motor that he can't carry corner speed without clutching and upsetting /unloading the kart to keep a usable power band or adding teeth and gearing himself out..it's a balance act.