Any reason I can't bore a 200 out to a 220

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Tioli
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Any reason I can't bore a 200 out to a 220

Post by Tioli »

Hi
I have a spare H model barrel that needs re coating so working on the theory that there is no replacement like displacement I can't see any reason not to put a aftermarket 220 piston in it?

As I see it without experience:
Move the rear boost port back 1.5 mm
220 head
Shave a bit off the front of the powervalve

Are the barrels the same height?
Are the top of the exhaust ports the same distance from the top of the cylinder?
Any reason?

Really apreciate others experience on this one.

Thanks
Tioli
2001 KX125 with a 1997 KDX Tioli Hp motor

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Re: Any reason I can't bore a 200 out to a 220

Post by dingerjunkie »

Given the plated cylinder, it may be less effort/cost to purchase a 220 top-end for the bottom-end you have. Nothing wrong with the idea of a bore/replate/piston match, but replacing with ready-to-go parts may be more time/cost/effort-effective.
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KarlP
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Re: Any reason I can't bore a 200 out to a 220

Post by KarlP »

Eric Gorr used to do a 225 bore for the KDX. I assume he still does.

Fredette Racing also is a good source for what can be done.

There are port difference between the 200 and 220 cylinder. I think when going bigger most people prefer to start with the 200 cylinder, so you are good there.
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Any reason I can't bore a 200 out to a 220

Post by pumpguy »

The 220 was designed with more milder porting for better low end performance. The books I have show the following:

On the 200, the transfer ports have an open duration of 120 degrees, 60 degrees either side of BDC, while the 220 has a duration of 112 degrees, 56 degrees either side of BDC.

On the 200, the exhaust ports have an open duration of (low speed) 157.6 degrees, 78.8 degrees either side of BDC. High speed (KIPS open) the duration is 185.4 degrees. My books show the 220 has an exhaust duration of 180 degrees, 90 degrees either side of BDC. Unfortunately the book doesn't say if this is with KIPS open or closed. I'm guessing this is with KIPS open. The book doesn't say what the other duration is.

What this all means is, what type of performance you are looking for will determine the port timing you will want to have in your cylinder. To really know what's going on, you need to mount a degree wheel on the crankshaft and take piston height measurements in the cylinder at the various positions shown on the degree wheel.

If you take a 200 cylinder and bore it out, you won't get the same performance as a 220, because you will still have the 200's port timing.

And then of course there's the question of exhaust expansion chamber dimensions, carburetor size and jetting, and ignition timing.

Lots of room for experimenting, that's for sure. Good luck!
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Tioli
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Any reason I can't bore a 200 out to a 220

Post by Tioli »

Thanks for the feedback so far guys.

The port timing is particularly useful. RB said from memory the 200 exhaust port is about 1mm higher.

It's been 25 years since Iv had a degree wheel out but from memory 185 degrees is pitched at about 10,500 rpm peak hp. The 120 for the transfers is a little low as a ratio to 185 more like 122. Then you do have a variable exhaust so there has to be a compromise. I have noticed the angle is step to the back which is more midrange but the roof is quite flat which it topendish. Not to worrie it all workers just fine and I have no need to change it. I like the drive it has with the RB package and then over 6k it's just wheel spin.

I'm prepping my barrel

http://www.trials.com.au/forum/viewtopi ... &start=420

And figure 20 extra cc will equate to 10% across the range. Then there is the clean up and a few other little individually meaningless touches
The difference in the degrees of the 200 to 220 would put RB's memory inline with the figures which has to be taken into consideration when he machines the head for me as that's one mm les compression.

Now anyone have a spare 220 head I can use. Don't mind if it's very second hand, Ron will do the best he can with it :grin:

BHW has anyone ever mentioned how good his carby mod is.
2001 KX125 with a 1997 KDX Tioli Hp motor

My KDX journey starts at the bottom of this page:
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Trials.com.au / Forum / All about...me! / My long time friend the prancing horse / page 9
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Any reason I can't bore a 200 out to a 220

Post by royadams »

When you bore it bigger you will also change the port timing, the ports are angled .and you can just have your head machined to fit the cylinder. Thats what Eric does with a big bore job.
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Re: Any reason I can't bore a 200 out to a 220

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Tioli
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Any reason I can't bore a 200 out to a 220

Post by Tioli »

The ports are reasonably flat across the top. The rear boost port will have to be recess the same amount as its bored 1.5 mm the rest seem like they will be ok. No doubt there there will be a change but I'm guessing it won't be to far off the mark.

RB said:
The KDX 200 head does not make a good 220 head as the spark plug hole is spot faced deeper into the head casting and because of the placement of the hole being offset the combustion chamber can not be re-cut out enough the give the proper volume for the 220. I’d go with a 220 head for your project.

Hence the need for a 220 head.

I want to go with a 220 piston because the associated parts are plentyfull and I want to do a bit more shaping on a wossner piston.
2001 KX125 with a 1997 KDX Tioli Hp motor

My KDX journey starts at the bottom of this page:
http://www.trials.com.au/forum/viewtopi ... &start=160

Trials.com.au / Forum / All about...me! / My long time friend the prancing horse / page 9
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