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Any porting experts?

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Im looking to port my 1995 WR250Z cylinder to get a few more ponies out of it.

Thing is, I have no clue about porting specs and how to find them, thus, any porting experts out there?

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Look up turner two stroke. He may have some type of software for porting? or send it off to eric gorr and tell him how you want to it.

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There are some things you can try to gain a bit of HP, before you decide to port the cylinder.

A proper porting job can also involve head mods, pipe and silencer combo, ignition settings,

or aftermarket ignition, reeds, carb, type of fuel, gearing, etc, to get optimum use of the porting changes

The first thing is to make sure the motor is in good condition,

because any minimal wear or worn out parts / leaks can slowly cause the HP to drop more and more. Guessing a WR250 has about 42 to 45 hp new, a worn out motor could easily be down

below 40 hp.

-proper jetting is #1 ...lots of online info for properly jetting a 2 stroke.

if the motor is rich or lean starting at the lower rpm power, it will affect the power curve through the entire rpm, and a 45 hp motor turn into a 40 hp motor really fast

-Most piston ring manufacturers recommend a minimum end gap of .004 inches times the bore diameter for the top piston compression ring, and as it wears, compression is lost.

New pistons also help with power

-a silencer with worn out packing can lose as much as 2 hp on the dyno, by affecting pressure waves of the pipe

-a pipe that is full of carbon / sooty residue will actually change the characteristics / powerband of the pipe, and could lose a couple HP. The engine uses the heat in the pipe, and different temperatures affect the speed of the waves in the pipe. The heat needs to be in the metal of the pipe, and a dirty pipe acts as an insulation barrier.

-check the engine for any leaks from the tip of the airbox, to the tip of the silencer. Any tiny airleaks can cause power loss / jetting to be off, etc. We once found a slightly cracked exhaust, that you couldnt even notice, and changing it was worth 2HP on the dyno. High temp engine silicone can be used to seal most leaks

An easy way to change port heights / powerband / compression ratio's, is to change the thickness of the cylinder base gasket, and can also use copper head gaskets for the combustion chamber, to keep the squish, head volume the same...as little as .010" could be a noticable difference in bottom end / top end power, and help to decide if / how you want to change porting specs

Also, as little as 5mm shorter or longer pipe can change the bottom end / top end power quite a bit. It might not lose or gain any hp, but it just shifts the power curve lower or higher.

Spacers can be made to lengthen a pipe, to see if it helps with low end power.

If you know any body that has a bit of VP C12 or similar race fuel, try running the bike on it

...if you notice a difference, it can be a tell tale sign the engine needs work.

I had a 93 YZ 125 that was like jekyl and hyde when i ran pump gas vs race gas in it

...felt like it was supercharged or something.

I've been building shifter kart engines for a long time, and have seen 125's with close to

50 hp, and some 250's with as much as 60hp. But those were a lot of time and money

to get that much HP out of, and that much power in a bike would probably just make it too hard to ride / and a pain to keep tuned all the time. I've always considered the pipe to be the real "magic" in any

2 stroke motor. I've actually seen as much as 8hp difference on a fully built 125 on the dyno, just by bolting on a spec or works pipe, vs a stock, or various other pipe / silencer combo's

Edited by yamaha7442
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Go read mac dizzy for a few weeks. Get the timing, jetting and squish nailed....and you will likely be pleased. Just remember that more power, does not always mean faster. Match the curve, gearing and riding style for best results.

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@Yamaha7442

Turns out the motor had worn its nikasil bore all the way to the aluminum, and a hole in the airbox let a bunch of grass and rocks into the motor. The machinisht that inspected it told me someone had already ported the cylinder. seems like thats why it had alot of starting issues and had no jump in its step.

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Just noiticed you're in Alberta...which city ?

There is a guy / company in calgary that does

cylinder replating, but you'll need a new piston

so he can size it properly to the new replate .

Theres also another cyl plating place in Quebec,

that does awesome work.

Sometimes this site wont allow

any contact info to be posted, but i can give you

the links to you're email or PM if you want.

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Nah, Ive looked at replating.. too expensive. bought a brand new cylinder for 300 from yamaha.

Skylark out of Calgary will do replating and diamond honing. I agree though, by the time you get an old cylinder replated and honed it will cost you more than a new one. If you are just going to do a top end he charges only $40 for a hone job and will check the new piston for clearances.

Edited by primerib108

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