PORTING a trailblazer 250 jug - ATVConnection.com ATV Enthusiast Community

quadtarded1 · #1 (**permalink**) 10-08-2009, 04:34 PM

I have a question.. I would like to know a little about porting on a 2000 250 tb jug.
I ported and polished the exhaust side "gasket matched " came out great... I need to know whats all involved with doing the intake side, some guide lines of do's and donts.. My father has done alot of chevy small block heads but the 2 cycle thing hes unsure about...
i have heard the term port up or port down.. does this apply to the 2 strokes with carbs or the ones running reed cages????
I know this is technical im sure nothing is easy with mods anyone with micrometer specs let me know...
Also im goin to run a gas oil mixture eliminating the oil take and pump, using a HPD oil block off kit.. inside the intake of the jug is the oil mixture nozzle do you just take this out and plug it ????
Any help with this portion of hopping up the motor will help... I can easily just have RCR do this work but I would like to do it myself 1 for knowledge 2 pride of saying I did everything on my quads myself and 3 knowing exactly what has been done..
thanks people

lslubecki · #2 (**permalink**) 10-08-2009, 07:58 PM

On a Kawasaki 750 Triple (H2) you raise and widen the exhaust port only 3-5 mm. On the intake you actually raise the intake side of the lower piston skirt about 3-5 mm. No reed valves on the triple. As the piston is reaching TDC the intake port is open sooner as the piston skirt is raised therefore more fuel sooner. Then as the piston goes back down the exhaust is open sooner letting the exhaust out and more fresh intake through the transfer ports, scavange, or the exhaust helps the fresh intake charge in.

quadtarded1 · #3 (**permalink**) 10-08-2009, 08:52 PM

So Porting the exhuast to match the gasket wasnt a good idea then? Or should i raise it still?

ftwflh · #4 (**permalink**) 10-08-2009, 08:58 PM

When porting these you dont raise the ports or you mess up the timing.

quadtarded1 · #5 (**permalink**) 10-08-2009, 09:07 PM

ok cool so the exhaust gasket matching will work im assuming then??.. ... so on the intake side what will i do?
and what do i do with the oil injecting nozzle

mrtwostroke · #6 (**permalink**) 10-08-2009, 10:31 PM

If you are trying to create, more top end power. You will lose on the bottom. rasieing the exhaust port will increase the exhaust duration. If you widen it you are increasing lift of the cam. To put it in fourstroke terms. Do you have an aftermarket pipe? Without an aftermarket pipe portng not work so well. I'd start by widening the exhaust port to 65% of the bore. leave the height alone.
On a piston ported engine intake porting can effect your low end power alot. Here read this
http://www.vintagesleds.com/library/...20Handbook.pdf
and this
http://www.kreidler.nl/artikelen/per...raham-bell.pdf
and check out this site
MacDizzy's Two Stroke Technology Exchange - TRX - YFS - YFZ - Glamis Sand Dunes

quadtarded1 · #7 (**permalink**) 10-09-2009, 06:23 PM

Wow theres alot of math involved with this.... thanks for the info I'll be reading for a few days trying to comprehend it all lol...
And as for power im looking for over all power gains.. more in the mid..
I will be using a HPD pipe on this motor and a larger carb also...
thanks again for the info any little bit helps..

ftwflh · #8 (**permalink**) 10-09-2009, 08:50 PM

drop me a PM I have some info but it is privalaged

mrtwostroke · #9 (**permalink**) 10-09-2009, 09:35 PM

a compression increase and squish reduction will be in order then. I'd say.
I bored a 92 250 trailboss today at work. the exhaust port looks pretty small. I did not measure though. sorry.
On the 400 I found the exhaust duration to be enough. the transfer duration seems a liitle shy. intake has lots as well. I haven't done a port map yet, to caclulate time area.
that will be a winter project.
So far I have raised the exhaust port 2.5mm, and widened it 5mm to 65% of 85mm.
The duration is now in the 195 degree mark. which is a little to much for 6500 rpm. It would seem. But need to do a tear down and measure how far the piston comes from the deck. In order to be more precise with my calculations.

What a 250 really needs is a reed cage welded on, i'd steal the flange from a 250 dirtbike cylinder.

ftwflh · #10 (**permalink**) 10-09-2009, 09:43 PM

[quote=mrtwostroke;2853718]a compression increase and squish reduction will be in order then. I'd say.
I bored a 92 250 trailboss today at work. the exhaust port looks pretty small. I did not measure though. sorry.
On the 400 I found the exhaust duration to be enough. the transfer duration seems a liitle shy. intake has lots as well. I haven't done a port map yet, to caclulate time area.
that will be a winter project.
So far I have raised the exhaust port 2.5mm, and widened it 5mm to 65% of 85mm.
The duration is now in the 195 degree mark. which is a little to much for 6500 rpm. It would seem. But need to do a tear down and measure how far the piston comes from the deck. In order to be more precise with my calculations.

What a 250 really needs is a reed cage welded on, i'd steal the flange from a 250 dirtbike cylinder.[/QUOTE

Dont raise the exhaust just widen.Intake lower but dont widen

I dont have the reasons or tech on this but it REALLY works