PORTING a trailblazer 250 jug
Oct 9, 2009 | 10:58 PM
#11
Pro Rider
Joined: Aug 2003
Posts: 379
Likes: 0
My Kaw triple was a drag bike. It was specifically ported to serve that purpose. Pipes, carbs, porting,etc specific. It ran 10.30s in 1975. That is crap now with the new 4strokes but in '75 that was fast. I did ride it on the street but it sucked. The power below 7000 rpm was like a 125 but when it hit 7000 hang on either the front end was going up or the tire was breaking loose or both. Not practical for anything but 1/4 mile. But it was great fun beating the 900 Kaws.
Oct 10, 2009 | 01:02 PM
#12
Weekend Warrior
Joined: Sep 2009
Posts: 18
Likes: 0
I just bought a modified Traiblazer '02. I do not have any technical advice though. But, this one is bored way over. I think 80. and it is ported and polished and head milled. Yes, it does need race fuel.
When I bought this I was told it did not need race fuel. But while riding it I could hear what I thought was slight pinging. So I mixed in some race fuel and problem solved.
This transmission was also modified I guess to handle the extra rip. Now it has a much higher stall speed, but works very well. Machine is pretty loud but for a Tblazer it rips pretty good, pulling the front end off the ground if desired in low speed.
When I bought this I was told it did not need race fuel. But while riding it I could hear what I thought was slight pinging. So I mixed in some race fuel and problem solved.
This transmission was also modified I guess to handle the extra rip. Now it has a much higher stall speed, but works very well. Machine is pretty loud but for a Tblazer it rips pretty good, pulling the front end off the ground if desired in low speed.
Mar 17, 2024 | 10:25 PM
#13
Weekend Warrior
Joined: Jan 2024
Posts: 4
Likes: 0
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.
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.
Jun 20, 2024 | 08:08 PM
#14
Weekend Warrior
Joined: Jan 2024
Posts: 4
Likes: 0
[QUOTE=ftwflh;2853725]
with lowering the intake port does that give it more low end or top end power?
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
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
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