"Smaller ports = more power"??

[jenndnn3]

Yeah but then so are 2 strokes..... Holy Crap I should Duck huh

<---- Jen runs for her life...

I love Jennings... His work matches the technology. But then when something works why change it eh.

Sorry Guys just a lousy opinion... dont take it hard...

[Billy Golightly]

There are lots and lots of things in Jennings book that IS still relevant, but there are sadly an almost equal amount that are not. His pipe formulas are archaic, and have been surpassed by the OEMs since about the time the book was wrote and by the aftermarket before then. The head designs he has, and his explanation/understanding of them has also been proven dated. I'm just saying, theres nothing wrong with using the book as a guide, or a door to learning more, but don't expect it to be the final authority on every subject written in it

[Louis Mielke]

yeah they are ... i'm wondering when i do the opposite to all the stuff i do ...
"Compared to them Pics"
Why is it FASTER ? ... HUMMMM

Ronnie do you do that much 4 stroke porting? I thought you were mainly a two stroke man. I get the feeling his theories and those pictures of the changes Yamaha is making are relevent to two-strokes.

[Billy Golightly]

How many cylinders have you seen that have the intake boost/boyesen ports epoxied up on a 2 stroke, hmmmm...?

[jason 32]

those ports utilize the stock cam carb-ect...
2strokers dont have a cam - -the faster air/fuel can enter ,and leave will eaqual
more power- as long as things are done right-- compression-exhaust bridge height-/transferports -ect...
where do you need more power??? bottom mid or top?- or everywhere??
backpressure-or no backpressure- depends on the application--
top fule?-- max port/-full flow all power-

[Kilborg]

Just caught this thread! GREAT read!

Iv been emailing the motoman and had some great discussion.

Quick story from my standpoint...Having paid for several topend jobs that were topend oriented and fairly unridable (Peaky, small powerband) and getting 52hp at 6800 rpm or so on my 85 atc250r, I was pretty unimpressed. Working in the automotive and diesel field for awile as well as being into bikes iv picked up alot about performance..

I have picked up alot more knowledge on welding at the shop iv been employed at for awile now. Iv gotten to the idea where "Why not try making the port a bit smaller, and then fooling with it some?" My topend was already hacked so I used my spare stocker as a "template"...Added some material and went to town with my dremel...after some tuning and a little trial and error, the machine was putting out 48 horses at 4700rpm, and the powerband is FAR wider. The motor runs more like a stocker with improved bottom end and midrange with more power then stock by a wide margin. Topend is very tame, however...much past 6000 it signs off. Sadly enough, the only shop I know of that did atv dyno tests is now closed. Seat of pants and overall performance against other machines still seems better.....

Not bad for an amatuer, I will more then likely attempt to improve it more over time as I get more ideas on the topic. Its great to see other people thinking outside the box and not just questioning my own sanity.

Also note, I dont reccomend the kinda work I'v done...As a youngin I basically ruined a few lawnmower and weedwhipper motors with my antics...But that is all part of the learning process sometimes I suppose ;p

[3WW Star-Yamahondaman]

Ronnie do you do that much 4 stroke porting? I thought you were mainly a two stroke man.

Yes iv'e done several 4 stroke's... it add's LOTS of torque... the best thing for them is bigger Valves "in the old cyl's" .. the NEW YFZ,TRX 450's are NASTY ..they don't need much
Hey Kilborg .HA HA .. i like what you typed .. i did the same thing when i was 10 years old.. it's like .. "Hey Dad can i fix the mower some more " !! . i used to take the heads off and rub them on block walls to get more compresion