View Full Version : "Smaller ports = more power"??

08-08-2007, 05:17 PM
Visit this link and tell me what you think. Somehow, I don't believe that everyone who has had their heads ported and polished is lying through their teeth... http://www.mototuneusa.com/think_fast.htm

08-08-2007, 05:47 PM
I think he absolutely 100% correct about how people think...

08-08-2007, 05:56 PM
Well their not necessarilly "lying." The other guys that port differently have found a method that they like. This guy has found his.

Its all about trial and error. This guys seems to have found something that works. Ive read half way through, Im going to sign up for his newsletter.

Pretty interesting stuff.

08-08-2007, 06:21 PM
but.... he said he was useing stock carbs on his bike

i can see a stock carb not likeing a huge ported head

if he is right why dont the nhra top fuel cars use stock heads....lol

hes right to a point but nothing is always right or true

Jason Hall
08-08-2007, 08:34 PM
I believe what he says It true. Velocity speeds up the air flow & kinda acts like a supercharger. If you pulled air through a paper towl tube the velocity would stay the same In & out. If you pulled air through a transmission funnel, the velocity would be much higher, your scooping alot of air & forcing It through a small opening.

08-09-2007, 01:46 PM
I look at my V-Force reed cage and understand what this guy is getting at. The intake side of the cage is real small, smaller then a stock cage. It helps to icrease velocity.

08-09-2007, 04:06 PM
its totally true, it isnt necessarily "smaller" ports, but correctly shaped and sized ports. if you canoe down a river, where the river get narrow, it speeds up right? well, thats how an intake port is supposed to work , and when the air is going fast right the at the narrow part, the valve opens and the air "rams" itself into the cylinder. the key to head porting is making this theory work its best.

08-09-2007, 04:45 PM
Oh Boy !!!!

08-13-2007, 03:02 AM
I just read a little part of it.

"Then some of the charge gets pushed back out of the cylinder and into the port as the piston returns up the bore during the intake charging phase."

"It gets worse !
On a carbureted bike the reversing charge will create an effect called double carburetion, which means the mixture will become even richer with fuel as it passes back over the main jet nozzle for a second time."

Ok now to test this theory take off your air filter and place a piece of paper over it If its blowing back out the carb then it will blow back onto the paper pushing it away from where the filter should be. BUT i have never seen this happen. Also with the increasing RPM's the more air is sucked so his theory of blowing back through the carb is even less effective. The only way this would work is if the valves arnt sealing.

Now im not saying everything hes saying is crap I do belive a high velosity port can be good. Some engines i port that way. Some i dont it depends on what they are looking for. In my experiences You will get more torque with a high velocity porting and high hp with BIG porting.

Diffrent strokes for diffrent folks Good porting is good porting who gives a *Edited**Edited**Edited**Edited* how its done, there is not right or rong if it runs good. He found what works for him but i will guarintee it wont work for everyone.

09-24-2007, 12:19 AM
These images seem relevant to this topic:

04' vs. 05' CRF250R

05' vs. 06' YFZ450

Billy Golightly
09-24-2007, 03:28 PM
Those are some very interesting pictures there GPRacer.

09-24-2007, 03:51 PM
Those are some very interesting pictures there GPRacer.

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 :naughty:

09-24-2007, 04:57 PM
Read this...


09-24-2007, 05:10 PM
Read this...


I like Jennings' book a lot. But I sure would like to see a new edition.

Billy Golightly
09-24-2007, 05:19 PM
Jennings book is great, but its about 30 years out of date :(

09-24-2007, 05:27 PM
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
09-24-2007, 06:13 PM
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
09-24-2007, 09:40 PM
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 :naughty:

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
09-24-2007, 09:59 PM
How many cylinders have you seen that have the intake boost/boyesen ports epoxied up on a 2 stroke, hmmmm...? :naughty:

jason 32
09-24-2007, 11:14 PM
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-

09-28-2007, 08:52 PM
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

09-29-2007, 08:59 AM
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 " !! :lol: . i used to take the heads off and rub them on block walls to get more compresion :crazy: