Jump to content
Sign in to follow this  

anyone done high velocity ports mod?

Recommended Posts

Has anyone tried the mototune high velocity ports mod ?

http://mototuneusa.com/think_fast_intake_porting.htm

It may be counterintuitive, but looks like it could add 2-3 HP to a DRZ. Same guy of "break in secrets" fame. There are testimonials from many engine modders that it works. Wondering if anyone has done it here?

Bob

Share this post


Link to post
Share on other sites

it isnt really counter intuitive. it is why stock cars still make big power with restrictor plates. It's why gsxr1000 superbikes still make big power with mini-intakes. The trick is to have the cylinder full when the valve closes and use whatever you can to make that happen (pressure differential drives the whole process, there is nothing else). All in/ex tuning is a balance between getting the best pressure in the cylinder (bmep=torquextime=hp) and acheiving a wide enough power band (actually a flat enough torque curve). The use of very high velocity totally changes the way gases behave though. At around 300ft/sec@standard atmosphereic conditions airflow changes from incompressible flow to compressible flow (read that in a book of airplane design). This introduces elasticity into the movement. That allows the late rush of high density charge to slam into the cylinder. Because the intake cycle begins 66 times a second at 8000 rpm, elasticity and compressibility can be your friend, creating a wavering column of air moving continuously towards the intake port. (my intuition) This guy is just very good at explaining it in a way that makes it sound ground-breaking. Gordon Jennings went over all of that stuff back in the 60's ("2-Stroke Tuner's Handbook") using Kawasaki "Big Bear" 350 singles and 250 yamaha twins as examples.

Share this post


Link to post
Share on other sites
... The trick is to have the cylinder full when the valve closes and use whatever you can to make that happen (pressure differential drives the whole process, there is nothing else). All in/ex tuning is a balance between getting the best pressure in the cylinder (bmep=torquextime=hp) and acheiving a wide enough power band (actually a flat enough torque curve)...

Gordon Jennings went over all of that stuff back in the 60's ("2-Stroke Tuner's Handbook") using Kawasaki "Big Bear" 350 singles and 250 yamaha twins as examples.

The mototune guy makes sense to me, there is some meat there in the explanations. It seems like the cam used needs to work in concert with the high velocity port concept, but maybe not. I was not aware that a typical cam kept the intake valves open past the piston bottom point of the intake stroke.

I can see where higher velocity yields greater momentum (MV, mass times velocity). And the momentum and port restriction will prevent part of the intake charge from going back out as the piston starts on the upward part of the compression stroke. So yes, this would fill the cylinder better.

All makes sense - what is curious is why has no one tried it? Or have they, and are keeping quiet? :thumbsup:

Seems like the increase in power across the band, not just in a band, like some specialized pipes and cams, would be welcome. The cost is low, but I guess the risk of screwing up the head is there.

BTW, I think you mean Kawasaki Big Horn 350 - I owned one in 1973. As the report here says, it was tricky to get running correctly, but was a great dirt machine in its day.

http://www.vjmw.org/tests/bighorn.htm

Bob

Share this post


Link to post
Share on other sites

BTW, I think you mean Kawasaki Big Horn 350 - I owned one in 1973. As the report here says, it was tricky to get running correctly, but was a great dirt machine in its day.

http://www.vjmw.org/tests/bighorn.htm

Bob

Thanks so much for the blast from the past about the big horn!!! :thumbsup: My friend had one when we were very young (1973). He had to stand on the picnic table to jump on the kick starter to bring it to life. :ride: He would always be watching in back of him to see the darn thing roost... :applause: Wonderful memories, thanks again.

Share this post


Link to post
Share on other sites
The mototune guy makes sense to me, there is some meat there in the explanations. It seems like the cam used needs to work in concert with the high velocity port concept, but maybe not. I was not aware that a typical cam kept the intake valves open past the piston bottom point of the intake stroke.

-yes they have to work together and the cam does keep the valve open past bdc to take advantage of the elasticity of a gas. Most of the gains shown are likely due to better matching the flow characteristics of the port to those of the carbs, pipes and cams used (whether he knew that or not-probably did but didnt want to bog readers down in physics). There is a lot of meat in there and it is put together well, though a bit too commercially inspired-boxes, colours, flashing signs...

I can see where higher velocity yields greater momentum (MV, mass times velocity). And the momentum and port restriction will prevent part of the intake charge from going back out as the piston starts on the upward part of the compression stroke. So yes, this would fill the cylinder better.

the velocity is a tool used to cram more air in. The port-restriction-preventing-backflow thing is the part that I dont agree with.

All makes sense - what is curious is why has no one tried it? Or have they, and are keeping quiet? :thumbsup:

you're riding one, just not perfectly matched so there is a hp or perhaps 1.1hp hidden in there.

Seems like the increase in power across the band, not just in a band, like some specialized pipes and cams, would be welcome. The cost is low, but I guess the risk of screwing up the head is there.

the proceedure I have read about (sport rider back around the time that website was created-1995-98) is to rough sand the ports, build up them up with epoxy or jb weld and sand for shape and contour. Dont think it's worth it on a 35-45hp bike.

BTW, I think you mean Kawasaki Big Horn 350

no, it was a gp bike, probably based on that engine-was an air cooled 350cc piston port single

Share this post


Link to post
Share on other sites

I had seen this thread and never had the chance to read the mototune article. All I can say is um ya okay whatever. Lots of cool boxes flashy things stating the obvious and generalizations.

Porting intake and carbs have to work together period. Anyone familiar with the old dodge long ram intake? It's been so long was it 53 or 63? That was a lesson on intake charge and inertia. Read up on YPVS and advanced 2 stroke cylinder filling and reed valves. Some great stuff out there on 2 stroke pressure wave manipulations as well. Finally for fun read up on all the car carb/intake runner manipulations and how you "tune" a cars performance by the carb selection.

There is no magic. Good physics, testing and application. Modifying flow velocity is great but it is also far harder to accelerate an already high speed flow. Eddies 475 must be a supreme example of high speed flow look at how much more air he moves than we do. Gotta be because of the high speed flow. He also must have made it slower by going to the 41mm FCR from the 39.

I hate being the skeptic.

Share this post


Link to post
Share on other sites

you can get to much velocity the port cross section needs to be corect for the displacement and power curve your looking for moto tune was working with some ports that were already to large for the cylinder and they benifited from a reducedport .when the first gsxrs started being produced they came with a diferent port cross section every year.porting alone with improvements in air flow will also raise the velocity this is why you need to use a flowbench and pito tubes to measure your changes instead of quessing .

Share this post


Link to post
Share on other sites
you can get to much velocity the port cross section needs to be corect for the displacement and power curve your looking for moto tune was working with some ports that were already to large for the cylinder and they benifited from a reducedport .when the first gsxrs started being produced they came with a diferent port cross section every year.porting alone with improvements in air flow will also raise the velocity this is why you need to use a flowbench and pito tubes to measure your changes instead of quessing .

from testimonials on this site, per eddie and others if i had the coin.... this would be the only man to touch my drz cylinder head. i've played with 2 stroke engines in snowmobiles with someone who knows what they're doing.(tim bender of Benderracing.com my old boss) and it truly is ALOT more than hoggin' it out with a carbide burr.

Share this post


Link to post
Share on other sites
He also must have made it slower by going to the 41mm FCR from the 39.

lol,and just think im going to slow it down more when i run a even bigger carb.

Share this post


Link to post
Share on other sites
lol,and just think im going to slow it down more when i run a even bigger carb.

I don't care how good you are, you ain't getting a 4 barrel double pumper in a DRZ :applause::applause:

How big you going Eddie.

Neil.

:thumbsup::ride::applause:

Share this post


Link to post
Share on other sites

I think what Ron said is what some people miss. Porting isn't just about making it bigger. It's about flowing better (faster, smoother). Just cleaning up any gasket protrusion and casting defects in the intakes can help when there is restrictions an actual porting. In some cases it is about opening the intakes up but not all.

I was always interested in the intake runner lengths and the effects of that on the characteristics as well. Not something many consider on motorcycles. Mainly I guess because it is tougher to modify. I have seen it come up on other models though.

There are some amazing things on the internet.

Share this post


Link to post
Share on other sites

exactly porting isnt just about making it bigger or just more flow at peak lift.

most people do not get into runner length etc on motorcyles becuase they are so good stock.

its very easy to make them worse.

its not a small block chevy.

the stock drz head flows better than a crf 450 head.

Share this post


Link to post
Share on other sites

Right now I'm porting & polishing my 03 yz405f just like the moto guy said. I'll let you know how it goes. I didn't take any pics first but I'll post some of it done.

Share this post


Link to post
Share on other sites
Right now I'm porting & polishing my 03 yz405f just like the moto guy said. I'll let you know how it goes. I didn't take any pics first but I'll post some of it done.

post before and after dyno graphs.

Share this post


Link to post
Share on other sites
post before and after dyno graphs.

And velocity numbers for the flow bench .. Please :busted: Would love to add another guy to my very short list of techs able to improve flow and power in a usable range by way or porting a motorcycle head. Absolutly.. Best of luck :moon: Looking forward to the results. :p

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×