"Mototune" porting: anyone try it?

[mik_str]

Check out the link: http://www.mototuneusa.com/think_fast.htm

Disregarding the boisterous presentation, the theory seems sound. Wondering if anyone has tried this on the VTR?

cheers

[tony.mon]

There might be something in it, Mike.
The carb throat size is getting marginal, because the intake cross sectional area flows too slow quite easily if you enlarge the throat size much at all.
The trick seems to be that you need to keep a steady forward flow of gas going on in the inlet tract, including the stack.
Otherwise the flow of gas stops and starts, and is said in the article, could even start to run back out of the inlet port through the valves until they close.

But a good flow has its own inertia, and the stream of air will continue to flow even when the valve shuts, building up some pressure in the inlet port and stack until the valve opens again.

I'd be concerned about small ports and short stacks as a combination, but with a decent inlet stack fitted it should help.

Ram air will help even more, as it pushes the air from behind, instead of allowing the vacuum generated by the engine to pull air in through the carb and port.

His theory only works re inlet porting, though, I think.
As long as the exhaust port and header is designed well the flow through the first part of the exhaust assists to scavenge the charge from the cylinder as the exhaust valve opens and all that way through it's open duration.

The easy way (well, easier anyway) to check this out would be to partially fill the inlet port on a spare head, set it up on the bench with shims, dyno the engine with a standard head fitted then swap the rear head over, and dyno again.

I think you could do this in a day, fairly easily- and the rear one is simpler to get at than the front one, no need to strip the plastics off, for example.

You'd need to drain coolant, pull tank, airbox and carbs off,disconnect plug lead and rear cam box vent hose, remove the thermostat hoses going to the rear head, then set the engine to the correct tdc on the rear.
You can then loosen the lower clamp on the read header, lever the rear header off of it's seat and out of the head, turn it through 90 degrees and wiggle it out of the way.
Cam box off, loosen rear cct and remove, then unbolt the cams and remove. Then unbolt the head and simply rebuild it in reverse.

You'd only need to pull the plastics off in order to refill the coolant system, so this is worth a try to save time:
Use one of the coolant hoses that go into the carb heater as a filling point.....
Or remove just the small internal section of fairing in the RH side and access the filler cap that way.

I haven't tried either of these options, so you might be just as well to remove the fairing completely and refill using the pressure cap as normal.


I reckon that could be done in four hours, and back on the dyno for a comparison run.
Let me know how you get on.....

[chris freckle]

I think that everybody involved in professionally tuning engines knows this already, but this guy tells a great story.

[8541Hawk]

Ram air will help even more, as it pushes the air from behind, instead of allowing the vacuum generated by the engine to pull air in through the carb and port.

I know it is not really important but as a vacuum tech I can tell you that vacuum does not pull anything.
Positive pressure pushes in to fill the "vacuum" in all cases.

I know this sounds counter intuitive but here is a way to look at it.

By definition vacuum is the absence of everything. So in simple terms you have a volume of "nothing" now a total vacuum is impossible so we are dealing with partial pressures here but for this example we will just say an absence of everything to keep it simple.

In order to fill the volume would be defined as "work"

So if the vacuum is pulling the air in, then "nothing" is doing "work"

This is against the laws of physics....... or if you can get "nothing" to do "work" then you would be a very rich lad.

What is really happening is the outside pressure is pushing in and at 14.7 psia (which is absolute pressure as apposed to psig or gauge pressure) it adds up quicker than you might think.

If we put on out math hats and use the carbs 48mm throat (as I don't have the intake port dia. handy) you end up with this as the area of the intake

48 mm = 4.8 cm
d = 4.8cm
d = 2r = 4.8cm
r = 2.4 cm
Area of a circle = pi * r^2
Area = 5.76*pi = 18.096 cm^2

or 2.812 in^2 now multiply by 14.7 which gives you right about 41 pounds of air pressure filling the cylinder.
and yes 41 pounds of air pressure pushing through a 2.8 sq in port will fill a 500cc volume to 14.7 psia in a very short time frame.



Sorry to ramble on but like I said, vacuum technology is what I do in the "real" world......

[CruxGNZ]

Now that's how you explain it!

[sirch345]

Very interesting

Chris.

[fabiostar]

say that again lol

[sirch345]

Very interesting

Chris.

[tony.mon]

That makes sense.
So why does pulling a plunger out from a syringe with your finger over the nozzle end get harder the more you pull it out?

[8541Hawk]

That makes sense.
So why does pulling a plunger out from a syringe with your finger over the nozzle end get harder the more you pull it out?

That would be due to the gas laws. http://en.wikipedia.org/wiki/Gas_laws

What is happening is that you start with 1 atm inside the syringe. When you pull the plunger the volume increases and as gas expands instantly to fill whatever volume it is in causes the pressure inside to drop.

This causes the outside pressure to push harder and harder on the plunger.

[grumpyfrog]

Bloody hell chap's, I have to ask about removing bolts and you lot are talking about laws of physics. doh.
great debate. keep it all up.

[mik_str]

Stick around... quantum physics is just around the corner.... super-strings here we come!!!!!!!

[Jamoi]

Don't get me started on the double slit theory!

Good thread chaps

[Virt]

Don't get me started on the double slit theory!

Double slit theory was the best part of my physics a-level


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[tony.mon]

Don't get me started on the double slit theory!

Double slit theory was the best part of my physics a-level


Sent from my GT-I9505 using Tapatalk

Is it a wave or a particle?

Well, have you ever seen the Queen particle? Have you, punk?

And she could afford to, if she wanted.