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Discussion Starter · #1 ·
I did this mod a few hundred miles ago....6 3/8" (well, actually 27/64th's) holes in each. Figured it would make it more responsive at partial throttle...yes! MUCH more power per degree of throttle turned. Passing is now easier and the throttle doesn't need to be cranked nearly as far to get adequate power to blast past traffic.

The only down-side would be the stock ECU tuning wasn't able to fuel it properly with the plates opened up. Really lean at WOT and mid-range revs. One way to tell is when you let off from WOT and it speeds up/pulls harder for a bit until you get the throttle closed down. Proper fueling should have the power reducing a linear amount as you close the throttle.

I have a Wiesco FI tuner box so I plugged it in. Added a bit of fuel in the midrange until the lean symptoms went away. NICE! Man does this bike run good now. They would have sold more of them if they had been set up like this.

So....just wanted to document the change and give it a big YES! If you have been thinking about doing the STV's.....and have a PC or some other way to compensate for the additional airflow, you'll like the results.
 

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Discussion Starter · #9 ·
You don't have to open the throttle nearly as much to make power now, just a quarter turn feels like half throttle before. The improvements according to the Portal (where I stole the idea) were decent in the midrange and top end. Couple horses or so. Sure feels more responsive and I like not having to make such dramatic throttle openings when passing people. Didn't feel right for a 1L w/56mm throttle bores. The STV's really choke it down until you get the throttle open pretty far.

Haven't seen a reduction in mileage, and it pulls cleanly at light throttle settings where the drilling has changed things the most. It did lean the midrange WOT a bit, so additional fuel was needed...but not a major amount. I DO have the air-box open a bit so the combination of STV and box opening was just a wee bit too much for the stock ECU tuning to handle.

If you like an engine that revs freely with just a little throttle...this mod's for you! I think it is good to leave the plates in as they must help with mixture distribution and vaporization, and many have reported a loss in mpg and bottom end power with their removal. This cost nothing at low rpm regardless of opening. Bike runs strong like this.

There is a section over on the Portal where they did extensive dyno running to prove the mod.
 

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Discussion Starter · #11 ·
There has been some discussion about the results obtained by the fellow who posted up a bunch of info on the Portal. His numbers didn't actually correlate, which lead some to question them.

At WOT, the STV's should also be WOT and presenting little restriction to the airflow. Biggest problem with them is they lag the main throttles by either a little or a lot...depending on your gear selection. They don't open fully in the lower gears if you don't have a TRE installed....at least that is what we figure.

My bike wouldn't wheelie much at all with the STV's in place. Drilling them allows more air to the engine even when they are closed. This makes for a much livelier throttle response which, to me, makes the engine feel happier.:)

In the end (now) the plates came all the way out as they were still restricting things even with the holes. They also played badly with the fueling as sometimes they'd be open and others not so much, but there is no way the PCIII (or whatever you are using) can tell what they are doing. If you have the fueling correct for WOT with STV's also WOT, at those times where the plates aren't open fully it will be rich....filthy rich. I didn't see a way around this without some way to communicate the STV angles to the controller...so they came out. Nice and consistent throttle now no matter what.

It is a very interesting thing to investigate and there sure is a lot of discussion about what exactly the STV's are there to do. Some say they increase the air velocity for better response and mileage much like the CV carbs work. Others say they are there solely to meet noise standards and mute the power delivery in the lower gears. I'm believing the latter now as there is NO need for additional intake velocities with fuel injection. The fuel sprays in regardless and, when properly set, the response is perfect at all throttle settings and engine rpms. Intake noise is much greater with them out too...so you've got to try it to see how much yours might be restricting things before making this call for yourself. Don't believe the 'hurts mileage' guys as I've seen 56 mpg's with them out and steady 65mph slab droning.
 

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Sure there is a need with EFI. Atmosphere is pushing the charge into the combustion chamber, if you keep the velocity up, the air keeps it's momentum and fills it faster.

It's quite possible that what you're feeling (better wheelies etc) is that you've created a flat spot in your torque curve, which is then highlighted by a sudden increase in torque, and up she comes. A bulgy curve like the SV always feels slower and flatter than a more exciting stepped curve like the TLR had. The SV won't wheelie much because it's a constant increase in torque... if you take away the bottom part of the torque curve, to get to the same peak figure somewhere you need to have a steeper increase in torque. And that's good for wheelies :D :D You can also see this in action by going WOT from idle compared to WOT up to 6, backing off, and then going WOT again. It might lift the front an inch in the first instance, but the second methods savage increase in torque will see it hoist much faster.

Go ride an old two stroke 250... they only have 55 off horsepower, but it feels much greater than that due to the style of delivery. Power valves were created for them not to increase the top end torque (they don't), but to lessen that steep hit of torque by boosting the midrange (and thus making it a straighter curve from low to high RPM). FWIW.
 

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@ RecoilRob

Do you have any pictures of the before and after? Did you have to wire in a resistor for the mechanism that operates them? Do you have any starting issues etc? Any help greatly appreciated.
 

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Do you have an Android or iPhone with GPS? Some back to back runs with and without the holes would give you exactly what you need to know :) If you've got an iPhone, I can find out what a friend uses on his (some datalogging GPS app).
 

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Discussion Starter · #15 ·
@ RecoilRob

Do you have any pictures of the before and after? Did you have to wire in a resistor for the mechanism that operates them? Do you have any starting issues etc? Any help greatly appreciated.
Actually, I took the easy way out and just removed the screws and pulled the plates leaving the actuator, shafts and sensors be. This way the fast idle works when it is cold and the dreaded 'FI' light stays out.

Best part doing it like this is that you can replace them if you don't like them out. Thinking about ditching the actuator/shafts et al this winter and fitting up the emulator to keep the ECU happy....but the small improvement in flow by removing the shaft obstruction might not be worth the effort on a street bike. We'll see how bad the snow gets and how cabin feverish I become.:)

And....no starting issues or running ones either. I DID have to add some midrange and top-end fuel on mine to make it run the best, but you'll have no problems with your PCIII once you fiddle with it a little.
 

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Discussion Starter · #16 ·
Do you have an Android or iPhone with GPS? Some back to back runs with and without the holes would give you exactly what you need to know :) If you've got an iPhone, I can find out what a friend uses on his (some datalogging GPS app).
That is a smashing idea right there! I've got a G-Pro somewhere around here and probably could get it to work on the bike....but would have no comparison data as I'll not go back to the throttle nannies. At WOT, I'm not at all convinced the bike makes more power without the plates than with. But, on each gearchange where the throttle is briefly closed, it hits the next gear much more solidly now that we don't have to wait for the STV's to open back up. That's where I notice it the most having them out. Oh...and the instant wheelies in first gear too......which it wouldn't do before.:)
 

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Discussion Starter · #17 ·
Sure there is a need with EFI. Atmosphere is pushing the charge into the combustion chamber, if you keep the velocity up, the air keeps it's momentum and fills it faster.

It's quite possible that what you're feeling (better wheelies etc) is that you've created a flat spot in your torque curve, which is then highlighted by a sudden increase in torque, and up she comes. A bulgy curve like the SV always feels slower and flatter than a more exciting stepped curve like the TLR had. The SV won't wheelie much because it's a constant increase in torque... if you take away the bottom part of the torque curve, to get to the same peak figure somewhere you need to have a steeper increase in torque. And that's good for wheelies :D :D You can also see this in action by going WOT from idle compared to WOT up to 6, backing off, and then going WOT again. It might lift the front an inch in the first instance, but the second methods savage increase in torque will see it hoist much faster.

Go ride an old two stroke 250... they only have 55 off horsepower, but it feels much greater than that due to the style of delivery. Power valves were created for them not to increase the top end torque (they don't), but to lessen that steep hit of torque by boosting the midrange (and thus making it a straighter curve from low to high RPM). FWIW.
I thought all day about a way to reply to you without writing a novel.:) Best I've come up with goes like this: The STV's don't increase anything...but turbulence. That I'll agree to. They restrict. That is their purpose. Once the air gets by their restriction (when they are only partly open) it then encounters the main throttle plates....where it is restricted again. So any theoretical increase in airspeed is defeated right there.

Carbs need to increase the airspeed flowing through them momentarily at the venturi to create the pressure differential that causes fuel to flow out of the needle discharge. Opening a large slide carb too far too quickly will indeed cause a major bogging. The farther you open the slide, the more air it inhales....just can't get fuel to mix with it until the speed is up. Add an accelerator pump and the hole gets covered by it squirting in fuel when needed.

The FI works like a super accel-pump, doing a much better job of atomizing the fuel spray so it burns pretty well indeed. There is NO bogging mate! Once the fuel mixture is turned up a bit it is responsive as you want it to be. In fact, I've got it turned down in the midrange a little to make it LESS responsive and easier to modulate. Quarter throttle with full fuel mixture makes quite a bit of power. For easier riding and better mileage a weaker mixture works better saving the full rich stuff for heavier throttle settings.

When you open the throttle, you get more air....until the manifold is at atmospheric, then further opening won't let any more in. If it should bog, you just need more fuel...which is easy to do. And remember that any velocity increase you might create in a throttle body (or carb) is negated when the mixture enters the much larger intake manifold. Bernoulli's Principal and all that. Once past the TB, the velocity is dictated by engine rpm's and manifold design.

Notice the SV has a fairly smaller intake runner vs the TL's. Obviously wanting to increase the velocity for better low/midrange running. It works pretty well too! Just trying to argue that any velocities created by the STV's doesn't make it out of the TB's. And NOT trying to argue that removing the plates makes any more WOT power. Maybe a little bit, but mostly the removal allows you to control the airflow into the motor without the nannies over-ruling you at times. You ask for it...you GOT it!:) (see...novel!)
 

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I just Removed the plates from the STV system!!
Wooow!!!
I am amazed!!
The throttle response is amazing!!
Like the bike is lighter 30kg!!!
Now if anyone has a map for the Power Commander,i would appreciate it,cause i have to remap it cause it has some lean spots in medium and high rpms..


p.s
was a 5min job..
 

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Great to know it's an easy job. I enabled the accel pump on the power Commander 75% sensitivity, 20% fuel increase, 15 revolutions (as power commander suggests for racers) I upped the RPMs a bit more to 1400 and the bike is even smoother now! The abrupt throttle is still there but not felt as much. I then brought the RPMs to 1500 and it was barely noticeable but the bike had almost zero engine braking which was a pain in the street so I brought it down to 1400 and it's much better. My next thing now is to take out the STV plates and see what happens.
 
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