Removing Secondary Butterfliesin

[Rick McC.]

I believe that the '14 Roadsters were the first to come with the 1-3rd gear restrictions removed.

 

[Speedy]

Secondaries - Somewhere I read that it's better to leave them 100% open than remove them - UNLESS you also remove the bar they pivot on.

Gentlemen, the use of the secondary air blade and the low gear ignition retardation is primarily to meet emission requirements. However, as Dougl states, the ignition should be less advanced at lower rpm because the burn rate is nearly constant regardless of throttle position or engine rpm. But if it is retarded even further than needed to optimize combustion, the exhaust temperature rises and the cat's efficiency goes up. Keeping the cat hot at low speed is needed as engine load is low and exhaust temps drop. This is accomplished by adding fuel and retarding ignition and then burning that mixture in the cat. Sounds weird but it is true. Even though the combustion is dirtier, the tail pipe emissions are cleaner. Hint, hint!

The secondary plates are used just like the vacuum slide in a CV Mukini; air is metered closer to engine demand. Recall the old Triumph twins with Amals: twisting the throttle too far too quickly slowed you down. Minimizing lag was why accelerator pumps where invented. But dumping extra fuel in doesn't lend itself to mileage enhancement or reduced emissions. A secondary use is to reduce torque. A "designer" torque curve can be created. Torque peaks can be shaved off so that engine response is nearly linear across a wide rpm range.

Someone mentioned seeing what happens on a dyno. While I haven't dynoed that test directly, my Rocket has been dynoed on a steady state eddy-current dyno at 10, 20, 30, 40, 75 and 100% throttle openings from 1,400rpm at the lower throttle openings to 6,750rpm. With secondary plates in place but fully open, my bike, for example, makes as much torque at 2,300 rpm at 40% throttle as it does at 100% throttle. Why? Because the engine at 2,300 rpm needs only 34% of what it needs at 6,750 rpm at 100% volumetric efficiency. More throttle opening than needed to meet engine demand does nothing to increase power.

So the upshot of this is if the plates are removed or opened fully in the tune more fuel is needed to prevent throttle lag when accelerating. However, adding fuel in the fueling tables adds fuel all the time at that throttle position. We don't have access to transition fueling tables using TuneECU. So, most tunes for open secondaries have more fuel for throttle response but are too rich for steady state running. Compromises are always required.

As to if more air flows with the blades in place and open versus removed, probably not. The shaft is quite far from the lower primary blades and if I recall correctly in a slighter larger bore. And the blades are not thin nor knife edged to enhance air flow.

I have my plates set at reduced opening at 2,500 rpm and lower and run my tune a little leaner than most. I don't wheelie so this works for me.

 

[dougl]

There you go, a real explanation. I had my first R3 dyno tested with the stock tors tune with the secondaries closed and then with the custom tune for tors with them opened 100%. There was only a couple of hp and ft lbs difference along most of the power curve but there was a big notch taken out in the 2300-3500 rpm range for the torque curve with the stock tune, a max of about 12 ft lbs. One would have to assume they did this to reduce stress on the transmission and drive train and to keep us from killing ourselves.

 

[dougl]

Here are those dyno runs (4th gear) and the secondaries table in the stock tors tune. The custom tune has them open at 100% and the fuel is higher.

The custom tune is the top (blue and red). It's a little higher throughout because it has more fuel. The big decrease in torque in the stock runs is associated with the low values in the table between 2250 and 3750 rpm. It looks like you can see an effect up to 5000 rpm but it isn't big.

 

[barbagris]

As to if more air flows with the blades in place and open versus removed, probably not. The shaft is quite far from the lower primary blades and if I recall correctly in a slighter larger bore. And the blades are not thin nor knife edged to enhance air flow.

I know who ever it was who posted it - had Dyno info to show the effect. But it's not something I've tried myself.

 

[1olbull]

WOW! What GREAT dope!
Thanks so much to all who responded to me for sharing your expertise!
THIS is what makes this THE BEST motor forum ANYWHERE!

 

[Tumwatertaz]

WOW! What GREAT dope!
Thanks so much to all who responded to me for sharing your expertise!
THIS is what makes this THE BEST motor forum ANYWHERE!

Best thread EVER.

 

[Claviger]

Power-Tripp did do some testing a few years ago involving complete removal, bar and plates, then filling in the left over holes. He said it showed some gains when paired with straightened junctions between the TB assembly and the cylinder head. What else was done to the bike, i have no idea, but I expect a good bit.

At some level of airflow, on a built motor bike, the stock diameter of the TBs wouldn't be enough to feed the motor to full potential. At that point, removing the blades and the bar would show gains. At that point, you'd be wanting to knife edge the primary blades and flatten everything as much as possible in the tract. Where that is, who knows, might be the 210, 240, or 265 kit, might be somewhere higher than that.

I will say this much, I ran the secondary blades removed for 2 years. When I put them back in, it was to try reduced blade opening below 2400 RPM, to try and increase the velocity of the air coming in at low speeds. Whether it had that effect, I have no objective data to present. What it did do, was smooth the feeling in the bottom end of the RPM spectrum and make adjusting low RPM fueling easier and more consistent. Possibly an indicator that intake velocity is better, because the fuel is being carried into the chamber better. One thing clearly changed, far less intake backfiring occuring, something a lot of roadster owners suffer from for whatever reason.

With secondaries in place I put down 154lb-ft @ 2450 RPM, and the curve looks like any other rocket curve, flat(ish) from 2200-4000(ish) and a gentle roll off from there, so it certainly didn't hurt performance in any way by putting the secondaries back in.

 

[1olbull]

Robert,
Thanks for your response. I always suspected so but, your experience seals it for me.
I removed them on my V2K (with only PCIII adjustment capability) and the response improvement was noticeable.
Since Tune ECU can hold them open, I left them in on my R3R.
Tis logical that with everything out there would be better flow. Likely minuscule and none on a stock engine.

 

[dougl]

IDK is right. You can open the secondaries and copy the igniton tables in TuneEcu. The tune for the 2012 is 20355. Make the secondaries table in 20355 look exactly like the one in 20776. Then copy I3 into I2 and I1.