Ok, I'm curious about the exhaust valves found in most of the world's premier sport bikes for the last two decades. Basically an electronically controlled throttle butterfly right in the exhaust stream.
Sales documentation say they decrease noise, and improve street driving manners.
Sport bike forums and youtube yell loudly that they either hurt power, or that they don't hurt power and do what the sales documentation says. A few dyno graphs show a tiny bump in high end power from removing the devices. No dyno graphs I can find show the devices improving mid range power (but you can't see driveability on a dyno graph).
Sport bike magazines seem strangely silent on this matter. Full race factory effort teams seem to ditch the valves.
So, signs point in all different directions. But the one I can't put in place is WHY do the bikes come with them from the factory?
Trying to decide if I go to the effort of installing on my challenge car or not. I strongly feel like there must be a benefit if it came from the factory on the bike. But if the benefit is lower noise, then I'm ok without the complication. If the benefit is better driveability, I'll install it.
How far is it from the cylinder head, in terms of plumbing? The further downstream, the less I'm inclined to believe it has any real impact on how the engine runs.
The general consensus in the Triumph Daytona world was that it was there solely to reduce noise at low rpm, or the typical city setting. Some had issues with them gumming up with carbon and sticking shut.
I was hoping to find Kevin Cameron addressing the topic, but no dice so far.
I wonder whether the meaning is "boosts power relative to the exhaust we'd have to run without one and still pass production standards for noise, etc."
¯\_(ツ)_/¯ said:
How far is it from the cylinder head, in terms of plumbing? The further downstream, the less I'm inclined to believe it has any real impact on how the engine runs.
In my case the valve is at the beginning of the muffler. so maybe 2-3 feet of tubing away from the exhaust?
Ransom (Forum Supporter) said:
I was hoping to find Kevin Cameron addressing the topic, but no dice so far.
I wonder whether the meaning is "boosts power relative to the exhaust we'd have to run without one and still pass production standards for noise, etc."
Totally.
And many bikes don't have an o2 sensor but do have the valve. So change the valve, and therefore engine airflow, but don't get the feedback to the ECU. So the dyno graph HP change could be from a side effect, like leaning the mixture just slightly. Now, you're still measuring incoming air, but still, side-effects seem possible.
I also read that on GSXRs in some years the north american ECU mapping closed the valve at idle, and then again near the top end, while european mapping only closed the valve near idle. If true, that would suggest the valve is meeting a governmental restriction.
In reply to Robbie (Forum Supporter) :
Toss it, I bet it changes nothing.
Well, I found out this morning that there are 14 pages in the factory service manual for the GSXR1000 k4 dedicated to the valve and the associated servo. Adjustment, testing, removal and replacement, etc.
For reference, the entire wiring diagram is two pages.
Seems like Suzuki wanted to be pretty sure that techs knew how to setup and test the system at least. I wonder if I can find the ECU map for it. That would probably tell a good story. Also, would be a neat trick to use the servo motor (and the ECU's ability to map and control the servo) for some active aero.
Here's an interesting link. This guy says the stock exhaust valve map is tied only to RPM (and not to throttle position). Also says that it is fully open at 6k rpm+ (though I'm not sure that's stock operation).
https://www.woolichracing.com/mapshare/item/638/ecu-flashing-tuned-map-exhaust-valve-re-mapped-and-fuel-deceleration-cut-removed.aspx
I'd sign up for the site and message the guy, but you need to buy their tuning cables and stuff to get an account. I still might do that eventually after I've got a running engine, since its about $400 to get full tuning capability to of the ECU, and once I look in there at stock maps I'd be able to have a much better idea of what the valve does.
