Vinni
I didn't do it
Can some one explain the "WW" modification to me?
Modifications
- Thread starter Vinni
- Start date
powerboatr
living well in Texas
Hoss 350
My GSP, Dutch
I'll take a crack at it...Vinni said:
First and foremost, it is not a performance mod, in the sense that installing a wicked wheel doesn't give measurable horsepower increases or make bigger boost numbers (but it can help you make boost more quickly, which I'll explain in a minute.)
The purpose of the wicked wheel is to prevent “surge” in your turbo. Each turbocharger is designed with a specific boost curve and fuel curve in mind, called it’s “compressor map.” The stock Powerstroke (PSD) turbocharger is designed to run a compressor map which matches (roughly) the fuel curve as programmed in a stock PSD. Adding a chip or tuner (or other fuel mods, like a 10K) can cause the fuel curve in the engine to be over the compressor map of the turbocharger at a given point in time. Most chips and tuners create surge at 75% or greater throttle, at around 7-12 psi of boost. What is happening is this…
The exhaust gasses driving the turbocharger create the energy that compresses the intake air. The more you compress the intake air, the more the intake air “pushes back” on the compressor wheel of the turbo. As long as the exhaust gasses push harder on the turbine than the intake gasses push on the compressor, you will have normal operation of your turbo. Under surge conditions, the intake pressure “pushing” back on the compressor wheel overcomes the pressure of the exhaust gasses on the turbine (exhaust) wheel. This causes a sudden, violent reversal of the turbocharger, as the gasses in the intake rush backwards through the compressor. Once the intake gasses have bled off enough so that the intake pressure no longer overcomes the exhaust pressure, the exhaust turbine takes back over, which effectively (and again, quite violently) reverses the turbocharger direction again (so now it is running the proper direction again). However, the problem is that unless the driver has changed something (ie, downshifted, let up off the throttle, or so on) the conditions for surge still exist. So, as the exhaust spools the turbine back up, the intake pressure will again overtake the exhaust pressure, and the violent double reversal will occur again, and again, and again, and again. This all happens in a split second, so that by the time you hear it happening, it registers in you mind what is happening, and you let off the throttle, it may have happened 6 to 10 times already.
As you can imagine, anytime something is running at 80,000 RPMs, which is about the speed of a turbocharger, and it is suddenly just thrown into reverse, then back into forward again, over and over again, it beats the ever loving dog crap out of it. Hence, surge is a BAD thing, and will wreck your turbo.
The wicked wheel solves this problem by changing the compressor map of your turbo. It, in a sense, has a little bit less leverage on the air coming in, giving the turbine wheel a comparative mechanical advantage over the intake wheel, so it tends to, at all times, be able to push harder on the intake wheel than the intake wheel can push back on it. Because of this mechanical advantage, the turbine wheel is able to “spool” the intake wheel up faster, which in turn creates boost faster. At a given, identical turbocharger RPM, the wicked wheel will actually make LESS boost than the stock wheel, but because of the mechanical advantage that the WW gives the turbine, at any given ENGINE RPM and fuel point, the WW equipped turbo will be spinning FASTER, and pumping more or less the same amount of air as the stock turbo.
So, performance is more or less unaffected, unless you count the quicker spool time of the wicked wheel (and the fact that surge will stop the creation of boost, hurt your power output, and also force you to pull out of the throttle, so you go slower and make less power). The idea is to save your turbo and to allow you to do pretty much anything without worrying about surging your turbocharger.
Now, STALL in a turbocharger is completely different. The wicked wheel does nothing to prevent stall (it cannot) and I am not completely convinced that it needs to. Stall occurs when you are on the throttle at high boost, and let off the throttle for a shift or to stop or whatever. You hear that “sneeze” sound as your turbo backbleeds the boost out of the intake. The reason I am not convinced that it is bad is this…
You have let off the throttle, so there is no pressure from the exhaust to create high stress to fight against as the intake reverses the flow, and it ONLY DOES IT ONCE. In a surge condition, you are still in the throttle, so you have BOTH the intake and exhaust pressures working in different directions on the shaft between the wheels. This equals HUGE stress. In a stall condition, the only thing driving the turbo is inertia of the spinning assembly, which weighs very little, so the stresses created in overcoming this force is nill. Also, in surge, it undergoes the huge stresses 6 times a second. In a stall condition, it undergoes the lesser force ONE TIME.
Anyway, that is my take on the situation. Hope I didn’t bore you to death. Sorry so long…
architect-builder
Full Access Member
Oh, thank God. I thought he was talking about a Wet Willy! 
Barrett
Barrett
dboyw
Full Access Member
Hoss, I read your post and I finally truly understand the difference between surge and stall. I just bought a WW and I am waiting for its arrival.
Thanks for the detailed definition, if it's right
Thanks for the detailed definition, if it's right
CHPMustang
Senior Member
I don't know about the naysayers of the Wicked Wheel but since we installed it back in December '02 our Excursion basically took off afterwards,if I could run two of them I surely would!
Hoss you can now take a breath after that post:tu:
Hoss you can now take a breath after that post:tu:
Rex-a-FORD
Full Access Member
Hoss 350 said:
Good job Hoss, excellent explanation..........
I've heard that the WW is very similar, if not identical to, an early 99 impeller. Do you kow if that's true or not.
-popcorn
CHPMustang
Senior Member
It should be an early 99 compressor wheel design.
95_stroker
Jefe
The 94-97 turbos also have the good wheel in them.
Glassdude
Full Access Member
Thanks Hoss. Now I get it. Are your fingers tired? Sounds like I better order a WW. I have learned about when to back off but every now and then I hear the classic pffft,pfft,pfft. I also agree with you that STALL is not a problem besides that it sounds kinda cool. Keep up your informative posts.
Mike
Sounds like I better order a WW. I have learned about when to back off but every now and then I hear the classic pffft,pfft,pfft. I also agree with you that STALL is not a problem besides that it sounds kinda cool. Keep up your informative posts. Mike