Let me restate. The car was tuned by AL but the dynograph and info was posted by the owner of the vehicle not by Al.

The id of the dump was the same diameter of the wastgate puck which is larger than the hole it covers. Take into consideration that the hole on an Evo turbine housing has a thick divider due to the twin scroll and it had even less area to flow than the dump itself itself. I would have bet alot of money that it would not have creeped but no matter what we tried same result. Pulled the car back down and redesigned the dump with a 20% larger tube and the upper midrange creep disappeared. Car held a very flat, consistant boost level.



Unfortunately you really don't seem to grasp how a wastegate works. It's not an intelligent being. It has no clue if you want high or low boost. It simply does what it's told based on the force (boost pressure) being exherted on the diaphram and exhaust flow through the engine. Once the pressure on the diapram exceeds the spring limit in the wastegate it opens allowing some of the exhaust gas, that is turning the turbine wheel, to bypass the turbine and either go back into the post turbine exhaust or be dumped separately. It will open as much or as little as it needs to maintaining the boost level assigned to it. Because an engine is dynamic device, then so must be the wastegate. In areas of an engine's power band, where the engine isn't flowing much exhaust gas, a properly sized wastegate has to do very little to keep up and regulate boost, but as the engine starts to make peak power, exhaust gas flow increases exponetially and the wastegate will have to open more - possibly fully open to regulate boost. If a wastegate is fully open at this point and can't bypass enough of the engine's exhaust, the exhaust flow ends up being greater through the turbine than through the wastegate and the condition aply named "boost creep" occurs.
Past the engine peak power, the volumetric efficiency of the engine will start to fall off - as will exhaust flow through the engine. At this point the wastegate will infact start to close but only enough to keep boost at a constant. However, in a car such as the evo, where the turbo runs out of breath before the engine reaches maximum RPM, the wastegate may in fact come close to closing to try to maintain requested boost level.

Sorry to be blunt, but this is just wrong!

 

I think you are both saying the same thing in different ways ...

In the most basic sense, a wastegate works like this:

- The WG opens to lower or hold a given boost level when the VE of the engine is high/increasing
- The WG closes to increase or hold a given boost level when the VE of the engine is low/decreasing
- The WG flap reacts to pressure changes via a manifold pressure source and a spring with a given resistance. So, when the engine VE drops and pressure begins to decrease the WG also begins to close, which in turn increases the pressure.

The dump is louder at higher engine VE since the WG flows more to regulate boost at those times. This is technically independent from the actual pressure at the manifold. Regulating 20psi @ 4000 RPM is much different than regulating 20 psi at 7000 RPM due to the compressor efficiency.

On the stock Evo turbo, the WG does operate at 100% duty (fully closed) at high (and very low) RPM.

However, from the sound produced by the atmospheric "dumpatron" and logs I've recorded, it seems that even at 100% duty at high RPM the WG flap is not entirely closed. The sound indicates that the WG is still dumping exhaust and the logs indicate a slight increase in airflow in high RPM/WGDC areas resulting from decreased backpressure.

It's may assumption that the pressure created by the exhaust flow at high RPM is enough to overcome the wastegate spring at high RPM. This is exactly why you can decrease boost taper at high RPM with an upgraded WG actuator and the stock WG. The increased spring tension does a better job holding the WG closed at higher RPM.

The external dump on the wastegate reduces the back pressure resulting from the turbulence created when this bypass flow through the WG mixes with the turbine flow in the stock/standard design O2 housing. This results in increased turbine flow capability across the entire RPM range and therefore less boost taper up top.

 

I think you and I are saying the same thing. Not so sure about dude though

Anyway I found a graph of and a-b comparison. Same car same day. enjoy!

 

Are you ****ing kidding me?!?

So if you want to run 15psi and 25 psi the wastegate opens the same amount and stays at the same opening?!? Ever hear of duty cycle? Why do you think even the stock BCS has a t-fitting pre turbo? THATS RIGHT!!! it bleeds off pressure to close the puck weather it be internal or external.

Sorry Drifto, you fail at your attempt.

Otherwise we said the same exact thing.

 

That graph is bull****. If a dump is to get rid of creep, how in the hell can it make more power that far under the curve?

Your not even near peak any output and boost just starts to come on where there is a power increase.

Come on man, this **** was tried and tested in DSM's 15 years ago and failed back then

 

As I said, it's based on engine VE and not boost level. PSI is not just PSI. The compressor and the engine are much more efficient at mid-range RPM and therefore the WG can hold a give boost level with a much lower DC than at higher RPM.

Guys, you are arguing the same thing. Drifto is basing his argument on engine VE (which I tend to agree is a little more correct) and Dennis is arguing boost level. At the most basic level, you are both correct. The WG opens to lower boost and closes to increase boost.

 

I'm kind of with you on that graph. It's obvious that the boost level had increased over the entire rev band and therefore isn't really a great interpretation of what the dump itself can do.

From what I've seen, at a given boost level the dump will only noticeably increase power output by reducing boost taper up top. Again, this power comes from an increase in boost, but it's directly related to the reduced back pressure resulting from the external dump.

However, the graph does give some insight in to the other things the dump will allow in terms of tuning. With the dump in place, you can run a little more boost across the entire rev band before you see knock. You could also use this extra padding by increasing timing advance through most of the rev band. You may not realize this extra tuning room at the higher RPM range since the boost is increased there already.

The gains are there to be made. My assumption is a baseline 10-12 WHP gain up top with a similar boost profile and no other changes. With tuning, I can see 15-20 WHP possibilities across a large chunk of the rev band. And, in my opinion, those numbers are conservative.

I'm actually trying to get some free cash to get one on my own car for some in-depth testing.

 

First off there is no reason to get hostile. I'm not getting hostile with you. I think you are confused about a few things and I was attempting to straighten you out. As far as the graph goes, it is what it is - A direct comparison of no dump vs. dump on the same car at the same boost level on the same day. I don't know how you can still call BS.
Another thing, I never said the external dump was for preventing creep. Not in anything I've stated here. I'll say it again. The dump is not a remedy for boost creep. The dump makes power so early because it increases the engine V.E. by reducing back pressure. The turbo is a huge restriction to exhaust flow and opening the exhaust up on a turbo car yeilds great gains. If it didn't people would just stick to the stock exhaust diameter. The dump is allowing more exhaust to exit the engine than can be efficiently carried out by the exhaust system. In very simple terms more flow = more power. That's all it does.
Lastly, comparing a DSM to an Evo is ludicrous. I owned a GVR4 and went from stock to a completely built, ported head, big cams,custom everything, big turbo ,stand alone, race gas and it didn't make the power I make on a small GT30r, stock engine, stock ECU, on pump gas in my evo.
You seem to be basing you entire argument off of your experience with your one DSM. I basing mine off of 10 years of working on, tuning on, and building turbo cars.

 

Now I don't agree with you either I have a graph of my Turboed M3 that had the external routed into the DP. I unbolted the rest of the exhaust past the DP and did a pull. The boost did go up .5psi (8.5 to9.0psi)but torque jumped up 40lb/ft and power came up 35whp. This was directly related to the increase in exhaust flow. I decided to build a 3.5"( up from 3.0") exhaust from the dp back. I figured it was the only way to keep the gains without running an open dp or dumping the wg to ATM was to enlarge the exhaust system. Went back to the dyno and lost 30wtq ( still up 10lb/ft over 3.0") but peak power still checked in the same as open DP, and even though boost was the same as no exhaust - 9psi - the car lost 20-30whp/trq in the mid range. Again, boost the same, exhaust flow not the same.
If you notice in the graph the dump makes more midrange power than no dump but as engine V.E. peaks and then starts to taper off the difference in power between the two graphs is much less dramatic. This is correlates with my findings on my turbo M3.


When you get some "free" cash let me know how to do this as well.

 

Drifto, I wasn't trying to be hostile, sorry if I came off that way.

I am not going to get into this to much more, but I had my car tuned very well by myself after I got it base lined. I know that an external did nothing fo rmy case. I am also basing my findings on owning lots of different turbo cars. Turbo stangs(2), t-type, turbo t-birds(3) 2 dsms, my current GN and my Evo. I have also been messing with thiese cars for more than 15 years at this point.

My findings and statements are what has come from my own experience. Now looking at that dyno graph, I can pick that apart pretty easily. 1, an external bolt on will not give 75whp at 3500 rpm (blow up the graph)

Run 1 made 175 at 3500 rpm or so, and the next run (which is titled run 4) is making well over 250. This totally leads me to believe that there was tuning and a boost increase, not sure though as power after 5252 takes a huge dump. I know I would be very disappointed at those results compared to run 1 which has much better usable power curve.

 

It's cool that you have owned so many turbo cars. Once you own one you will own more for sure. In my particular case I have never seen wastegate exhaust vented to ATM not increase power and torque. On my current Evo after getting tired of the noise I merged the wg back into the exhaust system roughly 3ft away from the turbine housings and introduced it on the outside of a bend. It was basically a straight shot into the exhaust system and I lost 30whp. Put it back out and power came back up.
I do believe you when you say you've haven't experienced a gain with it the same way I hope you believe me when I say it has always worked for me.
Thanks for the "lively " debate. It's fun to "get in to it" with other members from time to time. I keeps me on my toes.

 

Scott! How bout those dumps...

 

That graph looks real bad. Both power and tq drop real bad real fast compared to run 1. At 6500rpm, run 4 is making 75whp less then run 1. That is no improvement at all.

Also, look at the time and run number. It should only take an hour or maybe a little bit longer for someone who knows what they are doing to switch out an o2 housing. There is over 5 hours difference. No way does it take that long without any tuning or anything else. Even if you took lunch and supper.

Plus, what happened to run 2 and 3?

 

Take another look at the graph, there is no 75whp difference.

 

I just realized that you are confusing the 2 torque curves as one run and the 2 hp curves as on run. At no point on the graph does the open dump loose power to the std O2 housing. The initially larger values are the torque #'s for run1 and run4. At 5250 the two hp curves cross the torque #'s and continue up. In both cases run4 hp and tq trounces the hp and tq of run1. I do agree that tuning was involved to get the numbers provided in run4 but I'm pretty sure the OP stated that.