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More wastegate means more exhaust gas directed away from the turbine, slower shaft speed, and less boost? Not to nitpick but I saw you say that before and am curious what you mean.
More wastegate means more exhaust gas directed away from the turbine, slower shaft speed, and less boost? Not to nitpick but I saw you say that before and am curious what you mean.
You "can" make more boost,.. but it will be totally out of control. You end up with what you call "Boost creep".
The more power you "let" the engine make (by dialing in more boost),.. the more gate you "will" need shortly thereafter to keep the turbos in control.
If you don't have enough gate,.. the boost will continue to climb out of control until either you lift, the ECU cuts timing, or the engine goes BLAM.
When trying to make a lot of boost and the term "not enough gate" comes up, I think of two things.
1. The gate valve itself has a large surface area / spring pressure not great enough, and no matter how much boost you stack on top of the diaphragm, the exhaust gas pressure in the manifold blows the gate open, limiting how much boost you can run. Of course, this usually only occurs when you are trying to push the turbo in question, as typically exhaust gas pressure is roughly 2X what the intake manifold pressure is in a system that is flowing appropriately. Obviously this can get pushed much higher as the efficiency of both the turbine and compressor fall off when you push it.
2. Gates are too small, possibly hotside is sized a bit small for the power production requested. As stated above, as the gas volume increases due to increasing boost pressure, the gate has to be there to shunt the excess gas (power) away from the turbine wheel. Again, in a system that is running well within the efficiency islands, many times it doesn't take much additional power (gas volume) to drive the turbine to the higher rpm/ pressures requested, though the gas volume through the entire system goes up in a non-linear fashion. Here you need bigger gates to keep from creeping.
There's also a third option while we are talking about external gates. You can actually size the hotside of the turbo a bit small, and then plumb in a really well flowing external gate. This will give you a spool-up advantage while still allowing the engine to make great power at the desired boost pressure as once the gate opens, a larger percentage of gas is flowing straight out of the system and bypassing the turbine nozzle and obviously the turbine itself. OEMs back in the day with external gates like Porsche and Audi used this, and it worked well with the technology available at that time. I also used a similar idea on my GT35R powered Evo 8 back in the day. It spooled up well for a 2.0L, and made great power all at the same time using just a .63 A/R T3 backside.
This is the problem with dynos - its just a guess based on a formula. If the car had run acceleration and top speed runs over say 1/2 mile with and without the larger IPD y pipe I dare say there may well have been appreciable gains. A few tuners who use real data i.e. driving the car at wot on a racetrack think this is one of the best mods out there when combined with the larger GT3 throttle body and IPD 82 mm plenum. Other tuners who rely on dyno for data don't think its such a worthwhile mod. I know Longboarder proved it was a worthwhile mod with real data.
Some good points being made here, but in this case, pressure ratio is 1:1.1 so the hotside still has some room. Will be installing dual port internal gates to help keep them shut. The flappers have a large surface area, so just need a little more help keeping them shut.
Ahh,.. so the gates flow enough, but can't stay shut at the higher boost.
Is re-plumbing the gates enough? Or should you put in actuators with stiffer springs?
I ran a dual-port in my Subaru. First plumbed just to the bottom port on a Tial MVR-44 like most do,.. but then I plumbed the top and bottom. Much smoother control,.. and it got rid of the warbeling sound as the gate rapidly oscillated.
Like this. Is this what you mean,.. but with one 3-port solenoid per turbo?
That's a quick job at least.
I always want the smallest hot-side I can get away with. Small enough that the engine is choking slightly as it nears redline.
You spend 99% of your time in the 2-4k range,.. and almost zero time in the last 500 rpm before redline. (Even if you're roll-racing on a freeway you still have to start pulling the next gear 500+ rpm before redline to make sure you don't hit it).
And spool is king on the street,.. especially with a manual.
I never once lost to a 600-1,000 hp car driving my 360 whp Subaru. I'd be 10 car lengths out in front by 60,... and even 900 whp in the other car wouldn't be enough to get around me by 100.
You "can" make more boost,.. but it will be totally out of control. You end up with what you call "Boost creep".
The more power you "let" the engine make (by dialing in more boost),.. the more gate you "will" need shortly thereafter to keep the turbos in control.
If you don't have enough gate,.. the boost will continue to climb out of control until either you lift, the ECU cuts timing, or the engine goes BLAM.
Boost creep generally happens when you are trying to run too little boost. This means you have more backpressure in the wastegate than you do passing through the turbine wheel and exhaust, so even though the wastegate is open the air passes through the turbine wheel because it is the path of least resistance. That brings the turbo shaft rpm up, and hence more boost, as the control mechanism is unable to regulate it.
In a boost creep scenario you can just turn the boost up to wherever it creeps to - that's what it wants to run.
I think what ITguy is saying is that he's going to install a different turbine housing and/or internal wastegate configuration in the existing housing that has two flappers, for more flow without having too much surface area on an individual flapper. That prevents the wastegate from blowing open, allowing him to keep them closed longer and make more boost.
I've never run into that scenario myself, that's why people go with external wastegates - they work really well and are mostly immune to the problems we've been describing here. Internal gates can work really well, but they need to be tuned to the individual combination in some cases and aren't always as intuitive when it comes to tweaking. Hence the confusion of a discussion we're having right now. .
Sure you can run a stiffer spring, but that will further reduce resolution. The dual port turbosmart gates will solve the problem and provide MUCH more resolution, 10psi low 35psi high. Right now, we are stuck 20-28
I never once lost to a 600-1,000 hp car driving my 360 whp Subaru. I'd be 10 car lengths out in front by 60,... and even 900 whp in the other car wouldn't be enough to get around me by 100.
12-23-2015, 08:20 AM
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