Turbo+cutout=?????
03-31-2013, 07:02 PM
#11
So, you already have it tuned to 18-20 psi, correct?
What's ur WG doing then? Isn't it supposed to control boost to 12-13psi or what ever you set it to?
I am asking because my truck is tuned for 15psi through 3" DP and 3" straight through (when open) Varex remote controlled muffler. When the muffler is closed I can hardly build 4-5 psi but I did not push it too much because I don't drive hard with muffler closed as it's restrictive and very very quite as it's supposed to be when closed.
I am thinking to install 3" cutout before the muffler for track. Guess I will have to tune it for open cutout if my boost is going to increase to 18-20.
I noticed one time that my boost jumped to 20psi in third gear with current setup, muffler open and no cutout!!
I did not have time to test it again in 3rd gear because of transmission issues.
What's ur WG doing then? Isn't it supposed to control boost to 12-13psi or what ever you set it to?
I am asking because my truck is tuned for 15psi through 3" DP and 3" straight through (when open) Varex remote controlled muffler. When the muffler is closed I can hardly build 4-5 psi but I did not push it too much because I don't drive hard with muffler closed as it's restrictive and very very quite as it's supposed to be when closed.
I am thinking to install 3" cutout before the muffler for track. Guess I will have to tune it for open cutout if my boost is going to increase to 18-20.
I noticed one time that my boost jumped to 20psi in third gear with current setup, muffler open and no cutout!!
I did not have time to test it again in 3rd gear because of transmission issues.
With that in mind, turbines extract power based on a heat and pressure difference between before the turbine and after the turbine. The pressure part of this is called expansion ratio; the bigger the expansion ratio the more power the turbine can extract. What this means is it spins the compressor faster and thus makes more boost with the same amount of exhaust backpressure. If you put a speed sensor on your turbo, you will see the shaft rpm increase with a higher expansion ratio.
Coming back to wastegates, unless you have an active controller that reads absolute boost pressure and tries to keep it there, boost will increase with a higher expansion ratio. Most wastegates just work off a pressure difference between the gate fully closed and fully open. But the turbine works off the pressure/heat difference before and after the turbine. To make this more fun, if your wastegate dumps back in to the downpipe after the turbine, a less restrictive exhaust (open cutout in this case) will give the wastegate more authority. A wastegate dump to atmosphere is the best possible case for a wastegate for control due to it being the highest possible pressure difference (and thus, highest flow).
Tuning wastegates can actually get pretty complicated if you have multiple exhaust set ups (cutouts, etc.) and wrongly sized components. Most guys dont stay in the throttle long enough to really see this, but is exactly why a lot of guys have issues with boost creep...in that case the turbos rate of acceleration is faster than the engines rate of consumption even with the wastegate fully open. In that case you need a bigger gate, a better designed gate setup, or a larger turbine.
04-01-2013, 11:49 AM
#12
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Plus if the wastegate is too small or mounted wrong like i did mine.. it will show up with free flowing exhaust.
If you have a oversized wastegate then you shouldnt see much of a difference?
If you have a oversized wastegate then you shouldnt see much of a difference?
04-01-2013, 12:30 PM
#13
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Wastegates themselves work off of backpressure before the turbine if you just use springs to control it. You can use a boost controller and lines to the ports on the wastegate to make it open faster or slower depending on intake boost pressure, but the gate itself has no idea what is going on after the turbine, unless its dumped back into the downpipe, which ill get to in a second.
With that in mind, turbines extract power based on a heat and pressure difference between before the turbine and after the turbine. The pressure part of this is called expansion ratio; the bigger the expansion ratio the more power the turbine can extract. What this means is it spins the compressor faster and thus makes more boost with the same amount of exhaust backpressure. If you put a speed sensor on your turbo, you will see the shaft rpm increase with a higher expansion ratio.
Coming back to wastegates, unless you have an active controller that reads absolute boost pressure and tries to keep it there, boost will increase with a higher expansion ratio. Most wastegates just work off a pressure difference between the gate fully closed and fully open. But the turbine works off the pressure/heat difference before and after the turbine. To make this more fun, if your wastegate dumps back in to the downpipe after the turbine, a less restrictive exhaust (open cutout in this case) will give the wastegate more authority. A wastegate dump to atmosphere is the best possible case for a wastegate for control due to it being the highest possible pressure difference (and thus, highest flow).
Tuning wastegates can actually get pretty complicated if you have multiple exhaust set ups (cutouts, etc.) and wrongly sized components. Most guys dont stay in the throttle long enough to really see this, but is exactly why a lot of guys have issues with boost creep...in that case the turbos rate of acceleration is faster than the engines rate of consumption even with the wastegate fully open. In that case you need a bigger gate, a better designed gate setup, or a larger turbine.
With that in mind, turbines extract power based on a heat and pressure difference between before the turbine and after the turbine. The pressure part of this is called expansion ratio; the bigger the expansion ratio the more power the turbine can extract. What this means is it spins the compressor faster and thus makes more boost with the same amount of exhaust backpressure. If you put a speed sensor on your turbo, you will see the shaft rpm increase with a higher expansion ratio.
Coming back to wastegates, unless you have an active controller that reads absolute boost pressure and tries to keep it there, boost will increase with a higher expansion ratio. Most wastegates just work off a pressure difference between the gate fully closed and fully open. But the turbine works off the pressure/heat difference before and after the turbine. To make this more fun, if your wastegate dumps back in to the downpipe after the turbine, a less restrictive exhaust (open cutout in this case) will give the wastegate more authority. A wastegate dump to atmosphere is the best possible case for a wastegate for control due to it being the highest possible pressure difference (and thus, highest flow).
Tuning wastegates can actually get pretty complicated if you have multiple exhaust set ups (cutouts, etc.) and wrongly sized components. Most guys dont stay in the throttle long enough to really see this, but is exactly why a lot of guys have issues with boost creep...in that case the turbos rate of acceleration is faster than the engines rate of consumption even with the wastegate fully open. In that case you need a bigger gate, a better designed gate setup, or a larger turbine.
I was referring to tuning the AFR for higher boost. So, if someone puts a cut-out and his free flowing DP allows the turbine to spin faster increasing his boost for the same setting of boost controller, he should re-tune it for the higher boost or adjust the boost controller down to maintain same boost level (matching his current tune).
I have Precision 46MM WG and it dumps to atmosphere. I don't think it's undersized for my T76 BB magnum turbo and 348ci LS1 engine. And I have Hallman in-cab Manual Boost controller
What I noticed at my current setup, with no cutout, as soon as RPM reaches above 4000-4500 with full boost (15psi), my WG is open. So, I feel that WG dumps as soon as I step on it.
04-01-2013, 04:55 PM
#18
When you tune for an boost level, whether its SD or MAF, you are hitting a certain MAP row (or frequency cell) in the ve or maf table. Tuning for higher boost just means going further down the table. Therefor running less boost should have no effect in terms of AFR if the full table is tuned. Also, you can make a reasonable estimate for the higher boost areas based on the low boost areas, but at some point the fuel pumps start to fall off so the fueling tables get weird. Hence why I recommend my spreadsheet to set your base pressure!
Talking about timing though, on the gen3s, there is a limit since the table is maxed out at 1.2g/cyl, but what this translates to in boost will be different for every setup. So in that regard timing can vary between a high boost and low boost tune. In my opinion, tune it for the max boost you plan to run, and be happy with a safe setup at lower boost.
Talking about timing though, on the gen3s, there is a limit since the table is maxed out at 1.2g/cyl, but what this translates to in boost will be different for every setup. So in that regard timing can vary between a high boost and low boost tune. In my opinion, tune it for the max boost you plan to run, and be happy with a safe setup at lower boost.