Gotta love Clayton!

Thank for the assurance.

So, I assume EBC would not be a benefit for this purpose. I thought if it held more boost there would be more power to be had at top.

 

me my friend had this problem with our IXs all i did to eliminate it was put an AEM short ram on it and my boost stays steady through the rpm range when we hooked it up with the tactrix cable

 

Really, with open air intake you're able to reduce your boost taper?

Hmmm, what other modds do you have and dyno numbers?

thx!

 

yeah it seemed to reduce it when we were checking out the dyno the boost stayed constant throughout it didn't jump around and for other mods really all i have done is my friend has the tactrix cable and he just tuned the turbo to put out an extra two pounds of boost yeah i would put the dyno up but my jump drive is at my house and now i am down here at my friends maybe later i can put it up

 

You know some cars hold boost better because they wont flow as much air like say because of a restrictive exhaust. Simply put the better your engine flows the quicker your turbo is going to run out of breath.

We have drag racers here with the waste gate simply welded shut and they will still see taper because the turbo can't keep up with the flow numbers required at maximum rpm.

For example at a Volumetric effeciency of 95% @ 7500rpm:

18psi = 42.96lbs/min
20psi = 45.52
22psi = 48.09
24psi = 50.66
26psi = 53.22
28psi = 55.79
30psi = 58.35

As you may or may not know the most you'll see out of a 16G turbo is around the 44lbs/min mark but usually less. The only other way to keep your boost levels up higher is to have VE marks less than 95%. I used 95% just to test, most modern engines can see peak VE's around 98%.

 

Ok there is a lot of misinformation on EvoM with regards to boost taper.

For folks using the MBC, peaking at 24psi, you will likely be at 17 psi at redline.

For folks using the ECU / BCS or an EBC, you can peak at 24 psi and taper to more like 20 - 21 psi at redline (you may get a bit higher, but I have not seen it).

Ease of use / setup, nothing beats the MBC.

Getting a bit more out of the total powerband an EBC or ECU/BCS is technically better.

 

The boost taper has more to do with increased back pressure in the turbine housing. As the RPM's rise above 6k RPM the exhaust back pressure starts to get very high. This increased exhaust pressure is additive to the pneumatic pressure used to open your wastegate actuator. When you have a NON closed loop EBC or MBC, it does not take into account this additional exhaust back pressure in the inlet of the turbine housing.

If you look hard enough, and watch or video tape your boost gauge from 3k rpm all the way to 7600 RPM, everyone will see a taper if you have a stock based turbo, unless the tubine wheel is clipped (very large clip) or you have the LT based turbo from Buschur or Forced Performance. And these will still taper some, just not as much. RPM based boost control or closed loop boost control is the only way to hold solid all the way to redline.

Brian

 

i.e. Apexi AVC-R EBC?

In that case, I may transplant it from my GST to IX...thanks!

 

Absolutely not, a high tension wastegate actuator is used to get higher boost levels not reduce taper. Taper has everything to do with the turbo running out of flow. If it didn't drag cars with their wastegates wired shut and a stock turbo would never taper but that is not the case...

An example of such a case would be mike's car which ran a 11.2 quarter mile, see the drag racing forum. His wastegate is pretty much wired shut so the turbo will produce as much boost as possible. He says it tapers down to about 19psi by redline if i remember right.

Clipping does not increase the flow of the turbo. It simply reduces some exhaust restriction at low rpms. This will not help the turbo flow more air, the LT turbo has a larger compressor wheel and according the flow ratings should hold around 25psi to redline given a stock flowing motor.

RPM based boost control makes no sense

 

Road spike: You are incorrect on many fronts in your above statements. The higher tension wastegate springs will HELP reduce taper. They will not stop it either, because the increased Force of the stronger wastegate actuator still gets overcome.

I can produce 34 psi peak boost pressure with a stock actuator, but it will taper to the 20 to 23 psi range by 7700 RPM. I can get the same 34 psi peak boost with an upgraded actuator, but the taper is not as severe. Ask me how I know???? Because I HAVE DONE IT !!!! Both scenarios on the dyno.

A wired shut wastegate will still TAPER due to a limited flow rating on the compressor wheel AND the build up of backpressure in the turbine housing prevents any more speed of the turbine wheel (it has reached terminal rotational velocity). You can only flow so much exhaust thru a certain sized turbine housing.

If you have a compressor wheel that is capable of flowing more lb/min, then you will be able to hold a higher boost pressure IF you can keep the exhaust back pressure lower, as to not crack the wastegate flapper open, which in turn slightly slows down the compressor wheel.

If you think clipping doesnt help increase the flow of a turbo, then definitely do not look into buying the 20G-LT or EvoGreen from FP. That is the whole principal they are based upon. They use the same compressor wheel that is rated at 45 lb/min and couple it with a LARGER turbine blade (with accompanying machined turbine housing) to increase the airflow rating to 49 lbs/min. Clipping accomplishes the same purpose as a larger turbine wheel (except to a smaller degree).

And if you think that RPM bases boost control makes no sense. Then you are SERIOUSLY mistaken. I have one. I use it to maintain 21 (+ or - 0.3) psi from 3k to 8000 RPM. With the same boost controller without RPM correction. The car will peak at 21 psi and drop to 18.7 psi by 8000 RPM. By using this boost contoller with RPM based boost control I picked up 3 lbs/min at 7800 RPM. Thats approx 30 hp increase. That is with nothing else changed but using the RPM based boost control.

I base MOST of the things I say by experience, not by heresay.

Brian

 

Would you mind clarifying what you meant by not as severe? Did it hold higher boost or did it just taper down a little slower?

First are we comparing 20g's or 16g's to 20g's. I know for sure that the 16g has a smaller compressor wheel so I'll assume you mean 20g's.

I thought FP used a 69mm compressor wheel compared to the standard 68mm exducer. I understand that the larger turbine housing reduces blockage and may increase flow if the standard turbine was inadequate. There still is a limit as to how fast you can spin up a turbo though, once they reach near super sonic speeds the flow chokes and even a very large turbine wheel wouldn't gain that much in flow ratings.

Clipping reduces the turbine's surface area in essence making it smaller than stock but also reduces exhaust blockage.

Ah so you mean RPM correction not control that I totally understand

 

With the stock wastegate actuator, I believe we saw roughly 22 psi by redline on the stock 16G with 10.5 housing, with basically the EBC turned to 100%.

With the upgraded actuator, we saw the same peak spike but the boost held higher in the midtange, and only feel to around 25 by redline.

I was referring to a 20G-9-5 turbo VS the 20G-9-LT or EvoGreen turbo. They have the same exact compressor wheel, yet the large turbine wheel version carries a 4 or 5 lb/min higher rating.

Clipping the wheel allows for an opening for exhaust to go without going out the wastegate once the wheel is spinning at max rotational speed. The turbine blade reach such speed that it can basically be seen as a solid mass of material. The clipping or cropping of the blade allows a small opening in this virtual solid mass. This bypassed exhaust doesnt offer any more energy to the turbine wheel however it does reduce the back pressure in the turbine housing, which is indeed the cause of boost taper along with out flowing the compressor wheel at high RPMs.

With the 20G-9-5 and white rabbit compressor wheels, you should NOT be outflowing them at 21 psi, however the boost still tapers. So you can deduce from this that the compressor wheels flow rating is not the limiting factor in causing the boost to taper.

What I meant by RPM boost dependent boost control. Is that it basically allows you to change the duty cycle of the solenoid at different RPMs. You would want to increase duty cycle to combat the addtional back pressure in the turbine housing.

Brian

Brian

 

Neat I guess thats why i keep coming here Learn something everyday about these cars.

I'm not so sure the 20g-9-5 and the Evo green have the same compressor wheel though. According to Forced Performance's web page the Evo green has a custom CNC'ed compressor wheel which may account for some of the flow increase

 

Maybe your boost was erratic before, but adding an intake certainly did not make the boost taper lessen. If you didn't tune for the intake with EcuFlash, then that intake didn't do anything but hurt the car anyway. Also, you can't just randomly add 2psi with EcuFlash (you say tactrix cable, but it's EcuFlash that changes the ECU settings).

 

I have always heard that boost gauges were not as accurate as Map sensors, why is this?
What about electronic gauges which are basically map sensors with a display?