Hiboost

iTrader: (9)

I finally broke down and purchased an upgraded Forge Wastegate Actuator because there was very little actual data on what this mod would do for a car with Stage 3 bolt-ons with a stock turbo Evo X. There was much debate on what was causing the stock turbo to taper boost above 5000 RPM:

1) Stock Turbo Wastegate Actuator is getting forced open

2) Stock Turbo is running out of flow

Turns out I was forced to use some less than ideal OBD2 Logging software called "Proscan" which I'm returning via their 30 day money back guarantee due to extremely poor logging capabilities. I'm looking at a product called "ScanXL" that seems to have much more control and playback abilities but it's still mainly just an OBD2 diagnostic logger. The sad part is that from what I can tell the stock ECU and sensors seem to be limited to a 2.5 bar MAP sensor so all the PSI logging was clipped at 37 PSI absolute pressure which is around 23 PSI. The MAS Airflow readings also seem to hit 38 lb/min like they hit a brick wall and I'm unsure if it's the turbo or software/sensors/ECU.

I ran before and after logs of 3rd gear pulls at 26 PSI boost which was set identical in 5th gear pulls at the 3000-4000 rpm range with an MBC. I captured the boost gauge on video with my digital camera and paused it at 500 RPM increments to get a read off the gauge, although I really need to do that again during the daytime to see it better. I'll try posting the videos on youtube which will also give you an idea of what my ETS exhaust sounds like at WOT.

The Forge actuator had a 1/2 turn preload and the Stock actuator had 2 turns preload which resulted in 22-23 psi minimum boost in the mid rpm's for both actuators. I may look at raising the preload and see how that effects the boost in the 6000-7500 range. Another test would be to remove the Wastegate signal all together with some 100 octane gas in there for safety and go WOT at 6000 RPM and see what the max boost holds with it running "unlimited" boost. I'm betting the stock turbo still tapers off regardless of what I do, even if I wired it shut!

As you can see from my crude combined chart, even with identical 5th gear boost settings of 26 PSI, the Forge WGA seemed to allow higher airflow and better boost control in the low to mid RPM range and also reached the magic 38 lb/min airflow reading sooner. I can definitely feel that the car is faster in that range, and there is still zero knock or timing being pulled as verified by my knocklite and other logs of timing advance.

It seems the Forge WGA can only maximize the flow capabilties of the stock turbo as it runs out of flow in the 6000-7500 rpm range. I have seen higher boost at redline with the preload adjusted farther on the stock WGA, but that was due to uncontrollable boost creep and the wastegate flapper being restricted to a smaller opening angle. The boost you get by forcing it to run higher than it wants would likely be overheated anyways and the minimum boost levels would probably be too high for a 30 min road course session.

Once I get a real turbo on this car the upgrade will really shine, for now it's only benefit seems to be better boost control in the low to mid RPM's as compared to the stock WGA.

Massappeal

iTrader: (1)

good info!

STi2EvoX

Only problem is that your software might be what's limiting your logging abilities and not the ecu. The EVO X has a 3 bar map sensor, not a 2.5. Of this I am possitive as it's been mentioned in several analysis reports of the 4b11. I'm not surprised about the wastegate mod though, as I even told people this from the get go. This turbo is just too small to run any more boost than about 18-19 at redline.

That's not bad for a factory turbo though, as it's bigger than any other factory turbo that I know of and for damn sure bigger than the baby STi turbo, which is part of the reason that the power on the STi pukes and dies 1000 rpms before redline. What's interesting though is that the 4b11 continues to make power all the way to redline and beyond even as the boost drops because the head in this car is so damn good and the mivec is phenominal.

Hiboost

iTrader: (9)

I agree it's likely the lame OBD2 software I'm using right now, or it could be that in order to eliminate the part throttle overboost, or fuel cut from airflow, the values of what the ECU reports are clamped in some way. Perhaps some EcuTek tuners could chime in on that possibility. If it really is a 3 bar map sensor that is good news since it should be able to read 29 psi or so.

I have to agree now that the turbo is just a hair too small, a shame since that means there is really no way to go faster on a stock turbo by turning up the boost. When they quoted that the turbo on the X can spool up to 20% faster that is usually a bad sign for max power.

This is because you are typically in the 5000-7500 rpm range when running a quarter mile and the boost can only be increased from 3000-6000 rpm range, after that it's on autopilot and at max flow. I guess with a ported head, turbo, and exhaust manifold along with a higher flow o2 housing/DP combo we may be able to extract a little more flow out of the stock turbo setup. At that point we may as well just swap in a higher flow "stock appearing" turbo with better internals.

The head is amazing like you said though, somehow it keeps the engine flowing at 38 lbs/min from 5500 right to 7500+. I'm just curious what the max boost curve is like on the factory Evo 9 Turbos as a comparison. Seems like they can hold a little more boost than what we are seeing on the Evo X and also trap higher in the quarter mile which I'm sure is also influenced by weight and more mods.

There's a chance I'll be at the local drag strip tonight if the weather holds and I can see if any of this extra low to mid boost helps the quarter mile times at all.

gunzo

iTrader: (2)

Nope .. stock sensor clip at 1.55bar / 2.5bar absolute .. still dunno if this clipping is the limit of the sensor or the output not being a 2byte ..

Hiboost

iTrader: (9)

Ah well that's a stinker, I wonder if some changes to the ECU could be made to allow it to read higher. Has anyone gotten over the 38 lb/min flow on their MAS yet? I would imagine the people with upgraded turbos have done so for sure. BTW the car is just silly now in the mid range with 26 PSI and this cooler weather, the thing just pulls on the highway!

EVIL_EVO_VIII

iTrader: (5)

A IX turbo on a X would be so good and would fix alot of the boost taper problems imo..Too bad just wont bolt on

STi2EvoX

I am guessing that it's something to do with the output signal being limited because IT IS a 3 bar map sensor, read any of the tear down reports and analysis reports from perrin and tomei, etc.

Hiboost

iTrader: (9)

Seems like the Works BOV and Forge Actuator have improved my daily driving power levels more than anything. After 8 runs at the drag strip Wednesday night I got a handfull of 12.6's @ 109 with low 1.8x short times. Tires were spinning off the line pretty bad even at 30 psi tire pressure so the 2nd run of the night ended up being my best:

60' - 1.784
1/8 - 8.067 @ 84.88
1/4 - 12.552 @ 110.30

It's kind of frustrating when no matter how high you turn your boost, the 5500-7500 RPM's you are running the car at in the 1/4 are at the flow limits of the stock turbo. I'm lucky if I get 1-2 extra psi for 30% of the gear pull. Bah! Even if my Stock BOV was leaking above 24 psi, upgrading to the Works BOV wouldn't be a factor past 6000 rpm's either due to the stock turbo tapering off.

It was odd how the runs towards the end of the night had a decent launch and good shifting, only to find the same 12.6 @ 109 timeslips... felt like a bracket car! So in conclusion, it appears the Forge Actuator doesn't really help quarter mile times on the stock turbo due to the flow limitations, but it will make boost levels much more consistant up to about 6000 RPM's which is great for the street.

Massappeal

iTrader: (1)

Great info! I'll hold on this mod and just wait to get a bigger turbo!

Hiboost

iTrader: (9)

I think for the low and mid rpm boost control is excellent on the Forge unit, it's just not at fault for the flow restricted stock turbo in the upper RPM's. I'll give it one more go this next Wednesday where I'll try more preload at the expense of not being able to run below a certain minimum boost. It will be worth a test to see if it makes any difference in the trap speeds at the strip. I sent Mike at Forge a PM to see if he had any other ideas on how to hold boost longer on this flow limited turbo. While I think I can get a 12.3 - 12.4 if I figure out how to get more traction, the trap speeds are going to limit me unless I can figure out a way to get more boost above 6k rpm.

RREvoX08

iTrader: (1)

you do know that this turbo is only slightly smaller than the 16g the came on previos evos

Hiboost

iTrader: (9)

Indeed, but it's enough to cause the boost to taper off more than previous evo's at higher RPM's since they intentionally designed it to spool about 20% faster on the 4B11 engine. From what I've read the Evo9 people are only tapering to 20-22 psi @ 7500 where as the Evo X stock turbo is tapering to 18-19 psi @ 7500. Couple that with a 300 lbs heavier car and you have less airflow to move that weight. I think 20G's were able to hold 25-26 psi @ 7500 so they definitely went the wrong direction to power the heavier Evo X.

There are a few things that will help it such as portwork or better exhaust manifold/O2 to get it flowing better but if you are already messing around with that stuff you may as well just upgrade the turbo and be done with it.

Jason

I guess they set it up that way so that it drives more like a large displacement car, rather than a small displacement turbo car

RREvoX08

iTrader: (1)

i was thinking about porting mine, and putting an 18g or 20g housing on there and clipping it.