Mitsubishi Lancer Evolution Forums banner
1 - 12 of 12 Posts

·
Premium Member
Joined
·
1,566 Posts
Discussion Starter · #1 ·
Why exactly does the boost taper up top? Is it the head that can't keep up with the flow, or is it the turbine wheeel that can't keep up?
 

·
Premium Member
Joined
·
3,496 Posts
It's not related to the ECU.

Larry, the head outflows the turbo at higher rpms. The turbo cannot keep up with the amount of air it needs to push at a given PSI (e.g. 22psi) as the RPMs increase, so the psi drops to a level that the turbo can handle. One way to realize what I mean is to set the peak-hold on your SAFC when monitoring MAF HZ. You will see that you hit your peak HZ at around 7000rpm, which is where your turbo is only pushing 18psi or so. If you look at the peak HZ down at 4000rpm, the value is MUCH lower despite running 21-22psi or so.
 

·
Premium Member
Joined
·
718 Posts
Yup, 100% a turbo flow limit. That is why with a GT-35R I can push 30 psi to 8,000 RPM The overall flow capacity of the turbo is much higher than the flow capacity of the 16G. Now, if I were running a fully built block and were running 45 psi in the mid range, the GT-35R would also tapper off boost level as RPM's rise due to hitting it's flow limit.

Keith
 

·
Premium Member
Joined
·
718 Posts
Hey Larry,

I went through my old data log from back when I had the stock turbo, and combined them with some logs from now in an EXEL file to come up with this chart for you plotting the boost response curve between the stock turbo (03 stock turbo with 9.8 exhaust housing) vs the boost response curve with my GT 35R with .63 A/R exhaust housing and .70 A/R compressor housing.

Keith
 

Attachments

·
Premium Member
Joined
·
1,566 Posts
Discussion Starter · #6 ·
Hmmm, that's what I thought.
Now on to the next step; I wonder if this can be over come by clipping the turbine wheel?
 

·
Premium Member
Joined
·
718 Posts
Clipping the turbin wheel would allow more exhaust gases to pass through the turbin at the same turbo shaft speed. It increases the efficiancy of the flow on the exhaust side to increase power, it does nothing for compressor side flow.... and in fact I suspect it would lower your ability to hold boost at high RPM.

The limitation in the EVO VIII 16G is on the compressor side. The increase in compressor cover size for the EVO IX has helped with compressor flow at high RPM and the EVO IX turbo can hold higher boost to redline than the EVO VIII turbo even though the 05 and 06 have the same exhaust housing, and the same turbin and compressor wheel.

Keith
 

·
Premium Member
Joined
·
3,496 Posts
Which is why I'm searching so desperately for a used stock IX turbo to use here at altitude. My boost tapers from 26psi peak to 16psi by redline no matter what I do. At sea level just before I moved, I logged my boost via MAP sensor and got 26psi peak with 22.5psi at 7000rpm and 21.5psi at 7500rpm. The difference in that 5-6psi up top makes a world of difference when racing.
 

·
Premium Member
Joined
·
1,566 Posts
Discussion Starter · #10 ·
Warrtalon said:
My boost tapers from 26psi peak to 16psi by redline no matter what I do.
Wow! That's a huge difference.
We don't need the complete turbo right? We can just swap compressor housings since the wheels are the same right?
 

·
Premium Member
Joined
·
3,496 Posts
turbolarry said:
Wow! That's a huge difference.
We don't need the complete turbo right? We can just swap compressor housings since the wheels are the same right?
I thought the same thing, but when I spoke to Blouch turbo about possibly doing this, they took one apart and found that you CANNOT just change the compressor housing, because the guts are in fact different. I had always thought the wheel and shaft were the same, but apparently they're not...or at least not enough alike to just change compressor housings.
 
1 - 12 of 12 Posts
Top