GT-R turbos on the VQ37
 

I know I tell him all the time but he never listens!


Also, it looks as if like the wastegate is opening at 12 psi and not 8. I will check what's happening tonight.


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So I just did a log today to 5500 rpm (GTR map sensor)

The tune is running very low timing for now just for safety. Does this look like boost creep to you guys or just a higher psi spring?

https://uploads.tapatalk-cdn.com/201...a33d43baa3.png


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It looks pretty clear to me that your wastegates are set to ~12psi. It builds smoothly to that target and levels off.

I did some googling and it appears a stock GTR runs ~12psi... so it seems reasonable to me... though not exactly what I would have expected.

The million dollar question here is - can you change the springs on the OEM actuators, or adjust the tensioning?

Unfortunately not. I did research exactly that and everybody including my turbo said that running on just wastegate pressure (0 duty cycle in his gtr) it ran at about 8-9 psi. It's really weird that it's 12 psi on my car.


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Doing some more googling the answers seem a little all over the place.. though I haven't seen anyone say anything as low as 8-9... What model year did your turbos come from?

Here is the most informed-sounding (for what its worth) post:
Max boost for 2014 GT-R? - R35 GT-R - GT-R Life

I am seeing a lot of 11, 12, 13psi posts from people. I'd be inclined to trust that kind of number since it's backed up by your own data. The curve you posted looks pretty cut and dry to me... Does not look like boost creep to me at all.

Remember that the 3.8 and 3.7 are different motors. And the 3.7 is not a FI design. Any number of thing could cause the boost increase. Biggest I think is the difference in combustion ratios of the two. GT-R is 9 to 1, Z is 11 to 1.

This is true but I am not sure it applies in this case... If it was boost creep then these factors could certainly contribute. But to me this looks like his wastegates are opening at 12psi and they are activated purely on pressure alone...

Here is a great post from Visconti Tuning... It differs between years and it differs between gears. (Hence why it looks like most GTR owners have no idea how much boost they make in stock form)

Stock Turbos PSI - Engine - GT-R Life

The thing is, that's the PSI including the oem boost solenoid which does adjust boost to a certain level.


Another interesting thing I found is this chart. Look at the standard actuator psi!
https://uploads.tapatalk-cdn.com/201...29e3bf533e.jpg


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Not sure about that chart... kind of suggests that the spring pressure is 4psi but the boost control will take it up to 18psi... That's kind of out of whack... At that kind of differential I would start worrying that the pressure of the exhaust itself would push the wastegate open.

That being said.. if the standard boost floor was around 12psi I would expect the wastegate pressure to be a little less than that... but I can also think of reasons why you would want to set it up right on the target.

On way to test for sure is to pull your downpipes and run a regulated air pressure hose to your wastegates and slowly adjust until you see them start to open.... that would certainly take all the guessing out of it.

That's true. I will be verifying that the map reading is accurate with a boost guage just incase.


One more thing for you! Where did you route your wastegate lines? Mine is just ugly looking right now but I was thinking of running Hardline across the engine similar to the GTR setup.


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Last time I had to trouble shoot something like this on my old evo 3, I used one of those hand pressure/vacuum pumps and took note of when the actuator rod stared moving.

I didn't do anything fancy... I put a barb in the passenger side charge pipe (as instructed by the Gamma manual) and ran that up to about the middle of the front of the intake manifold, then tee'd them from there back down to each wastegate. Just like the BOV, my goal here was just to have an equal length of line going to each...

I did something similar. I guess I'll just keep it as is and see how it holds up.

Got my new 1000cc injectors installed today. Hoping this solves running out of fuel at the top end. I will be also getting a fuel pressure guage just to check on how safe it is. https://uploads.tapatalk-cdn.com/201...217916e318.jpg


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