High Flow Turbo Dropping Boost in the Top End

[25GTV]

Hi guys,

This has been covered before but I have read through a bunch of the threads and not found the solution.

I have a rb25det neo.  Hypergear highflowed OP6, Front Mount rtn flow cooler, 1000cc injectors and e85, 3 inch exhaust (no cat).

When tuned the car made 230kw on 14psi but when we added more boost it hit 16psi at 4200 than tapered down to 13psi by 5000rpm and 12psi by 7000rpm.

I've removed all mufflers and have a steel intake pipe.  

If we set the boost control to 18psi it makes 250kw at 4500 rpm then falls to 12 psi and 200kw by 5500rpm.  We think the turbo starts to cavitate.

It doesnt misfire and does everything else perfectly.  Could this turbo just be out of puff?

 

What other common problems cause this? 

[GTSBoy]

10 minutes ago, 25GTV said:

Front Mount rtn flow cooler,

That will be what Tao will say is your problem. What is the boost pressure at the turbo outlet while you get your 14 psi at the plenum?

You must make measurements of what is going on.

[25GTV]

Thanks GTSBoy, so is it a common problem that the return flow cooler setups cant flow enough air at that sort of power?  

[GTSBoy]

Basically, yes. There are some return flow setups that are not as bad, but the majority suffer from the sharp turn and smaller core height. So once the air flow rates get up a bit higher, the pressure drop skyrockets. The pressure drop goes up with the square of flow rate, so once it become significant, it becomes numerically much worse with every small increase in flow.

If you were running that turbo at 24 psi (at the outlet), to get 14 psi at the plenum, then you can see that you're actually working the turbo MUCH harder than it looks. That's why you need to know the data. Because if you're only losing 2 psi over the cooler, then you have to look elsewhere.

[Murray_Calavera]

6 hours ago, 25GTV said:

What other common problems cause this? 

What psi is your wastegate spring?

If its 7psi and your using 3 port boost control, I'd start there. Anything over double the base pressure is pretty difficult with a 3 port setup. 

[25GTV]

Has a kinagawa 12psi actuator.  Greddy OLED Profec boost controller.

[admS15]

Probably the kinugawa actuator, those things are pretty hit and miss. 

I have a 21u hf on my r33. Using a standard actuator with a few mm extra preload controlled by ecu via 3 port mac valve. Easily holds 19psi throughout the rev range, maybe drops .5 - 1 psi at 7k rpm. Also running a shitty return flow cooler. 

You definitely have a problem somewhere, that is not typical behaviour for a Hypergear hf turbo.

[Chris32]

I run a stock GTT actuator and a Turbo Tech valve and have no problems running 20psi dropping to 17/18psi - 280kw

Blitz turnflow cooler and HKS 2535 with the .6 exhaust housing

I'd be swapping the actuator or trying another boost controller

[25GTV]

What sort of power figure?

[25GTV]

I used another boost controller to monitor the boost at the turbo outlet compared to the manifold.  The turbo hold 20.5psi from 4500 to 7000.  The Manifold sees 16 at 4500 then instantly to 14 psi and 12.5 by 7000rpm.

[GTSBoy]

There's at least a big chunk of the problem.