Wastegate Boost Reference For Twin Turbo Rb26 Using Dual Port Gates

[burn4005]

Hi Guys,

I've gone a slightly different route with boost control on low mounts and am using a pair of turbonetics 30326 dual port wastegates on my HKS2530s and a 4 port MAC valve to suit.

idea is I can run very low boost pressure in Mrs/valet mode (preload will only be around 7.5psi) but can wind in 26+psi on E85. also, having the 4 port solenoid will assist in keeping the gates clamped closed until the ECU says otherwise.

my options for the boost source for the solenoid (which is located on the passenger strut right beside the turbos) are:

1) Tap each turbo and join with a Y piece into the wastegate solenoid.

2) Tap into the intercooler piping just after the twin-turbo pipe (which has the splitter mod done)

3) Just use the signal from the intake manifold pre-throttle plates.

my considerations are: shorter hose length and closer to the turbos = better control. I figured the faster pressure response would be a good thing when the solenoid is directing pressure to the back of the actuators to keep them shut during spool

the idea is to obtain optimum boost control with agressive ramp-on.

inter cooler is a 120mm Greddy unit, so I'm not expecting significant pressure drop over it.

boost control is being done per gear, with the TPS% position generating a MAP target with an Ethanol content modifier. so 100% thottle may be 20psi on petrol but 27psi on E85.

that map target is then used in a target MAP vs RPM table that dictates the waste gate duty cycle to achieve pressure target. also under WOT conditions closed loop correction activates using PID control for minor corrections.

the ultimate would be to use two separate solenoids, one for each turbo with its own reference but you would need to monitor turbo speeds to make the most of it I think.

Edited March 30, 2016 by burn4005

[GTSBoy]

The difference between 1&2 would be so small as to be unnoticeable so do whatever comes easiest out of those 2. The chances that either of them would offer you noticeably different control characteristic compared to sourcing it from the plenum are probably not much larger, but on the basis of paranoia simply rule out option 3 because it means more pipework.

[Navara96]

Hi mate, slightly off topic but have you actually got the twin port wastegates hooked up in the car currently? no clearance issues at all and bolt straight onto t25/t28 frame turbos with the stock bracket? i'm looking at doing the same thing ( running the 4 port solenoid) thanks!

[burn4005]

luckily I had HKS actuators, and they are bolted to the bracket rather than welded on (I think the garrett ones are welded to the backet, so won't work):

and the turbonetics ones also have the two bolts in the same place.

they went in with a fair bit of swearing, but only an hour or so work. the support rods on the HKS brackets are in the way when you're trying to get a ring spanner on the actuator bolts, but got there in the end. rear actuator ports point outwards, front actuator ports point inwards so they don't foul the intake piping.

you also need longer actuator rods.. i got mine from GCG. you need two of the 1/4 UNF thread 80mm actuator rods for them to reach the wastegate flapper.

4 1/2 turns of preload has them making 8psi on wastegate pressure alone.

making 14psi at around 40% duty on the mac valve, and they are VERY sensitive to duty cycle changes. only a few % here and there makes a few psi difference. had a few coil issues so didn't go any higher until that's sorted.

Edited June 16, 2016 by burn4005

[Navara96]

Thanks for that! I'll look into it