GT28RS.........Boosting 22psi when wastegate fully open......HELP NEEDED.

[Mark@VAGWORX]

Took the car for mapping yesterday and the mappers had to end the session early as the car was hitting 22psi at 7000rpm on 2/3 throttle load with the wastegate fully open.
The mappers were initially mapping the car N/A before going on to mapping it boosted. So, they disconnected the actuator rod in order for the wastegate to be fully open so that it would bleed off nearly all the boost.

But, even with the wastegate fully open it was hitting 22psi on 2/3 throttle. They halted the session because if connecting up the wastegate and actuator they expected the boost at the redline to go much higher than this level with minimal control.

The car is a stock AUM engine, with mk4 ATP GT28RS bolt on kit, internally gated. Other mods are USRT short runner, bespoke 3" intake pipe, turbo back 3" side exit exhaust with one box and Emerald standalone management system.

The mappers were saying that the 'pebble' hole that the wastegate covers is potentially to small as it can't bleed the boost off.

These guys aren't cowboy mappers, as they build and map various GT cars for races all over Europe, so really know there stuff.

Does anyone have any ideas what could be causing these problems?

All ideas or help are much appreciated.

Thanks.

 

[Mark@VAGWORX]

Any ideas??

 

[Feel]

Can't be the wastegate hole size itself - plenty of GT28RS's running fine, unless there's a manufacturing/casting defect on yours and the hole's not fully opened up. Doubt that though.

Now, I'm no expert and it feels to me like I shouldn't really comment, but:-

When you say "disconnected the actuator rod" you mean they've unscrewed it from the shaft the wastegate sits on? I dunno what pressure the wastegate's set to on a GT28RS (I would've thought less than 22psi) but if they've just disconnected the hose to the actuator, it's entirely possible that it could still make boost. Another possibility is that the actuator could be fubar and keeping the wastegate closed.

You say they were going to map it normally aspirated? How was that going to work then and what was it going to achieve? I don't understand that approach at all. Surely they can't map it NA with a turbo bolted to it - the wastegate will stay closed until the boost reaches the wastegate preload, then the wastegate will open. I can undertand then mapping it at very low boost to start with (8psi), then building the boost as the mapping progresses...

Where have you sourced this turbo, and who's the mapper?

 

[Mark@VAGWORX]

The vac line, boost solenoid were all still plugged in. The actuator rod was disconnected from the wastegate flap, so the wastegate was left open manually.

The car's running standalone, so doesn't use an O2 sensor/MAF but uses a map sensor instead so they map it NA to start with. They then have a base map to start with and start to dial the boost in.

It's an ATP turbo. Mappers are Track n Race in Rainham, Essex.

 

[Feel]

Got to be either something physically stopping the wastegate flapper from opening, shaft sticking/jammed perhaps, or something went wrong after they disconnected it, perhaps jamming the lever on the end of the wastegate shaft and stopping it from opening?

The wastegate must've been practically fully closed - I can't imagine it would let the boost creep up to 22psi...

 

[Mark@VAGWORX]

Got to be either something physically stopping the wastegate flapper from opening, shaft sticking/jammed perhaps, or something went wrong after they disconnected it, perhaps jamming the lever on the end of the wastegate shaft and stopping it from opening?

The wastegate must've been practically fully closed - I can't imagine it would the boost creet up to 22psi...

I can't see it myself either. The only other thing i though of was the exhaust. It's a full 3" bore turbo back and is a side exit with one very small box. Just wondered if the flow was so extreme that the quickest route for the gas to exit was through the exhaust wheel as apposed to via the wastegate hole.

Wondered if an extra box would back the flow up and make the gas slow down and have to go via the wastegate??

 

[caney]

These guys aren't cowboy mappers, as they build and map various GT cars for races all over Europe, so really know there stuff.



Thanks.

well if that's the case you shouldn't have to ask on here then,listen to what they tell you

 

[Mark@VAGWORX]

well if that's the case you shouldn't have to ask on here then,listen to what they tell you

I appreciate what you're saying, but how many 28RS's are in circulation on 1.8Ts, i can't see that the wastegate hole is too small?

 

[Feel]

I can't see it myself either. The only other thing i though of was the exhaust. It's a full 3" bore turbo back and is a side exit with one very small box. Just wondered if the flow was so extreme that the quickest route for the gas to exit was through the exhaust wheel as apposed to via the wastegate hole.

Wondered if an extra box would back the flow up and make the gas slow down and have to go via the wastegate??

maybe if a flexi or the wadding in the backbox had collapsed it might cause a problem, but the problem would be it not boosting, not the other way round.

well if that's the case you shouldn't have to ask on here then,listen to what they tell you

I was thinking something similar, but slightly different - if they're such experts, they would've seen a GT28RS (or similar) before, as Garrets are fitted to alsorts of makes of cars, and would know (or suspected) at a glance whether the wastegate aperture was undersized or not. If it's not that, they should know what to do to diagnose what it is.

Track n' Road are just mappers aren't they? What standalone are you using, Emerald? Who did the fitting?

 

[ibizacupra]

I can't see it myself either. The only other thing i though of was the exhaust. It's a full 3" bore turbo back and is a side exit with one very small box. Just wondered if the flow was so extreme that the quickest route for the gas to exit was through the exhaust wheel as apposed to via the wastegate hole.

Wondered if an extra box would back the flow up and make the gas slow down and have to go via the wastegate??

the wastegate and turbine outlet both flow into the same exhaust system tho do they not? so downstream of either in the same pipe is the same backpressure... so irrelevant.

wastegate flapper sticking or partially opening choking the wastegate puk

GT28 compressor wheel should'nt outflow the std wastegate porting and puk size.. what size is it?