boost drop - 57 trim ct26

[Mikael_7m]

Hi guys trying to keep this as brief and as informative as possible.

The issue:
Boost drop at high rpms. ~16psi down to ~11psi
...also worth mentioning it only makes 11psi max in 1st gear and 13 (also drops to 11) in 2nd. 3rd is where it will hit 16psi and then drop at around 5000+rpm.

Related Mods:
- Driftmotion 57 trim CT26 with ported wastegate (as it used to creep)
- stock wastegate actuator
- Tial 50mm bov with 10psi spring
- split-recirculating downpipe and 3” exhaust
- driftmotion intercooler kit in/out on same side
- Blitz SBC

I have performed a boost leak test and found no leaks, assuming i've done it correctly. (Pumped air into the turbo inlet and blocked of the end of the 3000 pipe?)

I've previously had the boost controller hooked up to the nipple on the compressor housing and just yesterday tried getting the vacuum source from the intake manifold instead to see if it would get it to hold boost but it does the same thing.

What may be the issue?
- Old/weak wastegate actuator
- boost leak
- BOV leaking

any help would be appreciated. cheers.

 

[ca91mkIII]

Where do you have the boost gauge hooked up at?

 

[Mikael_7m]

Boost gauge is also hooked up to a vacuum source from the back of the intake mani

 

[bloodasp90]

what kinda power are you making? just throwing it out there, but possably outflowing the turbo.

 

[hvyman]

That is likely te problem. It's a tiny exhaust housing and wi get outflowed easily in the upper rpms. Usually falls off about 5500.

 

[Mikael_7m]

It dyno'd 340 whp at 16psi and did the same on 17psi at the time. That was on stock Intercooler, with only a 1psi drop off at high revs.
Now with this larger Intercooler in drops off more.

 

[IndigoMKII]

CT26 can't flow enough to maintain boost pressure on a high flow setup.(Full exhaust and bigger intercooler/hardpipe)

The reason it was able to keep PSI to within 1 was all the restrictions in the stock piping, more restrictions=more pressure.

 

[Mikael_7m]

Thats rather crap... So if I increased restriction and managed to get it to hold 16psi would it in fact be quicker or just hot air?

I see you have a similar setup, does yours drop off too?

 

[IndigoMKII]

Mine goes to 16 PSI then falls off slowly in the higher end.

It doesn't do it as bad at lower PSI but at 16 it falls to 12 IIRC.

 

[ca91mkIII]

Glad the smart people got on here. I didn't even think of the 57 trim ct26 being out flowed. Not to thread jack here, but a 57 trim ct26 and say a turbonetics 57 trim turbo are not the same then?

 

[IndigoMKII]

Glad the smart people got on here. I didn't even think of the 57 trim ct26 being out flowed. Not to thread jack here, but a 57 trim ct26 and say a turbonetics 57 trim turbo are not the same then?

Compressor wheel might be close to the same size but the turbine wheel is more than likely much bigger.

The compressor side of the ct26 isn't the downfall, it's the turbine side.

 

[Mikael_7m]

Mine goes to 16 PSI then falls off slowly in the higher end.

It doesn't do it as bad at lower PSI but at 16 it falls to 12 IIRC.

It's good to know it's not only my setup that does this. I probably should have went with a 10 degree clip.

 

[emericaskater285]

When I was on a ct26 57 trim, depending on what i had boost set at it would peak out and then drop down at higher rpm's. its too much for the tiny wastegate, and if you have a shitty boost controller it could contribute to it some too. I had an ebay mbc on and it would peak out much worse, then i swapped to a blitz ebc, and it was a lot better.

 

[7M4EVR]

I have been pondering this situation..

I have been wondering how my 60-1 was going to handle higher boost as well, just havent been able to crank up the boost yet to tell. But I was thinking if I experienced boost drop, I would try picking up DM's 11psi CT26 WG and see if that helps any.

 

[IndigoMKII]

the new wastegate won't keep it from dropping off in the higher rpm.

its lack of flow around the wheel. you could weld the waste gate shut and it'll still fall off at higher rpm.

 

[emericaskater285]

the new wastegate won't keep it from dropping off in the higher rpm.

its lack of flow around the wheel. you could weld the waste gate shut and it'll still fall off at higher rpm.

I think he meant spring, but yes this is correct.

You would need to have the internal wastegate welded shut, and add an external wastegate to the stock manifold and get a decent wastegate to run with it (say tial 38mm) it will flow exhaust gasses past the turbo easier so you dont have a spike, and it will regulate that boost so it doesn't drop off pressure.

 

[hvyman]

Ya but the turbo will still fall off at 5500.

Better off using a sp51 or something.

 

[pete05]

I dont understand why driftmotion dont recommend a 10deg clip its pretty clear when you have a huge front wheel in a turbo and a tiny rear wheel there is going to be flow issues. When I spoke with Albert he said a clipped rear wheel is best.

 

[hvyman]

the wheel will help a little but the turbine housing is the major factor.

 

[SeeUSmile]

I'm dazzled by the amount said in this thread... Now I understand the way the old-school guys chimes into certain threads, they know the answers but they don't just spoon feed it to them. so I'll imitate it too..

So apparently you didn't have this problem on the factory setup. > Now you're having this problem ever since you swapped it out.....
Shouldn't that tell you something about this 'aftermarket' kit you installed then?

and the guy who told you "The reason it was able to keep PSI to within 1 was all the restrictions in the stock piping, more restrictions=more pressure" has NFI what his on about on that part.