External wastegate not sealing properly causing the lag? Exhaust bypassing the turbo.

I have had a turbo tech MBC fail on me, blue one with brass fittings. Deffo try wastegate pressure or try another MBC

Mrskylighter
Can you just try and run it without a boost controller? Just on wastegate spring pressure whatever that is.

Even with no boost at all the car should still have some power to go up Hills etc.

Maybe it's just a mismatched turbo and has heaps of lag then all of a sudden it hits really hard. Like the old Trust turbos T67, T78 etc

I can can give it a crack, though the wastegate spring is only 6psi. But the car has been more sprightly going up hills after turning the controller up.

I think you're on to something there. After doing more reasearch on the 20g's it seems that I'm only about 500-700 RPM off the norm. So maybe I'm just in a state of shock coming from how quickly the CT20b spooled and reached full boost.

You will find that if you switched the wastegate spring out for a 10 or 12 psi spring (as an example), you would increase response as the wastegate would be less likely to blow open from exhaust backpressure. Also with a 6psi spring, depending on how you plumb it, you wont be able to hold much more than 12-18psi of boost.

MCT_MR2
You will find that if you switched the wastegate spring out for a 10 or 12 psi spring (as an example), you would increase response as the wastegate would be less likely to blow open from exhaust backpressure. Also with a 6psi spring, depending on how you plumb it, you wont be able to hold much more than 12-18psi of boost.

Was about to suggest the same thing. 

Thanks for the input guys, Hadn't even considered the spring pressure being too low.
I'll go ahead an order a stiffer spring!

Update: 

I ordered and have installed a 13psi spring and sure enough it sorted out the slow spool issue. The lag is very much bearable now. I have also been trying to sort out an oil leak that I have had from the turbo oil drain flange. I went through 3 new gaskets before I gave up and decided I will get MRC to sort it out when it goes in for tuning. 

The car has now been at MRC for a little over a week. I have had the Injectors installed along with the ECU.
I have had to swap out the stock MAP sensor as apparently the VIPEC isnt able to work well with stock one. I have done away with the MBC and have had a boost solenoid installed which will run off the VIPEC as it will be a more reliable way of controlling pressure. I was against switching to a boost solenoid at first as I have had bad luck with them being in the engine bay and failing before. So I have opted to have it installed in the boot near the ECU away from dust and general engine grime. 

It has had a basic fuel map put on it at the moment but unfortunately the engine stutters in specific areas of the rev range. I noticed this after I had the new dump pipe installed whilst still running on the stock ECU; whether this is related or not is unknown but I suppose it could just be due to it being more audible due to less restriction in the exhaust system. MRC has been logging all engine parameters whist its been on the dyno but nothing unusual shows up when it stutters. 

A new distributor cap, rotor and HT leads have been ordered with hope this may solved the issue. 

More updates to come next week. 

Hi Deco.     How did you go with this miss fire ?    Did the high tension bits change it or not ?
The igniter can sometimes be at the heart of this sort of symptom.  The OEM coils seem to be pretty good but they sure have to work bloody hard along with the king lead too.
I have used 28 thou.  Even 25 thou. plug gaps to overcome these type of hesitations but that is probably just masking a weak coil or something.

Falcon
Hi Deco.     How did you go with this miss fire ?    Did the high tension bits change it or not ?
The igniter can sometimes be at the heart of this sort of symptom.  The OEM coils seem to be pretty good but they sure have to work bloody hard along with the king lead too.
I have used 28 thou.  Even 25 thou. plug gaps to overcome these type of hesitations but that is probably just masking a weak coil or something.

Unfortunately the new rotor, distro cap and leads didn't solve it. I was thinking whether it could be the igniter; no testing has been done on it but the igniter in there is all of maybe 25k old. But its on the list of things MRC will be checking. They also threw new plugs in and properly gapped them but that had no affect on the miss fire either.

No real progress has been made on the car this last week. MRC is currently overworked and understaffed. With any luck some progress will be made after Easter.

I finally have an update after a lot of head scratching and frustration. 

The car was on the dyno over the Easter break but refused to make any power whatsoever. It put down 147kw which is gut wrenching knowing that my stock Gen3 put down 155kw on 11psi. 

Anyway fast forward to today, MRC managed to find that my cam timing was out....big time! 30 degrees advanced on the exhaust and 10 degrees advanced on the inlet. The timing must of shifted somehow whilst the T-belt was being changed over. But am glad that it was something fairly simple and not something more serious. With any luck fixing up the timing will sort out the lack of power issue completely and hopefully also sort out the stutter.

Also whilst the car was on the dyno; it appears that my intercooler isnt up to the task of cooling the intake charge. The IAT sensor was apparently seeing 70 degrees and what we should ideally be seeing is around 40 odd degrees. Which has me quite confused as I have a Phoenix Power SMIC and have seen others make more relaible power on the IC than what I plan on making.
 
Looks like a W2A IC is on the cards...