Porsche Turbo Lost power mystery...

Hi all, I thought I'd start a discussion on here regarding a project we're struggling to diagnose to be honest.

We've added a pair of turbos to a 987 3.4 Cayman S.

Now we've experience of turbocharging several of these cars and they normally see about 450bhp at about 6.5 psi of boost.

This particular car made 457bhp immediately after fitting the kit... fantastic news. However a second run and it dropped to 430bhp then 400 then to where it currently remains at about 360bhp.

We suspected the cats had collapsed... inspection showed no damage. We removed the cats and fitted equal length headers whilst we had them off. No power increase...

Checked for blocked inlet pre and post turbo no luck...

Checked for air leaks... Nothing.

Got annoyed and went full Syvecs S7... still the power evades us...

So it's a 11:1 CR engine

6.5psi of boost

Charge temperature climbs from 30°C to 60°C on a full pull

Max timing 14° btdc

We're a little stumped at the moment.

Anyone have any ideas?

I've attached the first 457bhp run then a lower run at 349bhp

What duty cycle does the waste gate controller have?

Are the waste gates working? Or are they stuck open?

What boost is being generated under load?

Hi Stephen,

On the OEM Bosch ecu we were just running gates on spring pressure producing 6.5psi

They seem to be working just fine we're now controlling gates via a mac valve and the Syvecs ECU. Rather than just pushing more boost though it we'd like to get it to make the power we know is possible at that boost. However increased boost just pushes our ACT higher & faster resulting in us pulling timing out.

We've had several car's all making 450bhp at about 6.5 psi. 🤔 They've been in ther region of about 20° advance. We're stuck in the low teens and even in single digits when ACT climbs past 60°C

Will be upgrading the charge coolera in the next month or so but this doesn't explain this one car with the lower output... 🤔

I suggest you go back to basics, most likely something mechanical if changing the electronics made no difference.

Verify ignition timing. Check operating fuel pressure, and check fuel filter. Check throttle travel. Leak down / Compression Test. Smoke test of intake and exhaust plumbing. Does that engine have varioram? Is it operating?

What other diagnostic testing has been performed?

Engine compression and leakdown testing?

Smoke test with sufficient pressure for boost leaks?

No chance one of the 2 gates or turbos has an issue, resulting in expected MAP, but perhaps via one bank?

I know it may sound an odd guess, but one WG or turbo having an issue resulting in the other side working rather hard to achieve the MAP you're used to would result in low power output, higher IAT than you're used to, knock requiring reduced timing.

No fuel related issues from looking at the fuel map and data logs. We've swung the timing several degrees either way nothing gained other than a little knock in the advance direction. It does have Variocam and again swinging that gains us nothing. You can see the cam lobes changing over in our data logs ok too. Throttle opening fully and monitored by the two internal tps.

Will be checking compression again sometime this week and also adding a sensor to log the crank case pressure.

We had the intake all apart last night and nothing obviously leaking. Will be performing another smoke test to 1bar later this week.

Humm a single gate or turbo fault would explain what we're seeing 🤔 essentially the 'good' turbo could be running way out of its efficiency zone I supposed. Good shout!

It may not be your issue, but worth checking if you've already checked the basics. I've seen it when one gate has a pinched or torn diagphragm, when one is missing the fire ring, different spring rate in the 2 gates, one of 2 turbos has an issue. It can be a lot of things on a twin setup.

It's really easy to spot when you have per bank turbine inlet and compressor outlet pressure sensors, a bit more work to narrow down without.

That it was as expected on the first run suggests it's something that developed after that - I doubt it's something as simple as a shop-rag partially blocking a charge cooler, but it may be something else like a collapsing hose, sticking or unseated wastegate, etc. heck, could be something stupid, like a failed/seized turbo' or broken shaft?

There are some sound suggestions already made, but that first run will need to be factored in, as that suggests the basic build was good.