loss of power when boost is raised, 2.0 16v.

[nabilhpe]

Hello,

we have been experiencing a loss of power when we raise the boost a little bit on our car, car specifications are as follows

Fiat Ritmo body shell
Lancia 2.0 16v turbo engine-stock internals
2.0 16 N/A camshafts, inlet and exhaust.
Garrett T3/T4 60trim with a stage 3 hot side and a .63 A/R
Front mount intercooler, from a Nissan Sunny GTI-R
Fornage ECU
2.5" free flow exhaust pipe going out under the passenger door.
dual fuel pumps

thats in brief, the car now runs 0.8bar boost and the A/F ratio on the wideband are about 10.5:1 and 11:1, the car is silly fast, its weighs 890Kgs . when we raise boost over 0.8bar (1bar 1.1bar etc...) the car lose power, even if we added fuel to compensate and kept A/F mixture in the 10.5 or 11:1, could it be the spark power is failing under boost? the engine is totally rebuilt,fully balanced before assembly.

Thank you
Nabil

P.S. Guy, its Gozzoli, I miss spelled it.

[Guy Croft]

Not easy to diagnose.

A problem like that could potentially be excessive exhaust back-pressure, the turbine may be too small. Detonation? You know the signs by now. What is the peak exhaust gas temperature when the power loss at the higher boost is discovered?

GC

[pietch]

Nabil, another very interesting post!

Well I suppose you can minus your ECU from the equation, right?

The only other suggestion I can think of is that your injectors may be at there maximum duty cycle and that an increase of fuel pressure may longer help provide the fuel needed for extra boost? What injectors do you have? I know that mine (384cc Integrale type) are on 90% duty at about 3.0 bar.

[nabilhpe]

yes ECU is out of the equation I have tried 3 different ECUs with the same results.

I am using the integrale injectors they flow 65cc/15sec at 25psi fuel pressure on the flow bench, so I don't consider 1bar to be high boost for the 2.0 16v turbo engine, even if the turbo would flow 50% more air than the stock Turbo, under boost fuel pressure goes to about 4.2bar so I doubt injectors are hitting their duty cycle limit. add to that, the mixture on the wideband is still 10.5 and 11:1 so its not leaning out.

Guy, about the back pressure, the car has just a 2meter pipe with a 2.5" diameter going under the door, without any muffler, and the turbine side of the turbo, has a stage3 wheel and a .63A/R housing, so I doubt that would be restrictive at 1bar boost, unless the stock exhaust manifold is the restrictive item!!!

cannot this be an ignition related issue? I mean spark power?

Thank you
Nabil

[Guy Croft]

Nabil, hi

I'm not really into A/R numbers and stuff like that, doesn't mean that much to me really in this context. One assumes that you ahve a turbocharger speed probe (if not get one) and have assessed the capabilities of the turbocharger wheels against theire respective maps. If you haven't then, well, no offence but it's a bit hit-and-miss. I speak as a former Chief Engineer with Napier. It is faintly possible that the impeller is too big for that turbine and there isn't enough power to generate the boost level you want. It is possible you are going into in a choking or surge regime. Who knows?

At a more practical level, although you have not remarked on it in your reply you do need to check for the presence of detonation. I would be for taking the head off to check this, it may not be visible on the plugs.

If there is no evidence of det then it is (relatively) safe to try the higher bost again. I stress IF. The other diagnostic is direct (non Lambda) analysis of the tailpipe CO and HC levels right in the fault zone, by means of an infra-red gas analyser. If the ignition is failing the HC level will shoot up and fluctuate as it reaches peak boost. I'd be looking for steady 4.5% CO or maybe fractionally higher (4.8) but no more than that. Too high means too rich and it may fould the plugs, too lean and it can detonate readily.

I cannot offer any other substantive fault finding ideas at this time, actually I think there may be no other way of determining the problem.

GC

[pietch]

From experience I had a similar problem, it was a faulty after market rising rate fuel pressure regulator... try turning down your fuel pressure... you may be suprised! If this is the problem buy a SARD regulator, they work perfectly!

Apart from this my only one and last suggestion is to use Iridium spark plugs. By the way my car flows 329bhp with the standard 2 1/4 inch exhaust.