Tuning Fiat Coupe 16V Turbo for economy

Road-race engines and ancillaries - general discussion
Posts: 9
Joined: July 5th, 2011, 6:34 am

Re: Tuning Fiat Coupe 16V Turbo for economy

Post by keithwwalker » July 21st, 2011, 2:10 am

KJ16v, care to tell us what your baseline mileage is at the moment? Also what kind of modifications have you done to the 16vt?

For comparisons sake the stock mileages are:
ECE 90/120/city (comb.):
7 / 8.5 / 11.5 (9) l/100km
40.4 / 33.2 / 24.6 (31.4) mpg (imp.)
33.6 / 27.6 / 20.4 (26.2) mpg (U.S.)
14.3 / 11.8 / 8.7 (11.1) km/l

In my book that isn't a bad mileage spec, although there are always questions of real world economies that I imagine you are grappling with.

Since your post is concerning mileage, I am assuming that you are finding out that your turbo is not 'spooled up' to speed in order to make the combustion as efficient as it could be.

So counter to the advice to 'drive gently' and use as little boost as possible, I would try the opposite if you are up for a mileage test. If your drive to work (or where ever you normally go) is at the speeds where you can either drive in 4th (at say 3500rpm) or 5th gear (2500 rpm) - try driving one week only in 4th. At the higher rpm, your turbo would provide more boost and it may improve your mileage!

Of course if your mileage improves it may only be 5% at the most. What the test would really be demonstrating is where the 'boost threshold' is for your auto. The boost threshold is the point at which the turbo is ineffective under a certain engine speed.

Remember that most normal everyday driving is at part throttle, I would say at normal highway speeds 1/4 to 1/3 throttle. Now since the Coupe' Turbos were meant to make a 'statement', they were designed - as Italians would design - for top end power.

In the past ten years or so, turbo technology has really made some strides to eliminate lag (inefficiency at part throttle).
First was variable vane geometry turbos, but the turbo impellers were still heavy to deal with the heat load.
Other tricks were tried, but smaller lighter turbos have been on the market for a while now. Couple that with smaller lighter impellers (cermamic anyone?) and newer bearing technologies have spawned 'low inertia' turbos.

They are optimised for making optimal boost just off idle (1500rpm) for great fuel economy.

So I agree with Guy, you need your turbo at close to max boost all the time. But to do it efficiently, it has to be a smaller turbo than what you have on there, so that the effective boost threshold range of your turbo is closely matched to your driving style.

Personally that sounds like a complicated project, but you also have some of the diagnostic equipment to see it through!

kj16v wrote:Hi all, I'm currently attempting my toughest project yet - trying to get decent fuel economy from a Fiat Coupe 16V Turbo!

As above, I am trying to tune my Fiat Coupe 16V Turbo for better fuel economy - without luck so far.

My setup:
TunerPro RT editing software
Winlog datalogging software
TechEdge wideband lambda
det-cans (for listening for knock)

I have already leaned fuel to 15:1 afr at steady cruising conditions (2500rpm-3000rpm, 0.4bar-0.6bar absolute). This hasen't made a dent to cruising fuel economy. Can anyone tell me whether it would be 'safe' to lean steady-crusing as far as 15.5-16.0 afr, as long as there is no knock?

As yet I don't have an egt sensor. Do I need to know egt to be able to lean the mixture safely?

Would it signicantly improve economy (due to better fuel atomisation?) if I increase the fuel pressure to 3 bar, from the standard 2.5 bar (and of course adjust the fuel map accordingly)?

Thanks in advance for your help.

By the way, before anyone mentions it, I already know being light on the throttle helps thanks!
Lancia Scorpion

T. Christian
Posts: 3
Joined: March 12th, 2011, 10:39 pm
Location: California

Re: Tuning Fiat Coupe 16V Turbo for economy

Post by T. Christian » August 12th, 2011, 4:28 pm

I would like to add a few remarks refelecting my opinions to some thoughts expressed and not expressed.

Firstly, I suggest using an EGT probe if the mix is anywhere near that lean. Especialy if you do not know the thermal tendancies of the exhaust manifold. Some are quite poor. Within the chambers the temperatures can avalanche nearly instantly and create a high pressure wall which will actualy fight against you quest for efficiency. Exhaust valve guides, valve and seat contact surfaces and even the piston can be compromised to failure. In the case of the piston, failure may occur immediately and with no warning.

Please consider the use of mileage improving tires and light wheels. These are not high performance tires. Fuel economy is a performance, but not as thrilling to the soul as it is to the wallet. A truly obvious difference will be seen.

As per turbochargers, Guy is absolutely correct in the efficiency of a turbocharger being at full boost. Similarly, there is 1.0bar of pressure being offered to any engine, We all operate our engines below that level with concerted efforts to achieve full use of this available pressure.

HUGE dynamics are engineered into many of today's fuel efficient turbo motors. A diesel can run a turbo quite well with its realtively short power band. A 1600 petrol engine has an inherantly wide power band and I have yet to see a perfect turbo per the wide range of different targets aspired for. An economicaly efficient turbo will run out of its boost range well before the motors top end. Driving a motor at 7200 rpm is not efficient anyways.

An enthusiastic driver can be inspired to achieve a fuel economy of less than half with a friendly turbocharger fitted. And do it again after fill up.
GCRE edifies. Trevor

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