Performance

The engine took quite a while to bed in properly, I think due to the new rings which had to seat

into the old cylinder wall profiles as it had not been re-bored, just lightly honed. Having now done

around 12,000 miles the acid test was a run on a rolling road.

The engine had been re-assembled to its standard format with no porting and original injectors.

In preparation for some work in this area I wanted to know how the engine was performing now,

so that I could assess whether or not the extra work made any real improvement.

It should be noted however that at this stage the mods so far are:-

 

1. Chip  (Marshy type II, if you're a member of the Autobahnstormers you'll know what this is all about,

otherwise join up to find out)

 

2. Modified Scorpion Exhaust.

 

3. K&N air filter.

4. Extra 1 1/2" dia hole into air box, fed air from same place as existing intake trumpet.

5. Cats replaced with straight through silencers.

 

The test was carried out 3/11/00 at S.A.S Performance in Aldershot Hants.

They have a new rolling road system capable of testing up to 1000bhp including 4 wheel drive vehicles.

The bottom line max ouput was measured at 212.0bhp to DIN 70020

(this std takes into account variables such as temperature/air pressure/humidity etc. of which air temp 16degC,

Air pressure 981mbar, oil temp 88degC) The standard book quoted figure is 204bhp.

 

 

The left hand scale is bhp and the right side is torque (lbf/ft)

 

I am quite pleased with the result, the fueling they said was spot on.

The work which I want to do next is:-

1. Injector clean

2. Match inlet ports and fuel injector manifold and inlet manifold.

3. Slightly re-profile area just in front of the injector nozzle, (cylinder head inlet  work.)

4. RB stainless steel back box and stainless steel mid boxes (all straight through).

5. New airflow meter (this was unexpected, but,cured regular shorts bursts of missfire )

26th January I visited SAS once more. The results below clearly show an improvement overall.

Interestingly there is a slight drop in power around 2500 - 4500 rpm although the car actually feels

stronger when driving. The peek calculated power was measured at  238BHP to DIN 70020

Air presseure was 984mbar and air temp was 15degC, pretty much the same as previous run.

 

A very pleasing result justifying the work that I've done so far.

Will Reeve also attended the dyno and ran his car just after mine,

this gave me the opportunity to remove the exhaust restictor plates

that were located at the engine end of the cat replacement silencers.

With previous trial and error research it was found neccessary to

replace some of the back pressure in order to get the car to "feel right".

Having removed the plates and doing another dyno run, the difference

was quite suprising and obviously worse ! The explaination for this I have

"borrowed" from Will:-

 

Now the cat pipes and restrictors: Rich ran his car up first, recording both
a continuous and then a discrete point power run. The car was fitted with
restrictor plates. This yielded good results with his engine sounding
smooth, quite and the figures bearing this out.

He then went home and removed the plates, replacing them with standard
gaskets. Back at the ‘road the operator reported it was impossible to
measure the discrete points run, during the run, apparently the engine
wouldn’t hold the rpm at open throttle when the ‘road was loading the engine
to measure the torque. The engine was running lean (according to the exhaust
gas analyser which was in use).
Conclusion being that restrictor plates, do just that and restrict the
breathing of the engine, removing the restrictor plates allows more out of
engine for a given time and hence more air into the engine, which isn’t
being met with more fuel, result weaker mixture.

Arrrrr. What about the ECU and the lambda sensor you ask. Well load and
hence fuelling is determined mainly by the AFM (air flow meter) which will
be fully open at much above 4,000rpm and so offers no input to the ECU with
regards air intake, the lambda only works in closed loop mode at part
throttle and idle so at wide open throttle the ECU runs open loop. Hence it

uses maps only folks and the maps weren’t meant to fuel an engine with
Richards free flowing exhaust and his inlet manifold tweaks, hence
under-fuelling. That's the general idea anyway.

My car is still running Walker mid boxes which offer some restriction of the
exhaust, but one would assume the problem is worse with a BB head and free
exhaust, and even worse with a MAF (mass air-flow meter conversion), and
free flowing exhaust!

What we are doing? Well we have an air-fuel ratio meter, but unfortunately
it doesn’t like running on the same lambda sensor as the ECU, or rather it
doesn’t mind but the ECU does! I plan to persuade rich to weld an additional
boss into the down pipe and fit another lambda sensor for monitoring
purposes.
The rolling road operator estimated that we need 2 to 3% more fuel above
3,000rpm at wide open throttle, so that’s a starting point. He suggested we
use the air-fuel meter to get the mixture spot on (rich of stoichiometric).

At low rpm and load when the AFM is working within it’s operating range, the
ECU will fuel correctly as it will measure the additional air intake, and
fuel correctly. Hence what I always feel, that part throttle “urge” seems
stronger than full throttle “urge”. So it would seem the backpressure from
restrictor plates = bad, but good if you don’t adjust the maps to enrich WOT
situations.

It looks like a full RB stainless straight through exhaust system (cat pods,
twin mid’s, and back box) needs remapped wide open throttle maps to reap the
full benefits of it’s free flowing design, for the time being restrictor
plates will emulate the cats well enough to keep the fuelling correct. I
think most of you run this way anyway and have walker/Vx back boxes as well.

Fuel Consumption

It would be natural to think that an increase in performance would increase fuel consumption,

this is true to a certain extent in that more power needs more fuel to be burnt and yes the potential

to burn more fuel is certainly there. However, with the fuel now being burnt more efficiently the increase

in performance at light throttle application has actually improved MPG's.

 

2 weeks ago I installed a Kenlowe block heater. I ran the car for 3 days to and from work with the engine

being warmed up before the trip to work but not on the way home. My journey to work involves 3 miles

urban, 14 miles motorway and 3 miles urban, the same for return home. Speed was kept between

55 - 60mph, air temp averaged 3 - 5degC.The car achieved 36mpg as an average for the 3 days. I have

never seen this kind of return before, especially during winter. The summer figures will be interesting.

 

Update 31/3/01

Now with extra lambda installed and connected to a fuel meter we are starting to try different wot map

settings. I have removed the  restrictor plates and have been running a richer wot map for a while.

Checking mpg's over same 3 day period with hot one way starts have produced 36.5mpg overall average.

A trip to London along M3 from Farnborough re-setting the comp after getting up to speed (60mph)

produced 46.5mpg at the end of the motorway. Previous best was around 41