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Optimum Fuel Mixture Settings for PI


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Does anybody have the optimum Lambda settings for the 6 cylider CP 2.5ltr engines?

 

What sort of figures are the guys with rolling roads trying to get?

 

I have been reading with interest Tuning Rover V8 engines, and they seem to be setup much different to new car engines lambda

 

Low/idle rpm 0.92 Lambda

Full throttle 0.88 Lambda

Cruise 1.05 Lambda

 

Should I be trying to get near to these figures for the TR engine? I know they were originally set to be a bit more on the rich side to compensate for the lack of an accelerator pump for acceleration.

 

I understand also that these were not really sophisticated engines in their time, and so will benefit from a slightly richer mixture.

 

I also note that sometimes the std cast exhaust manifold is actually better than the 6-3-1 free flow ones, are there some opinions on this as well?

 

I'm not trying to build a racing engine, but would like it be best for performance and economy, but that's probably not the way to look at it!

 

John

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Hello John L,

 

Concerning the TR6 PI CP case, interesting question and approach with the search for the targeted Lambda values, I shall follow the outcome of this question. Same concerning the std cast exhaust, few fox told me the std one is the one to keep.

 

Regards

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TR6 EMISSION RESULTS

Fuel system - roller cell pump set to 103 psi, injectors all set to 50 psi,

throttle butterflies all balanced.

Ignition system - Aldon Flame-Thrower coil,cooper S points, new BP6ES plugs

set to 30 thou. Timing set to 10' btdc at 850 rpm & 28' btdc at 2500 rpm on strobe,

dwell at idle 33' & 34' at 2500 rpm.

 

Ignition readings

Av. kv at idle 1.1 at a duration of 1.7 ms. Av kv at 2500rpm 1.2 at a duration of 1.2 ms

 

EMISSION READINGS at idle CO 2.59%, HC 376 ppm , CO2 11.34%, 02 3.14%, Lambda 1.057

 

EMISSION READINGS at 2500rpm, CO 3.41%, HC 165 ppm, CO2 12.01%, O2 1.53%, Lambda 0.963

 

All above results taken using PACE 100 engine analyser & Chrypton 700 series analyser

 

 

Harvey S.Maitland

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I am told that Pi tends to run lean at high revs, so that for performance will be set to run a bit rich at idle, but this is your choice.

 

Moderns, of course, monitor Lambda through the ECU and will vary the fuelling continuously, to 'hunt' about the ideal, whatever it is.

No carburettor or mechanical fuel injector system can do this.

 

John

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HSM

Thank you very much for a very comprehensive analysis, :) I have something now to aim for, I just hope I can get near to your figures. I can only monitor AFR.

A couple of things I would like to know if possible please, what vacuum are getting at idle, and I presume you are using the std early PI cam, and are you using the cast exhaust manifold?

Thanks again John

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Hi

I have done a fair bit of AFR (like lambda) measurements with my PI over the past few years. The work best set a little rich say 13:1 as they have no accelerator enrichment. Else they bog on rapid throttle openings. Cheers tim

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Vac. settings as requested, at idle -.28 bar & at 2500 rpm -.34 bar.

Cast iron exhaust manifold with sports twin silencers, K&N air filter

fitted in front of radiator, standard 150 bhp camshaft, rocker cover

breather connected to separate oil catch tank to prevent oil mist

entering air box & reducing air quality to nos 5& 6 cylinders.

 

Harvey S.Maitland.

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John,

1 bar equals 29.53 InHg( or 14.5 psi)

So 0.28 bar equals 8.27 InHg

0.34 bar equals 10.04 InHg.

Best regards,

Waldi

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John says, and so doo others !!

 

I am told that Pi tends to run lean at high revs, so that for performance will be set to run a bit rich at idle, but this is your choice.

 

a few reasons for this, and sort it, then its no a choice.

 

1, yer fuel filter is blocked,or too small

2, yer inlet filter blocked or too small

3, yer pumps no capable of delivering 110 PSI at WOT an sustained revs

4, yer inlet feeds are too small ID

5, yer power supply, an earth are too small

 

 

 

 

As to ev,n yer MU set rich for transient snap throttle, Rubbish,

 

sort oot the MUs built in enrichment device, which is no set up right,!!!

folk just cant see the Forrest for the trees,!!

 

Me own, it can run L1, butt, I only use it on idle

if yer running closed loop, at revs, then yer engine will give alot less MPG,

as its running farrr too rich

 

at cruise, 16-3000, them im running 25% weaker than L1

and it runs fine

 

So, forgit the Lambda settings, run it to what engine is easier at

 

Note,

gaa,n to weak, will actually use moer fuel

why, simples really, ye gotta put yer hoof doon further, t,get the same acceleration

 

put,n yer throttles open moer, alters the TPs read oot figures, alot moer, than running 5-10 clicks richer on fuel on the map figs

 

what seems a good idea, can become a bad idea

if yer able t,fiddleate wid fuel / ign settings at click of a button, and see what diff its mek,n instantly !!!

 

 

 

M

Edited by GT6M
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Harvey

Something that bothers me with your vacuum readings at idle, for a std CP setup, I don't understand why yours are so much higher, is there something else that has been changed? Do you have the air bleed adjuster on the #1 intake?

Could anybody advise what items in the engine actually change the vacuum?

​Is your MU setup on a rolling road, or by somebody who understands the vacuum readings?

John

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Hi John

 

Metering unit originally set up on Lucas test equipment by a friend who had the equipment & set up

units for the local Lucas depot in Manchester. Adjustments to vac settings changed by myself over the

Years to compensate for wear, datum track always set at 0.058th & 0.002th as spec. Vac at idle depends

on a number of factors,ignition timing, compression, valve settings, camshaft timing. The book vac at idle

is 12.5" ( 3.81 cm hg ). The problem of setting units on a rolling road are that on full throttle the

fueling is on max. regardless of engine speed ( no air flow measurement ). Setting them on a Lucas test

rig that measures fuel quantity over a range of vac. settings is the best method. Fine tuning under

driving conditions can then be made to suit individual cars ( as vac readings will vary from car to car )

But an in depth knowledge of Lucas shuttle metering is really required before making any adjustments.

 

 

Regards

 

Harvey

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Harvey

I have been studying the Lucas manuals for the CP's it states it should be 7" of Mercury, and only the later ones I think the CR's it went up to 10", the saloons were much higher according to the Lucas info of 10-12" So interested to know why the big difference in vacuum of yours if the engine is to the std spec.

Would you know what diaphragm springs you have fitted?

I will try and play with this next week.

John

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Hi John

 

 

Metering unit fitted with red springs. Before making vac. adjustments check datum track

settings, turn A2 adjuster 1/4 turn at a time ( this gives approx. .5% change to co )

& make notes of all adjustments so as not to loose original settings. Clockwise more

fuel anti-clockwise for less.

 

Regards

 

Harvey

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I have been playing today, but now I'm getting popping on the overrun, with a road test, I think this is due to the fuel not been cut off enough, so should I screw out the top adjustment a little, am I right?

John

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