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For the same inlet manifold depression - which is what the MU senses - the 150 cam will allow the engine to take in a bit more air. So the tendency will be for the mixture to run a little bit leaner. However the mixture is normally run rich to avoid the pinking upon suddenly opening the throttle. So if the engine doesn't pink for as second or two when you floor the throttle from cruise at ca 3000 rpm its probably OK across the load range anf rpm range.

Peter

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As the manifold pressure & power is different you will need another setup

but before that another spring set inside the MU should be fitted.

 

Also under full load you had 125HP before and will now have 140

so you also need the max. fuel amount being increased by 10%

if it was a proper set up before.

 

Ignition advance curve also is different.

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The inlet manifold is also different between CR and CP, not sure what that will effect. Have you spoken to Neil Ferguson, he's very knowledgeable about all things PI

.

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The likelihood is that the metering unit will be set sufficiently rich to cope with either cam. Perhaps not optimal but probably fine (The whole mechanical injection set up is a compromise compared to a modern EFI)

 

You could get an exchange metering unit from one of the suppliers - they are essentially the same but with differing springs and fuel curves so unlikely that the rebuilder would be concerned that you return a CR one in exchange for a CP one.

 

Rolling road - the whole point of that is that you can make changes to fueling and ignition and test them in terms of power output to optimise the set up. This is much more relevant if you have made changes to the engine and exhaust that are outside of the standard CP or CR setups. So if you've got a non standard cam, gas flowed head, extractor manifold and the like it is unlikely that you will get the best from your set up with a standard distributor and metering unit.

 

The reality is there are very few rolling road operators who have the faintest clue how to adjust a Lucas PI system so it's important to find out before shelling out on what could be little more than an expensive power test!

Edited by andymoltu
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This slide show is a good summary of the si engine operating characteristics.

http://www.powershow.com/view/1e2c2-NmY0Z/Chapter_IV_Spark_Ignition_Engines_22703_powerpoint_ppt_presentation

 

Slide 3 shows that going to richer mixtures has little effect on power.

Fuel/air Equiv Ratio (this is 'phi' not lambda) of 1 = 14.7.Air Fuel Ratio.

FAEqR 1.5 = 9.8 AFR.

So from AFR 14 to 11.3 the power curve is moreorless flat.

Going lean kills power.

Fig 4 shows the same effects for different throttle positions, see also fig 46 and 47

 

Peter

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I'm with Neil. My Mu was reconditioned by Neil Ferguson but for a CR (bearing in mind my engine was a saloon). I then found my CAM was actually CP so replaced the throttle bodies with reconditioned CP ones also from Neil. All was not really quite right. On Alec Pringle's recommendation I went to a rolling road in Gillingham, old chap called Peter (can't remember the rest but Alec could help). He certainly knows the Lucas MU. He replaced the springs and adjusted the mixture. What an improvement! The key I think is a rolling road AND someone who knows the MU. Bearing in mind (as was pointed out to me at the time) after 40 years and various wear and tear, actual specification is probably only a starting point.

 

Anyway, that was about 3 summers ago and it's been lovely ever since. (all other usual niggles aside!)

 

Quentin

Edited by Quentin
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So from AFR 14 to 11.3 the power curve is moreorless flat.

Going lean kills power.

 

There is a large difference between 14 and 12.5 AFR.

Can clearly be noticed without a dyno.

I would expect as a rule of thumb 10HP from a TR6 PI engine.

 

I tried that out reliable by changing the AFR mapping of my EFI TR6

what gives a true and fast online compensation to achieve the keyed in AFR data.

Just a data change at laptop and immediately I have the new setup to compare.

 

Typical AFR on a PI shows rich at low revs and lean at high revs:

 

http://eficonversions.co.uk/comparison.html

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There is a large difference between 14 and 12.5 AFR.

Can clearly be noticed without a dyno.

I would expect as a rule of thumb 10HP from a TR6 PI engine.

 

I tried that out reliable by changing the AFR mapping of my EFI TR6

what gives a true and fast online compensation to achieve the keyed in AFR data.

Just a data change at laptop and immediately I have the new setup to compare.

 

Typical AFR on a PI shows rich at low revs and lean at high revs:

 

http://eficonversions.co.uk/comparison.htm

The indepedence of power on rich mixtures - the figure I showed reveals about 2% ( ie 3hp on a TR6) - is welll known. These data are always made on engine dynos in standard conditions with spark optimised at each point, standrdies intake temp and pressure..

If an engine diverges significantly from such behaviour then explanations can include:

1. more fuel evaporating in the inlet manifold before the inlet valve, increasing intake density and power in proportion to the gain in density.

2 more large fuel droplets evaporating in the cylinder after ivc, shrinking the charge, and so allowing more spark advance before knock limit.

3 assumptions that fuelling and AFR measurements are as error-free as lab equipment.

4 mixture quality

 

Your observation of 10hp ( 6% ) gain between AFR 14 and 12.5 would be accounted for by

2% for richness ( my figure) and 4% from other effects.

An air density rise of 4% requires a fall in intake temperature of 8deg C (http://upload.wikimedia.org/wikipedia/commons/8/8e/Air_density_vs_temperature.jpg ) which is not possible. About 1 to 2 deg C max could be expected from extra richness, giving a density gain of 1% .

That leaves 3% unexplained, and probably due to poor mixture quality. The curves I cited are made in lab conditions of mixture preparation. This involes a large vapour tank to feed the engine, where all the fuel is fully vapourised - there is no carb of injector droplets. Engines rarely replicate such perfection. If a proportion of the injection spray fails to vapourise fully in the combustion process some of the larger droplets fail to burn fully and carbonise as smoke ,and do not contribute to power. In that case squirting in more spray as a richer mixture can lead to more combustible vapour and more power, but also more smoke.

So some of that 10hp gain from ar ciher mixture is due to injection mixture quality being non-ideal.

 

That's not surprising from looking at PI sprays. The ideal is a 'fog' with droplets around 10-20um daimeter that follow the air flow well.

Figure here of a foggy spray versus a sharp-edged cone of a spray with bigger droplets:

http://www.powermag.com/microns-matter-proper-design-of-fogging-nozzles/?pagenum=2

 

 

Peter

Edited by Peter Cobbold
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To be honest I did not measure the difference in HP.

 

As we are discussing here how to proceed to adapt the MU

to the engine and I did exactely that with the Innovate several times

I wanted to point out that the AFR at full load for highest power must be 12.5-12.7.

 

The reason for that and why I felt the large difference compared to AFR14 is not evaluated by me.

What I can add is that the Porsche 964 also tends to go very, very rich and goes below AFR 12.

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To be honest I did not measure the difference in HP.

 

As we are discussing here how to proceed to adapt the MU

to the engine and I did exactely that with the Innovate several times

I wanted to point out that the AFR at full load for highest power must be 12.5-12.7.

 

The reason for that and why I felt the large difference compared to AFR14 is not evaluated by me.

What I can add is that the Porsche 964 also tends to go very, very rich and goes below AFR 12.

Andreas,

Oh I see. Those very rich mixtures are not to make combustion itself better, 'more powerful', but to get that bit extra mixture density through extra evaporative cooling. And to add a bit of effective octane through the bigger droplets evaporating after inlet valve closing. If injectors are poor and droplets big, then the extra fuel may be needed to ensure the vapour reaches the minimum richness to give full power.

I often wonder why port injectors point towards the inlet valves. I'd expect better evaporation of droplets if the fuel spray was made 'against the wind', giving a bit more cooling and denser mixture. There must be a reason..maybe transient wetting processes get worse...dont know..

Peter

Edited by Peter Cobbold
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Looking at Andreas thread from EFI Conversions, I see that this proves once again that the 150 BHP CP cam / engine is not 150BHP but only 124.9 HP at the flywheel? Using the same make of Dyno, my car obtained 127.5 HP. But my car's A/R was a consistent at 13, due to an air leak on the inlet manifold, across the whole Rev. range . As everyone else says put your car on a rolling road!

 

Bruce.

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Looking at Andreas thread from EFI Conversions, I see that this proves once again that the 150 BHP CP cam / engine is not 150BHP but only 124.9 HP at the flywheel? Using the same make of Dyno, my car obtained 127.5 HP. But my car's A/R was a consistent at 13, due to an air leak on the inlet manifold, across the whole Rev. range . As everyone else says put your car on a rolling road!

 

Bruce.

Bruce,

 

The AFR13 you report is actually correct for full throttle work, at all rpms.

 

Rolling roads habitually measure AFRs at wide open throttle operation which is how that torque curve is obtained. Far more relevant to road driving is the AFR at cruise loads, which rrs cannot replicate unless the inlet manifold depression has been measured while driving. Then a rr can be used at part loads.**

A wideband AFR sensor fitted in the exhaust allows AFR to be measured while driving and setting of the cruise AFR which should be leaner, for economy/emissions

 

** in absensce of a manilofd depression measure we guesstimate at the hp needed at cruise. Run the engine at cruise rpm, say 2700rpm, and adjust the rr until the torque corresponds to around 20 hp. Set AFR to 15. If it rattles its pistons upon flooring the throttle go richer.

Edited by Peter Cobbold
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Sorry Peter

Disagree ,a good rr operator will set the car up under all conditions and should not give a monkey about power output.After all it is not his car.

Neil,

I think its more the owners who worry about power. It still leaves the rr operator guessing at the cruise torque, better to have a measure of manilofd depression to give him.

And then he'll find the lean spike prevents going as lean as most engines will at cruise.

Peter

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My main concerns are that I don't want it too lean that it does damage, or too rich that its too thirsty.

 

I doubt it can be set lean enough to do damage. If it were, you'd hear pronounced pinking upon sudden opening the throttle. Unlike almost all other petrol engines the TR6PI is odd and lacks 'acceleration enrichment'. So the cruise mixture has to be set rich in anticipation of the 'lean spike' and pinking upon suddenly flooring the throttle. The lean spike is a manifold-wetting phenomenon, and the reason why carbs have throttle pumps ( Weber) or piston dampers ( SU)

Full explanation here:

https://supertrarged.wordpress.com/2013/06/12/the-lucas-pi-lean-spike/

 

The inability to lean out the cruise mixture because of the lean spike is also why the vac advance capsule on the PI engines was never connected up. The vac adv gives more time for lean mixtures to burn....but we dont have a lean mixture.

 

For those reasons the PI is thirstier at cruise than it should be.

 

Peter

Edited by Peter Cobbold
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Dear All,

 

My torque at the wheels was 120 ft/lb for 2700 RPM or 150 at the fly wheel! But it starts to fall away at 3200, which surprised me. Does this fall into your line with your thinking? Lastly looking at some rr data that Bengt Nylen some years ago regarding torque when he tuned his car. It appears that the Moss twin exhaust system TT1200 & FS5204 does not generate as much torque as a 6 into 1 system at 1500 RPM 115 v 143Nm. Sorry I do not know the conversion factor to ft/lb! Has anyone else had experience on this subject?

 

Bruce.

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Bruce,

All the power curves shown by Andreas #12 show a rather sudden change in slope at 3200rpm. The cam change ( last traces) reduces the inflection but it is still there. Put a ruler along the curve to see the inflection. On the torque traces it is more obvious.

More on Google images, eg:
http://www.kolumbus.fi/triumph.tr6pi/dyno-page.html

 

That sudden inflection does not to me suggest air- or fuel-related restrictions. I suggest it is more likely to be due the the centrifugal advance

running out of swing. The inflection might be reduced by a little more advance above 3200rpm. Worth a try.

 

Nick Jones gives data in post #34 here:

http://www.tr-register.co.uk/forums/index.php?/topic/29582-distributer-advice/page-2

- his table shows his electronic ignition adding 5 deg(crank) between 3000 and 5500rpm.

( top line of the table is at wot) The standard disy wont do that.

 

 

Peter

Edited by Peter Cobbold
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