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Petrol consumption versis CO Values


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I have a new engine in my TR the petrol consumptiom is 24 MPG. :( Before as a bog standard early US engine with Strombergs 33 MPG. :)

.

The new engine now has 2 SUs, PI head, PI cam, exhaust etc. So a lot more power. perhaps 130 BPH

 

If I understand correctly new engines should be run a bit rich at the start, also a stiff engine increases consumption.

I was expecting about 28 MPG.+ running in consumption.

 

So now the question has anybody got any realtionship between the CO values and the consumption The old engine had CO values from about 2.5 now I have 5.5.

 

Does this new CO value explain away a lot of the increased consumption?

 

I don't expect double the CO value double consumption but there must be a link-up some where. ..

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If your CO has gone up that much you are wasting fuel hence higher consumption.

Stuart.

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CO is from partial combustion and that will result from too rich or wrong spark timing, or both. Assuming the sparks and plugs are good.

 

In tuning for mpg the disy is very important particularly the vacuum advance. If the head is 9.5:1 compression you want about 10-12 BTDC static, rising on the centrifugal to around 30BTDC at 2500rpm and above. The vacuum then should raise it to about 40 maybe 45BTDC. You need to know which capsule to fit and exactly where to take-off the 'vacuum' above the butterfly. Your best bet is to replicate the 2500 TC carb saloon engine tune and work from there. But use a bit more static to compenste for the 8.5 compression. Some had SUs so use that needle and find the butterfly edgetake off position.

Cruise AFR needs ideally to be about 15 possibly 16 for best mpg. That can be measured with a wideband UEGO sensor.

 

Peter

Edited by Peter Cobbold
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I do not have a vacuum advance anymore they have taken it off.

As it is so new I will not touch anything but I looked at the plugs and the front 3 were somewhat richer as the back 3 plugs. Nothing extreem.

The firm that did it, are very experienced in this type of work. They have been doing this type of conversion for many years and also have been very successful on the Track.

Edited by Peter Douglas Winn
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I do not have a vacuum advance anymore they have taken it off.

As it is so new I will not touch anything but I looked at the plugs and the front 3 were somewhat richer as the back 3 plugs. Nothing extreem.

The firm that did it, are very experienced in this type of work. They have been doing this type of conversion for many years and also have been very successful on the Track.

Peter, Tuning for mpg needs the vac advance. Tuners for the track dont bother because race cars rarely operate at cruise. However a road car will likely be at cruise for 90% of driving. Track tuners will also set it up to run rich , typically AFR 12 to 13, for max power. But best cruise bsfc needs a slightly lean mixture. Without vac adv and leaning you will be stuck with 24mpg.

No use to you, but I will be covering this in IWE talk.

Peter

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Often made mistake is to judge from the plugs.

This can only give a correct information if they have

been choosen correct for that engine!

If engine has been modified this is not the case!

 

The vacuum advance is good for about 0.6 litre/100Km gain in fuel consumption.

Depends widely how often engine is used at part throttle.

If you go full throttle all the time there is no positive effect at all.

Keep in mind that the vacuum advance must meet the cam fitted because

the manifold pressure drops with hotter cams and makes that system somewhat useless

if not properly adapted to new situation.

 

If spoken about AFR there is not one correct AFR for one purpose except for a

race engine that goes rich all the time at about 12.7 AFR.

 

We want high AFR at part throttle/low load to save fuel and low AFR at full throttle for max power.

 

Full throttle AFR again is about 12.7 but the part throttle depends again on the cam.

Some close to stock cams allow up to the mentioned AFR16 but that is rare.

I am happy if I can go up to 15 with no negative effects.

 

At low revs/part throttle the AFR often must be richer about 13.5-14 to have a nice engine.

The AFR at idle does not play a role in that game, it could be simply an indication

how far away you are from the correct setting.

 

To find a proper needle that suits the modified engine needs a wideband controller

like the Innovate and maybe a USB laptop minicam to watch the position of the carb piston

and an eperienced co-driver to do that job.

 

Not to go through that process of finding a proper needle might spoil most of the tuning effort.

Turning the needle up and down in the carb to find a suitable position does not solve the problem.

The shape of the needle must be different. I would start with a BAM on a modified TR6 with SUs.

Edited by TriumphV8
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Often made mistake is to judge from the plugs.

This can only give a correct information if they have

been choosen correct for that engine!

If engine has been modified this is not the case!

 

The vacuum advance is good for about 0.6 litre/100Km gain in fuel consumption.

Depends widely how often engine is used at part throttle.

If you go full throttle all the time there is no positive effect at all.

Keep in mind that the vacuum advance must meet the cam fitted because

the manifold pressure drops with hotter cams and makes that system somewhat useless

if not properly adapted to new situation.

 

If spoken about AFR there is not one correct AFR for one purpose except for a

race engine that goes rich all the time at about 12.7 AFR.

 

We want high AFR at part throttle/low load to save fuel and low AFR at full throttle for max power.

 

Full throttle AFR again is about 12.7 but the part throttle depends again on the cam.

Some close to stock cams allow up to the mentioned AFR16 but that is rare.

I am happy if I can go up to 15 with no negative effects.

 

At low revs/part throttle the AFR often must be richer about 13.5-14 to have a nice engine.

The AFR at idle does not play a role in that game, it could be simply an indication

how far away you are from the correct setting.

 

To find a proper needle that suits the modified engine needs a wideband controller

like the Innovate and maybe a USB laptop minicam to watch the position of the carb piston

and an eperienced co-driver to do that job.

 

Not to go through that process of finding a proper needle might spoil most of the tuning effort.

Turning the needle up and down in the carb to find a suitable position does not solve the problem.

The shape of the needle must be different. I would start with a BAM on a modified TR6 with SUs.

Andreas, The vac advance does not follow MAP, its not like a efi set up. The capsules are fed with a venturi depression created by fast-moving air above the edge of a part-open butterfly. The cam wont make much difference to that venturi depression as the air flow past the butterlfy edge will be set by the cruise power requirement not the cam. Tuning a capsule is tricky as it needs that depression to be measured on the road and a capsule chosen to match. Which is why I suggested using the TC saloon settings.

Peter

Edited by Peter Cobbold
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The firm that did it, are very experienced in this type of work. They have been doing this type of conversion for many years and also have been very successful on the Track.

Have you asked them to explain your high fuel consumption and CO?

 

Pete

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So now the question has anybody got any realtionship between the CO values and the consumption The old engine had CO values from about 2.5 now I have 5.5.

 

 

Forgot to say: Lambda, CO and AFR are only different ways to say the same:

 

Lambda AFR ......... CO- % ....... Drehmom.

1,2 ......... 17,6 ......... 0.1 ......... - 26 %

1,15 ......... 17,0 ......... 0,1 ......... - 18 %

1.1 .......... 16,2 ......... 0,1 ........ - 11 %

1,05 ........ 15,4 ........ 0,25 ...... - 6,6 %

1,00 .......... 14,7 .......... 0,5 ........ - 3,5 %

0.95 ......... 14,0 .......... 1,3 ........ - 1,3 %

0,90 ......... 13,2 .......... 3,5 ........ - 0,5 %

0,85 ......... 12,5 .......... 5,3 ........ - 0,0 %

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Forgot to say: Lambda, CO and AFR are only different ways to say the same:

 

Lambda AFR ......... CO- % ....... Drehmom.

1,2 ......... 17,6 ......... 0.1 ......... - 26 %

1,15 ......... 17,0 ......... 0,1 ......... - 18 %

1.1 .......... 16,2 ......... 0,1 ........ - 11 %

1,05 ........ 15,4 ........ 0,25 ...... - 6,6 %

1,00 .......... 14,7 .......... 0,5 ........ - 3,5 %

0.95 ......... 14,0 .......... 1,3 ........ - 1,3 %

0,90 ......... 13,2 .......... 3,5 ........ - 0,5 %

0,85 ......... 12,5 .......... 5,3 ........ - 0,0 %

Andreas,

Lambda and AFR are indeed arithmetically related.

But CO will not have a strict relationship with AFR. CO will vary with engine ( eg compression ratio), rpm, load and spark timing. I agree the trend will be for CO to rise as the mixture is richened. But measuring CO will not give an accurate measure of AFR, there are too many variables.

Peter

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This is all very interesting.

I told the garage I wanted some more power to keep up with the modern day traffic. I also said I live in a large 20 mph zone and it must be drivable. They offered me a SU solution to which I said if, the consumtion is about 28 MPG then OK. They said no problem. I am still waiting for the engine details. I do know they had a lot of work to get the right needles. When I asked about the vacuum advnce they said it would not help with the combination of PI Head, cam, exhaust that is why they took it off. Not being an expert about these things I had to accept their word. The car must go back for some other things that were not finished on time. Before, I am trying to get some ideas if the changes are acceptable. Also what is it like, now that I have done about 1500 miles, hence the measurements and a look at the plugs to see if the Carbs are well balanced. It is starting to run a bit jerky below 2000 rpm the plugs show a small diffence in colour between the front and back carb. Nothing drastic. As the garage is 600 miles north of here I want to get all points listed before I drive there and make the trip back with pubic transport and afterwards with publlic transport to pick it up.

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Andreas,

Lambda and AFR are indeed arithmetically related.

But CO will not have a strict relationship with AFR.

 

I use AFR because my Innovate gauge shows that but in literature a reationship can be found.

 

The above was not from me and here is another more scientificial:

 

www.pro-physik.de/details/articlePdf/1105967/issue.html

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It is wrong to remove it for any engine because the engine needs additionaly a timing related

to the cylinder filling that is directly related to the manifold pressure = vacuum.

 

As the advance system needs proper setting related to the engine (I am not following

Peters opinion in that case because I set several 123tune with SUs and they all had

been different) it might be only a small disadvantage in your case to cut it off.

 

The result will be more fuel consumption and less power at part throttle when removed.

There is no disadvantage to have it connected.

 

Some cars dont have it because there is no provision to pick the vacuum.

TR6 PI and engines with Weber DCOE are some of those.

 

Your problem seems to be related to wrong needles for that state of tune.

Edited by TriumphV8
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So coming back to my basic wish specification is the removal of the Vacuun advance wrong or not.

Wrong as far as getting the best economy from the engine. But right as the workshop had no information to tell them what vac capsule to fit - there are dozens of them. http://www.distributordoctor.com/vacuum_units.html

 

One of the 2.5TC saloons had a vac adv capsule fitted, but most did not:

http://www.teglerizer.com/mgstuff/advance_curves.htm

 

The 2500TC uses a Lucas “ 5.10.8 “ vacuum advance, meaning:

advance starts at 5inchHg vacuum and is maximum at 10inchHg with a max advance of 8

distributor degrees, or 16 crank degrees.

If the static is set to 12 BTDC and the centrifugal brings that up to 22BTDC at 2500rpm then that capsule would take it, at part loads, to 38BTDC at 2500rpm cruise.

Its worth a try. Connect the capsule to the throttle edge take-off here:

http://0.tqn.com/w/experts/MG-Car-Repair-3786/2010/07/SU-HIF44-Carb.jpg

 

You could try posting on a saloon forum to get ideas for the best timing owners have found for a 9.5:1 compression head..

Peter

Edited by Peter Cobbold
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That's a good idea as I have had many many saloons sinc 1969 with even up up to 180BHP but that is past..

Now I still drive in Munich a bog standard MK2 2000 saloon. Pop, Pop, Pop. The dogs overtake me.

 

We were at Malvern last year so that is why we are giving Lincoln a break and this year we are going to Scotland for the Saloon National.

 

In spite of that we need the TR in top condition for the European meeting in September in Tuscany.

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That's a good idea as I have had many many saloons sinc 1969 with even up up to 180BHP but that is past..

Now I still drive in Munich a bog standard MK2 2000 saloon. Pop, Pop, Pop. The dogs overtake me.

 

We were at Malvern last year so that is why we are giving Lincoln a break and this year we are going to Scotland for the Saloon National.

 

In spite of that we need the TR in top condition for the European meeting in September in Tuscany.

Tom here has TR250 data, and I think that was a 9.5:1 compression engine.

http://www.tr-register.co.uk/forums/index.php?/topic/27605-tr6-distributor-vacuum-advance/

""The TR250 had 26 degrees of mechanical advance + 10 degrees static + vacuum advance of ~ 10 degrees ( not sure about this last figure ) for a total of well over 40 degrees ""

I shall be using that as a starting point for my disy tuning for cruise.

W eneed to be sure the compression was 9.5.

Peter

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I am still waiting for the engine details They have promised me a complete list. They were in such a hurry to get it drivable for our large whitsun meeting, some things fell by the road. So the car will have to go back. When I bring it back it is nice to be armed with this sort of information.

The person responsible is like you. Peter C. He gives technial presentations to the German TR Register and was for many years our tech director . He has at least 50 years of experience in the garage and on the track. I think his logic is sound but from what I am reading he may have done an overkill. I did not want a fast road car, those days have long gone. I wanted just to get from A to B in comfort in modern day traffic, with resonable consumption. Money is not the problem it is the scarcity of filling stations nowdays.

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I am still waiting for the engine details They have promised me a complete list. They were in such a hurry to get it drivable for our large whitsun meeting, some things fell by the road. So the car will have to go back. When I bring it back it is nice to be armed with this sort of information.

The person responsible is like you. Peter C. He gives technial presentations to the German TR Register and was for many years our tech director . He has at least 50 years of experience in the garage and on the track. I think his logic is sound but from what I am reading he may have done an overkill. I did not want a fast road car, those days have long gone. I wanted just to get from A to B in comfort in modern day traffic, with resonable consumption. Money is not the problem it is the scarcity of filling stations nowdays.

Peter, Its much quicker to tune for power at wide open throttle. He got you running in short space of time. But it will still be possible to get that 28-30mpg target, ( assuming you have 9.5 compression or better ) maybe better.

Tuning for best fuel consumption at cruise is, I find, a fascinating topic in itself. But there are several variables that need to be measured. I would tell him you normally cruise at say 2400 rpm. ( or whatever) at say 70mph. If you can measure yourself the manifold depression ** while doing that, on a flat-ish road, you can then give him that rpm and depression reading and get him to replicate both on the rolling road , operated at constant load. He can then measure AFR with an exhaust probe and the SU piston lift by eyeballing it. Thats tells him the region of the needle that needs to be leaned for cruise, and it will likely be the first eight of an inch or two down. He then fits a needle to give AFR around 15. Then he needs to play with the spark to get best torque while still keeping the rpm and manifold depression the same as you measured. He need not be finicky: try 35, 40 and 45 BTDC, and pick the best of the three. Then he needs to measure, again in those same conditions of rpm and depression, the vacuum at the butterfly edge tak-off on the SU. Knowing that he can find from Disy Doctor the right v-a capsule that will advance the spark to 45 BTDC ( if that is what was best for torque). This needs a rolling road that can measure the torque from around 25hp and detect 1 to 2 hp change - not easy.

So another method is to run on the rolling road at your cruise settings and AFR 15 and simply advance the spark until he hears pinking just starting. Then back off the timing say 5 crank degrees - but I would not go beyond a total of 45BTDC. When setting up using knock use the worst octane fuel you expect to have to fill up with.

Hope this helps.

Peter

 

** you could tee a gauge into the servo line ro simlar postion between inlet vlaves and carb, downstream from the butterfly

Edited by Peter Cobbold
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By chance I've just started MAP logging to go with the piston lift logging, and thought the two attached pics were interesting. One is taking the vacuum from the carb butterfly port and the other directly from the manifold. These are from two virtually identical WOT runs. Note on throttle shut during gearchange and full lift using carb takeoff vacuum disapears completely, whilst manifold vacuum goes sky high! During WOT and cruise they aren't that far apart.

 

post-12405-0-42402100-1464633486_thumb.jpg

Carb

 

post-12405-0-22448100-1464633486_thumb.jpg

Manifold

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By chance I've just started MAP logging to go with the piston lift logging, and thought the two attached pics were interesting. One is taking the vacuum from the carb butterfly port and the other directly from the manifold. These are from two virtually identical WOT runs. Note on throttle shut during gearchange and full lift using carb takeoff vacuum disapears completely, whilst manifold vacuum goes sky high! During WOT and cruise they aren't that far apart.

 

attachicon.gifwotpullcarbvacuum.jpg

Carb

 

attachicon.gifwotpullmanifoldvacuum.jpg

Manifold

Alan,

Whats the colour coding and scales?

The butterfly port will show more depression than the manifold at small butterlfy openings. The position of the take-off is crucial, as is the cruise load ( via butterfly angle). Try a sready top gear 50 mph on the flat. The venturi action there adds to the manifold depression.

Its a highly localised depression. I expect when it get to tuning the v-a capsule to have to drill new take-off positions - but I am only using one SU !

Peter

Edited by Peter Cobbold
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Alan,

Whats the colour coding and scales?

The butterfly port will show more depression than the manifold at small butterlfy openings.

 

Sorry blue is vacuum - 0-5 volts where 5 volts "top" is zero vacuum. Yellow is TPS the peaks are sustained WOT, the black and purple are AFR front & rear carbs. Red is RPM peaking around 6.2K

 

Re small openings, whilst I normally never look at the cruise parts of the logs, a couple of extracts below from today are interesting.

 

They were both taken at cruise at around 2k rpm in 4th with the throttle hardly open, i.e foot resting lightly on peddle and TPS hardly registering, i.e any lower and its shut. NB the carb take off position on the Strombergs is right on the edge of the Butterfly i.e. it is actually covered when the butterfly is shut, thats why vacuum goes zero on the carb logs when the throttle is shut.

 

post-12405-0-51594600-1464637432_thumb.jpg

Carb vacuum at cruise

 

post-12405-0-67852600-1464637432_thumb.jpg

manifold vacuum at cruise

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Sorry blue is vacuum - 0-5 volts where 5 volts "top" is zero vacuum. Yellow is TPS the peaks are sustained WOT, the black and purple are AFR front & rear carbs. Red is RPM peaking around 6.2K

 

Re small openings, whilst I normally never look at the cruise parts of the logs, a couple of extracts below from today are interesting.

 

They were both taken at cruise at around 2k rpm in 4th with the throttle hardly open, i.e foot resting lightly on peddle and TPS hardly registering, i.e any lower and its shut. NB the carb take off position on the Strombergs is right on the edge of the Butterfly i.e. it is actually covered when the butterfly is shut, thats why vacuum goes zero on the carb logs when the throttle is shut.

 

attachicon.gifcarbvaccruise.jpg

Carb vacuum at cruise

 

attachicon.gifmanvaccruise.jpg

manifold vacuum at cruise

Its very difficult to read the depression as the top of the graph, at atmospheric pressure, is unclear. There are 14 to 15 divisions in total, close to one per psi, atmos press being 14.7psi. If the carb recording is one division off atmos, that's 1psi or 50mm Hg. That's enough to actuate a capsule.

The SU vac-adv take-off is on the piston side of the closed butterfly, not covered by it.

Peter

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Its very difficult to read the depression as the top of the graph, at atmospheric pressure, is unclear. There are 14 to 15 divisions in total, close to one per psi, atmos press being 14.7psi. If the carb recording is one division off atmos, that's 1psi or 50mm Hg. That's enough to actuate a capsule.

The SU vac-adv take-off is on the piston side of the closed butterfly, not covered by it.

Peter

 

I think thats about right, zero vacuum or atmospheric 14.7psi causes the 1 bar MAP sensor to register 5v as vacuum is applied it seems to pull down linear to about 0.5v at atmos -1. So at gentle cruise in the graphs its about -1psi.

 

Looking at a couple of SU's I have here HIF44 and HS6 both of those have the vacuum take off in exactly the same place as the Strombergs i.e. when the Butterfly is shut the vacuum port is closed, the microscopic drillings appear to be about the same size on both SU's and Strombergs so I'd expect them to give nearly identical readings, which is good to know if considering a carb swop and your using vacuum advance. I junked using vacuum advance long ago as I'm not tuning for economy and the risk of a failure (i.e. it activating) at high RPM's.

 

I think the positioning of the vacuum port on the carbs is intentional as if you shut the throttle at high RPM's you don't want to suddenly throw in vacuum advance, positioning it where they are means that vacuum and any associated advance goes zero instantly at that point.

 

Alan

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