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Engine mapping using a 2wd rolling road


zoltan
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Anyone have any opinions on the wisdom of running a Defender on a 2wd rolling road with either the front or rear prop disconnected and the diff locked? It is a standard power output 3.5 Efi V8, I want to play about with the mapping or at least making sure that the mapping is right.

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Thanks.

I should have explained better - I have free use of a rolling road but it is a 2wd one. It quickly won't be so free if I mangle my transfer box up! I can't see a reason why it won't stay in front or rear drive for what I'm doing, isn't as if it is a 5.3 race engine doing power runs

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Transfer case will be fine with no front prop and difflock engaged.

The only concern is your putting all the power thru one axle, but given you wouldnt be shockloading it then it should be ok, espeically as its not that powerful an engine.

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Depends what you're doing, if it's MegaSquirted you don't need to rolling road it as the datalogging & tuning software gets so close it's not worth it.

I hear what you say but it's also nice not to have to worry about steering or oncoming traffic and have the luxury of a range of hills to load the engine.

I mainly want to see what ignition settings work best with LPG

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I would suggest that while on-the-road mapping will get things close, you'll never get it perfect becuase its not particularly easy to optimise the ignition timing, nor the accell enrichment while driving. You end up with a blend of accell and main fuelling most of the time (because its not really possible to hold the engine at say 70% load at one particular RPM site to get the fuelling bob on) which will work, but it wont be optimal, and you will tend to leave the ignition timing well alone, which probably isnt anywhere near optimised for the particular engine.

Given the ignition timing alone could make a huge difference to how it drives and to the fuel economy, and the rolling road is free, i see no reason why not to take advantage of it, and to produce a perfect ignition map for LPG and Petrol.

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In answer to your initail Q

Yes you can, but as others have siad - your shoving 2 x the output thgrough the CD and Rear Axle train

Also the power loss between a 2WD set up and a 4x4 set up is very different, so a LR mapped as a 2wd will not be the same Fuel Spark and ACel Enrich as a LR mapped in 4x4 mode. The losses are far greater in 4x4s than 2wd set ups.

Nige

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In answer to your initail Q

Yes you can, but as others have siad - your shoving 2 x the output thgrough the CD and Rear Axle train

Also the power loss between a 2WD set up and a 4x4 set up is very different, so a LR mapped as a 2wd will not be the same Fuel Spark and ACel Enrich as a LR mapped in 4x4 mode. The losses are far greater in 4x4s than 2wd set ups.

Nige

You have that a little muddled Nige,

while you are absolutely correct in stating that the losses will be very different, you forget that the engine does not care about losses, it gives power as required full stop! the rolling road can load the engine until it stalls if need be so the engine load can be anything you need it to be with either two or four wheel drive rr setups.

The only difference will be that the rollers will have to do more work, nothing else.

The axle and centre diff should be fine as long as you are not daft with it!

Lara

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Interesting Lara,

I not sure about this, maybe we end agreeing to disagree but my logic was say you have a LR mapped with 35" tyres and 3.54 difs, my expereince is that the powerband / fuel to spark needed changes when say you fit 4.75s ?

My logic therefore was that 2wd vs 4wd might make the engine behave different, a bit like the LR with a Trailer / and then without the trailer the demands / p[owerband is different. ?

My thoughts are that with any combos of the above all would run the engine fine, but whichever is the 100% target for being used majority of the time there would be minor variations in the mapping ?

:)

Nige

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The changes to the tyres etc will affect the load areas you run in most often, but it wont affect the amount of fuel the engine requires at any given RPM and load site. Thats dictated by the engine itself, ie heads, cams, manifolds etc.

I suspect it appears to require adjustments due to the imperfect way megasquirt tuning works, as your tuning to a dynamic engine state and hoping to get it more or less correct, rather than tuning to a static engine state and getting it spot on.

The only way you can get the correct fuelling for a given RPM and load site, is to hold the engine in that site while you adjust the fuelling.

If you do all your mapping using on-the-road style megasquirt tuning, you end up with a blend of accell enrichment, and steady-state fuelling, plus the interpolation from the sites around the one your currently in, all affecting the fuelling.

Lets say for example your accell-enrich is too aggressive, this means the sites that you most commonly accellerate thru, will end up lean, and the ones you cruise in, will end up pretty accurate. Now you alter the gearing, which changes those cruise sites and the areas your most often accellerating thru, so the map is now incorrect and requires retuning. The gearing didnt cause the problem, simply highlighted errors in the orignal map.

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The changes to the tyres etc will affect the load areas you run in most often, but it wont affect the amount of fuel the engine requires at any given RPM and load site. Thats dictated by the engine itself, ie heads, cams, manifolds etc.

I suspect it appears to require adjustments due to the imperfect way megasquirt tuning works, as your tuning to a dynamic engine state and hoping to get it more or less correct, rather than tuning to a static engine state and getting it spot on.

The only way you can get the correct fuelling for a given RPM and load site, is to hold the engine in that site while you adjust the fuelling.

If you do all your mapping using on-the-road style megasquirt tuning, you end up with a blend of accell enrichment, and steady-state fuelling, plus the interpolation from the sites around the one your currently in, all affecting the fuelling.

Lets say for example your accell-enrich is too aggressive, this means the sites that you most commonly accellerate thru, will end up lean, and the ones you cruise in, will end up pretty accurate. Now you alter the gearing, which changes those cruise sites and the areas your most often accellerating thru, so the map is now incorrect and requires retuning. The gearing didnt cause the problem, simply highlighted errors in the orignal map.

Well, I guess everybody on this thread is correct in one way of another, however, MS is more intelligent than the above statements suppose…………….. ;)

Using the public highway as a rolling road is the poor mans answer to tuning. However, you will always end up with a map that only has the useable sites tuned pretty much on the nose. There are some sites (quire a lot actually) that never get visited during various drive cycles and these sites tend to be best guesstimate numbers. So, when Nige changes his gearing the useable part of the map changes and he starts to visit the edge of some of the previously unobtainable sites. The fuelling algorithm number crunches the required sites and becomes staggeringly obvious that the map needs a tickle around the edges to bring it into line. The sites that are difficult to manage in this scenario are high RPM and low RPM at both light and heavy loading. Is also difficult on the rollers, but near impossible in a drive cycle.

The best dynamic range can only be achieved by removing the engine and placing it in the engine dyno environment………. That way the rev range and full dynamic loading can be explored in detail.

MS on its own actually does quite well and the blend is not quite as portrayed above. When logging is taking place the ECU also returns a run state code that is part of the log file data and filtered to remove the obvious anomalies such as acceleration enrichment etc. This is achieved by setting various bits in a 6 bit word.

The decimal run codes are,

1 = Running

2 = Cranking

5 = Running and afterstart enrichment (this includes settle time)

9 = Running and warm-up enrichment

13 = Running and afterstart enrichment and warm-up enrichment (the cross over phase)

17 = Running and acceleration enrichment

25 = Running and warm-up enrichment and acceleration enrichment

33 = Running and deceleration lean off

All the above combinations are filtered to leave just the steady state running info. Also add to this that with a WB linear probe the software can be preset to a target lambda map and the VE map is then updated as required. Further filtering can be applied to limit the rev range data and also to apply an IAT correction curve.

For me, given the option, then I would always opt for the engine dyno, followed by the rollers and lastly the ‘on road’ testing. However, the first two options are expensive and at the end of the day you only really need the useable portion (drive cycle) of the fuel map to be correct. However, setting the spark map does really require the dyno and MBT requires to be measured.

I found setting the high end of the map incredibly difficult on the road and I ended up doing all my runs in the early hours of the morning........ often running into 3 figures and using smaller diameter tyres to give me the load I required.

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