3 BAR MAP Sensor

[lotusgirlmarie]

Hey all,
how many people have te 3 bar map sensor and how does it differ from the stock 1 bar other that the obvious preasure difference. As an added bonus question, at what altitude do you live?

As if the first two questions weren't bad enough, I've been thinking alot about a 2 bar instead. Any thoughts?

[tigerdog]

Hey all,
how many people have te 3 bar map sensor and how does it differ from the stock 1 bar other that the obvious preasure difference. As an added bonus question, at what altitude do you live?

As if the first two questions weren't bad enough, I've been thinking alot about a 2 bar instead. Any thoughts?

OK, now we're talkin'!
First of all, I believe the stock sensor is a 2 Bar sensor. Why? Because Smaug has a 3 bar sensor and Elanscan shows all the readings to be off by 1/3. For example, the MBC is set for approx 16 PSI (as displayed by the Autometer gauge) but at max boost, Elanscan shows .75 bar.

.75*3/2=1.125
1.125*14.5 = 16.3125 PSI

That's at sea level; I'm a 100 or 200 feet above, so the actual number is very close to what's reported by the gauge.
This means, if you drop in a 3-bar MAP sensor without changing anything else, the ECU is going to be dramatically under-fuelling the engine. Houdini seems to have gotten around this by exchanging the injectors as well. IIR, the stock injectors are 325cc units; Smaug is fitted with RC engineering 550cc injectors. Assuming the flow increase is linear across the injector's operation, it's not quite a 3/2 increase. It appears to be close enough for the ECU to compensate.


The real question is what happens to boost if the ECU is left to run the boost control valve using the standard program. I posted a note in Smaug's project thread earlier today on this subject. Take a look, but let's keep the comments in this thread for consistency.

[lotusgirlmarie]

2 BAR MAP sensor? Can anyone confirm?

If the readings in elanscan are 1/3 of the OEM readings wouldn't that mean the stock is a 1 bar?

[tigerdog]

2 BAR MAP sensor? Can anyone confirm?

If the readings in elanscan are 1/3 of the OEM readings wouldn't that mean the stock is a 1 bar?

Poor phrasing on my part... readings by Elanscan are 33% lower than as measured by the gauge.

In searching around, I found RobieTheRobot has already done the hard work of decoding part numbers on his web site. The Electromotive Sensors web site describes 1 bar sensors as being used on NA engines, 2 bar for boost up to 14.5 PSI and 3 bar for higher boost. This makes a certain amount of sense. If we had a 1 bar sensor, we'd not be able to measure anything above normal atmospheric pressure.

[Doug]

stock sensor for turbo cars in general is 2bar
Elan is 2bar

[John_W]

You just have to remember what your datum is (psig -gauge pressure, or psia- absolute pressure).

1 bar is approximately equal to 1 atmosphere = 14.7 psi, so a 1 bar sensor would not be able to show any pressure greater than atmospheric.

Our boost gauge goes up to 1 bar, but it is calibrated to read boost (not absolute pressure), ie pressure above atmospheric, so the gauge reads to atmospheric plus one bar. Therefore the standard sensor must also be 1+1= 2 bar.

I think you need a 3 bar sensor, Marie.

John

[tigerdog]

So where does Marie go next? A 3 Bar sensor alone will wreak havoc on the fuel/air ratio unless its used in conjunction with some way to compensate for its altered output. Smaug does this with larger injectors (at least, that's the theory I'm working from.) I suppose it could also be accounted for with a different computer. In reviewing the documentation, I see Haltech have incorporated an initial setup option for either a 2- or 3-bar sensor.

From what I experience, in closed-loop operation the stock ECU can compensate for the difference between 2-bar/325cc and 3-bar/550cc. The upside is, the stock .65 BAR peak becomes .975 BAR, a respectable number. There's a risk here, though: the safety features built into the chip now become useless. For example, under cold engine operation and detonation the chip reduces boost to .5 bar. With a 3-bar sensor, this becomes .75! Worse yet, the fuel cutoff of .92 now becomes 1.38 bar (20 PSI!!!)

I believe once we establish this 2/3rds ratio as constant, the next steps might be:

- dyno Smaug or some other car with similar setup to check overall fuel/air ratio and make sure there's nothing dramatically wrong
- Create a special chip (or teach us how to tweak our own) to reduce the fuel cutoff to some number just above our target boost and reduce the cold/detonation from .5 to .33 bar in the computer to achieve the desired .5 cutoff in practice.

Either that or we all go out and buy Haltechs and each pay our own freight as far as dyno tuning and map development. I'm just hoping there's a way to avoid that expense and to take advantage of all the work that's gone into the stock ECU programming.

[lotusgirlmarie]

ALAN!!!!!! WE NEED A DE-TUNED CHIP!!!! 550cc injectors are next up on the list. The major question I have with this is after a long discussion about fueling with one of my old racing buddies he had said that 550's may be too big and cause a catostrophic engine failure due to fuel in the oil. This would cause the oil to thin and for the engine to spin a bearing. Now I'm no expert but this would be a bad thing. Any thoughts.

The formula he was using for a turbo car was this:

(desired realistic BHP*0.55)/cylinders = lbs per hour

[tigerdog]

The formula he was using for a turbo car was this:

(desired realistic BHP*0.55)/cylinders = lbs per hour

I'm no racing expert, just trying to think this through. The injector on/off (and thus the flow) is controlled by the ECU, right? If yes, then the risk of you're friend's scenario would be greatest at idle and low-load situations. Why? Because there must be a lower limit to the smallest amount of fuel an injector can deliver. As long as the ECU can pulse the injector at a sufficiently small burst to limit the fuel delivered at idle and low-load, we should be OK.

550cc injectors are next up on the list

Unless you're planning to use a Haltech, I believe the injectors must not be "next", they need to be installed simultaneously with the 3-bar sensor. Otherwise, we'll under-fuel by 30% with the 3-bar sensor. If we install the 550cc injectors first, we'll over-fuel.

RC Engineering has a very handy calculator for injector sizing on this page. Depending on the assumptions being made, it turns out 550cc is just about right for 250-275 HP from a four-cylinder engine.[/quote]

[lotusgirlmarie]

Hunn,
I understand that they need to be installed at the same time. I'm crazy...not stupid. I'm refering to my shopping list, not my install list. Case in point; when I did the turbo install I gathered all of the parts I would need long before I actually did the install. Hence the reason my car was only off the road for a few days. Ekapol can attest to this as I did his install as well.

I really like to research an upgrade before I go and do it as not all upgrades will produce results that I want and can live with, plus be reliable and road worthy for an exended period of time. I'm all about form AND function. Not one above the other.

Getting back on point. Haltech would deffinitely be one way to go. I'm looking for something abit more factory. That said though I still have a greddy profecB specII installed and am not planning on removing it as it too has a lo and a hi boost setting. My current goal is 260-290 WHP at sea level. Any more and I feel the car may not be very streetable and will loose what Lotus has fought so hard to maintain with the FWD setup. This is also why I'm looking very carefully at what I'm putting in the car as an upgrade. CA SMOG is also a concern as I am not taking my car with me when I move out to Chicago.

Tigerdog I know that your in So Cal at sea level or there about, this is also why I was looking at what Houdini had done to the car. He and I had talked a few years ago about the very upgrade you have in your car and I have in mine well before either one of us actually did it. We had also discussed the use of 450cc injectors in the hopes that they would be enough fuel but not excede their duty cycle. This is the source of all of my questions. I want to double check that this is indeed the best route (550cc) for me and what I want to achieve from the car. I can already keep up with Elise, much to their surprise, and do not want to jeapordise my engine in the process of extracting alittle more power. I hope this makes sence. Soapbox sermon over.

BTW the chart from RC is handy isn't it.

[tigerdog]

Hunn,
I understand that they need to be installed at the same time. I'm crazy...not stupid. I'm refering to my shopping list, not my install list.

Open mouth, insert paw! Sorry if I offended.

Haltech would definitely be one way to go. I'm looking for something abit more factory... CA SMOG is also a concern...I want to double check that this is indeed the best route (550cc) for me and what I want to achieve from the car.

I think you and I have similar objectives: a streetable, dependable power boost that retains enough of the standard components and behaviours to pass California smog tests without replumbing the engine every 12 months. Ideally, we'd find someone who makes 487.5cc injectors (1/3 more than 325) but RC offers only 440 and 550 options.

Clearly, the only way to be sure is to spend a lovely weekend in San Diego, drop a timing belt in Smaug then go out with ElanScan and make some full-throttle runs!

[lotusgirlmarie]

No worries. I'm pretty easy going. Soooo do you need help with the timing belt? Do you have one already?

[Ekapol]

Ekapol can attest to this as I did his install as well.

Yep, a lot of preparation steps went in to every single LGM project. I'm pretty sure she was the very first person researching into Garrett turbo long time back and came up with her suggestion for GT2560R model and possibility to make this model to work with our cars by reindexing the turbo, etc., very constructive information which she shared with me and Houdini.

Turbo installation on mine went in so smoothly in 2 short afternoon. Could actually be done in a day. We even actually did order an extra exhaust manifold to save installation time and hassle of what might go wrong with it -- possible cracks, etc. I've never seen anybody working on a project like this with no down time at all.

In short, I was very impressed.

[tigerdog]

No worries. I'm pretty easy going. Soooo do you need help with the timing belt? Do you have one already?

I haven't purchased the parts yet. Since I don't think I have time or patience to do it myself, I was going to leave parts acquisition to the shop. My brother the (ex-)mechanic says this is better form than walking in with a handful of parts. Did you have something in mind (a good parts source, etc?)

[tigerdog]

Alan's post on the subject of ignition advance tables points out another point requiring optimisation when moving from a 2-bar to 3-bar sensor. Recognising the tables in the post are absolute pressure, it implies that using a 3-bar sensor will result in the application of more advance than optimal, potentially increasing the possibility of detonation. For example, when the ECU sees 1.6 bar absolute at 5500RPM, it's applying approx 30 degrees advance. In reality, that 1.6 bar is really about 2 bar (abs) and so advance should be down in the low 20 degree BTDC range if you follow the standard curves.

Boy, this gets more complicated by the minute. You truly gain respect for the effort manufacturers put into ECU tuning.

[GeoffSmith]

You truly gain respect for the effort manufacturers put into ECU tuning.

And even greater respect for those who reverse engineer the ECU code/maps and make mountains out of molehills.

[tigerdog]

And even greater respect for those who reverse engineer the ECU code/maps and make mountains out of molehills.

yeah, verily!

[Ekapol]

My brother the (ex-)mechanic says this is better form than walking in with a handful of parts. Did you have something in mind (a good parts source, etc?)

I like another approach of having the parts handy and then go to the shop.

My mechanic told me to source all the parts, cause they normally don't have much idea about what are needed for our engines.

I know it's but might be useful for you.

You might conveniently find your SHOPPING LIST here.



My last timing belt was done with LGM big help. I ordered all OEM Isuzu parts, as LGM told me how much more reliable they are. She also showed me how her aftermarket waterpump looks like after 6 months of service, leaked and well rusted inside YMMV.
Back to 3 bar MAP ...

[Paul.P]

Not trying to but in chaps, but how did Costas do it ?

[tigerdog]

Not trying to but in chaps, but how did Costas do it ?

If I recall, his technician burned a special chip for the standard computer. I saw a thread somewhere and will add a link here if I can chase it down.