Attention ESM and others contemplating 3 BAR MAPs

[tigerdog]

I'm going to hook up ElanScan to Smaug sometime this week and take a series of scans with only the stock boost control and California chip, but with the Garrett GT2560+3Bar MAP sesor+550 injectors. ESM, if you're reading, what kind of scans (full throttle low-to-high RPM in 3rd? steady state 3000RPM cruise?) would be helpful in a longer-term effort to produce a custom chip for the LGM turbo cars? I'd like to produce info that's as helpful as possible.

[ESM]

In essence three things need doing

1) I need to re-code to correct the scaling of the MAP and boost variables

2) I need to create map data for the 2->3bar interval for all table that use boost or MAP as a lookup variable. I can resample the 0->2bar maps into the new 0->3bar scaling.

3) The constant (I assume there is one) that corrects for injector volume has to be located and adjusted appropriately

I'm not sure that logs help all that much. Maybe some runs in the 2->3 bar boost range would tell me if the current timing & fuelling is producing knock anywhere in the 'new' condition envelope.

[tigerdog]

Maybe some runs in the 2->3 bar boost range would tell me if the current timing & fuelling is producing knock anywhere in the 'new' condition envelope.

If I understand correctly, the "2->3 bar boost range" essentially means boost above 1 bar, correct? I can provide at least some information there; we have a lovely long uphill grade and I can set the MBC for anything that sensibility will allow. I've been running approx 16 PSI with no negative results using California 91 (R+M octane rating, somewhere between 93-95 on the scale used in the UK) with no registered issues. I believe I'll need to recheck the base timing first, though, before the info will be useable.

[ESM]

Yeah 2->3bar absolute = 1->2bar of boost. Actually some off boost cruising would be useful as well because it'll give me an idea of how much correction the ECU is having to put into the fuelling in closed loop operation.

[tigerdog]

Here are scans taken from Smaug with GT2560R + 3Bar MAP + RC 550cc injectors. Standard 9949 California chip, standard boost control in place. Base timing was set to 16 BTD just before the logs. Fuel is California-quality 91 Octane (R+M/2 method), roughly equivalent to 93-94 octane according to UK measurement - consider it a worst-case scenario. Many thanks to to Sparky, my 11-year-old son and co-pilot, who managed the logging and file saving for this trip. Start at the bottom (baseline) for chronological view.

Boost never went above 10 PSI on my autometer mechanical boost gauge, which (I think) reads a little high. At this point, ElanScan shows .45 Bar boost and 80% wastegate duty cycle. At no point could I get boost to reach a computer reading of .65 Bar. Instead, the computer seemed to be holding close to the standard .65 Bar boost. Wastegate duty cycle never went above 80%. Interstingly You'll note the knock counter jumped quite a bit between a couple of the runs but I unfortunately lost the circumstances causing this due to ElanScan operator error. At one point I hit the rev limiter in 2nd while accelerating - that might have done it. Next plan is to reinstall the MBC and produce runs at higher boost, watching the knock counter, of course!

[tigerdog]

OK, I've been working under the assumption the boost delivered by the ECU using a 3 BAR MAP will be 1/3 higher than with a 2 BAR MAP. I've been perplexed because I rarely get above about 9 PSI shown on my autometer boost gauge. This corresponds very closely to the stock .65 BAR boost here (about 50 ft above sea level.) How can this be?

Well, the MAP thinks the static air pressure is .72 BAR. ElanScan shows my max boost at .4 BAR. The difference is about .65. .72+.65 = 1.37 BAR, or about .4 BAR of boost. Alan, if this is the case, then it appears the ECU calculates boost relative to the measured barometric pressure. My head is really spinning at this point but the maths keep bugging me. It gets even harder to calculate, because the ECU is really looking at the MAP sensor output voltage. From what I've read, this is a linear function from 0V ("absolute" vacuum) to 5V (max sensor pressure). I found a handy spreadsheet and graph someone else calculated which purports to show the relationship between the two GM parts.

2v3BARMAP.jpg

This helped visualize why the ECU thinks the barometer is .71 instead of around 1 here.
Still, the more I think about this, the more confused I get. My brain hurts now. I think I'll put at tax on people who stand in water...

[GeoffSmith]

Just a thought.... does the stock memcal adjust the AFR for the apparent low ambient barometric pressure? Off-boost the O2 sensor should keep things sweet, but it may be lean (even with the bigger injectors) when boosting.

[tigerdog]

In another thread,

on upgrade note, not sure how many are going 550cc injectors, but even at 2100ft above sea level i am pig rich under 13psi. at the 6200ft i was as rich as 10.1:1 A/F.

I think we're definitely in the experimentation phase here but it seems just the opposite may be true, if others experience the same thing as Crambury.

[Elanlover]

I have to say that I have a bit of an interest in this as well. I'm getting to the point now where, with the elysium chip fitted, I could stand to gain a few more horses. I'd love to see about 250hp or so (with some extra power in the lower rev range) as I'm figuring I'm at about 215 - 220 with all the various enhancements. I'm at a bit of a loss though when it comes to the reasoning why a bigger turbo will give more horses. This is due to my own lack of knowledge in this area of course

I suppose I'm struggling with the notion that the boost level, no matter how big the turbo is, will still be limited by the overboost limit and the wastegate will still open when its supposed to meaning you'll only get .9 bar (with chip fitted). Does the turbo need to be accompanied by a new program set to allow greater boost levels and would the engine take it?

I'm anxious to be educated

[tigerdog]

I'm anxious to be educated

At the risk of the proverbial "blind leading the blind," I'll try. Your struggles have paid off and you the points essentially correct; the bigger turbo, in and of itself, won't change the engine power. What it allows is a higher volume of air at higher boost pressure. To take advantage of this capability, we need the other things you mention. We need to increase boost pressure through modified wastegate control (chip, EBC, MBC, etc) Then we need more fuel to match the air; that's where the larger injectors come in. Next, we need to modify the computer behavior to be aware of the potential for greater fuel and air requirements. The 3 Bar MAP sensor does this through crude approximation: it provides a signal to the computer saying the manifold pressure is approx 30% lower than reality. The 550cc injectors flow approximately 35% more fuel. It is very rough but it works to a point. We'd be much better with a well tuned chip. Also, since the MAP tells the computer the manifold pressure is lower than reality, the overboost protection does not get triggered.

Still, this is all very crude. A well set up reprogram of the computer to make full use of the 3 Bar MAP sensor and RC 550cc injectors is really what's needed. I started this thread in hopes that the intellectual challenge might entice Alan to pursue such a program. If the thread doesn't maybe access to a UK car with the changes done, a dyno and a promise of cash will do so.

[Elanlover]

Thanks Doug, this is kinda what I thought. I suppose there would be some benefit to a more "modern" ball bearing turbo with regard to spool times, etc. but I figured there had to be some other stuff required to make it all work and take advantage of the larger turbine. I'm not thrilled with the idea of "approximations" when it comes to fuel mixtures and all that. Just fearful of damaging the engine at some point. As you say, a properly programmed ESM chip would be ideal. Don't you think Alan?

I never thought to ask this question of LGM before but do you know how she's handling the larger turbo, fuel mixtures and overboost with the kit from her previous group buy? Is this what you have? Thanks!

[tigerdog]

If I recall, LGM uses a 3rd party Electronic Boost Control to regulate the wastegate. She may be using the stock computer but I remember at one time she was contemplating the switch to a Haltech programmable ECU. As I noted in my earlier post, the overboost protection is essentially negated by the 3 Bar MAP sensor.

[JIMBO]

Hi,
You guys seem to be on the button with your assasment of just fitting the larger turbo.
I am dissapointed with mine as it is, but I have a 3 bar map sensor to go in, and 550
injectors hopefully on their way.
Gerald at GSM who fitted my upgrade has mentioned the problem to a chap who does
mapping for a formula one team. However, I am not in a position financially to take
this further. Perhaps next year, unless Alan can work his magic
Regards
Jim

[tigerdog]

Yeah 2->3bar absolute = 1->2bar of boost. Actually some off boost cruising would be useful as well because it'll give me an idea of how much correction the ECU is having to put into the fuelling in closed loop operation.

Part throttle under partial boost may also merit some study. The attached scan shows some incidence of knock as the boost crept upwards during 20-25% throttle. Please note, this run was taken with only an MBC; the chip was not controlling the boost. It appears the computer tried to keep stochastic mixture as the boost came up, resulting in knocking. To those who have made the conversion AND are running a manual or external electronic boost control, please look for similar behavior. To me, this is just one more argument in favour of an electronically managed wastegate with a boost curve that increases proportionally to throttle position and RPM... in other words, the exact chip ESM may someday undertake.

Having driven the car with the stock chip managing the setup, max boost is 11-12 PSI. I find the car much more driveable with the stock chip - but 11 or 12 PSI just doesn't cut it, especially with the late onset of max boost in the stock setup. I really liked the way the Elans in the UK felt with their mountain chips while I was at the 60th. I shall just have to be patient and await the ideal mountain chip that will peak at 16-17 with our new turbos/MAP sensors/injectors, but with graduated boost curves like the Everest. Then I will

[ESM]

I've downloaded the logs now (sorry it took a while). I'll have a look...

[tigerdog]

It dawned on me the other day, the 3 Bar MAP sensor appears to defeat any semblance of overboost protection from our engines. Since the stock fuel cut occurs at a voltage deemed dangerous from a 2 Bar sensor, by the time that voltage is output from a 3 Bar sensor, our engines will have self destructed. If/when Alan is able to create a chip for our 3 Bar/550cc setups, one of the things we'll need to agree on is what level of protection is "sensible"? I'd vote for 1.3 Bar / 19 PSI. Long hours reading through posts from Costas, Dave M and others point to stock pistons being good only for about 18-18.5 PSI max boost. Let's use this thread to decide for ourselves what we would wish for in such a chip.

[GeoffSmith]

I don't think it's as bad as you think Doug.

Assume that the 2 bar MAP outputs Vmax/2 at 1 bar and Vmax at 2 bar.
The Everest fuel cutoff occurs at an overpressure of 0.98 bar which corresponds to 1.98/2×Vmax = 0.99×Vmax or 0.49×Vmax above ambient.
With the 3 bar sensor, the voltage corresponding to ambient pressure is Vmax/3, so fuel cutoff will be at (1/3+0.49)×Vmax = 0.823×Vmax.
This corresponds to an actual overpressure of [(1/3+0.49)×3-1] bar = 1.47bar.

[tigerdog]

Assume that the 2 bar MAP outputs Vmax/2 at 1 bar and Vmax at 2 bar.

Although the more I look, the more I question the accuracy of the chart above, it seems like 1 Bar doesn't happen at Vmax/2. If I'm reading the chart above correctly, the equivalent on a 3 Bar sensor is just above 2.2 Bar boost. And really, isn't the difference between 1.47 Bar and 2.2 Bar just in how spectacularly your engine blows up?

Robie the Robot (our Isuzu compatriot) includes a couple of charts on his page that bear up your assumption, including this one:

[tigerdog]

Looks like Alan is making a bit of progress. The topic is split among two topics, but let's try to focus development work here.

[tigerdog]

Found this link to a home-built MAP compensator. Amazingly simple in theory: replace the ECU's standard 5V supply to the MAP with an adjustable regulated supply. Decreasing the initial supply voltage creates a corresponding decrease in MAP output voltage, causing the computer to operate in a leaner part of the MAP table. Of course, there may also be lower and upper limits programmed into the tables that ignore manifold pressures below a certain level but we'll have to rely on Alan to ferret this out of the code.