Playing around with the 2.7 software (ECU and TCU)

[RTB]

Originally Posted by Adrian D

Hah, I'll visit a friend and get his ECU binary and compare

Do you know someone with a Black Pearl? I read there were only 75 made in the CRD. 145 all up including the V8.

[RTB]

Teach a man to fish hey.

Went to another website with a full calculator. Not relying on my dodgy maths skills in Excel.

https://www.boosttown.com/forced_ind...calculator.php

All looks good though.

2100 rpm on a 2.7 with 1.5 bar gauge = 14.8 lbs/min

3800 rpm on a 2.7 with 1.5 bar gauge = 26.9 lbs/min

That can be a baseline for that RPM range and I will crunch more numbers to work out the ramp up and ramp down pressures and IQ's.

Here's hoping that turbo flow map is the right one.

[JeanLuke]

Originally Posted by RTB

Can someone please check my calcs here.

...

On the low side, a minimum airflow of 14 ibs/min is required to avoid surge. (With a little margin)

I think your 14 lbs/min is a tad low. 15 lbs/min looks better. The issue is that at a pressure ratio of 2.5 and 14 lbs/min you are in the region where the flow curve intersects the 2.5 line twice (it curls over at lower flows). This is what causes flow surge. [EDIT - very badly drawn markup of flow chart attached, but good enough to give you the idea.]

I have not checked your maths yet - just eyeballing the flow chart.

https://www.ausjeepoffroad.com/forum...1&d=1649894059

[RTB]

I've purposely kept away from the surge line running vertically down the left. That's why 14 was the min. 2100 RPM has me at 14.8, so pretty happy with that. Efficiency is reasonable, and the rotor speed is still good. 3800 RPM keeps me below choke, slightly less efficient, and nearing top rotor speed. All good though. Time spent at 3800 is minimal, and I will be focusing on never having to rev this high anyway. Nothing is outside the map though. I'm also happy to back out boost and IQ above 3500 RPM as I really don't like reving this high.

Normal cruise will be very different.

You've mentioned that the speed line you have drawn will put me near surge? I'm not sure I understand. The surge line is on the left. I can't see how I am getting anywhere near it if I keep the pressure ratio at 2.5 from 2100 RPM to 3800 RPM (14.8 to 26.9 lbs/min). I've never known the speed lines to be anything other than information on these maps. I'm not questioning it, just never known the speed line to be a concern. I might need to go through my old stuff and find out the effect of speed line profile on surge when not near the surge line. I've also sent the question to Garrett. Hopefully they can answer even though I'm not paying them for their time.

Below 14.8 lbs/min (2100 RPM) I will drop both the boost pressure and IQ so that my AFR says happy, and I keep away from the surge line. Just haven't done that part yet. The red boxes I have drawn are just to link the PR with just the 2 flow points.

[JeanLuke]

I'll have another go at explaining it. I did such a crap job before...

To hit 14lbs/min @ 2.5 pressure ratio, the turbo needs to run at around 150000rpm (blue line on the flow chart). However, at a pressure ratio of 2.5 and 150000rpm, there are two valid flows - 14lbs/min and 17lbs/min (the two green circles). This is classic pump instability - when there are two valid flows under a given set of conditions. This is avoided if you stay to the right of the added black line. It's only a sliver of area, but my advice is to stay to the right of it.

https://www.ausjeepoffroad.com/forum...1&d=1649902879

There are a few additional things that I suspect have not been considered:

1. The MAP is at the manifold while the flow chart is at the compressor. There are losses between the manifold and compressor meaning the compressor discharge pressure will be higher than the MAP sensor reads.
2. Atmosphere is near enough to 1bar at sea level. At 1000m it is 0.9bar, which means to get 2.5 bar MAP the pressure ratio becomes more like 2.8 (plus the aforementioned losses). There are plenty of places in Australia >1000m altitude.

[JeanLuke]

oooh (again!) Just got the notification that a package has arrived. That's my Easter cooked!

[Adrian D]

Originally Posted by RTB

Do you know someone with a Black Pearl? I read there were only 75 made in the CRD. 145 all up including the V8.

There's one local, I borrowed wheels from him at some point, I'll ring him up to see when we could meet

I never knew the Black Pearl had more power.