Ford Power Stroke Nation banner
1 - 7 of 7 Posts

·
Registered
Joined
·
15 Posts
Discussion Starter · #1 ·
All I've found is the same shitty scan on every forum, so I'm working on plotting it and putting it into Excel for folks to use. I'll post it here when done. However, some of the numbers are illegible. Anybody know what they are supposed to be? The efficiency islands seem to mostly start with 7, and the "horizontal" shaft speed lines look like 46100, 50599, 84019, 96255, 105547, 113083, 120203, and 1XXXXX. Ha. Perhaps knowing a pattern would help. Should they be linear? Or logarithmic? Same for the efficiency percentages. Anybody more familiar with these charts to shed light?


Slope Map Rectangle Font Parallel
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #2 ·
I am confident in the data points themselves, but not the % or RPM labeling. Someone correct me if you know they're wrong. It wouldn't let me attach the *.XLS so I put the *.TXT containing the data points.

Rectangle Slope Triangle Line Font
 

Attachments

·
Registered
Joined
·
15 Posts
Discussion Starter · #3 ·
I've added plottable points to plan mods. Is there a way to post an excel sheet on this site, or is it not allowed?
Next task is to plot points from usage. I don't have a boost gage, and anyway I'm out of state for a while, so I can't drive my truck.
Anyone have data they'd like to share from? What RPM, boost, % throttle, situation, and tune, on a stock turbo?

Rectangle Slope Triangle Font Line
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #4 ·
Map vs RPM lines. So, it seems the turbo is struggling by 3000 RPM and dead after. Interesting. It also seems it holds efficiency the longest around 2300 RPM.
And, best efficiency at RPM and PSI range:
1000 65% 3 to 8
1200 69% 3 to 8
1400 72% 5 to 9
1600 74% 6 to 10
1800 76% 7 to 11
2000 76% 6 to 13
2200 76% 6 to 15
2400 76% 6 to 15
2600 76% 8 to 12
2800 75% 8 to 12
3000 72% 7 to 13
3200 68% 6 to 13
3400 <65% ANY

Slope Rectangle Triangle Font Parallel
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #5 ·
Actually, you know what? Those RPM lines make some assumptions that may not be very accurate. I'll have to look at the formula, but I believe it assumes that Volumetric Efficiency is constant at 90%. I will have to some more homework to find or make a graph of VE for the 7.3, and see how much that change affects the plot. It would also be neat to include temperature change, but that might be more complicated than necessary. Is 180*F a good estimate anyway, or is it too high?
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #6 ·
Well now I've myself all kinds of confused. 😕 This is supposed to be the factory turbo map, right? The rule of thumb is ~10hp per lb/min of MAF. So the factory rating of 215HP gives roughly 21 lb/min MAF. Garrett's website is a little more exact, and uses MAF=HP*AFR*BSFC/60 with diesel AFR=18.0 and diesel BSFC=0.36 which comes out to 23.22lbs/min. Either way, that puts the factory-tuned motor, running at full tilt, way to the low left of the center efficiency island. So at full tilt best case efficiency is at only 7psi and not even making the second island. And anything less than 170HP is barely spinning the turbo at all.

What am I missing here?? One step forward, two steps back...
 

·
Registered
Joined
·
15 Posts
Discussion Starter · #7 ·
Ah, OK! I forgot about something I discussed in a different thread on diesels: they have no air throttle! So the airflow to a N/A diesel would be a direct function of its RPM, though affected by changes in volumetric efficiency. So my RPM lines were accurate assuming constant VE. [I'm not sure about that, yet again.]

Well, that only made sense for a minute. So I can relate the RPM to airflow, but now I can't reconcile fuel consumption and power production with those two. The 1994 7.3 Power Stroke was rated 425 lb-ft @ 2000 RPM, which works out to [HP=TQ*RPM/5252] 162 HP, and of course that's with full throttle at that RPM. At that speed in 4th my truck is doing 52MPH, so imagine roaring up a steep grade with a heavy trailer with the pedal totally floored and it will go no faster.

If the turbo were disconnected, and assuming 80% VE at that RPM, the motor naturally pumps (444cuin/1728/2*2000*0.8=206CFM >> 206CFM*0.0709lb/[email protected]°F=) 14.6lb/min MAF. Using Garrett's suggested 18:1 AFR and 0.36 BSFC for 162 HP give (MAF=HP*AFR*BSFC/60 >> 162*18*0.36/60=) 17.5 MAF. The MAF ratio is (17.5/14.6=) 1.2, which is achieved by an absolute pressure ratio of the same amount, which assuming 14.7 ambient gives (1.2=[?+14.7]/14.7 >> 1.2*14.7-14.7=) 3 psi.

Really? Huh. I figured it would be more. Then again, for a given HP, MAF (boost) and AFR balance each other. As a general rule I've read 16- for max power, 18-19 for normal, 20+ for low EGT towing.

HP | AFR | MAF | MAFR | PSI
162 | 14:1 | 13.608 | 0.9337 | -0.9742
162 | 16:1 | 15.552 | 1.0671 | 0.9866
162 | 18:1 | 17.496 | 1.2005 | 2.9474
162 | 20:1 | 19.440 | 1.3339 | 4.9082
162 | 22:1 | 21.384 | 1.4673 | 6.8690
162 | 24:1 | 23.328 | 1.6007 | 8.8299

Well now I'm just confusing myself more. Hmm. Plus, the turbo here isn't externally controlled at all, it's output is a function of the engine exhaust, engine draw, and its turbine and compressor characteristics. Perhaps the way to look at it is that, for a given RPM the diesel engine's power output is predominantly dependent on the timing and amount of fuel injected, which is ultimately the only thing the computer decides. The turbo speed changes in response to the laws of physics, with the dominant factors being its design characteristics, the engine's exhaust flow. The resultant balance can be quantified by calculating the AFR, and there happen to be side effects to different balances of AF, the primary positive one being lower EGTs with higher AFR.

It's sort of a chicken-or-egg thing, I suppose.

Anyway, I'm still confused why the PS air requirements don't seem to match the turbo. Let's redo the MAF table above, but at full tilt:
1994 rated 210 HP @ 3000 RPM. At 80% VE N/A at that RPM, the motor pumps 21.86 lb/min.

HP | AFR | MAF | MAFR | PSI
210 | 14:1 | 17.640 | 0.8069 | -2.8382
210 | 16:1 | 20.160 | 0.9222 | -1.1437
210 | 18:1 | 22.680 | 1.0375 | 0.5508
210 | 20:1 | 25.200 | 1.1527 | 2.2454
210 | 22:1 | 27.720 | 1.2680 | 3.9399
210 | 24:1 | 30.240 | 1.3833 | 5.6344

These are all still stuck in the bottom left corner of the map, and it doesn't make any sense. I'm quite certain folks can get more than 8psi on a stock tune, with a stick turbo!

Wat am I doing wrong??
 
1 - 7 of 7 Posts
Top