Engine/Transmission (1998.5 - 2002) Max boost / stock turbo

[darkhorse]

I think the MAD will act as a boost fooler,



Yes, if that's a CaTcher program it does boost fooling.

 

[JesseJ]

I have question for the people out there smarter than I, so if I go to Colorado and am up in the mountains, should I be using my adjustable boost elbow to turn the boost down? How far should I turn it down to? It's set at about 32-33PSI and I'm at 1000ft. Elev.

 

[ERuhl]

NoSeeUm, thanks for the reply. I was beginning to think I was the only one interested in this. Fwiw the lb/min does get adjusted due to density changes with elevation, temperature, etc. If I understand this correctly, the author should have used . 076 lb/ft^3 instead of . 069 lb/ft^3 for the sea level calc (according to the US Standard Atmosphere).

Assuming the compressor map in the linked post is accurate, at 4000 ft elevation I calculate that 30 psi gauge pressure puts you right on the 144k rpm line at ~3000 rpm (~63% efficiency). At my 32psi setting I hit the 144k rpm line at ~2700 rpm (~66% efficiency), so it seems I'm OK as long as I stay below that "redline".

 

[NoSeeUm]

NoSeeUm, thanks for the reply. I was beginning to think I was the only one interested in this. Fwiw the lb/min does get adjusted due to density changes with elevation, temperature, etc. If I understand this correctly, the author should have used . 076 lb/ft^3 instead of . 069 lb/ft^3 for the sea level calc (according to the US Standard Atmosphere).

Yeah, take a look at that map. The sectional part with the horizontal line at the PR = 2. 3 - 2. 5 (20 psi boost sea level) is really fat and with the engine at the right rpm the efficientcy is very good. That is the sweet spot for that compressor. IMO it is pretty well matched for the ISB in stock and slightly modified form. Cooler lower boost would probably be better than higher hotter boost in allot of cases, but people always seem to want more boost.

Assuming the compressor map in the linked post is accurate, at 4000 ft elevation I calculate that 30 psi gauge pressure puts you right on the 144k rpm line at ~3000 rpm (~63% efficiency). At my 32psi setting I hit the 144k rpm line at ~2700 rpm (~66% efficiency), so it seems I'm OK as long as I stay below that "redline".

Case 1

85 Ambient

20 Boost

3000 RPM

70 CE

76 IE

49. 8 Lbs/Min

Sea Level

2. 4 PR

302 Tcompressor

137 Tmanifold

Denver

2. 6 PR

334 Tcompressor

145 Tmanifold



Case 2

85 Ambient

34 Boost

3000 RPM

62 CE

76 IE

75. 0 Lbs/Min

Sea Level

3. 3 PR

444 Tcompressor

171 Tmanifold

Denver

3. 8 PR

492 Tcompressor

183 Tmanifold



IIRC roughly 1 F change in Tmanifold = 1. 5 F change in EGT.



It also seems to me that allot of people worry about maximum boost with the HX35. Mostly because it is what they have and what they are running. I tended to worry more about maximum drive pressure. From my experientation, you could multiply the boost number times about 1. 9 to 2. 3 to get drive pressure for over much about 20 psi of boost. The drive pressure really seemed to rise quickly over 20 psi of boost. Up until 20 psi boost, multiply by about 1. 1 to 1. 3 to get drive pressure. Higher drive pressures also effect EGT's significantly.



In the end, find the right the lowest boost value that you can run at with the lowest EGT at the speed / rpm you like to tow. That is what I did until, testosterone made me lose all reason.



Jim

 

[ERuhl]

The numbers you post seem to indicate that 20 psi would be better than 34 psi due to the higher compressor efficiency and lower manifold temp? I can offer this bit of experience, when I had only the EZ installed I ran back and forth over the passes using both the stock elbow (~21psi) and Edge's elbow (~28psi). 28 psi worked MUCH better for controlling the egt's, in fact I couldn't get it over 1200 no matter what I did. At the stock 21 psi I was driving with one eye on the EGT and feathering the throttle. I broke the Edge elbow , otherwise I wouldn't have had the "opportunity" to even try towing with the EZ at stock boost.

After adding the sticks 28psi wasn't cutting it anymore (Edge sent me a new elbow), so I opened it up to 32 psi. I'd have to say the difference is negligible, maybe a smidge lower egt's.

At 2200 rpm the compressor efficiency nearly tracks right along the 74% line as boost changes from 21psi to 34psi. Similarly 2400 rpm is right in the middle of the 74%-76% curves across that entire boost range. 2600 rpm on up seems to be where the efficiencies really take a hit with increased boost. This is at 5280' btw. If I drop it to sea level then the efficiency hit kicks in around 2400 rpm. The next time I'm towing I'll pay closer attention to what rpm range I'm in, but I'm pretty sure I'm around 2200-2400.

I plugged all of this into an excel sheet and digitized the HX35 compressor map, otherwise this would be a real pain to plot out one point at a time by hand.

 

[NoSeeUm]

Part of what not really explained on a compressor map is what the EGT will be @ XX Hp. A huge factor for control EGT's is "excess air". Consider it requires the same Hp to pull your trailer up a given hill at a given speed. Now consider if fuel = Hp, or pretty close. At 28 psi of boost your combustion runs leaner IE more excess air. The break over in EGT occurs, (the magical 34 psi number) when the intake air temperature gets too hot. This is caused by running the compressor off its efficientcy map (and overspeeding it)



But yeah, that is why the aftermarket for turbo's is alive and well. They allow the user to run higher boost at a better compressor efficientcy.



FWIW the HX35 does pretty well in my experience.



Jim

 

[NoSeeUm]

I plugged all of this into an excel sheet and digitized the HX35 compressor map, otherwise this would be a real pain to plot out one point at a time by hand.

Nice! My spreadsheet just crunches the numbers via some Ideal Gas Laws and constants that I have no clue as too the origination. Can you calculate turbo rpm?



Looks like you were editing, as I was typing and eating.....



Jim

 

[ERuhl]

Overspeeding it was my initial concern, but after playing around with this now I see the rpm/boost areas where the efficiency really takes a dive. If I run 34 psi up here I'll be over speeding it at 2400 rpm. That's here on the "flat land", if I run up to 10,000' or so over the passes then it looks like 32psi is too much. 30 psi puts it right on that 144k rpm line.

 

[NoSeeUm]

The numbers you post seem to indicate that 20 psi would be better than 34 psi due to the higher compressor efficiency and lower manifold temp?

Look at the Lbs/Min, it is half again as much at 30 psi.



The whole symphony is a balancing act anyways.....



Jim

 

[ERuhl]

Can you calculate turbo rpm?

No, I just plot the data points right on the compressor map. I can specify boost per rpm and specify the elevation. It uses a curve-fit of the US Standard Atmosphere to get the density at altitude. I attached a sample (compare to the labeled version in the link), the data points are 1000-3000 rpm in 200 rpm increments, 5280' elevation, ramping up to 32 psi by 1800 rpm (a guess). This plot shows me hitting the 144k rpm line at about 2600 rpm.

 

[ERuhl]

Here's another one, again at 5280' elevation. This is at a fixed 2400 rpm, but varying the boost from 14psi to 34 psi in 2psi increments. It follows right along the ~75% efficiency line as I mentioned above.

 

[NoSeeUm]

Very Nice!



The inner island is what, 75% efficientcy? Notice how large it is both in width and length. Pretty good compressor matched for the ISB.



Your first chart shows some interesting data points.



Anything to the left of the surge line is trouble. I ran (or tried to run) my Dodgezilla there, and it hated life. You are likely not running there at all. Or you would hear allot of barking, snorting and / or complaining.



Anything to the right of the maximum rpm line, is well, into the grenade zone. I doubt you are running there very much either. Particularly the upper right portion where your data points are.



The second chart is what I came up with when I started looking at compressor maps myself. Basically, boost (PR) slides up as you have illustraded. But it slides up with increasing engine rpm (lbs/min) / boost and would be more of a curve near the bottom.



In theory, if the turbo is matched to the engine then the angle of the surge line mimics the angle that the data points slide up at. Continueing, then the data points flatten out and follow a rpm line horizontally but do not extend past the maximum rpm line at the right. This is when the wastegate opens and boost pressure stablizes.



Ideally, this vertical angle slide occurs within one of the higher efficientcy islands on the map and the horizontal flat line slides back and forth across the fat section of the same island.



Jim

 

[ERuhl]

Your first chart shows some interesting data points.



Anything to the left of the surge line is trouble. I ran (or tried to run) my Dodgezilla there, and it hated life. You are likely not running there at all. Or you would hear allot of barking, snorting and / or complaining.

Agreed, it's probably not running there as I don't have any of those issues. I keep forgetting to see what the boost is at those rpms so I can map the actual points. Consider those placeholders

The second chart is what I came up with when I started looking at compressor maps myself. Basically, boost (PR) slides up as you have illustraded. But it slides up with increasing engine rpm (lbs/min) / boost and would be more of a curve near the bottom.

I'll overlay a few different rpms and see what it does.



I was hoping for a broader availability of compressor maps, but so far I've been a bit disappointed in what's out there. If the turbo suppliers don't share compressor maps, then it seems this exercise is limited only to the HX35, and even that map is questionable (unknown source, not from Holset). It's a fun exercise though

 

[NoSeeUm]

I was hoping for a broader availability of compressor maps, but so far I've been a bit disappointed in what's out there. If the turbo suppliers don't share compressor maps, then it seems this exercise is limited only to the HX35, and even that map is questionable (unknown source, not from Holset). It's a fun exercise though

First thing I discovered as well. It seems that Garret and Turbonetics are more open with their maps than most others. The rest seems like a who knows who sort of deal as far as getting reliable maps.



I think that you can also over analyse the problem as well. There are many tried and true combonations. If I were to rewind about 1. 5 years I would study those options more closely than simply trying to figure it all out for myself.



But, thats what happens when one has a greater abundance of time than money... .



Jim