Have any of you documented the boost pressure drop from the turbo outlet to the plenum inlets under typical WOT conditions? There has to be some drop, or the air wouldn't move, but is it 0.5psi? 5psi? Something else?

I'm asking because I've been disappointed with my MST's performance, and many of you have helped me with that in my "down on power Excursion" thread. Perhaps I shouldn't be, though, as part of my spring-turned-to-summer-then-fall project was to replace my old Western Diesel gauges with Isspro ones, and as part of that I moved the sensor from the driver's side of the spider, right off the turbo outlet, to the more commonly used AIH port. I'm now topping out at 25-26psi, whereas I remember hitting 30 occasionally under my old setup. (Alas, I never logged boost, or even MAP, before, so I'm having to go off memory.) Those numbers really aren't comparable, though, unless the pressure drop between sensor locations is known. Before I test it, I thought I'd ask if any of you have.

The easiest way to test would be to look at the Isspro gauge during a boost leak test, but I think that would under-report the difference. While air does flow, through valve seals and by piston rings, that has to be a lot more restrictive than eight gulping cylinders, and that extra restriction would tend to equalize the pressures. Apart from having dual gauges, I think the best I could do would be to move the sensor back to the old location, and plug the AIH port, and make test runs like I have been.

Mark

 

I have not tried to compare pre and post IC boost readings, but in the thread below, CSIPSD mentions we'll see a 3-5psi difference in locations - higher readings at the turbo outlet.

https://www.ford-trucks.com/forums/1...l#post12318632


@Tugly did you ever try a boost reading comparison on Stinky by moving your sensor and AIH plug per this thread below?

https://www.ford-trucks.com/forums/1...on-better.html

Wondering what difference you measured on that rig.

 

My opinion is you will not see the drop during a boost leak test. This is a (nearly) static condition.

The boost drop should occur during high flow times as I believe the drop will be due to some flow restrictions within the intercooler.

 

I have done pre and post cooler boost sensors, always with less then 1 psi difference between the two

 

That is exactly the info I was looking for, but couldn't find. Thank you!!! More on why this matters to me, below.

Yeah, that's what I was thinking. There doesn't need to be a restriction for there to be a drop, though. Think about a straw: The pressure is less at the top, where your mouth is, than at the bottom, with essentially no restriction (other than surface tension, and gravity). If you equalize the pressure (after accounting for gravity), the liquid will stop moving, appearing to be suspended in the straw. If gravity goofs up the analogy, think about an astronaut "drinking" his Tang. (Yes, I grew up in the '60's.) The same logic applies, he just has to use less of a pressure difference to move the Tang from its container to his mouth.

Why does this info matter to me? Two reasons: First, as many of you know, I chased my tail for months, and burnt time some of you will never get back, trying to replicate what I used to see when I first installed the ported housing wheel years ago. The "only" change I made was that I installed KC's turbine upgrade, but it didn't seem right that it decreased turbo performance. Thanks to Charlie, and several of you, I did find some entirely self-inflicted problems that, when fixed, got me to the aforementioned 25-26psi, but not to the 29-30psi I saw before. It finally occurred to me the other night that, while I knew intuitively that there would be some pressure drop seen between my former and current sensor locations, that difference was not negligible, as I'd assumed. Joe's 3-5psi number puts me right back where I remembered the turbo being, which tells me I've gotten all there is give from an MST with my setup and conditions. (e.g. altitude) Do you guys agree??? (I've clearly gotten in trouble with assumptions before...)

So what? Well that brings me to the second, and more important, reason I asked the question. I'm thinking of moving away from the MST, likely to a KC Stage 1. All I'm really after is lower EGT's, that'll let me tow with a 60ish HP tune up our Colorado passes. Knowing that I'm getting all there is out of what I have makes me a little more likely to fire the rather large caliber Buck$ooka round it'll take to get one of those under the dash.

Some of you will suggest a tuning change, and I'm working on that. (Hydra sitting next to me right now, and tunes in my inbox.) I just have this feeling I'm going to be disappointed...

I have a couple of small quibbles with something Joe said in his very informative post. First, I think there is a "right" and "wrong" place for the boost sensor to go, and that is as close to the MAP sensor as possible. (Like the AIH port.) Unless one is in the business of testing turbo output, the "close to the turbo" location I used to use, and Joe illustrated, results in a "vanity" number. Yes, it's high, but you'll never get the benefit of it, and using it as a reference can skew expectations. It's kind of like your 401k balance: You may own it all, but you'll never see it all. Uncle Sam will take his cut, and he'll let you know what that is later. Thinking in terms what you can actually use leads to better decisions, both about money and boost, IMHO.

Second, I don't think "anything above 30psi doesn't do you any good, it's just superheated air" is true, at least in the absolute sense. It may be true of the stock turbo, but the "superheated air" is seen on the turbine side, in the form of high drive pressures and EGT's, with no corresponding increase in boost past 30psi, or so. If I spend the money on a turbo, it's because I'm expecting a little more usable (read "at the MAP sensor") boost than I see today, with a little less heat on the turbine side than I see today. In other words, a more efficient turbo than what I have. Am I thinking about his correctly?

Please, if any of you take issue with my assumptions or new-turbo-justification logic, tell me now! Black Friday is coming, and I'll need to make a decision while tempted by a sale price I hope to find. Clarity of mind is of the essence.

Mark

 

Ummm, that's interesting, and confusing to me, given the posts above. When you say "pre and post cooler", were the sensors in the common locations - right off the turbo for pre, and AIH port for post?

Your experience is valuable to me, and making me think I should test this for myself, particularly before spending money. Thanks!!

Mark

 

My take is boost is best measured from the AIH port. Firstly because that is closest place you can measure what the cylinders are actually getting. Secondly because it's super simple and convenient and the commonality removes all question of location bias. Well maybe that's a few reasons, not just second.

Bias can also come from the sensors and gauges. The things we use for this ain't precise. That would cost real money, and be a waste. So a bit of slop is to be expected in boost readings.

On the turbo question you want max CFM in the RPM range you will be using to blow up the fuel. So tunes play as much a role as turbo. More CFM is always good. Does not necessarily correspond to boost psi, but boost a simple easy way to know you are getting more air in your specific configuration.

 

I had a sensor in the tapped port in a 364.5 compressor housing, annd one in the csd intake y. So pre and post charge air cooler, the factor that affects the boost psi recorded is not restriction, but more due to thermal dynamics, as the air cools through the cooler it compresses more efficiently.
In my mind it is a waste of time to worry about or test any more. Basically stick the boost sensor in the most convenient location, or the best looking location and monitor your boost to aquire a baseline, and then from there just as a way to know if something has changed.
Remember, more boost is not always better, efficient boost is. We should strive to get fast spool and move the needed air, while having the lowest max boost needed, aka, properly sized turbo that spools and drives to match the rest of the trucks configuration, drivers driving habits, and the use/location of it.

 

You mentioned super heated air. This is not just related to the exhaust side. Compressing the charge causes heat. At some point you could get far enough outside of the turbo map to have diminishing returns. Basically creating more heat than added “boost”. This is probably why he referenced 30psi as a limit.

Eric, good point about the cooled charge impacting pressure drop.

To go along with those thoughts…
I did not read the CSIPSD thread but am going to assume he was using a stock(ish) turbo. Eric’s sensor location testing was with the SXE which is much more efficient. So turbo outlet was probably not as hot therefore may have less cooling and drop across the intercooler compared to the stock turbo.

 

Thanks guys. I swapped the locations this morning before heading to the gym. 26psi in a place in the road and tune where 22-23 is the best I saw before. Faster spool, too, though that is also an illusion. Will try to test more later.

Mark

 

Was the outside air cooler amd/or moister?

 

I think that's it - there will be more of a temperature differential across the IC with the stock turbo creating more heat - that turbo being a less efficient design, especially at higher boost numbers.

I had the boost sensor on the spider at the turbo outlet on my previous truck, and remember hitting 30psi easily with DP tunes, and an ATS housing.




I'm not close to hitting that now it appears, based on the MAP sensor numbers. Granted, MGP is limited to 25psi due to the sensor, but I can see the boost leveling out as it hits the sensor limit - it's not going much further.

Will get a boost gauge installed soon to confirm my numbers, but it sure looks like Mark is seeing this same 3-5psi difference based on sensor location, and his boost is actually pretty good for an MST at high altitude.

 

The efficiency discussion is important to me, so I'll come back to it in a second. Meanwhile, I was able to make a short test run in my hottest tune (DP 80h), on a ramp I've used to use for this purpose over the years. It's a little lower, at about 5400-5500ft, than I see closer to home. Anyway, it hit 28psi on the gauge, which is about as good as I could consistently see before. I rolled into it to avoid smoke, and that seems to limit the boost peak I see in 2nd gear, and I couldn't stay in it long enough to see a peak in 3rd. The net of this is that I'm thinking my turbo is performing as good as it ever has. I logged the run, as well, and saw a 26psi peak MAP where I saw 28 on the gauge. Like Jeff's, it was flattening, so there wasn't much there past the sensor limit, if I even hit it.

When the sensor was in the AIH location, it tracked MAP almost perfectly, as nearly as I could ever tell. That tells me that, at least in my application and environment, the 3-5psi number isn't far off. Five seems a bit of a stretch, but three seems pretty likely. That's important, because if I add 3 to the 25psi I saw in my tow tune last week, that would match the best I'd ever seen in that tune, no matter where the sensor was placed. That's a big deal, because it screams to me, "Mark, stop working on this thing unless you want to really change things, as it's performing as good as it's going to."

So, to the efficiency discussion. I'm considering a stage 1 drop in, largely so I can easily swap back to something that says Garrett on the side if things here in Colorado continue as I expect them to. Is that likely to get me an efficiency bump large enough to matter when towing, and to justify the expense? If not, is the limitation something about the stock plumbing, and would a two-piece spider like is common in the T4 world make a difference? Or do I just need to bite the bullet and go T4 if I'm going to do anything? My current setup isn't bad, but I've wished for a little more in the dozens of times I've towed my 4Runner over the hill to Moab in the last 18 years. If I'm going to get a little more, now is the time.

Thanks for your input!!

Mark

 

In all honesty, I think you have it set up well and it sounds like you are getting good performance.
If you are above 5,000' elevation towing, I would stay with what you have, (assuming stock injectors?) I believe the kc stage 1 may not light as good as you would desire, your gains with the stage would be above 2700rpms.
When towing how are your egts?

 

Thanks Eric. EGT's are the issue. They are generally manageable, but there are a couple of non-optional passes (Vail Pass WB and the WB climb to the tunnels, both on I70), where it's really tough to stay under 1250. The Isspro alarm helps, because without that I could hit 1400+ if I wasn't watching. By the time I climb the 3000ft in eight minutes to the tunnel at 11k+ feet, I'm barely into the pedal, at a point where traffic converges from three lanes to two. Not the most comfortable situation.

Yes on stock injectors. The most I'd ever likely do would be 160/30's, or I may take a page from your book and do AD30's, or Matt's hybrid split-shots. My current ones seem fine at 172K, so it's hard to justify spending that kind of money if nothing is broken. At least I could sell my MST upgrade parts if I bought a turbo, but core charges don't make that possible with injectors.

Mark