Is all boost created equal?

[Ondonti]

sounds like with that turbo your tune is crap.
turbos are not created equal so the tunes cant be equal.

[turbovanman²]

Who's running 1/4" piping? That seems a little small....I'm confused now.

Thats the new standard, didn't you know???? All the fast guys are using 1/4" pipe, no LAG,

[Vigo]

i havent looked at the maps but it is possible that the current turbo is far LESS adiabatically efficient at the given pressure ratio than a mitsu would be, and that would affect power, BUT, 15 psi should be able to spin the tires from a brake boost launch no matter what. Something else is going on.

Especially with your cam advanced on a stockish 2.5, you should be making a LOT of torque on 15psi at low rpms. It could be that your cam gear is one tooth retarded, and since its set 4* advanced its effectively only 5* retarded instead of the 9* (not sure of the exact number) it would normally be, leaving you just enough driveability to think the cam isnt off. Just a thought.

Either way, that turbo is just too darn big for a stockish motor in a heavy van with an auto.

[BadAssPerformance]

After being convinced that the turbo on my mini is too big, I have a question: is 10 psi from a T3/T4 .57 trim the same as 10 psi from a Garrett TII turbo? I mean, is the same amount of cfm getting into the chamber?
I understand (now, anyways) that the .57 trim is not the best turbo for an 8-valve. But what I can't understand is why at 15 psi with a Mitsu turbo (stock) the mini pulled pretty well, but with this .57 trim at 15 psi it feels like an n/a. It seems to me like the cfm would have to be the same in that both compressors are feeding enough air to creat 15 psi of back pressure. Is this right?
What am I missing? Keep in mind that I am not a turbo guru, which is why I am asking. I am reading "Maximum Boost" for the third time and get a little bit more each time I read, so don't flame me. I just need to know why! This turbo came off of my Miata, and it dyno's 263 rwhp at 19 psi. Granted, it took a while to spool, but when it did it pulled like a madman. I took it off of the Miata with about 5000 miles on it, and I put it on the van. But this van ain't pullin' at all (well, very slightly).
How are the boost levels different? Thanks!

-Les

This is an easier way to understand. Ok, lets say you have a 1/4" pipe, this the garrett, so with the tap fully open, its coming out fast and with some high pressure, now change to a 2" pipe, tap fully open, what happens, you have the same amount of water but its not coming out very fast and volume is lower. Now if you put a pump inline and try again, the 1/4" will be busting at the seams and you'll strain or damage the pump, but with the 2" pipe, its all good now, Make sense?

Building on Simons piping example... think of the same amount of water coming out as CFM of airflow, so with the larger pipe, at the same CFM, the exit pressure is much lower than the smaller pipe... a larger turbo will flow more cfm at lower pressure.

OK, now before we lynch the turbo, look at your supporting mods. What do you have on it for a head, valves, cam, etc? A stock or poor flowing head will work better with a smaller turbo running the same CFM at a much higher psi pressure...

So the moral of the story and solution to most problems.. it needs Head!

[pauly_no_van]

Some good reading here, thanks!
I'm hoping you vets have more to contribute and hopefully help with this thread making us rookies a little smarter...

Does anybody know where this compressor stands with regard to the 2.5?
I run it in my van but it doesn't seem to get happy til 14 15 psi, same issue as above.
I am waiting for a sbec adapter to start running tunes/3bar/+20's.

Side by side wheels t2 and t4...

Its part of my t3/t4 hybrid.

paul

[mcglsr2]

Building on Simons piping example... think of the same amount of water coming out as CFM of airflow, so with the larger pipe, at the same CFM, the exit pressure is much lower than the smaller pipe... a larger turbo will flow more cfm at lower pressure.

OK, now before we lynch the turbo, look at your supporting mods. What do you have on it for a head, valves, cam, etc? A stock or poor flowing head will work better with a smaller turbo running the same CFM at a much higher psi pressure...

So the moral of the story and solution to most problems.. it needs Head!

increasing the size of the head (thereby increasing engine flow) is equivalent to increasing the size of the pipe in the example given by simon.

[BadAssPerformance]

increasing the size of the head (thereby increasing engine flow) is equivalent to increasing the size of the pipe in the example given by simon.

Right, and the point is that the 2" pipe cannot flow into the 1/4" well at the same pressure...

Some good reading here, thanks!
I'm hoping you vets have more to contribute and hopefully help with this thread making us rookies a little smarter...

Does anybody know where this compressor stands with regard to the 2.5?
I run it in my van but it doesn't seem to get happy til 14 15 psi, same issue as above.
I am waiting for a sbec adapter to start running tunes/3bar/+20's.
....
paul

Same question for you... a bigger turbo wont be able to help without the supporting mods.

[tkelly27]

Something else is wrong. Even if it is way off it's efficiency map http://www.turbocharged.com/catalog/compmaps/fig15.html which it shouldn't be any worse than the mitsu at 15psi, if it's making 15psi it should still be able to get out of it's own way.

I would check cam timing, spark timing, and boost leaks. All you did was change out turbos, or did you change anything else?

[BadAssPerformance]

Good point, once it gets to 15psi it should still run better than the mitsu at 15psi, way better, even with a stock head, unless there is an improper amount of fuel or something changed like tkelly27 said...

Btw, welcome to the forum tkelly27

[Frank]

i have some thoughts on your question. i have read that book (and severl others) quite a few times, and here is my understanding of things. bear in mind that i could be completely wrong WARNING, long post...



essentially yes. we are talking about flow vs. pressure ratio (10psi). thinking that different turbos produce different cfms at the same boost is a misconception IMO (unless i am way off on my thinking - if so please correct me!). to see that the flow is the same, just look at the two compressor maps. here's an exercise: using Frank's turbo calc, put in some data points for your car (values don't really matter). adjust the HP until the calc tells you you need 10psi. then select some different turbos, like the 40, 46, 57 and 60 (under the T04E Series). take a look at the first 1.68 (10psi) point in each map, then look down at the airflow. this is the amount of cfm (in lbs/min) that the turbo will flow. notice for each turbo, that point is at the same cfm. thus different turbos will (roughly) produce the same cfm at a given pressure ratio.



okay, so if 10psi = 10psi, why do some turbos pull better or produce more power? the reason is because of the adiabatic efficiency of the the turbo at a specific pressure ratio (PR) and the RPMs of the shaft. if you look back at those maps, you'll notice that the efficiency "islands" shift around the points. if a point on one turbo is lower in efficiency then the same point on another turbo, the first turbo will heat up the charge more then the second. and heat = less dense charge = less fuel that can be injected = less power. essentially, a smaller turbo operating in it's peak efficiency range will produce MORE power then a larger turbo operating way outside it's peak efficiency range at a given PR. this is because the larger turbo is heating the charge more as it compresses the air.

also, you have to take the shaft speed into account. in order for a turbo to produce the desired PR (1.68, 10psi), the compressor and turbine must be spinning at a certain RPM. exhaust is what gets this shaft spinning. larger turbos [in general] don't need to spin as fast to produce the desired PR. so why doesn't my larger turbo produce boost faster then, since it can spin SLOWER and make the same PR!? the reason is because the weight of the compressor wheel is a lot heavier then that of a smaller wheel, which means it takes more exhaust energy to get it spinning. so even though the larger turbo can spin slower, it takes LONGER to get to that slower speed then it does for a smaller turbo. this why BB turbos are great - they can have the benefit of the larger compressor wheel (and slower shaft speed), but since the resistance to get the compressor wheel spinning is lower (thanks to the ball bearings), it can spool faster and create boost sooner.

so, given the above, the reason you feel a difference is that the mitsu is small, so therefore it doesn't take long to produce boost. so, based off the seat-of-the-pants feel, it feels like it pulls hard. cause your butt tells you so. the larger turbo, though, takes a lot longer to produce the same boost (because of the compressor wheel weight). so boost onset is more gradual, and your butt-o-meter says i'm not accelerating as much. question: are your above statements based off seat-of-the-pants feel, or your took the car to a dyno or drag stip? also, you will get max boost on the mitsu SOONER in the rpm range then the larger turbo. this is where your engine/cam come into play. if you make most of your power/torque lower in the rpm range, the mitsu which gives you max boost sooner, will have a larger affect on overall performance (because it's boosting more power under the curve), whereas the larger turbo reaches max boost later on in the range, quite possibly where your engine is running out of breath - thus no power for the turbo to boost. this is why OEMs typically use smaller turbos on stock street-driven cars, because the cars spend most of their life at lower RPMs and it gives a more "peppy, i have crap loads of power" feel (and then falls on it's face at higher RPMs).

in summary: 10psi=10psi at roughly the same flow, but that does NOT equal the same power (due to charge air temp, density ratio, etc). a larger turbo will require more exhaust engery to get going, and thusly will require more time (or more flow) to get going.

all of this is why proper turbo-sizing is important.

thoughts everyone? i hope this helps...assuming i'm not completely wrong. do you guys think i am way off here?

I read through the thread skipping your post because it was long. I was frustrated at the examples, because they were flawed. I then I came back to this post and was very happy... very awesome explanation of how it works!

[mcglsr2]

I read through the thread skipping your post because it was long. I was frustrated at the examples, because they were flawed. I then I came back to this post and was very happy... very awesome explanation of how it works!

thanks! i think it's right fastasleep asked a very good question and my initial reaction to does 10psi = 10psi was no. i searched the web and found a few forums where people there confirmed that initial reaction. but the more i thought about it, the more i thought that 10psi DOES equal 10psi. the limiting factor (for the most part) here is the ENGINE, not the turbo. the engine will flow a fixed amount (without upgrading it like a ported head) so therefore it has to be a fixed variable. since PR is fixed and flow is fixed (after all, that's how a compressor map is used), then the turbos have to produce boost at the same CFM (for that specific engine).

and sorry about the long post, i just didn't know any way to say it shorter and still get the concept across.

EDIT: there IS a time when 10psi does NOT equal 10psi on the same turbo - that's when comparing two different engines. a super60, running at 10psi of boost, will flow X cfm on a 2.2, but on a 3.0 it will flow Y. i don't know what the numbers X and Y are off the top of my head - what matters is that they are different (and therefore different HP).

[Frank]

thanks! i think it's right fastasleep asked a very good question and my initial reaction to does 10psi = 10psi was no. i searched the web and found a few forums where people there confirmed that initial reaction. but the more i thought about it, the more i thought that 10psi DOES equal 10psi. the limiting factor (for the most part) here is the ENGINE, not the turbo. the engine will flow a fixed amount (without upgrading it like a ported head) so therefore it has to be a fixed variable. since PR is fixed and flow is fixed (after all, that's how a compressor map is used), then the turbos have to produce boost at the same CFM (for that specific engine).

and sorry about the long post, i just didn't know any way to say it shorter and still get the concept across.

EDIT: there IS a time when 10psi does NOT equal 10psi on the same turbo - that's when comparing two different engines. a super60, running at 10psi of boost, will flow X cfm on a 2.2, but on a 3.0 it will flow Y. i don't know what the numbers X and Y are off the top of my head - what matters is that they are different (and therefore different HP).

Exactly why I created the v3 of my turbocalculator. It just doesn't cut it when you don't start from HP and work backwards - temperature and BFSC are key!

[fastasleep]

If I have 155-150-152-155 psi for compression for 1-4, wouldn't this mean that my cam is pretty close?
Also, I have a ported head with a fresh valve job, ported 1-piece, and ported stock exhaust mani. But no, the van won't turn tires at 15 psi.

-Les

[turbovanman²]

Some good reading here, thanks!
I'm hoping you vets have more to contribute and hopefully help with this thread making us rookies a little smarter...

Does anybody know where this compressor stands with regard to the 2.5?
I run it in my van but it doesn't seem to get happy til 14 15 psi, same issue as above.
I am waiting for a sbec adapter to start running tunes/3bar/+20's.

Side by side wheels t2 and t4...

Its part of my t3/t4 hybrid.

paul

Measure the wheel larger and smallest diameters. It looks like a 50 trim in a T4 housing, so that makes total sense why it come alive at 15 psi.

If I have 155-150-152-155 psi for compression for 1-4, wouldn't this mean that my cam is pretty close?
Also, I have a ported head with a fresh valve job, ported 1-piece, and ported stock exhaust mani. But no, the van won't turn tires at 15 psi.

-Les

Yes, 150 is perfect. I find a neat way of getting the best low end performance. Advance/retard the cam for highest cranking compression, disconnect HEP connectors so you don't spray fuel and affect the readings.

Brake torque the van, what rpm can you reach? sounds like you might have a dead TC.

Can you build boost and spin the tires???? Remember if the turbo is laggy, it won't spin the tires off the line unless you leave with boost,

[fastasleep]

I advanced and retarded the cam a tooth either way tonight. With the thing retarded one tooth from where I had it, vacuum dropped by 4 inches and compression went down. But, when I advanced, the compression came up to 160-155-160-160 roughly, but it didn't run as well; the vacuum at idle went to about 18 inches. When I put it back, the vacuum went back to 19 inches at idle. I thought if cranking compression went up, vacuum would increase as well.
Yes, I can brake torque it until I have 15 psi boost, but it still will not spin tires. I could probably hold it past that, but I don't because I know that has to be heating the trans fluid terribly. I don't know yet where my RPM's are, but I was suspecting my torque converter as well too. I need to install my tach.
How do I check to see if my TC sucks besides just brake torqueing the hell out of it?

-Les

[fastasleep]

Yeah, the thing starts to pull but then once it gets up to about 10 or so psi it lays over. Any more thoughts?

-Les

[mcglsr2]

Exactly why I created the v3 of my turbocalculator. It just doesn't cut it when you don't start from HP and work backwards - temperature and BFSC are key!

agreed. and it's a great program

[boost geek]

I had a stock T2 Garrett on my car, ported everything, 2.2, 2 1/4" swing valve, 3" FM downpipe, 3" to the dump, then 2 1/2" out the muffler. Car felt crazy, would hit 20 psi no problem, and shred the tires.
Now I have a Super70, stock housing, .63 exhaust scroll, and a TU 2 1/2 s.v.. The car feels like a slug, wont give me 20 psi anymore, UNLESS I remove my cap, and run straight 3". THEN the car acts like an animal again, this larger turbo seems sensitive to exhaust back pressure, where the stock Garrett wasn't affected.
What size exhaust are you running?

[bakes]

Is the trans starting off in 2nd gear , I have seen the gov stick and not alow 1st at a stop.

[fastasleep]

The trans. is starting in first. I can manually shift it and it does the same thing. My exhaust consists of a 2.5" swingvalve, followed by a 2.5" to 3" adapter to a 3" 90* and then it goes right out from under the body right behind the front passenger's side tire. The whole thing stretched out is < 40 inches long.
But thanks for your consideration!

-Les