How do you read a compressor map?

[Frank]

opps... forgot to attach map.


my avatar is not working.

[4sfed4]

Quote:

Originally posted by TrboVan Boost will spike about 2 psi when power hits, then settle and hold a steady 34 psi.

Ok......well that means that you are nowhere near the absolute flow limits of that comp wheel. I might try to milk what youve got for a bit :big grin:

My opinion is that you are not going to gain all that much more peak power from a comp wheel swap at the current power level (or even at the +50 hp level). If you go larger on the turbine side, youre definitely going to lose spool. For what its worth, on my car, a 60-1/Stage 5 / 0.82 spooled about 500 rpm slower than a Super 50 TO4E / Stage 3 / 0.63. Driving around town it felt like a whole lot more than that. Below 3 grand there was absolutely nobody home. By 4000 rpm, appreciable boost arrived, with full boost hitting around 4700 rpm. With the TO4E Super 50/ Stage 3 / 0.63, full boost hit at 4200 rpm. With the current turbo (TO4E "regular" 50 / old school Stage 3 / 0.63 BB), full boost is 500 rpm sooner than that.

After messing with a few iterations of turbos on my car, I have come to the conclusion that, all thing considered, its better for the turbo to be a little too small than a little too big.

Your goals may differ since it might be a drag only car. You just want to be careful that you dont select a turbo that requires too much rpm for the engine.

[4sfed4]

Quote:

Originally posted by fkatzenb Since this is as good as thread as any, here is my map for the turbo I am putting on my 3.0L. (demand lines are at 2500 and 3000 to 8000 rpms respectively left to right). The compressor wheel you are looking at is a DBB GT37. I will be matching it up with a GT31 turbine that contains a GT30 wheel which creates a GT3037. This should compensate for the lower flow that my engine has when compare to better flowing 3.0l's that use the full gt37 package or the super large a/r of the gt3037 setup. The gt3037 turbine a/r's availabe are .63, .82, and 1.06. I probably wont decide which of the two smaller a/r's to use until i have recieved flowbench numbers from my head work that Brian Slowe will be doing shortly. The compressor map is a different story. I want an all around car... road race (& autocross), street, and drag - in that order. So initially I was thinking that i would want the 76mm (or T04) housing, however, i would sacrifice the high end that I feel that this motor can grab (with custom manifolds and intake). So should I go with the 82mm? I dont know how the 82mm would effect me with my autocross and low end. The other thing to note that in the autocross/road racing, I will be barely pushing 25psi, but on the drag, 30psi. And again, another aspect to note is that the gt3037 setup flows less at high end then the full gt37 setup, so will i even achieve the high end of the 82mm compressor? Plain and simple, its all a mess :big grin: Any suggestions would be golden. Frank

Everything I have ever researched is that the larger comp housings, all else equal, will create some lag, especially transient type lag. That would be bothersome to you on the autocross I would think.

That turbo you are selecting is a very nice one :big grin: I thought about going with something like that but I am far too cheap to pony up that type of dough!

Its hard to guess about turbine sides (since you have a 3.0L) but I think that the 0.63 is going to be more to your liking. A buddy of mine has the same basic turbo as you on a 530+ whp 2.0L Nissan. He did extensive dyno tests and basically found the 0.82 wasnt really giving all that much more peak power (10-15 whp if I recall) over the 0.63, but response suffered. You have to keep in mind the GT30 turbine wheel is tiny!

Since turbine housings arent all that hard to change, the worst case is you can try both. Id try the 0.63 first. If you find it spools very fast and backpressure readings are too high, then you can pop up to the 0.82. The bummer is that you never know until you try

The more I play with turbos, the more I tend to favor the slightly smaller turbo over the larger one especially if you want response. 10 whp wont hardly be noticed, but 500 rpm of lag will certainly be.

Its taken me 4 turbos on my R/T to find the right one (for me), but now I think I have it nailed down.

[xrattiracer]

4sfed3, you dont ever want to be on the edge of compressor flow limits, as that would place you well out of the good efficiency island, and probably also into dangerous shaft rpms.
turbo sizing is really a matter of preference. I for one cant stand the choked off feeling you get in the higher rpms from a "low lag" itty bitty turbine housing. i will gladly trade lag for that high rpm sink you in your seat horsepower curve. that being said, i am going to be using a Holset HY35W on my car (from a cummins truck). I expect usable boost in teh 3500 rpm range or so, and will be using a 7000 or 7500 rpm redline. of course the other advantage of a large turbine is the ability to run wild camshafts I also plan to help combat lag by using a mild anti-lag program in my SMEC.

[4sfed4]

Quote:

Originally posted by xrattiracer 4sfed3, you dont ever want to be on the edge of compressor flow limits, as that would place you well out of the good efficiency island, and probably also into dangerous shaft rpms.

Of course not! I was just using that to illustrate that the compressor on Bryan's car isnt on the edge of its flow limits yet. If it was, boost would plummet! Ive learned that twice! Once with the stock T3 55 trim and once again with the TO4E Super 50 trim. The turbo will let you know very clearly when it just cant move the air you request :big grin

Quote:

turbo sizing is really a matter of preference.

Aint that the truth! Everyone has a certain "feel" they like.

Quote:

I for one cant stand the choked off feeling you get in the higher rpms from a "low lag" itty bitty turbine housing. i will gladly trade lag for that high rpm sink you in your seat horsepower curve.

I am with you there. I also dont like the choked off feeling. The trick is to be able to "have you cake and eat it too". With the right turbo, you wont lose all the much on the low end, and youll still get the top end rush. Its a balancing act. Of course, it all has to be tempered with your particular wishes. I for one used to not mind lag all that much. Now, I really dislike it. I like to just step on the gas at say 2500 rpm and have the car be able to pick itself up by its bootstraps and go. The TO4E 50 / Stage 3 / 0.63 turbo can do that as well as provide the same basic top end as the larger 60-1 I tested. (Dyno confirmed same top end).

In many cases, youll find the "break point" where the larger turbos arent offering anything more than lag (i.e. little power gain up top). Thats when you know you went too big. In my case, the 60-1 / Stage 5 / 0.82 was that "break point". It didnt offer any more peak power over the smaller turbo, just lag. Granted, if I was running the 60-1 to its max potential (about 650 hp) , it would have certainly had more power ptoential than a TO4E Super 50 trim. That would have been the tradeoff for the lag. But, that was not the case for my car as I was not going to run the 60-1 to 600+ hp, thus it was not a good match.

[turbovanman]

Stupid question but what is that line called "surge limit" for and what is surge limit?????????????????

[DakotaKid]

Quote:

Originally posted by turbovanman Stupid question but what is that line called "surge limit" for and what is surge limit?????????????????

Surge line:
The map width is limited on the left by the surge line. This is basically "stalling" of the air flow at the compressor inlet. With too small a volume flow and too high a pressure ratio, the flow can no longer adhere to the suction side of the blades, with the result that the discharge process is interrupted. The air flow through the compressor is reversed until a stable pressure ratio with positive volume flow rate is reached, the pressure builds up again and the cycle repeats. This flow instability continues at a fixed frequency and the resultant noise is known as "surging".

[Frank]

Quote:

Originally posted by turbovanman Stupid question but what is that line called "surge limit" for and what is surge limit?????????????????

Garrett says this about surge....

Quote:

4. Surge Line – The surge region, located on the left-hand side of the compressor map, is an area of flow instability typically caused by compressor inducer stall. The turbo should be sized so that the engine does not operate in the surge range. When turbochargers operate in surge for long periods of time, bearing failures may occur.

Jeff Lucius from www.stealth316.com defines it as...

Quote:

To the left of the surge limit line on the flow map is the surge area where compressor operation can be unstable. Typically, surge occurs after the throttle plate is closed while the turbocharger is spinning rapidly and the by-pass valve does not release the sudden increase in pressure due to the backed-up air. During surge, the back-pressure build-up at the discharge opening of the compressor reduces the air flow. If the air flow falls below a certain point, the compressor wheel (the impeller) will loose its "grip" on the air. Consequently, the air in the compressor stops being propelled forward by the impeller and is simply spinning around with the wheel, which is still being rotated by the exhaust gas passing through the turbine section. When this happens, the pressure build-up at the discharge opening forces air back through the impeller causing a reversal of air flow through the compressor. As the back pressure eventually decreases, the impeller again begins to function properly and air flows out of the compressor in the correct direction. This sudden air-flow reversal in the compressor can occur several times and may be heard as a repetitive "WHEw Whew whew" noise if the surge is mild (such as when the by-pass valve is set a little too tight) to a loud banging noise when surge is severe. Surge should be prevented at all costs because it not only slows the turbocharger wheels so that they must be spooled back up again but because it can be very damaging to the bushings or bearings and seals in the center section.

i think he explains it far better then i ever could.

frank

[turbovanman]

Thanks. I have my Talon BOV valve crushed a little too much and was in a while at low rpm, when I get off the gas, its makes that chattering whew noise, is that bad! Other than that, its fine.

So as for surge limit, this could happen when driving if its sized wrong, so say you doing 80 km/h, it would make that chatternig sound if its operating in that zone?

[glhsken]

Quote:

Originally posted by xrattiracer 4sfed3.

LOL Only when his cah (he's from Maine) isn't running right!!! "thumbs up

[glhsken]

You'll klnow surge when you hear it.. Sounds like a car without a blow-off valve, BUT when the car is accelerating.

As for the overspinning... There is a trade-off... That's why BIGGER coolers are made.

[contraption22]

Quote:

Originally posted by 4sfed4 Everything I have ever researched is that the larger comp housings, all else equal, will create some lag, especially transient type lag. That would be bothersome to you on the autocross I would think.

I had read something claiming the exact opposite last night. Given the same compressor wheel, a smaller compressor housing will be a restriction at lower pressures, but me more efficient at higher pressures.

[altered7151]

Just wondering, what are you guys using for an assumed VE when you do your calculations? Also how much do you assume a good ported head or say a 16v head improves your VE when you do your airflow calculations?

[Frank]

Here is a guestimation for a general (no disquishing between swirl or g) unmoddified 8 valve.

RPM 6,000 5,000 4,000 3,000 2,500
VE 77% 83% 87% 89% 88%

you can expect a 3% increase with a good porting in the 2500 to 3000rpms and a 1-2% on the other rpms.


Here is a guestimation for a 16 valve.

RPM 7,000 6,000 5,000 4,000 3,000 2,500
VE 83% 85% 87% 92% 93% 90%

no idea, on what kind of gains you could see for the 16valve. you might want to rely on 4sfed4 for that. i am still learning alot of the VE stuff. i have been told there is a way to reverse guestimation it from a dyno chart, but i am still tying to get that because you have to know your pressure and fuel ratio. then matching it to a compressor map (back to ideal situation), you can guestimate what your VE was within 1% or so, but you can form a more accurate curve with many more rpm points in there.

frank

[4sfed4]

Quote:

Originally posted by fkatzenb Here is a guestimation for a 16 valve. RPM 7,000 6,000 5,000 4,000 3,000 2,500 VE 83% 85% 87% 92% 93% 90% no idea, on what kind of gains you could see for the 16valve. you might want to rely on 4sfed4 for that. i am still learning alot of the VE stuff. i have been told there is a way to reverse guestimation it from a dyno chart,

When I did the "reverse guessitimation" using dyno charts and the compressor maps, etc using your spredsheet, I am getting VE's well over 100%.

For a 12 psi dyno run, here is how the numbers worked out---

RPM 7,000 6,000 5,000 4,000 3,000 2,000
VE 100% 130% 140% 145% 110% 100%

I have no idea whether this is realistic or not!