JETmn

Yeah, because they make the COMPRESSOR maps while the turbo is on the car.

If the turbine wheel had anything to do with a compressor map, it would not be called a compressor map. I have never seen any documentation saying that Garrett tests their turbo's to SAE standards and have been told the contrary by a Honeywell engineer. They spin the turbine side of the shaft with an electric motor, not their finger. That way they can control the RPM exactly and give you the nice little map. They don't even have a turbine wheel hooked up while they do it, so how can it have any effect on the map?

Ever seen a Garrett compressor map that made any reference to the turbine side of the turbo? I never have. They do tell you the wheel and compressor housing it is in though.

engineermike

Thank you Mr. Obvious. Then again, we're not talking about the same strokes per minute are we? A larger motor has the capability to make the same power at a lower rpm. So, here we are, back to my original point, that it takes the same amount of air to make the same amount of hp regardless of the engine size. . .

Case study, eh? My grandpa smoked his whole life and lived to 80. Smoking must be healthy. . . Anyway, there's a whole bunch of things that can account for the difference there. Unless both cars had the same tranny, converter, exhaust, heads, cam, intake, ignition, tune, etc. . . the test is invalid. I won't even begin to try to explain to you sonic velocity limits of gas flow through the turbine and it's affect on exhaust backpressure and wastegate opening. . .

Oh, that's a new one. . . never heard that before. People who say that are the ones who don't understand the theory behind what happens. Did it ever occur to you that I might have real world experience also? My 383 with the 76 S-trim will go to 18 psi with no detonation on 93 octane with the proper tune.

JZ 97 SS 1500

iTrader: (2)

Here is the schematics of a turbo test stand. SAE J1826....




Turbo test stand

Right click and save as.

Any other questions.... BTW, we have all the documentations for a reason. We are working to do compressor map testing for one of the large turbo companies. Anything else

Jose

Race-Prep

Everything I have read states that a compressor map is for estimation purposes, not a definative absoulte reference. I also have seen my share of turbos go well beyond their designed capability, I am simply saying they will do more than the compressor maps say they can. Just because it gets a little inefficient doesn't mean it can't keep going beyond optimum. I understand what your point is, but the reality of the matter is that a larger engine will simply make the power sooner. Obviously, if you put a T60 on a 454, it won't work very well and run out of steam at like 4000 RPM or less, but if it is close to what you need, like my GT76 on a 382, it will likely work fine and spool VERY fast if the proper A/R is used. I deal in AVERAGE power and it is what makes a vehicle FAST and in my opinion it makes more sense to trade a little peak high rpm power for a flatter power curve, it ALWAYS goes faster that way. This is just what I have seen in the last 12+ years of experience after graduating from SAM in the top 1% of my class and building everything from IRL engines to 800" big blocks making 2000+HP. Your point IS valid and I am not saying ignore the Map's but you need to admit it, you have seen it, the little fatory turbo on some car going WAY beyond its intended capability, making more power than it should. It may not be the optimum way to do it but it CAN be done.

-Bryan

NA$TY-TA

iTrader: (21)

ha ha good one Jose........................

Zombie

iTrader: (2)

Ok, here is a visual representation of some calculating I did yesterday.

The small blue dots represent 3500 rpms, the big blue dots represent 6000 rpms. The single green dot was a 346 at 6000 rpms. This represents my current motor. At 14 psi of boost I made 625 rwhp, if you look at the map I should be flowing roughly 66lbs/min. 67lbs/min * 10.5 = 703 HP which seems to be pretty close assuming a 12% drivetrain loss for a M6. 703 * 88% = 619 rwhp. Maps and calcs seem to work pretty good to me.

Each dot is a 5psi incriment upto 20 psi. The maps are used to get you in the ball park. The new wheels extending the maps to the right slightly further, ITS rates my 76 at a hair over 105lbs/min. Graphs assumed a 370 motor.


T76

T80

As you can see on the 76 map it's geting close to the choke line.

JZ 97 SS 1500

iTrader: (2)

Bryan no one said that once you come off the compressor map island it won't make anymore power. We are just stating the efficiency will drop tremendously and the consumption air becomes super heated, therefore the power output will drop. Now take an engine that runs that turbo at an efficient level and the boost will hold steady, plus power output will be greater. Also on a 382 you will get to a point with a 76 where the compressor simply can't make anymore boost. Just check into the DR class guys running BIG GT47-85's on only 360ci engines. Spike to 22-24psi, then drops to 19-20psi. This means you are running the compressor dry, plus the backpressure is VERY high (more then 2:1) for a T6 thumper chassis unit. Their is a fine line you dance on with turbo efficiency, wheel sizes and spool up. The A/R can be fudged with an independent wastegate controller, so I will leave that out as a variable at this point.

CHRISPY

What a great thread!

JZ 97 SS 1500

iTrader: (2)

My fingers are cramping after this one...lol

TeeKay

FWIW, I ran some numbers a couple of weeks ago on a 383 @ 90% VE.

I looked at low boost of 8 & 10 psi @ 3500, 5000, and 6500 rpm and plotted them on a T76 compressor map wanting something in the 750-800 chp range. Both showed that at 3500 the data points are in the most efficient (78%) range, at 5000 there is only a small drop to 70+%, but at 6500 its pretty close to the choke at an efficiency below 65%. So I'm thinking that the T76 would support 6000 RPM at 10 psi and make somewhere in the neighborhood of 720-750 hp out of a 383. The most efficient boost level (according to the map) appears to be at about 12 psi and looks like it would make about 800+hp on a 383.

What that says to me is that a T76/383 combination would make a very powerful street/strip setup with only a mild trade-off over 5500-6000 rpm. I would think that a 370 would be close to the same thing since it's only about 3% C.I. difference. And, oh yeah, it would need meth or an IC to get away with it on anything like 93 octane.

How does that fit with what Jose and Nate et. al. are saying?

JZ 97 SS 1500

iTrader: (2)

That sounds about right. I will have to run the numbers myself to confirm it.

Jose

TeeKay

Thanks, I feel better now since I'm kinda new at this!

Rpm2800

Jose, when you say that a turbo is out of it's efficiency range and less efficient pressure ratio , do you mean that it will basically start pushing "hot air" , (at least when the boost is raised too high). And...........


What do you mean when you say, higher pressure ratio? Do you mean more and /or cooler oxygen per cfm the unit pumps.

JZ 97 SS 1500

iTrader: (2)

Yes the turbo begins to push superheated air. So power is lost.


As for the PR. Its a representation of PSI(compressor output) vs Engine consumption. IF the PR ratio does not reach a certain level the compression of air from the compressor wheel starts to loose efficiency. Take a look at the compressor maps posted within this thread. You will see, if the engine consumption is high with relative low boost the turbo will start to blow hot air and reach the choke line. The opposite of that will take you to the surge line (diagonal line on compressor map). Which is the turbo outputs more then the engine can consume at a certain level.

Jose

engineermike

Pressure ratio = (boost + 14.7)/14.7

JZ 97 SS 1500

iTrader: (2)

That is correctomundo.

LSONE

iTrader: (1)

so pressure ratio = bar = atm?

JZ 97 SS 1500

iTrader: (2)

That is right

JETmn

Yes, the pressure ratio is just the atm of air going into the engine. That is the vertical axis on a compressor map. 14.7psi/atm is standard for sea level, but if anyone is at a high altitude, things can change quite a bit. For most people 14.7 is close enough though. Just something to keep in mind for the Denver guys.

engineermike

Actually, let me correct myself. Pressure ratio is measured just upstream and just downstream of the compressor, so you have to correct for other losses by:

Pressure ratio = (Boost pressure + Pressure drop from turbo to intake + Pressure drop upstream of the compressor + 14.7)/14.7

Thos 2 corrections can make substantial changes to Pressure ratio. For instance, if you're running 20 psi boost, then:

Pressure ratio = (20 + 14.7)/14.7 = 2.36

However, if you're losing 1 psi upstream of the compressor and 3 psi downstream, then it becomes:

Pressure ratio = (20 + 3 + 1 + 14.7)/14.7 = 2.63