found this over on turbominis forum of what they think the t2 specs are + an old comp map
not sure if they are right but the comp map looks old enough to be genuineCompr Trim 49
A/R 0.48
Inducer Dia 35
Turbine Trim 58
A/R 0.35
Exducer Dia 36
found this over on turbominis forum of what they think the t2 specs are + an old comp map
not sure if they are right but the comp map looks old enough to be genuineCompr Trim 49
A/R 0.48
Inducer Dia 35
Turbine Trim 58
A/R 0.35
Exducer Dia 36
If it's right, that is something that's been missing from this club all these years!
We need one of the RTOC turbo techies to check it out.
Looks goodIts a bit hard to make out the pressure ratio but you can if you stare at it long enough like a magic eye puzzle !
Look at the RPM, you can see why they get a bit unreliable after a bar / 150hp
I might be able to see, if I had any idea how to read the chartOriginally Posted by Scoff
you can see why they get a bit unreliable after a bar / 150hp
Ok so the y axis (veritcal) shows pressure. I assume that as it starts at one, that is supposed to mean atmospheric pressure, so 2 is actually 1bar (or 14.7psi).
I can't work out what the x axis (horizontal) is supposed to represent. It says corrected air flow but I don't understand what that is.
Then on the map I can see the rpm calculations and a load of six digit numbers......... oh, that's the rpm of the turboright I get it. So up to almost 200,000rpm at the extreme.
So, that still leaves me short though, I don't understand what the %'s are that are tagged to the contour lines drawn on the map and I don't understand how these things relate to the air flow axis (or what that means).
Also, does the smallest island on the map represent where the turbo is running most efficiently? Are the %'s therefore showing efficiency rates?
i wish there were an idiots guide to reading them damn maps
Fordy, at the bottom it says 'T2 50 trim, 48ar' Is that right? It doesn't say whether that's referring to the inducer or exducer.
Maybe this could be sent to Garrett for identification?
I'm an idiot and I've nearly worked it out bud! We just need someone to close the loop for me. Maybe someone could take the pic and put some arrows/explanation on it.i wish there were an idiots guide to reading them damn maps
Where's sparkie or mart or scoff or andy cooke or marky or one of the turbo dealers when you need em
Raj, I've had a go myself, see if this helps:
It's not complete but maybe someone else can add to it.
Trev, 50 trim 48ar can only refer to the compressor. 50 trim is the relationship between inducer and exducer. 48ar refers to the 0.48ar cover.
A rough rule of thumb way of reading a map at a glance would be:
Y axis is pressure ratio, that's an absolute reading, not gauge. So yes, 1 bar on that scale is 0psi of boost. 2bar is 1 bar of boost, 14.5psi.
The X axis is airflow. Most charts use lb/min, others use ltrs/min.
Consider that power is directly related to airflow, always, and that it takes about 10lb/min of air to make 100hp.
On to the map itself: See the island in the center ? That's maximum efficiency, usually 70-odd %. As you progress further outward from that island the efficiency drops. In other words, the compressor is no longer as capable of doing what you're asking of it.
Consider the GTT in standard form. 115hp and about 0.7bar (?) of boost. Intersect 1.7 and 12lb/min on that map. It should be pretty close to the efficient portion of map. Renault didn't choose that turbo by accident
Then consider 1.2bar (2.2 on that plot) and 18lb/min. Things arn't very efficient anymore. But we already know that. If you're up there, it's time to upgrade.
The lines that intersect the map are shaft RPM. Smaller turbo's can deal with higher RPM's, but 180krpm is getting a bit silly and things like 270deg thrust bearings don't last long at that.
So armed with that you can look at a compressor map and, at a glance decide if that compressor is going to be any good for your application. For example, if you wanted 220hp and knew that you would realistically need 1.5bar to make that you could choose a compressor that was most efficient where those 2 values intersect. (Read: T3 60trim - found on Sierra Cosworth 4x4 and most of the T28's found on GTT's)
Finally, the hard line that apears to "chop" the map on the left hand side is the surge line. You don't want to be running a compressor left of that line.
'X' is air-flow through the turbo/engine (either in lb/min or cfm). If I can find it when I get home, I'll upload what I calculated (roughly) air-flow of the C1J.
'Y' is a ratio of atmospheric outlet pressure divided by atmos' inlet pressure.
For example, if you wanted to run 1.5bar/~22psig (gauge) at the manifold, that would be 22psig + 14.7psia (atmos') = 36.7psia (absolute atmospheric pressure in the manifold).
To work out the pressure ratio (for ref' to 'Y' axis), divide the total (36.7) by 14.7 (atmos' pressure) to give a 2.5 (as near as damn it) PR.
Bear in mind that intake restriction and height above sea level can alter the PR though, but not that much to worry about in this country...unless you're at Ben Nevis
Now you can cross-reference the PR value to the map (through the efficiency islands) and see if the turbo is happy at that level of boost, plus checking it's a 'safe' distance from the choke line (with ref' to the 'X' axis air-flow at peak engine rpm).
The 'ovals' are the compressor efficiency islands. Ideally, as you say, you want the turbo running in the smallest oval as that's peak efficiency, but in the real world it'll be outside of that island, and probably the next couple as well.
I'm not 100% sure what defines 'efficiency', but I've always thought it as how much extra heat the turbo would be adding to the compressed outlet air; ie, the further away from the small oval island, the harder the turbo is working, thus the hotter the outlet air (boost) will be.
The 'rainbow' type lines are rpm at which the comp' wheel is spinning - Most turbo failures occur due to over-spinning the wheel (supersonic); ie, into the choke zone.
The surge line is the furthest line to the left, and something which most Evo owners seem to suffer when cranking up the o.e blowers
2 types of surge: Surge under load is when the compressor is too large (or too efficient at a lower rpm), that the engine can't ingest all the boost air present.
And the other type of surge (off-load) occurs when backing off the throttle quickly after being on boost - The air-flow is now somewhat reduced, but yet the turbo is still spinning & making boost.
We all know that one, from the 'chirping' noise we then hear (unless a dump valve is fitted).
Too slow again
Unlucky, thats about the longest post I've made in 6 monthsToo slow again
It's ability to turn energy (from the turbine) in to compressed air. Yes, heat, but also the more ineficient the compressor is the more the turbine has to work to keep it going.
Brilliant info, thanks guys.
Ok, it would be possible to add choke and surge arrows onto the chart, which I've done.
According to Mart's input, the PR ratio is not how I've described on the doctored map. Maybe someone else wants to change it. Or do a new one with better tags.
Your PR description is fine Trev, the same as Mart's, you just describe it in different ways. You just need to subtract 1 from the PR bar readings.
Does anyone have such a compressor map for the tomcat T25?
Tomcat is 55trim, there should be maps on the web.
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