This is a guide for those of you who are new to turbos and don't really understand how to properly match a turbo to your engine. It's not as simple as "this turbo is small, it should spool quick", or whatnot. A turbo which is too small may spool quick, but it will be highly inefficient and won't work well with your engine. Conversely, a turbo which is too large will operate in surge and won't spool.

A properly matched turbo will give you a quick spoolup and will remain efficient throughout your engine's operating range. But how do you figure out just how of a turbo you need? Good question.

All turbos have what's called a "compressor map", which is a chart which shows the airflow and efficiency range of the turbo. By doing some simple calculations, you can plot values on this map that will show you exactly how suited this turbo is to your application.



Here is a map for the T3, 0.60 trim turbo. Notice the raised part in the very center of the map? That's the "efficiency island", the area of greatest efficiency.

Notice, on the X axis you have engine airflow in lb/min. This is very important. You need to calculate how much air your engine is flowing at various RPMs, so that you can plot on the map. But how do you do that?

Use this formula: (CID x RPM) / 3456 = CFM

We'll start at 1000 RPMs and work our way up to 6000.

(225 * 1000) / 3456 = CFM
225000 / 3456 = CFM
65.10 = CFM

So, we just calculated how many CFM our engine flows at 100% volumetric efficiency. However, no engine is 100% efficient, so in reality this number will never be achieved. We don't know exactly how efficient our engine is, so we'll have to guess. Most engines will have a volumetric efficiency between 80-90%. Let's guess our engine is 70% efficient (which is probably about accurate for a bone stock, carbed 225).

CFM * VE = CCFM (corrected CFM)

65.10CFM * 0.70 = 45.58CFM

Our engine flows 45.58CFM at 1000RPMs. But, there's one last step - we need to convert this to lb/min to plot on the map. Just multiply by 0.069.

45.58CFM * 0.069 = 3.14lb/min

Our engine flows 3.14lb/min at 1000RPMs. Now, we need to calculate this values for several RPM values, up to our redline RPM. I'm going to assume a redline of 6000RPMs. I invite you to calculate all these values yourself to familiarize yourself with how this process works, but to save time I will go ahead and list the values I've calculated:

1000 RPMs - 3.14lb/min
2000 RPMs - 6.29lb/min
3000 RPMs - 9.43lb/min
4000 RPMs - 12.58lb/min
5000 RPMs - 15.72lb/min
6000 RPMs - 18.87lb/min

So, we've got the airflow values for the engine. Before we can plot points, however, we need to calculate a few other factors.

Notice, on the compressor map's Y axis we have "pressure ratio". This is a ratio of how much boost pressure you will be running, versus atmospheric pressure (14.7psi at sea level). To calculate this, we use the following formula:

(P1 + P2) / P2 = Pressure Ratio

Where:

P1 = Desired boost pressure
P2 = Atmospheric pressure

So, for a desired pressure of 10psi, we calculate:

(10 + 14.7) / 14.7 = 1.68

A boost pressure of 10psi equals a pressure ratio of 1.68. If you live in a high altitude area, you should figure out what the atmospheric pressure is there and recalculate.

There is one last thing we need to cover before we plot points on the map. Originally, when we calculated how much air the engine is flowing at various RPMs, that was for a naturally aspirated (non-turbo) application. Now, we need to compensate for the extra airflow that the turbocharger is causing the engine to flow. Thus, we need to multiply all our airflow values that we calculated previously by the pressure ratio that we just calculated. While, in theory, this is a very rough approximation (because we're not taking into account the boost pressure rising as the turbo spools), in practice this method works fine.

Naturally aspirated flow values:
1000 RPMs - 3.14lb/min
2000 RPMs - 6.29lb/min
3000 RPMs - 9.43lb/min
4000 RPMs - 12.58lb/min
5000 RPMs - 15.72lb/min
6000 RPMs - 18.87lb/min

New flow values, at 1.68 pressure ratio (10psi):
1000 RPMs - 5.28lb/min
2000 RPMs - 10.57lb/min
3000 RPMs - 15.85lb/min
4000 RPMs - 21.13lb/min
5000 RPMs - 26.41lb/min
6000 RPMs - 31.70lb/min

Now, let's plot those ratios on the chart:



Take a look at these values. The first plot is to the left of the surge line. Normally, you wouldn't want this, but in reality the turbo is still spooling up at this point and it doesn't really matter.

As the engine revs, the points go through the efficiency island and come out the other side, falling off the map above 5000 RPMs. This indicates that the turbo will run out of steam above 5000 RPMs and will be operating very inefficiently. The percentage numbers on the map indicate the turbo's efficiency at that range and the numbers represent how many RPMs the turbo shaft is spinning at (yes, turbos do spin 100,000+ RPMs!).

What we see from this plot is that while this turbo is a tad too small for the engine, it is a pretty good match, especially if the engine is bone stock and at such a low boost level. On the other hand, this would be the *smallest* turbo recommended for a bone stock engine.

If the engine is modified, to the tune of exhaust/intake work and head work, this turbo will quickly become too small for the application and an upgrade should be considered. I would recommend a T3/T04e hybrid turbo, which is a T3 turbine section mated to a T04 compressor section. You can select several different combinations of compressor and turbine wheels with this setup. Talk with a good turbo shop for details.

I hope this turbo guide has been enlightening. I welcome all questions and corrections.

Hey shiftless, how's it going? This is a very informative post BUT I've got a few quick questions for you.
What do you mean by 0.60 trim? Is this the A/R ratio? The turbo I just pulled off my 86?, 87? new yorker 2.2L has an A/R ratio stamped onto the compressor side that says 0.42. Is this the correct compressor map for me or am I missing something? I'm under the impression that this IS a T03 (because these years were ALL T03's, correct?) but it's not ID'ed as such (that I can tell).

Thanks
Welly

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Grip it and rip it

welly: Yes, you have a T3, albeit a small one. The "0.42 A/R" stamped on your compressor housing refers to the size of the compressor housing. The size of the compressor wheel is referred to as "trim". You probably have a 0.48 A/R turbine housing as well, which is small. This turbo is too small for the slant.

I would sell that turbo to an owner of a small engine (such as a Honda or Saturn) and get a bigger T3. The ideal T3 for the slant has a .63 A/R turbine and Super 60 (60 trim) compressor wheel.

Ok so now I'm really scratching my head??? Did Dodge put different size t3s in different cars/years? I'm off to slaughter my 85 lazer, am I going to find another 0.42 or something different/bigger/smaller? I thought T03 WAS the size of the turbo. If that's not it then what does T03 mean?

Thanks

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Grip it and rip it

A T03 is a particular turbo model made by Garrett. A T03 has a builtin wastegate and is used mostly on 1.5l to 2.5l 4 bangers. The larger .60 A/R ones are used on 3.0l six bangers.

The rational for using a T03 turbo on the 3.7l \6 is that they are cheap, plentiful and have a builtin wastegate . Also some people make the claim that a 2.2l engine at 6000 rpms has the same airflow are a 3.7l engine at 4800 rpms. The above chart makes show this to be true. So if you are building a low rpm, stocker, a T03 off the 2.2l would be a good candiate and would propably be good for about 160hp.

Welly225, Chrysler did indeed use quite a few different sized turbos on the various iterations of the 2.2 / 2.5 Turbo. Check out <a href="http://www.thedodgegarage.com/">Gary Donovan's site</a> and look up his archive of turbo information - he lists a lot of different ones. Somewhat surprisingly, I've estimated that the Mitsu turbos used on some 2.5's is a decent match for a slant six running low (around 8 psi) boost in the 2,000-4,000 RPM range. It's not a good turbo if you want your slant to rev though.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

As has been stated, the T3 is a brand of turbo made by Garrett, but the compressor and turbine wheels come in various sizes. The above maps are compressor maps, which shows the efficiency of the compressor at various pressure levels and flow rates. There are also turbine maps available which are for the turbine side. If you want to get a compressor and turbine map for your particular turbo (0.42 A/R compressor, 0.48 A/R turbine), just go to the Garrett website and contact them. They've been very forthcoming in providing this information to people who want it.

I have to say though that your turbo is way too small for a slant. According to my calculations above, the 0.60 A/R compressor is a tad too small, and you have a 0.42. The 0.48 A/R turbine side is also hurting you.

I would recommend sourcing a T3 turbo off one of the following cars: 83-86 Thunderbird TurboCoupe (5 speed), 84-86 Mustang SVO, 83-89 Merkur XR4Ti (5 speed). All of those cars listed came with T3s, and the 5 speed cars came with a 0.63 A/R turbine. They also all came with 0.50 A/R compressors (if I recall), and any competent turbo shop can modify them to accept a Super 60 compressor wheel, which is the one you want. This operation is not very expensive and you will have a turbo that is well matched to your engine. Note, avoid the 87-88 TurboCoupes, because they came with an IHI turbo which is junk.

I would also recommend running a 3" downpipe and elbow. Go to www.turboford.org and get in touch with bob40fordlee, he enlarges the stock elbow (the exhaust piece which attaches to the back of the turbo and allows a downpipe to be connected), which is very restrictive, and it will result in much faster spoolup and power gains. He makes downpipes as well. His work is top notch and his prices are good.

I haven't begun the dismemberment of the Laser yet (probably friday). According to The Dodge Garage it should have the same turbo as the New Yorker (Both 84- 87 TI's Non- intercooled). What if I use them both instead of looking for one bigger turbo? There is that pic somewhere on the site with two turbos strapped to a slant.

Dilemma dilemma.

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Grip it and rip it

Not only is it going to be twice as expensive to mount, plumb, tune, and maintain two turbos, it's also less efficient. You'd be better spending your money by buying a properly-sized single turbo, even if you had to get a new one. I understand the need to do it cheap (perhaps more than most) but there are some things you just can't do cheap and get good results.

Ok, fair enough, One final question. I tracked down some compressor maps for T03s, is a 0.42 A/R a 40 trim or 45 trim or do I have the wrong maps? I just want to fool around with the numbers to try and learn a little more about it.

Welly

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Grip it and rip it

I'm not sure, but it could possibly be a 45 trim. I don't know much about those smaller ones.

Thanks for the primer on turbo applications Shiftless. I enjoyed the reading.
My question is around waste gates . . . I read about the T3 with its built in gate and I see pics of applications with quit elaborate external setups. I'd appreciate a discussion on the pros and cons of each?

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Cheers!
Al T