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[Helstrm]

I have a garrett M24 A/R .60 and MI .63 Anyone know anything about this turbo and if it will work on my P-car?

It is huge and I know there will be some fab work to mount it.

[ESC944]

I have a clue about them, first notably, they have been used by Canepa Design in their 959 US market legal conversions. I quote:

Because Porsche designed the 959's engine case and innards for the 956, McCrocklin knew it would withstand the modifications he envisioned. "This motor has fabulous combustion chambers," McCrocklin said. "Everything is magnesium—the case, the intake manifold, even the valve covers." Without changing a thing inside the long block, McCrocklin upgraded the battery, rebuilt the alternator for increased output and replaced the water pump seals as a factory-recommended upgrade. His redesign of the intake plumbing eliminated one of Porsche's dual wastegates. He relocated the remaining one next to the left side of the engine, changing its springs and spacers but keeping it otherwise stock.

He bolted the 90,000-rpm Garrett M24 twin turbos to custom support struts and manifolds. He retained the stock twin Behr intercoolers. He also retained Porsche's dual fuel pumps, but changed the delivery nozzles on the secondaries to provide more than twice as much fuel at full boost.

With Different Compressor and exhaust sizes it was used on the 300ZX TT.

Its basically a T3 of sorts, the sizings put it in the 3-5 liter range. On a 2.5 you would have boost well into the 7-8000 rpm range without exhaust lock.

The compressor side is like the T4 or the Grand National. The .60 and .63 in a 2.5 would proably be at full boost around 3300 RPMs and hitting around 12-14 PSI in a typical configuration.

Ideally for a street car and the 6500 RPM limit you would want a different size exhuast opening, something a litttle smaller, you could rebuild her and size it more to the 2.5.

I will post some more details on this later.

Baiscally though its a T3 similar to a T25. Very good choice, for large boost and CFM. Its like a larger T3, closer to a T4 with the .60 and .63 in fact very close to 3.8 Buick setup. On a smaller engine the large exhaust side can be a issue and cause a delay in making max boost.

Lot of people go with the .60 on the compressor side and .48 on the hot side, then you are typically seing max boost by around 2300-2500 rpms. At about 12 PSI. With the .60 you can expect to be able to deliver 450-500 CFM, more than the 2.5 would need at 6500. If I remember my old notes and calculations the 2.5 needs about 440CFM at 6500 so that is not an issue. But the larger exhaust side, means it will be a little laggy on the 2.5, a larger engine is better suited to that opening... so instead of a thimble you have a shot glass on the exhaust size... very easy to fill with a larger motor... but the good thing is the turbo will support some serious boost.

[Helstrm]

So what is your opinion on this turbo and my 2.5 ... Modify it. Sell it and buy another one? Or bolt it up? How would I go about rebuild her and size it more to the 2.5????

[ESC944]

Before we get started on the turbo, it would be helpful for you to have a basic understandings of a couple things.

First of all, turbochargers make torque, not horsepower. Horsepower is a function of how much torque the engine has at a given RPM (ie. It is speed related).

In order to increase HP without increasing torque, you will need to increase the RPM. Most of the wear, tear, and abuse in a engine is going to come from increasing the RPM because of a simple law of physics: Force increases with the square of the speed increase. In simpler terms, as you double the speed of an object, it's force increases fourfold. These are the forces that tend to tear an engine apart not add power so be aware of that when you design and build your engine. They are also the same forces that require you to spend the big bucks on the expensive high RPM parts.

A much safer and cheaper way to make the car go faster is to increase it's power output while staying in the same RPM range. This can only be done by increasing torque. With a properly sized turbo you could double the torque of the motor at a given RPM while only increasing the peak force on the engine 20% or so.

Yes it sounds far fetched but here's how it works:
Keep in mind that the pressure in your combustion chamber is a combination of the how much pressure your piston created when it compressed the fuel mix and the pressure from the burning mix. This fuel mix will burn in your combustion chamber at a certain speed depending on mixture, pressure, and other factors, but for simplicity sake just be aware that it does not burn instantly. In a combustion engine the peak pressure is reached near the top of the stroke when only a small portion of the fuel mix has burned. After that point the piston is accelerating downward and the cylinder pressure drops off rapidly while the fuel is still burning.

In a turbo engine under boost, you may have twice as much fuel mix in the combustion chamber, but since it does not all burn at the same time this additional pressure does not add much to the total cylinder pressure that would have existed in a normally aspirated engine. Now as the piston is accelerating downward there is more burning fuel in the combustion chamber and this burning fuel mix pushes harder than a normally aspirated motor. This is where the real power increase in a turbo takes place. At about 90 degree crank angle the turbo engine's fuel mix is pushing on the piston 3 or 4 times harder than a normally aspirated engine would push. The pushing pressure is still less than the peak pressure which occurred near the start of combustion so it does not create the "overload" to the engine that most people would expect.
So you see that while the peak pressure in the cylinder has not doubled, the average pressure pushing on the piston over the entire stroke has doubled. This higher average pressure translates into more torque at the rear tires at the same RPM.

[Helstrm]

Good to know, but what do you think about using the turbo described above in my application. Keeping in mind that I am building a full 951 engine minus the head which I am porting an NA head to take care of and replacing the valves with ones from a turbo head. I already have a 951 intercooler, an aftermarket oil cooler, Much larger than stock. 951 DME and KLR. Just got a 951 intake and throttle body.

[ESC944]

The above explanation is a summary of a fairly complex topic. For a more in depth explanation you should look in the "Maximum Boost" book or others, the MB book has a fairly good explanation of the entire process.
The above may also help you further understand why the racers use low compression motors with turbos and why turbo cams have different valve timing. In short, you want as much fuel/air mix as possible in the combustion chamber and you want it to push on the piston harder and longer.

As an added bonus, a properly designed turbo car will be more drive-able at low speeds than an equally fast non-turbo car with the same size engine. Remember turbos like relatively docile cams. The low overlap turbo cam will provide better low speed driving and more low speed torque than a high overlap "race" cam.

The point where the turbo comes in depends on a lot of things, cam, ompression ratio, design of intake and exhaust manifolds, and the turbo itself.

Different snail shell housings change the "Turbine Map" of when and how it pushes air. The lower the AR number (.42, .48, .6, .8 etc.), the less CFM it takes to get it going.

In other words it spools faster, since we are talking a 2.5 you are not moving as much air as say a v8, so you dont want a .8 or something crazy... unless you want insane boost levels latter in the RPM range, its all a compromise.

The other issue is the compressor side -- the larger the AR the larger the relative CFM you are displaceing and delivering... it also means more work to move it... AR is not the raius or diameter.

The A/R in a relationship that is obtained when dividing the interior area of the turbine where the inner walls are found, through the turbine housing radio from the center to the tongue.

A/R values are expressed as .35, .47, .68, .84, 1.00, 1.15, etc.

A small A/R indicates a small interior volume in the small turbine and a large A/R indicates a greater volume.

At a minimum A/R the motor's response is produced at small revolutions per minute but at high revolutions we will not achieve an adacuate caudal. We should always find a compromise between achieving the lowest response possible and have enough caudal at high revolutions.

The disadvantage of too small of an AR number is that you will exceed the limits of what it can push at higher engine RPMS.

You need to match the output of the turbo to that of the cam profile of your engine. A good example is say you have an engine that you don't want to go above 5500 RPM. Well, for a 2276 with an Engle Turbo grind of their 120 cam, using the Chrysler T-3 off of a 2.2 Liter Daytona, the engine will be into full boost by about 2400 RPM (12 PSI) and by the time you get to a little above 5000 RPM, the engine starts to quit pulling so hard, kind of like someone put a nail in the tach.

What you would find out is that the exhaust is starting to back up and can’t get out fast enough, to produce more on the intake. This is where the "Pumping" losses take over. To correct this, say I now want my engine to go to over 6000 RPM (providing that the rest of the engine stays together), all I need to do is change the exhaust snail shell from an AR of .48 to .6.

What I just did was slide the turbine map upward. Now what happens is I don't make full boost until about 3300 RPM but hang on all the way through 6000 RPM!

Each turbine wheel y compressor wheel model generally have the same turbine diameter (highest diameter), but different steps (lowest diameter). Each type of step (trim), has different blowing characteristics.

TRIM values are expressed as 45, 50, 55, etc... and can only go from 0 to 100. A value of 100 means Dp = Dg
A large TRIM indicates a large turbine diameter.
A TRIM of 55, gives 10% more caudal than a TRIM of 50.
TRIM is used in the same way for turbine wheels as for compressor wheels.
TRIM is calculated through the following formula.

TRIM = ( Dp / Dg )² x 100
Si Dg = 50 mm y Dp = 35 mm
TRIM = ( 35/50 )² x 100 = 49

Pay attention to what kind of motor you want. From the example above you can build a good play motor with good bottom end and loads of fun at the top, or, by changing the cam, and other engine components to handle extreme RPMs, you can build an 8000 RPM engine at the cost of loosing bottom end. So again, are you a drag racer, or all around play car? Now the 2.0 or 2.5 Porsche isn’t going to rev to 8000 RPM unless you spend a Metric Ton of cash on it.

Use the IHI RHB52 or Ford Probe turbo for anything under 1835cc's. Use the Chrysler T-3 for 1915cc's and bigger.

On big engines or high RPM engines, you will have to change the AR of the exhaust to a larger number so it will not exhaust lock on you. Exhaust lock is when no more exhaust can get out, so no more boost can be put in. These are things that the individual has to play with. If you just start with these initial pieces, you will be happy. Then start modifying and you will see what effects what and when.

So you want it to spin up faster? You don’t want no stinking lag or as little as possible, well with out looking at your cam profile or exhaust configuration, the easiest thing to do is reduce the size on the Exhaust side. So you build a hybrid you remove the larger exhaust housing/impeller and replace it with a smaller size.

I will tell you that in most of my setups on the 2.5 I have used a .60 on the compressor side(air out put) and a .48 on the exhaust side. This yields a super fast spool up. And can flow enough air to keep me in boost up to 6500-7000 RPM and then sum. But boost begins to fall off because of the exhaust side restriction, the CFM is their.

I will post some compressor maps and relative boost pressure and turbo relative RPM.

In short the easy answer is bolt up a smaller Exhaust side from a different T3 or a T4.

Here are some numbers to look at
Garrett T03 85-86 Ford Thunderbird .60 .60 (Automatic)
Garrett T03 84 Nissan 300ZX 60 Trim .63 Not watercooled
Garrett T03 85-87 Nissan 300ZX 2960cc 60 Trim .63 watercooled
Garrett TB0344 Mercury 85-86 Capri, Cougar/Merkur 85-88 XR4Ti .60 or .62 or .63?? (Automatic) .48 (Manual)

Now if you want smaller exhaust:
T03 1987-1990 Chrysler 2.2L (Turbo II) W/Intercooler 86' Shelby Omni GLHS .42 .48

Basically the T3 and T4 turbos bolt together and also the M24 is not the type of turbo, it’s the turbo group… like the old Air Research(garrett) are often stamped with M10.

Part Number Types
Garrett parts have 10 digits.

The first 6 determine the part in general and the following four the versions or modifications of the part.

The first of the second four explains to which market the part is directed.

466506-0005 Turbo sold to auto factory or made for the assembly line.
466506-5005 Turbo sold to auto factory for replacement vehicle
466506-5005S Turbo sold through GARRETT distributor
466506-9005 Reconditioned turbo

Part number can help you lock down exact turbo model you have.

[924guy]

hmmm, soo basically, Big honkin turbo+ small displacement stock engine=BOOM! not vroom??

I look at it this way, Porsche actually reduced the size of the 931 turbo, and got better results (more power, torque, less lag) .. so going larger on an otherwise stock engine could easily surpass tolarance specs, and cause major issues. its possible to do it ofcourse, as Wes has pointed out above, but theres much more to it than changing a flange or two. If your just wanting a quick power update, id forget it and chip the 2.5 instead.. Or wait for Wes or someone else to come out with a complete kit to accomplish this safely..
_________________
Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
http://www.cardomain.com/id/924Guy
Performance by Pasha

[Helstrm]

I really don't mind not spooling until 3300, I mean I am not a drag racer. If I was I would be looking at American Muscle cars not P-cars. I am more into handling at higher speeds than a straight line driver I would like to "build a good play motor with good bottom end and loads of fun at the top"

I also plan on using the Lindsey stage 4 MAF and mafterburner setup.

[speedsta2003]

do you have any flow charts for this turbo?
_________________
My Old Porsche Thats Sold
http://members.cardomain.com/jatbballboy15

[Helstrm]

Nope, I have some pics of it next to a KKK K/26

[Helstrm]

This is what the turbo shop said...

the new turbo is a T04E/T3
57 trim , stage 3, .63