dean1484 Dork
5/25/09 9:24 a.m.

I have been playing with adding a M62 to my 924s. the plan was to run between 7-10 PSI. However due to issues with mounting a FMIC in this car I am considering changing over to a turbo. This would allow me to install a top mount IC where the M62 would go. This would make the packaging / plumbing MUCH easier. So to at least evaluate the feasibility of this I need to learn about turbo sizing. Is there a place out there on the web (or here in GRM) that will allow me to do basic sizing as well as take some of the complexity out of the world of turbos.

What I am sizing to and some of my wants:

I am putting this on a 2.5L motor 9/1 comp

I am only looking for 7-10 PSI boost

I would like it to come on around 2K rpm and run up to 6K. The red line of the motor is 6800 but I have the motor limited to 6K as power drops off after 5700 in NA form. This is also going to be used for the most part on the street so the car will see alot more use in the low rpms.

Small physical size of the unit would make things easier.

Oil cooled. (easy plumbing in the location I would put the turbo.)

Other modifications to the car include

Larger injectors (stock from 951), Inter cooler, EDIS ignition and Micro Squirt ECU, (EDIS is already in place and running) RR FPR (stock from a 951). Oil cooler.

Any help would be appreciated!!!!

P71 Dork
5/25/09 9:33 a.m.

Do yourself a favor and grab a copy of Corky Bell's book Maximum Boost. You'll learn everything you need to know.

Raze Reader
5/25/09 9:46 a.m.

T3 off of a SVO, XR4Ti, I'd shy away from the IHI on the TurboCoupes though cause they spool faster but run out of breath faster...

Volvo turbos off their 2.3L, basically anything in that class/size.

Most turbos for these 2.3L engines run 10-15psi from the factory and can support around 20psi before they're maxed out. Plus they're cheap ;)

mad_machine SuperDork
5/25/09 9:57 a.m.

how about a turbo off of a Saab 9000 2.3/ Viggen?

suprf1y Reader
5/25/09 10:26 a.m.
P71 wrote: Do yourself a favor and grab a copy of Corky Bell's book *Maximum Boost*. You'll learn everything you need to know.

Do yourself a favor and don't. That is an awful book.

Street turbocharging is many times better.

erohslc New Reader
5/25/09 10:51 a.m.

These online turbo tools will help, but you still need to know something about what's involved.

The Turbo Match tool will help get you into the ballpark.

The Turbo map tool shows your operating line projected onto the turbo compressor map.

The turbo should never run to the left of the surge line, ideally you want to get as much of the operating line on the 'island' on the compressor map with max efficiency.

But relying on just these tools to do the actual sizing is like doing brain surgery based on watching a commercial for Tylenol for headache pain.


AngryCorvair Dork
5/25/09 5:17 p.m.

Turbochargers, by Hugh MacInnes, is still the bible.

best DIY turbo book evar

procainestart Dork
5/25/09 6:14 p.m.

Street Turbocharging is much better than Corky Bell's book, the tone of which is arrogant and the writing poor. Incidentally, my understanding is that Street Turbocharging is a revision of the MacInnes book; it came from the same publisher. The former came out a couple years ago, the latter came out in the '80s.

This site has some info on sizing, IIRC:

wherethefmi HalfDork
5/25/09 6:19 p.m.

that 6000 rpm limit may need to change too once you're force feeding air and addin fuel.

InigoMontoya Reader
5/25/09 7:42 p.m.

Depending on what sort of HP you are looking for I would say a GT28R might fit the bill. Good friend of mine used one on the 1.8L toyota celica engine (just in an elise) for autocrossing and boost came on quick and started dying right around 6K or so, gt30 if you are willing to sacrafice a tad of spool up. Either way they are nice ball bearing turbos, when he had it new, you could hold the turbo and blow and the thing would start spinning.

My legacy gt 2.5L stock turbo is full boost at 2700 and peaks out at just over 6, and is about 280 at the engine or so, used ones are fairly easy to find and others out of the subaru world might work just as well.

ignorant SuperDork
5/25/09 8:01 p.m.

This is the bible.. All other books are just not as complete nor as good. This book was on the desk of every engineer at my old job at Holset.

Now.. I'd show you how to do it quick and durty, but my old boss took my books when they fired me. Blah.. company property blah..

RossD Reader
5/25/09 9:43 p.m.

I've read through garretts website a couple different times. Here

It starts out on the simple side then dives into the technical side. What could be wrong with free?

Brust Reader
5/26/09 3:07 p.m.

Here's what you want:

dean1484 Dork
6/1/09 6:27 a.m.
Brust wrote: Here's what you want:

I have been playing with and ti is a great tool. One question I have is that can you tell how a unit will spool by the graph?

The other thing I am noticing is that since I am only looking for 230HP MAX from my 2.5 l motor my graphs seem to have me operating in the bottom of the turbo graph. about the best one I can find (if I am reading this thing correctly) is the very bottom of the list.

Here is the graph:

How important is getting the line to run in parallel with the angle of the circles as well as how important is it that you run up though the center of them. It looks like with this unit it will come on fast and then pull like mad till read line if I am reading this rite. Do I want a smaller unit? Of if I pushed the line out further in the graph would that result in a slower less "light switch" type feel.

Am I reading this rite ?

Once I get what I think it a good line / map overlay How do you go about getting the specs of a unit so that I can get the equivalent Garrett / Volvo / Mitsubishi / ford units? (basically a unit that others are tossing for an upgrade)

ignorant SuperDork
6/1/09 6:59 a.m.

I can't read the graph.. It's too small to get proper numbers off of it. At the plateau in your line is where your waste gate is opening. Meaning no matter how much more flow you pump through it you won't get any more pressure ratio out of it..

But the way I learned to size is to plot multiple speed lines on the Map and make sure that you are never going to "fall off the map" in normal running.

How fast you spool is more of a function of turbine size rather than compressor size.

dean1484 Dork
6/1/09 2:16 p.m.

How about this

This also seems like a good option.

The T3 60 trim. A supper 60 is virchally identical

dean1484 Dork
6/5/09 10:41 a.m.
Inigo Montoya wrote: My legacy gt 2.5L stock turbo is full boost at 2700 and peaks out at just over 6, and is about 280 at the engine or so, used ones are fairly easy to find and others out of the subaru world might work just as well.

What YMM was this car? Or do you know what turbo it was? It seems to me that the Subaru's used Mitsubishi units

From you description that sounds like it would be what I am looking for. In fact since I am only looking for 7-10 PSI it may actually be a bit more than what I need in terms of total boost that it can make but that just allows for upgrades in the future.

Brust Reader
6/6/09 7:57 p.m.

No idea how to figure out how fast it spools. I think that's the black magic, as it depends on the tune, wastegate control, etc. I understand ball-bearing center sections come on about 500rpm faster than journal bearing, but it's all conjecture.

InigoMontoya Reader
6/7/09 12:37 a.m.

The car in question is a subaru legacy GT, 2006, turbo is an IHI unit called the VF46, it would be equivalent to around a 16g mitsu unit. Depending on the condition they got for anywhere from 100-400 bucks over at There is not a ton of demand for them since they are a different fitment than the older WRX models, the new ones are the same (I can drop a new STi turbo into my car now!)

I know my factory one for that HP boosts at 14 psi. If you want something slightly smaller than one of the early 2.0 WRXs might fit the bill, they are slightly smaller.

Basically the Legacy turbo is right between the wrx and the sti turbo sizes.

xFactor New Reader
6/7/09 2:23 p.m.

The mitsu td04-13t used in the 2.0l rex was also used in the 2.5l rex. It would have killer spool in your application. They are all over the nabisco ( for $100 - $200. They're watercooled, but that's not really an issue.

later, matt

dean1484 Dork
6/16/09 11:34 p.m.

One of the most useful sites for figuring out that turbos are what (especially when shopping ebay)

Need I say but scroll down before you click there are many ways to use this page

For-instance every wanted a list of all the turbos used on Subi's? Well here you go

Also a great junkyard tool.

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