How to choose a turbo?

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How to choose a turbo?

Postby justin_l_ » Fri Jun 26, 2009 2:31 am

I have started researching but don't really know where to start. My goals are low boost (5ish psi) and modest hp (220ish). This is going to be on an M50NV so I figured that maybe Yoshi could help too. Also you guys think that the stock head gasket is going to be able to hold that type of boost? I am going to be using a TRM tune as I just can't grasp this MS thing lol. Help me guys!
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Re: How to choose a turbo?

Postby Yoshi » Fri Jun 26, 2009 2:50 am

Basically you size a turbo based on over all volume your car pushes out. Basically liters and how fast you want it to boost. a T3/T4 would do you fine. an HX35 would do fine too. You can hit about 8psi on a 100% stock setup with a TRM tune and do about 300whp on an M50NV. Any less than 8 really is pointless. Go for 8! I did 260whp with a bad exhaust leak pre turbo lol 8psi.
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Re: How to choose a turbo?

Postby justin_l_ » Fri Jun 26, 2009 2:59 am

I am going to be using a top mount bought from a member on the tech. What flange is on the HX35? T3? It is going to be a street car, not track or anything so turbo lag is going to be considered.
What is the .60 ar .63 ar, ect mean?
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Re: How to choose a turbo?

Postby Yoshi » Fri Jun 26, 2009 3:04 am

It's T3 flanged. Holsets use CM^2 not AR. Basically the bigger that number, the more lag. The smaller the number, the more you choke your motor. any turbo that will work on an M20 should work fine on an M50. Do a bunch of reading.
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Re: How to choose a turbo?

Postby justin_l_ » Fri Jun 26, 2009 6:36 am

I got the bigger the number the more lag, so does it have to do with the configuration of the compressor wheel? I'm continiously reading.
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Re: How to choose a turbo?

Postby inkk » Fri Jun 26, 2009 7:55 am

Its the size of the exhaust turbine we are looking at here. With the Holsets as Yoshi said, its the number/size of the exhaust housing which we will take a look at. The HX35 for example (don't take this as gospel coz im new to this too) has anything from a 9cm-22cm housing. We are basically measuring the diameter inside the housing, there is also width we measure, it could be either 2 or 3cm im led to believe (someone will hopefully verify). Now the smaller the housing, the faster it will fill with exhaust gasses, pressurise and spin your turbo, the larger of course the opposite but if its too small and too fast your turbo will reach its maximum flow capabilities too early in the rev range thus choking your engine because it can't dispense the gasses at a fast enough rate. If it is too large it will take forever for it to fill with enough gas to pressurize thus spooling late or what we tend to call lag. Now, what you want is to find a turbo that suits what you want. After the research i have done on this, I have opted for a 14cm. For what you want i think a 12cm should be fine but no smaller. It should spool fast enough and stay on 8psi all day.
As Yoshi said, read some more and you will see what you want to do. Try to get an understanding of how the psi thing works too.

Hope this helps.
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Re: How to choose a turbo?

Postby Yoshi » Fri Jun 26, 2009 2:11 pm

12cm^2 to 14cm^2 sounds about right for a holset. I need to figure out what mine is...

As far as Garrets? I had a .42AR saab T3 that had 8psi before 3k. It worked well but could have made more power. It was choking the motor out. I upped the boost to 12psi and lifted the head. So... all I know is .42 AR is too small :-p I think .60 is about right but don't quote me on that.

Look around the net and see what other 2.5 liter guys are running. The closer you can get to your engine the better. EG RB26s are the same bore/stroke and are dohc as M50s.

also, learn to read compressor maps. I mapped out my HX35 to exactly what I wanted. Now it would do it if I didn't leak exhaust everywhere..
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Re: How to choose a turbo?

Postby inkk » Fri Jun 26, 2009 4:56 pm

Yoshi, if you look at the back of the exhaust housing there should be a number or you can try measuring the housing by using the shaft as the centre and measuring the radius to the roundest part of your housing then double it and then subtracting what seems to be a logical thickness for the casting. When i first measured mine i came up with 14cm and then i found out about the number too.

A Garret .63AR or even .82AR would be good for a 2.5, i would personally go for the latter but then again if i paid for a Garret i would want 500hp.
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Re: How to choose a turbo?

Postby Yoshi » Fri Jun 26, 2009 5:12 pm

Theres a stamp on the inside of the exhaust housing on most models. I just need to crack it open and take a look at it. I had troubles getting my Vband to seal so I'm weary of taking it off just to look. Maybe when I redo my adapter.
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Re: How to choose a turbo?

Postby inkk » Fri Jun 26, 2009 6:02 pm

Well hurry up and redo it already. Time for 350whp.
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Re: How to choose a turbo?

Postby Yoshi » Fri Jun 26, 2009 6:07 pm

nah. I have so many other things to do to the car. 260whp already is uber super fast. It'll make it that much better when I get bored with the power level I have now :)
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Re: How to choose a turbo?

Postby justin_l_ » Sat Jun 27, 2009 1:34 am

I want to be super fast! I am looking at a turbonetics turbo, but I am waiting to get the specs off it to see how well it will work for me.
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Re: How to choose a turbo?

Postby inkk » Sat Jun 27, 2009 2:32 am

justin_l_ wrote:I want to be super fast! I am looking at a turbonetics turbo, but I am waiting to get the specs off it to see how well it will work for me.


I thought you said a mild 8psi???
If you want a Turbonetics speak to Ben Fenner over at the tech. He has had experience with one on Dan Martins build. Now that thing huffed and puffed.
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Re: How to choose a turbo?

Postby justin_l_ » Sat Jun 27, 2009 3:39 am

I want to go fast, what I can afford is a completely differetn thing :(
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Re: How to choose a turbo?

Postby inkk » Sat Jun 27, 2009 6:36 am

Go with a Holset and a modified ebay mani.
Yoshi has done the hard yards already just copy him.....kinda.

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