CFM and turbos
 

A friend of mine an I was talking today and he asked me what cfm my turbo was rated for. I was at a loss, I dont have a clue. For now I have a factory turbo on the truck. I would like to restart this conversation with him and seem at least a little knowledgeable next time. I have a van turbo Im waiting to put on my truck because lack of funds for the flange and new up-pipes, and my wife and I are buying our first house. 3 Questions
1. What cfm is the factory turbo rated for?
2. Waht is a van turbo rated for?
3. What is the 38r rated for?
Thanks

Good question. Like that answer also.

I do not know CFM, but I know how to read the compressor maps.

http://i22.photobucket.com/albums/b3...ressormaps.jpg

This is a good indicator of how both the GTP38(red) and GTP38R(blue) perform. I ran into the choice of rebuilding mine or replacing it with the 38R.

Looking at the comparison chart submitted by garrett, the stock turbo boosts a tad bit quicker than the Ball bearing(BB) replacement.(as you can see the boost climb on the lower left corner) It also holds a better surge line.
(the left side/slope) However, it can only peak 34 psi. Where the BB peaks at 43 psi, and holds out at the upper rpms. (Note you never want to run at those peaks or run beyond the right of line otherwise you will be stalling the turbo.) The wicked wheel upgrade widens the gap between the BB variant and spool is also quicker. However there isn't a compressor map available, but there is plenty of information online that supports that the wicked wheel does spool quicker and surges less. Which is an indicator that the red line/slope would shift more left.

Additionally, you can rebuild the journal bearing turbo for $50 by yourself. Where the BB turbo is garbage and full turbo replacement is needed.

Since I do not use the higher RPMS or wish to crank the boost up high and I like the idea of rebuilding my turbo for cheap. I decided to stay with my GTP38. Click me to see my rebuild result

Actually Garrett offers a CHRA exchange service. Garrett Ball Bearing Service Probably isn't cheap but less then a whole new turbo.

CHRA: Center Housing Rotating Assembly

Yes, you are correct. :-drink

But in the long term perspective I cannot trust the CHRA service, especially if the 38r goes out of production or that that center cartage replacement gets more pricey as it ages. So in the end the turbo is junked. ;)

To get a rough estimate of the cfm of a turbo from the compressor map, take the lbs/min and divide by .07. That is a fairly accurate measure to some extent and is used by alot of people. From every thing I have read before on a 38r, it flows right around 1050 cfm.

So if the stock turbo peaks out at 58 lbs/min, that is roughly 828 cfm.
38R looks to peak at 74 lbs/min, so around 1057 cfm.

Thanks Ziggy, what about the van turbo?

Van turbo and stock use the same compressor, and therefore the same cfm. The van turbo has a larger exh wheel and is able to drive the turbo better and more effeciently than the stock turbo.

That is why you can get more with a van turbo, because it is taking less heat energy (drive pressure) to spin the turbo. So more of the engine's energy can be used to make power to the wheels vs power to drive the compressor.

i thought the van turbo had a bigger exhaust wheel only

Is that not what I said Jam? or did I mess up my wording somewhere?

Awesome, I bought the van turbo knowing that it was better but never really looked into why lol. Thanks for the info guys I appreciate it. In all reality what kind of difference should the van trbo make when I install it? Im waiting to put it on because Im gonna buy bellowed up-pipes and install them at the same time, my up-pipes are leaking and Im only able to make 18lbs of boost

i was trying to go this route and the CHRA cost more than a whole new 38r per clay......

ur right cory i read what u wrote wrong

briefly, what does the ATS ported shroud compressor housing with larger intake opening do for the stock Garrett. I know it is supposed to eliminate surge. And with a larger intake, I guess it flows more? moves the line to the right? what about spool up?

Good question Im also curious about this