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Old 06-17-2008, 11:56 PM   #21
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Originally Posted by Thucydides View Post
This is great information, gentlemen, and I appreciate all of your input very much. There's no other place I could have gotten this much useful information, from so many sources, so quickly. Thanks to everyone!



Using Garrett's approach, 250 brake hp requires almost 16 lbs boost (2.38 PR) and a 27.5 lbs/minute flow rate. Plotting that on the GT2554R efficiency chart puts the point way at the upper right of the very last line, and at the 60% efficiency level. Maybe it's doable, but only barely, and a very big intercooler is probably a good idea.

On the GT2560R chart the point is also at the upper right corner, but right between the 72% and 73% efficiency lines; it's a good match for those numbers. Any more HP and you're looking at the next size up.

By the way, J.T., do you drive a white NA with blue racing stripes? Saw one yesterday going through Sacto.
fixed

And if you don't mind me askin where you got the 27.5lb/min?
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Old 06-18-2008, 12:08 AM   #22
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I found max boost and am gonna guess that it doesn't quite take 16psi since theres people doing it lower. I would do the calculations but I'm a lil lazy.

Edit: I'll put my foot in my mouth, I threw some numbers at the equations and came up with around 15psi. So a PR of right about 2. my bad
Well, there are some assumptions you've got to make (air/fuel ratio, brake specific fuel consumption, volumetric efficiency, etc.) and I went conservative on them because what the hell do I know. No doubt there are tuners out there that are optimizing these parameters and are therefore making more power with less boost, so your guess might be the one that's closer, at least for some folks.
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Old 06-18-2008, 12:16 AM   #23
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fixed

And if you don't mind me askin where you got the 27.5lb/min?
That is calculated from the power goal (250 HP), the Air:Fuel Ratio (12:1), and the brake specific fuel consumption (0.55 lb/HP/hr). There's a constant in there also (60) to convert hours to minutes so you can end up with lbs/minute.

So the formula is:

Flow rate (in lbs/min) = HP*AF ratio* (BSFC/60)

250*12*(0.55/60) = 27.5
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Old 06-18-2008, 12:22 AM   #24
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Oh ok, cause what I found in Corky's book lead me to 24.7ish. But I assumed Volumetric efficiency of 85% and it didn't factor in all that other good stuff
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Old 06-18-2008, 12:22 AM   #25
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I run both these turbos on my 2 94's.

My 2560 has ZERO lag but I have the fabled AbsurdFlow kit with custom tubular manifold, full 3" exhaust including downpipe with no angles sharper than 55 degrees. My intake air temps are awesome with an 18x12x3 FMIC.

My 2554 DOES NOT spool as quickly. It's part of a BEGi S kit with the restrictive base downpipe and restrictive Racing Beat naturally aspirated duals. I see much higher IATs with the smaller turbo, partially due to the smaller FMIC I run with it.

I'm sure if the 54 was on the AbsurbFlow kit it would spool before I even got out of bed and started the car so it's really not a fair comparison. Just illustrating that the rest of the system plays a huge role in how the turbo performs.

I went with the 54 on my daily driver because I wanted the spool to be close to what I am used to with the Machine(2560) without going the custom route. I occasionally auto-x this car too so quick spool was important. I am planning on having Tim build a 3" dp for it though. If I was to do it again I would opt for the 2560. Actually, I am kinda actively looking for a good deal on a 2560 for my daily and then save the 54 for the girlfriend's 94.

I think the 54 would be an excellent choice for a 1.6 although I just installed a 2560 BEGi S kit on a friend's 90 and even that had acceptable spool.

So in closing I say go for the 2560.
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Old 06-18-2008, 02:20 AM   #26
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Now there's a comparison for you...
For anything better you'd have to take a flight to NJ and see for yourself!
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Old 06-23-2008, 12:58 PM   #27
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Originally Posted by paul View Post
I run both these turbos on my 2 94's.

My 2560 has ZERO lag but I have the fabled AbsurdFlow kit with custom tubular manifold, full 3" exhaust including downpipe with no angles sharper than 55 degrees. My intake air temps are awesome with an 18x12x3 FMIC.

My 2554 DOES NOT spool as quickly. It's part of a BEGi S kit with the restrictive base downpipe and restrictive Racing Beat naturally aspirated duals. I see much higher IATs with the smaller turbo, partially due to the smaller FMIC I run with it.

I'm sure if the 54 was on the AbsurbFlow kit it would spool before I even got out of bed and started the car so it's really not a fair comparison. Just illustrating that the rest of the system plays a huge role in how the turbo performs.

I went with the 54 on my daily driver because I wanted the spool to be close to what I am used to with the Machine(2560) without going the custom route. I occasionally auto-x this car too so quick spool was important. I am planning on having Tim build a 3" dp for it though. If I was to do it again I would opt for the 2560. Actually, I am kinda actively looking for a good deal on a 2560 for my daily and then save the 54 for the girlfriend's 94.

I think the 54 would be an excellent choice for a 1.6 although I just installed a 2560 BEGi S kit on a friend's 90 and even that had acceptable spool.

So in closing I say go for the 2560.
Paul, what IAT's are you seeing with the 54?

BTW. It's Joe with the white '94 from PNC the other day.
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