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Old 04-09-2012, 11:58 AM   #1
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Default Intercooler pipe sizing and spool/ turbo efficiency

I have been debating about my car lately. My SR20 turbo and FM hot side parts is a really reliable setup. I thought about going with a Godspeed 3076 turbo, and running low boost to set my power goal around 250whp, but I am thinking again. My Garrett SR20 has been the most reliable turbo I ever had on my car, and I am kind of attached to it. I have been driving my car for the past year on 7psi with my stock injectors, and I am happy about the way it feels. I dyno'd at 225whp/207wtq 3/26/11 on right around 12 psi (when I ran RX7 460's). The car felt really fast at the power level.
I really like this turbo, as it's cheap and reliable, but the only thing I can say I don't care for is the super fast spool.
My intercooler is a Flyin Miata intercooler, and it uses 2 1/2" couplings. I actually have 2 1/2" to 2" reducer couplings on it, because my old I/C setup used 2" piping. The current plumbing setup I have now is 1/2 assed and I want to redo it with 2 1/2". If I do, this will also increase the volume that the turbo has to flow the air through, so what will happen? I'm guessing that my turbo should spool later than it does? Would this change the efficiency level of my turbo? If so, how?

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Old 04-09-2012, 12:06 PM   #2
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I'm curious as to the opinions on this, as well. My previous setup was 2" on the hot side charge piping, and 2.5" on the cold side up to the TB. New setup will be 2.5" throughout unless I have a compelling reason to re-create what I had last time.

Also, this answer may be difference once you're sliding up over the 250whp level into the 300's, as at that point you're pushing a ton of weight volume through the IC tract anyway with a bigger turbo, and the increased volume is likely somewhat negligible.

However, I'm rusty on this type of stuff since I've been away from the game for so long.
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Old 04-09-2012, 12:18 PM   #3
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I also just gutted my (spare) upper plenum, I wonder what kind of effect that will have with a small turbo. I mean, sure I'm making more boost, but I'm also not moving as many CFM's. I'm thinking the gutted plenum won't be beneficial for my application, but the 2 1/2" plumbing will slow my spool a bit. I have no idea what will happen to the turbo's max boost level though.
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Old 04-09-2012, 12:19 PM   #4
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So let me get this straight: you want slow spool and low power? sounds like the worst combo ever lol.

going from 2" to 2.5" on such a low boost/small turbo setup will do very little change.
friend went from 2 or 2.25 to full 3" with a WAY larger ic and saw like 300rpm delay in spoolup if that.
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Old 04-09-2012, 12:22 PM   #5
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Quote:
Originally Posted by 18psi View Post
So let me get this straight: you want slow spool and low power? sounds like the worst combo ever lol.
I want to run my 425cc injectors and run around 12 psi boost again, not 7. I also want to clean up my I/C/ plumbing and make it look not so rigged up. I just don't want to cause a negative effect in doing this and am curious if that's going to happen.
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Old 04-09-2012, 12:24 PM   #6
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well just re-do it 2.5 all the way and clean it up but dont expect any real difference
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Old 04-09-2012, 01:43 PM   #7
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Whats wrong with super fast spool up to the op?
Also I would stay 2inch intercooler piping if I were to do it again.

I've seen 2" flow enough to make 450wtq\440hp~
V8 but still pretty interesting to see that much power with that little piping.
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Old 04-09-2012, 01:46 PM   #8
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"its possible" =/= "its efficient"
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Old 04-09-2012, 02:03 PM   #9
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I never said anything about it being efficient. Just that it was possible.
I still would stay with 2inch sub 250wtq~
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Old 04-09-2012, 02:19 PM   #10
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I ran 2-1/2" piping right off the outlet of my old 2554. Spooled like a light switch.

Thirdgen, I'd go with a larger turbo at less boost. I've been having fun with the .86 2870 that replaced my 2554. It's getting replaced with a much larger turbo later this year, too.

Why not swap out what you have for a .86 2860/71 and see how you like it?
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Old 04-10-2012, 02:06 PM   #11
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You people want SLOWER spool? I often wish I had a 2554 instead of my 2560 just for a few extra RPM of spool. I have heard those won't quite do 240whp, though, so I will stick with what I've got. Crazy fools.
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Old 04-10-2012, 02:45 PM   #12
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Not necessarily slower spool, but a power band shift.
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Old 04-10-2012, 02:47 PM   #13
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i want a larger powerband.
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Old 04-10-2012, 03:05 PM   #14
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I want vtak powerband: nothing nothing nothing nothing SPOOOOOL
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Old 04-10-2012, 03:48 PM   #15
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I saw the following info posted in a DSM forum. If it is correct then it looks like 2 inch is OK for most situations.

Quote:
0.4 Mach is the point at which air becomes turbulent and losses in efficiency start to occur exponentially. The key is to stay under that speed. You want to use the smallest piping possible that still flows enough to meet your needs. Larger than necessary piping increases lag time with no measurable gain

The velocities are in miles per hour and mach, and the flow rates are in cfm. Measurements for the piping are in inches.


2" piping
1.57 x 2 = 3.14 sq in
300 cfm = 156 mph = 0.20 mach
400 cfm = 208 mph = 0.27 mach
500 cfm = 261 mph = 0.34 mach
585 cfm max = 304 mph = 0.40 mach........approx 390 bhp


2.25" piping
3.9740625 sq in = 1.98703125 x 2
300 cfm = 123 mph = 0.16 mach
400 cfm = 164 mph = 0.21 mach
500 cfm = 205 mph = 0.26 mach
600 cfm = 247 mph = 0.32 mach
700 cfm = 288 mph = 0.37 mach
740 cfm max = 304 mph = 0.40 mach........approx 493 bhp


2.5" piping
4.90625 sq in = 2.453125 x 2
300 cfm = 100 mph = 0.13 mach
400 cfm = 133 mph = 0.17 mach
500 cfm = 166 mph = 0.21 mach
600 cfm = 200 mph = 0.26 mach
700 cfm = 233 mph = 0.30 mach
800 cfm = 266 mph = 0.34 mach
900 cfm = 300 mph = 0.39 mach
913 cfm max = 304 mph = 0.40 mach........ approx 608 bhp
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Old 04-10-2012, 04:01 PM   #16
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that's cool and all, but does it account for bends/transitions/beads/ports and other things not found in a straight and true pipe? I'm thinking no.
300bhp is something like 290-310whp or something like that? I bet 2" is definitely restrictive for those power levels, especially past 5k rpm. I'm open to being proven wrong though.
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Old 12-05-2012, 11:26 PM   #17
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bumping this thread to say that I'M going to TRY to prove MYSELF wrong
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Old 12-05-2012, 11:51 PM   #18
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Quote:
Originally Posted by 18psi View Post
bumping this thread to say that I'M going to TRY to prove MYSELF wrong
I'm following that discussion as I've for a while wanted to redo the hot side on my MSM. That stock setup is far from optimal. But then again, it seems to flow well enough for right ~200whp. The cold side on the other hand seems pretty decent.

I'm thinking 2" should be just right for around 300hp and 500cfm @ 7000rms. My "long" term goal.
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Old 12-05-2012, 11:54 PM   #19
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My hotside will hopefully be a lot shorter and smoother. Like my previous:




but in 2" and hopefully even still a little shorter

we'll see.
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Intercooler pipe sizing and spool/ turbo efficiency-0722101656-01.jpg   Intercooler pipe sizing and spool/ turbo efficiency-0722101744-01.jpg  
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Old 12-06-2012, 09:40 AM   #20
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that's where I'd put my intake if I had a hole there. Its actually something I've always wanted to do.
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