OEM catless vs. aftermarket up pipe DEBATE
 

There seems to be an on going debate whether or not it makes sense to add an aftermarket up pipe to a car that already has a catless oem up pipe(ie, All sti and 06+ wrx). we’ve cut apart the oem catless and found some pretty nasty ridges around the oem flex joint which definitely aren’t good for flow. We’ve seen dyno comparisons on nasioc but I don’t recall seeing actual flow comparisons. Over the next few days we will be running some comparison tests on the flow bench to get some hard data for you guys.


CONSOLIDATED RESULTS FROM THREAD:

UP PIPE

Subaru OEM Cat'd Up Pipe at 28" - 164.7 CFM <--- BOOOO!
Subaru Gutted OEM Up Pipe at 28" - 216.1 CFM
Subaru OEM Catless Up Pipe at 28" - 244.6 CFM
Grimmspeed Up Pipe at 28" - 292.6 CFM

CFM increase of 20% or 48 CFM at 28" of water

I am honestly quite shocked by the difference between the catless oem and an aftermarket up pipe. My initial thought was that the aftermarket version would flow better but not by this much. I can only imagine what the difference is between an aftermarket and a cat'd oem.

Remember, this isnt max flow, this is just the flow at the industry standard of 28" of water...it is used for comparison, not determining max flow.

Subaru OEM Catless Up Pipe
http://www.grimmspeed.com/images/pro..._flowbench.jpg

GrimmSpeed Up Pipe
http://www.grimmspeed.com/images/pro..._flowbench.jpg



Ok here are the Cat'd OEM Up Pipe results
Subaru OEM Cat'd Up Pipe at 28" - 164.7 CFM <--- BOOOO!
CFM increase of 78% or 127.9 CFM at 28" of water vs. an aftermarket up pipe.

OEM Catted Up Pipe
http://www.grimmspeed.com/images/pro..._flowbench.jpg

Here is a graph of all three tests:
http://www.grimmspeed.com/images/pro...ch_results.jpg



Subaru Gutted OEM Up Pipe at 28" - 216.1 CFM

I was rather shocked by this number compared to the oem catless up pipe. The oem catless is still about 30cfm more than a gutted oem.


Subaru Gutted OEM Up Pipe
http://www.grimmspeed.com/images/pro..._flowbench.jpg




CROSSPIPE

Subaru OEM Crosspipe at 28" - 230.4 CFM
Grimmspeed Crosspipe at 28" - 315.5 CFM


Subaru OEM Crosspipe
http://www.grimmspeed.com/images/pro..._flowbench.jpg



GrimmSpeed Crosspipe
CFM increase of 37% or 85.1 CFM at 28" of water vs. oem crosspipe.
http://www.grimmspeed.com/images/pro..._flowbench.jpg

Justin

I like hard data. I would like to see how big the gain is.

The real first question is, what is the actual exhaust flow per cylinder at say 6000RPM at 20PSI boost at sea level at say 10:1 A/F?

After that you can evaluate the headers, crossover pipe and up-pipe.

Turbulence is bad, but in a pipe that flows 200% the required amount, it is not terribly significant. In a pipe that flows 90% the required amount, it can be a killer.

Buschur Racing did some dyno comparisons between an aftermarket uppipe and the stock STI one on a stock manifold. This was back when they were in the Subaru game. I forget the numbers but it was a significant increase - 5 or 10hp at the Stage 2 level.

Subscribed!

RESULTS ARE IN!


Subaru OEM Catless Up Pipe at 28" - 244.6 CFM
Grimmspeed Up Pipe at 28" - 292.6 CFM

CFM increase of 20% or 48 CFM at 28" of water

I am honestly quite shocked by the difference between the catless oem and an aftermarket up pipe. My initial thought was that the aftermarket version would flow better but not by this much. I can only imagine what the difference is between an aftermarket and a cat'd oem.

Remember, this isnt max flow, this is just the flow at the industry standard of 28" of water...it is used for comparison, not determining max flow.

Subaru OEM Catless Up Pipe
http://www.grimmspeed.com/images/pro..._flowbench.jpg

GrimmSpeed Up Pipe
http://www.grimmspeed.com/images/pro..._flowbench.jpg


Justin

That's cool. Any "real world" power gains on a typical setup dyno results?

we aren't doing that right now because its been done a bajillion times on the forums. :)
we wanted to do these flow bench numbers because we've never seen these types of numbers on the forums before.

Justin

Link?

i'd have to search nasioc. i know buschur was probably one of the last to do it. if you want to find it i'd search for "buscher dyno".

Is there an echo in here? ;)

Unfortunately the Buschur build/test thread has been deleted from NASIOC. I don't think he and the NASIOC Nazis got along very well. He tested things like uppipe stock vs. aftermarket, TGV's vs. TGV delete, intake stock vs. SRI vs. CAI, etc. It was an informative thread.

Actually... Google cache ftw:
http://74.125.155.132/search?q=cache...ient=firefox-a

http://img.photobucket.com/albums/v2.../WRXStage2.jpg


I'll let Grimm explain why 2.25" ID might be a little big on stock-mount turbos. :D

It's sort of like trying to blow out birthday candles by yawning. ;)

So that was a stage two 2.5L WRX? Doesn't look like it added much area under the curve, but a nice shift to the left is always nice.

What pipe did Buschur use? Was it a flex joint piece like the Grimspeed?

I'm just trying to help Grimmspeed. If I was in the market for a new UP, I'd want to see real world gains on a setup similar to mine.

Actually it's more an issue of 2.25" being larger than the gasket holes and the turbo hotside inlet diameter.

It was their own design with no flex IIRC.

So, yawning at a straw to blow out candles? :oops:

Ok here are the Cat'd OEM Up Pipe results

Subaru OEM Cat'd Up Pipe at 28" - 164.7 CFM <--- BOOOO!

CFM increase of 78% or 127.9 CFM at 28" of water vs. an aftermarket up pipe.

http://www.grimmspeed.com/images/pro..._flowbench.jpg

Here is a graph of all three tests:
http://www.grimmspeed.com/images/pro...ch_results.jpg

Needless to say, any type of aftermarket up pipe is going to be superior to any oem up pipe, even the oem catless up pipe.

Justin

Nicely done, Justin.

Personally I am sure that a good aftermarket up-pipe (like the GS one) would result in an increase in power over the factory catless one, especially with bigger turbos. But I don't think that flowbench numbers are the absolute last word in which one is "better". There is the velocity factor where higher velocity is better, and a bigger up-pipe will have lower exhaust gas velocity. Also there are up-pipes on the market that are likely too big in diameter, which would probably "flow better" on a flowbench, but they might be worse because of the lower exhaust gas velocity and the mismatched diameter steps at the inlet and/or outlet of the pipe.

The Grimmspeed up-pipe is a nice design that avoids the flow-killing step-up/step-down and is about the right size for most applications.

This is a great place to ask:
Does anyone know what the best uppipe would be to mate with a GruppeS UL header. I have not put the header on yet and now after reading this I think I should upgrade the uppipe as well. I would like to avoid the "flow killing step up/down". Does anyone have any aftermarket uppipes off their car I could take a look at? I do plan on staying with a stock mounted turbo. Curious about the Cobb Inconel, are they worth the price? Grimmspeed..? I think Perrin has a specific pipe size to minimize loss of velocity...

I ran the Perrin UP on my car when I had those headers. It seemed good, but I couldn't quantity it since I changed a ton of other stuff at the same time the headers/UP went on.

It seems you a fairly picky when it comes to car parts/upgrades, would you reccomend/run the same setup again?

I can't say I ever had any problems with it. Not like my Vishnu uppipe years ago that used to blow gaskets all the time.

Seriously. Like I had nothing better to do back then besides mail you new gaskets. :mad: :lol:

:lol:

Damn that was a long ass time ago. I've actually still got a stockpile of like 6 header to UP gaskets from the days when I had to swap them like once a month at the track.

Should I mention the JIC debacle? :p