OEM catless vs. aftermarket up pipe DEBATE

**GrimmSpeed** · #1: 03-10-2010, 11:05 PM

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

GrimmSpeed Up Pipe

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

Here is a graph of all three tests:

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

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

Subaru OEM Crosspipe

GrimmSpeed Crosspipe
CFM increase of 37% or 85.1 CFM at 28" of water vs. oem crosspipe.

**LosAngelesLGT** · #2: 03-10-2010, 11:26 PM

Quote:

Originally Posted by GrimmSpeed

...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....

The people demand PICS!

**Infamous1** · #3: 03-10-2010, 11:37 PM

Good stuff, very interesting!

**GrimmSpeed** · #4: 03-10-2010, 11:55 PM

Quote:

Originally Posted by LosAngelesLGT

The people demand PICS!

i'll look around the shop. it was awhile ago that we did that and we recently moved shops so i'm not sure if i can find it any where.

if i can't find it i suppose we could always do another sacrificial bandsawing

Justin

**LosAngelesLGT** · #5: 03-11-2010, 12:03 AM

Quote:

Originally Posted by GrimmSpeed

i'll look around the shop. it was awhile ago that we did that and we recently moved shops so i'm not sure if i can find it any where.

if i can't find it i suppose we could always do another sacrificial bandsawing

Justin

Justin,

I hate to say this, and you certainly do not have to do it but... If you REALLY want to illustrate the difference, it would be super cool to have a halfed GS and halfed OEM next to each other. It would look sick on your site too. If you cannot, it is totally understandable!!!

BTW- I am am completely, totally bonkers

over your 12 layer up to manifold gasket.

MMMM, 12 layer burrito gasket...

**snow05gtRI** · #6: 03-11-2010, 12:29 AM

nice...always good to see data

**m sprank** · #7: 03-11-2010, 12:28 PM

Which oem flex joint? My 08 uppipe was solid all the way. No EGT, no flex joint. I replaced it with a Cobb because the Cobb was lighter. Inner pipe of the OEM not as smooth as the Cobb. Where the pipe penetrates the flange OEM left a ridge/gap.

Is WRX/Sti uppipe different from LGT in some way?

**Bolksey85** · #8: 03-11-2010, 01:45 PM

*In for results*
I've kinda wondered if there was an advantage to an aftermarket one over OEM. I assumed there was considering how much of a bottleneck the DP is. Hopefully this will prove there is an advantage to a GS piece over an STi/gutted OEM/08+LGT UP.

**GTTuner** · #9: 03-11-2010, 01:49 PM

Let the numbers speak, I don't care what they look like inside.

**blakout** · #**10:** 03-11-2010, 01:51 PM

Very interested in this...subscribed

**black318i** · #**11:** 03-11-2010, 03:26 PM

I'm pretty sure the GS will flow better, but I'm more interested in acctual dyno numbers/curve and how spool is affected.

**captainhook** · #**12:** 03-11-2010, 03:27 PM

Interesting indeed, in for results.

**BoozeRS05** · #**13:** 03-11-2010, 07:30 PM

I'm using an 07 LGT UP and I got $5 says there's no real difference. Factory heatshields might even help on the OEM UP..?

**biz77** · #**14:** 03-12-2010, 10:29 AM

It's too bad David Buschur's build-up on thier shop 2006 WRX TR over on NASIOC was deleted. He showed results with a VF39 with stock U/P, his own U/P and then his own U/P with ported exhaust manifold. Each addition was retuned to maximize the gains and the results were surprising.

**GrimmSpeed** · #**15:** 03-15-2010, 10:09 AM

RESULTS ARE IN NOW!

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

GrimmSpeed Up Pipe

Justin