O2 Downpipe style = most power?
True but divorced wastegate and open dump are essentially the same, except open dump will allow slightly more power since you relieve that little extra back pressure. Divorced wastegate is still a great comparison between bellmouth.
Proceed with caution on that piece written by Cobb. Do you know how old that is? I remember seeing this several years ago. It tends to be Subaru biased in many sections. It doesn't consider open dumps because Subarus typically don't run them.
NOTE: You will run yourself in circles trying to get a definitive answer to never find one. A wise man once told me, open dump downpipes are a gimmick. For several reasons, I believe this "wise man." Therefore, I decided to buy the AMS unit. It's a proven piece that doesn't crack and performs.
NOTE: You will run yourself in circles trying to get a definitive answer to never find one. A wise man once told me, open dump downpipes are a gimmick. For several reasons, I believe this "wise man." Therefore, I decided to buy the AMS unit. It's a proven piece that doesn't crack and performs.
Last edited by Clark_Kent; Feb 4, 2010 at 11:49 AM.
Proceed with caution on that piece written by Cobb. Do you know how old that is? I remember seeing this several years ago. It tends to be Subaru biased in many sections. It doesn't consider open dumps because Subarus typically don't run them.
NOTE: You will run yourself in circles trying to get a definitive answer to never find one. A wise man once told me, open dump downpipes are a gimmick. For several reasons, I believe this "wise man." Therefore, I decided to buy the AMS unit. It's a proven piece that doesn't crack and performs.
NOTE: You will run yourself in circles trying to get a definitive answer to never find one. A wise man once told me, open dump downpipes are a gimmick. For several reasons, I believe this "wise man." Therefore, I decided to buy the AMS unit. It's a proven piece that doesn't crack and performs.
I'm a newbie, been reading (using the search) a lot and I think I'm more confuse than anything... so here are the 3 setups that I'm going for (can you guess which ones?)… AMS, ETS, Rexpeed. What I'm looking for is reliability and no check engine lights. Why does ETS use J-Pipe O2 bung versus AMS using a normal bung? Will I need a spacer with the AMS or Rexpeed? Is the AMS the only one that keeps using a high-flow cat? I should also let you guys know that eventually I plan on upgrading the stock turbo (and all the goodies that need to be upgraded) but that will come in a year or so. I will be getting the car tuned once I get the exhaust and intake bolt ons, I was told its smart to ride the car for ~1000 miles before getting it tuned once I get the bolt ons?
Last edited by erniebu; Apr 7, 2010 at 10:51 PM.
Are you referring to the test pipe? If so, we use a J-style bung to prevent any type of check engine light in the system. We also add a bend to the pipe so it will not rattle against the drive shaft shield.
ETS vs Competitor test pipe. You can see how the competitor pipe will rattle against the drive shaft.
The O2/Downpipe we use a standard o2 bung (not sensitive to CEL like the test pipe) The downpipe we build also separates the wastegate from the exhaust gases to prevent any type of turbulence when the wastegate opens and closes creating a very high flowing o2/downpipe.
The flange on our downpipe matches the turbine housing perfectly.
We also provide flange gaskets for the turbine and exhaust side.
Thanks!
Michael
ETS vs Competitor test pipe. You can see how the competitor pipe will rattle against the drive shaft.
The O2/Downpipe we use a standard o2 bung (not sensitive to CEL like the test pipe) The downpipe we build also separates the wastegate from the exhaust gases to prevent any type of turbulence when the wastegate opens and closes creating a very high flowing o2/downpipe.
The flange on our downpipe matches the turbine housing perfectly.
We also provide flange gaskets for the turbine and exhaust side.
Thanks!
Michael
Search on the Cobb website. They had a white paper posted with all the different packaging, power and complexity trade offs that goes into down pipe design.
But why bother? Just get the AMS:
- big bell mouth
- 3 inch
- cast
- flex section
- race proven
You won't be disappointed.
But why bother? Just get the AMS:
- big bell mouth
- 3 inch
- cast
- flex section
- race proven
You won't be disappointed.
if you dont care about noise i would get a open dump dp they make power and hold boost better at high rpms
We designed all our parts to work with there oem counter part. Test pipe works with stock downpipe and catback, downpipe works with stock cat and catback works with stock cat 
Evolving Member
Joined: May 2008
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From: Oxnard, CA
Originally Posted by Jason Kavanaugh@Garrett
As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal but I've never seen one in use (and doubt it would be measurably superior to a straight diffuser). The wastegate flow would be via a completely divorced (separated from the main turbine discharge flow) dumptube. Due the realities of packaging, cost, and emissions compliance this config is rarely possible on street cars. You will, however, see this type of layout on dedicated race vehicles.
A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.
If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.
A large "bellmouth" config which combines the turbine discharge and wastegate flow (without a divider between the two) is certainly better than the compromised stock routing, but not as effective as the above.
If an integrated exhaust (non-divorced wastegate flow) is required, keep the wastegate flow separate from the main turbine discharge flow for ~12-18" before reintroducing it. This will minimize the impact on turbine efficiency-- the introduction of the wastegate flow disrupts the flow field of the main turbine discharge flow.
Comparing the two bellmouth designs, I've never seen either one so I can only speculate. But based on your description, and assuming neither of them have a divider wall/tongue between the turbine discharge and wg dump, I'd venture that you'd be hard pressed to measure a difference between the two. The more gradual taper intuitively appears more desirable, but it's likely that it's beyond the point of diminishing returns. Either one sounds like it will improve the wastegate's discharge coefficient over the stock config, which will constitute the single biggest difference. This will allow more control over boost creep. Neither is as optimal as the divorced wastegate flow arrangement, however.
There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.
There's more to it, though-- if a larger bellmouth is excessively large right at the turbine discharge (a large step diameter increase), there will be an unrecoverable dump loss that will contribute to backpressure. This is why a gradual increase in diameter, like the conical diffuser mentioned earlier, is desirable at the turbine discharge.