Would someone mind explaining the difference in down pipes - some are a single pipe, others have a second pipe open and a third has the second pipe reconnecting to the main pipe.

while there are down pipe threads I have not come across one that explains the differences.

 

regular downpipe replacement: http://www.maperformance.com/megan-r...sdp-mle08.html

cat-elim downpipe: http://www.maperformance.com/invidia...s09mexdpn.html

o2 elim downpipe (note the internal or external wastegate dump option): http://www.maperformance.com/map-sta...e-ss-evox.html

o2 elim downpipe with bellmouth (style used primarily on Subarus): http://www.maperformance.com/ams-wid...-evox-wdp.html

The downpipe replacement and cat-elim (built in testpipe) styles are straight forward enough. An internal route o2 elim dp keeps the gasses passing through the wategate seperate until downstream in the downpipe; this is done to reduce turbulence while still keeping the exhaust much quieter than an external dump. The external dumping o2 elim dp routes the gasses passing through the wategate directly to atmosphere; this minimizes turbulence but is very loud when the wastegate is open. The bellmouth style (AMS o2 elim dp) is similar to the design used on a lot of Subaru downpipes and the Evo X stock o2 housing; it is very simple but will have the highest amount of turbulence in the exhaust flow post-turbo. Although this method has proven to be effective, it is still not ideal.

 

Thank you very very much. My son just picked up an Evo X last week and we want to do a complete exhaust so we are just starting our research. Its overwhelming the choices available for these cars.

 

There are a lot of AMS fans but I've always thought it was an inferior design. I appreciate your posts on the X forums. There are probably more X owners that could benefit from your wisdom than the 8/9 guys.

 

The AMS DP is cast, which should be more durable over the long term. It also uses the stock engine mounting bracket for a sturdier attachment. It has a flex section (some of the tubular ones have it too) for independent movement between the DP and the rest of the exhaust.

 

All very true as well. The AMS design does have some very beneficial advantages as well. I don't think their is one ideal o2 elim dp design on the market currently, but I feel going with the AMS, ETS, or MAP is a smart bet. I prefer the ETS over the MAP b/c of the wastegate outlet flange design, but it also more expensive and again both have proven to be very effective.

 

All of those designs will yield similar gains based on what I have seen. A lot of it is personal preferancne, and how loud you want the car to be.