M.B. Doc or Benzmac 16v exhaust question
 

M.B. Doc or Benzmac,

i know this has been discussed before but i can't find a good answer to this question.

i've got a question about exhaust on my 16v. currently i have a 2" galvanized steel pipe that runs from the 2 to 1 collector, near the drive shaft, and under the driver's side rear subframe to an ANSA muffler. I had this put on when i didn't know that the stock size is larger than 2". anyway the 2 to 1 collector has a crack that has been growning for the past 10k miles (likely from when i had some serious driveshaft vibrations causing cracks in other areas of the exhaust). since i've got to have the collector welded i figured i should have a whole new pipe bent and a new universal muffler installed. this time i would like it to stay on the passenger's side of the drive shaft and go under the passenger's side of the rear subframe, to keep it away from the fuel pump and to tuck in up under the car a little more than it is now. my engine is stock with exception of a K&N filter. ignition timing is advanced and fuel mix is richened slightly. i'm not planning on any major engine modifications anymore (wish i could but i've got to be practical). my question is, for a custom pipe bent from the 2 to 1 collector back to a universal straight through muffler (no cat or resonator) what size pipe will give me the best flow, 2.25" or 2.5"? and, for the tight bends that will be necessary for the section under and behind the subframe, should i use mandrel bends? is it worth the additional investment in parts and labor (since i will have someone do this for me) compared to standard pinch type bends produced by a normal pipe bender?

thanks as always for the significant time you spend helping people on this board,

Doubt that the 2.5" pipe can be bent to make the sharp turn by the differential. OF course mandrel bends do work better & won't drop the HP like crimp bends.

With 2.25" pipe that uses mandrel bends you will get more flow than a 2.5" with crimp bends!

so, if i use mandrel bends for the tight turns near the rear should i go for 2.5" or 2.25"? it looks like the 2 to 1 collector outputs into a 2" pipe. to properly run 2.25 or 2.5 i would have to cut off the collector more forward to get a larger diameter opening. will this ruin my scavenging?

thanks

You should be OK. You can buy the bends then have the welded.

with either size i plan to buy mandrel bends and have them welded in. is there going to be any benefit to using 2.5" over 2.25" on a 2.3L 170HP engine? i want to use whatever will flow best, not just the largest possible diameter.

thanks again,

edited portion:

i found the answer. the 2 to 1 collector collects down to a pipe about 2.2", so to keep the turbulence down i'll just use a 2.25" and call it good.

thanks everyone,