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the previous exhaust set-up was a 2.5" high-flow cat, 2.5"piping and a flowmaster 40 series with a 2.5" inlet. On the S-afc i would get Airflow readings in the 88%-94% pretty consistently depending on how high i revved the motor. I put in a thrush muffler/resonator (2.5" in/out, perforated center) and got rid of the flowmaster in favor of my old arospeed bomb muffler (2.5" inlet, perforated center, 4.5" tip). Now my Airflow readings are in the 60%-67% range??? If anything i thought this set-up would be higher flowing... i don't understand it at all.
I really can't say it feels any slower or faster. The flowmaster was so god awful loud (think BIG aluminum trash can) it "felt" and sounded like I was doing mach 1 all the time. Now the tone is really deep but quiet at the same time.
I'm just really confused by the numbers and was hoping some one might have some insight.

i really dont know why that set-up would be more restrictive, that kinda sucks though. I'm gonna do my exhaust this weekend, 2.5in piping straight through to an unknown muffler because i dont know what to get (apexi, magnaflow, flowmaster, etc). I've been choking the bp with this stock 1 7/8th exhaust, i wonder how much power i'm losing....I'll let you know how it goes with mine, and if you know about how much power i am losing on the stock exhaust, let me know. Peace

flowmasters are better designed than those cheap ebay "canister' style mufflers....put it back on

mitmaks wrote:flowmasters are better designed than those cheap ebay "canister' style mufflers....put it back on

Flowmaster's are for v-8's. The "can" will flow better considering it's a straight through design. I had one long before I did my engine swap, and it did'nt sound too bad on the 4cyl. oh well.

not just for v8's they make them for 4, 6 and 8 cylinders, gotta call your local muffler shop and verify availabitlity, and theyre PROVEN muffler to gain hp and one of best mufflers out there

i still dont understand it: i took a grinder to the canister in the back (leaving the strait through perforated thrush resonator/muffler intact) and the AFL% went up 10%. but that is still almost 20% down from what it was. the only thing i can think happened is the guy seriously messed up a weld or something but i still don't think it would effect it that much? this is approaching $200 on different exhaust set-ups (just in labor and piping not mufflers) and i'm done with waisting the money.

Actually there is a simple explanation. The problem is you went from a chambers muffler to a "glasspacked" muffler. The problem with the packing in these mufflers is that not only do that adsorb sound they also absorb and retain heat. This retained heat creates a boundary layer of super heated gases that may not be moving at the same speed as the cooler gases flowing at the center of the pipe. This causes a restriction and turbulence as the exhaust gases pass through the packing in one of these muffler as the gases temp increases. The hotter they get the worse they flow and it is not unusual to see the packing to be blown out of the muffler in turbo cars if the interior diameter of the muffler is not sufficiently oversized at which point does little to muffle the sound. Mufflers such as the Flowmaster or even a Dynomax turbo muffler do the opposite. The chamber design has the advantage in that the chambers actually improve flow by expanding the hot exhaust gases when it enters each chamber. As the gases expand and loose thermal energy creating a low pressure zone behind a higher pressure zone. Or basically it creates a vacuum pulling more hot gases down the pipe from the engine that the exhaust system flows more gases through the pipe that what could naturally flow through a pipe of a continuous diameter. I am running a Flowmaster 60 delta with my 1.6 and it is only slightly louder at cruising speeds than stock and no cabin resonance at any rpm. Adding a resonated tip the extents past the rear bumper would drop the sound level a few db's more.

the problem is your piping. 2.5" is ludicrously large for a 1.8 BP.

Unless turbo'ed u should use 2" for the best powerband and 2.25" if you want to sacrifice low-midrange for slightly more top end.

Yoda wrote:Actually there is a simple explanation. The problem is you went from a chambers muffler to a "glasspacked" muffler. The problem with the packing in these mufflers is that not only do that adsorb sound they also absorb and retain heat. This retained heat creates a boundary layer of super heated gases that may not be moving at the same speed as the cooler gases flowing at the center of the pipe. This causes a restriction and turbulence as the exhaust gases pass through the packing in one of these muffler as the gases temp increases. The hotter they get the worse they flow and it is not unusual to see the packing to be blown out of the muffler in turbo cars if the interior diameter of the muffler is not sufficiently oversized at which point does little to muffle the sound. Mufflers such as the Flowmaster or even a Dynomax turbo muffler do the opposite. The chamber design has the advantage in that the chambers actually improve flow by expanding the hot exhaust gases when it enters each chamber. As the gases expand and loose thermal energy creating a low pressure zone behind a higher pressure zone. Or basically it creates a vacuum pulling more hot gases down the pipe from the engine that the exhaust system flows more gases through the pipe that what could naturally flow through a pipe of a continuous diameter. I am running a Flowmaster 60 delta with my 1.6 and it is only slightly louder at cruising speeds than stock and no cabin resonance at any rpm. Adding a resonated tip the extents past the rear bumper would drop the sound level a few db's more.

this makes sense, just the way I thought