Would a chmabered muffler be too detramnetal the the performance? I kno weveryone usual goes for straight through designs and I will most likely go with one as well but I was just curious how much back pressure a large 4" chambered muffler woudl cause the stock twins?

Man, if you had flowmasters, it would be deep and loud as hell! haha!

See thats the thing I dont want ultra loud...cops around here are douch bags and I get tickets around here form them every 6 months just cuz. Deep is good though, I wos looking at 1 large 70 series flow master used for trucks haha I thought it woul quite it up and give a good flow rate and maybe one dynomax race muffle rin the middle. Maybe with a ultra high flow metal substarte cat?

Do NOT run a chambered muffler. I don't know who told you they flow well, they just don't. If you want to really quiet your car down, get a larger-body offset entry/exit straight-through muffler. Magnaflows work well, Dynomax bullets are good if you want to add a little more muffling, and Borla XR-1s are a good choice as well. Again, if you care about your car, don't go cheap and get a chambered Homaster 70 series, just get a straight-through, stainless-steel packed muffler and be done with it.

and I know at least for the new mustangs flowmasters have been having trouble with quality lately

Thats exactly what I wanted to hear SNUB, thanks, no one told me anything I was just curious actually. I was actually looking at a magnaflow and dynomax, I wasn't sure abotu borlas though.

Here is your answer based on actual tests.

First off, the stock muffler can cause approximately 4 -->5 PSI of back pressure under the maximum performance conditions one could expect to achieve with good twins and all the mods.

Second, forget about Flowmaster; their flow is mediocre and it's too noisy for the amount of restriction they cause. There are better choices. I do like the Dynomax super turbo series; most flow pretty well and they are real, chambered mufflers that are reasonably quiet.

The stock FD muffler flows about 274 cfm at 20.3" (H2O). Using this figure, you can compare it directly to the Dynomax models in their catalog. Now, because back pressure varies as the square of flow, if you select a muffler with twice as much flow as stock at the same reference pressure (i.e., 548cfm @20.3"), you can expect that muffler to produce only about 1 PSI of backpressure under the max conditions (or about 25% of stock).

Finally, regarding CATs. The stock cat flows around 375cfm @ 20.3" of water, 2-1/2" pipes and all. The 3" high-flow cats that I have tested (based on catco & carsound) were about the same at 377cfm. (Yes you read that correctly--the reason for this is that HF cats are high flow per unit area, but because they are much smaller than the stock cat there is NO significant net flow gain. Based on the foregoing flow rates, you can expect a properly functioning cat to cause about 2 PSI back pressure under the maximum performance conditions described above.

Hope this helps.

I have an rx7store resonated midpipe with the magnaflow muffler, and an apex GT spec catback. I'm sure if you went with a second magnaflow it would be even more mellow. I actually bought a thermal research catback, and I'm interested in how it will sound. I must warn you though, this combo will produce lots of boost creep, even with a ported wastegate in our weather on stock twins.

Here's a clip of my FD so you can hear it.

http://videos.streetfire.net/video/b...7c015a1f66.htm

Thought I'd repost this with a title that makes it more seach friendly.

:-) neil

At the least, it would be great to include as a link in the FAQ thread.

Those 2 paragraphs alone are more valuable than that BS 20 page thread about buying an exhaust based upon pictures...