Well, I used to work for Dynomax & I can assure you, a 2.5" version of the Super Turbo flows better than a 2.5" or 3" 2 chamber, 3 chamber, or Delta flow Flowmaster. The 3" Flowmaster versions had flow rates of around 350 scfm, while the 2.5" Dynomax Super Turbos have flow rates of around 410-420 scfm. Comparative OE mufflers have flow rates of usually under 200 scfm. I remember buying a pair of 16" bodied Chrysler "Hemi" mufflers from Mitchell Motors back in the early 80's - to replace the 20" bodied originals on my old '71 Hemi Charger. The mufflers from Mitchell flowed like CRAP - I could immediately tell they were restrictive. Back then I didn't know crap about exhaust. I should have installed a set of Walker Red Line Z mufflers, which evolved into the Super Turbos.

The big differences internally between a Dynomax Super Turbo & an OE muffler are two things: the size of the internal perf tubes, & the Super Turbos have flow directors (bank turns) at each end, & OE's do not, and most other performance mufflers won't either. If you buy a 2.5" in/out Super Turbo, it will have 2.5" flow tubes inside. An OE type muffler with 2.5" inlet/outlet, will usually have 2" dia internals. A CHEAP, crappy turbo muffler (like the Thrush California Boss Turbos) have 2 flow tubes internally & NO packing, plus the flow tubes are smaller diameter. Super Turbos have a fiberglass mat that wraps around the center section of the muffler (you can see it in the photo someone posted), but this mat breaks down in about a year or two, & the mufflers will get louder - especially the 14" ones. Some oval mufflers have two flow tubes, some have 3. The Super Turbos are GOOD turbo mufflers. The Dynomax Ultra-Flow mufflers are straight-through, & they do not "tune" the sound like Super Turbos do, so they sound different than each other. From a flow standpoint, the scfm of a 2.5" 14/20" Super Turbo offset/center is around 410, and a straight-through Ultra Flow is around 1100. There is a HUGE difference in flow, but do you really need the extra flow of the Ultra Flow? Only a few dyno runs could tell you. Bob Karakashian & many of the other guys running in the Pure Stock Drags are using the Dynomax Ultra Flows. Those WAAAAAY outflow flowmasters & all other non straight-through oval mufflers. The stainless Ultra Flows with the stock-style spun-locked heads, flow the same as the Dynomax race series welded construction mufflers - also now called Ultra Flows. The welded series are offered in bigger flowpath & bigger in/out than the stainless ones, so there is more variety. On a closing note, I don't know what the internals are like in the Accurate mufflers, & I don't know who is building them for them - I doubt they have the equipment to build them & especially fab the spun-locked heads. If they do, then that's impressive.

There are quite a few mufflers currently in the Dynomax & Thrush line that I suggested & partially designed. There were also ones that I tried to get them to bring to market, but was unsuccessful. One was reverse flow Super Turbos in 2.25" & 2.5" versions for AAR's & T/A's - the standard oval size but 20" long. *They currently offer these reverse flow mufflers, but they are only 14" long bodies - not long enough. Those were referred to as "fabricator" mufflers. I have been building my own chambered exhaust mufflers & mufflers for AC Cobras since 2002.

John,
747 is 2.25 in and out
and should be here by the end of the week

oh thats even worse , I thought I read it was 2.5 in ... need to get my glasses updated