[scottj]

JAM,
Nothing I've seen out-performs the perforated-core straight-thru design. The straight-thru LOUVERED-core mufflers are the ones that perform poorly.

Most of the time on our dirt engines a 3-1/2" perf-core makes more torque than an open header. 3 weeks ago I saw an 820HP 418 cid Ford SC1 dirt engine pick up 5ft/lb of torque on the dyno using a Dynatech Split-Flow muffler. The shop that built the engine does allot of circle track stuff, ranging from local dirt and asphalt to super-speedway lease engine programs for Busch and Craftsman Truck. They are also the shop that did all the Dyno development for Dynatech on their Tri-Y dirt headers. I’ve seen similar gains with the Borla perf-core when that was the spec muffler for the series now known as the World Of Outlaw dirt Late Models.
I’ve also raced at tracks that required the Lobak spiral-core and that design is only used when noise requirements make it absolutely required by the track. It kills the throttle response on the track to a much greater extent than the dyno losses indicate. Everyone I know that had to use them on a dirt car ran a Y-pipe off the header and ran 2 per side.

As I said previously, my engines are built and tuned as open exhaust race engines. A high-backpressure muffler like the Lobak really took the fun out of the Cobra due to lazy throttle response. It just lacked any crispness that I knew I should have. The jetting on my engine combination is just very-slightly fat with the Lobak and not the cause of the losses felt and seen on the dyno.

I think Red has an excellent design with the louvered core. But, I can’t speak to how much benefit it is to performance on a street build when compared to the Lobak or any other design. I also can't comment on what will be required to tune for them. I just don’t have any first-hand experience testing with street-type builds.
Scott
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