Anyone have these? It seems like the install would be a breeze. They advertise 12.2 hp and 12.3 ft-lb gains. They cost $150 more than Macs but they are 50-state legal. What numbers do Macs give? I have ground clearance issues where I live so I can't go the long tube route. Thanks in advance.

 

Macs are enviro-wacko friendly too!! And with the price difference, why would you go the route of less power?

 

Mac's are not technically smog legal becuase they move the cats from the stock position. That's why you only see CARB exemptions on shorty headers. From what the CA guys tell me, they'll fail the visual inspection if the cats aren't in the stock location.

As for the original question, those of us with '00-'02 model year cars have the new cast manifolds, and usually don't see any noticable increase in peak hp or torque. Some have argued that the 1 5/8" primaries increase off-idle power, but since no one ever posts anything but peak numbers those claims have been hard to verify. If you have a '98 or '99 LS1 with the older style manifolds then you'll see small gains, however not the 10+ hp & ft*lbs that JBA is quoting.

Now, I'm assuming that you've got an internally stock engine, since you're concerned about smog. If you're running an aftermarket cam and/or heads, you may see larger gains with shorty headers.

 

those are flywheel #'s not at the tire.. the macs make more than that at the tire

 

JBA's are worthless. If you bought them it would be an appearance mod, not a hp one.