I got these cherry bomb mufflers because they were cheap. Only have about 100 miles on em, and finally did some high reving of the ZZ4. I guess some mufflers just can't flow. Might explain why I felt the top end was not quite right. Better get some Flowmasters? Any other suggestions? Also I have 2.25 inch dual pipes. Is this too small for 400hp? I know the recommendation is 2.5inch but wondering how much it's really limiting the power. I don't rev high too much, and wondering if the smaller pipes might be helping the low end torque. I have Thorley Tri-Y headers and no H-pipe.