I just replaced my stock muffler with a straight through muffler( stock one get all rusted). since I have this new muffler the car seems to shift to 4th gear at 115 mph. With the stock muffler it would shift to 4th at around 125mph. I'm talking without playing with the OD. Is this happening beacuse of loosing backpressure?
anybody know what I should do? get a bpipe maybe?
any info would be great. thanks.

 

Time to start playing with OD. Keep"OD off" until redline in third gear...130mph.

 

thanks,
but I'm trying to find solution without playing the OD.
also, I have a nice deep tone, but still too loud for me, what do u think if I add one more resonator beside the stock one? will it soften the muffler sound? what about performance wise with that extra resonator?