What Flowmaster to use???????

[69 longhorn]

I would go with 2 1/2" pipe,& a set of 50s. The 40s arent too bad till you get out on the road. 4.10 gears will make em right on that resonance point at hyway speed. On the longhorn,you can move em back,& that will help tone em down. also an addition of an H pipe in the system will mellow them. I run a 383(approx 390 hp/440 tork),& had headers,2 1/4 pipe,muffs just behind the cab,40s,& 2 1/4 tail pipes straight out the back/with 3 1/2 X 18" cans.....it was too beligerent! I have gone to 2 1/2 " pipe,added an H pipe, & moved the muffs back to hang at the cross member just ahead of the axle. I just have turn downs (for now),but the system is quieter......untill you stand on the throttle. Good luck.....69 longhorn.