billybob6110

hello I have an issue I cant seem to figure out. I have hooker shorties 1 5/8 primes to 3" collectors. off that I have 2.5 inch pipe to 3 inch dynomax bullet mufflers. the issue im hearing is when im only at cruise speed 55-65 mph I get a noise out exhaust that sounds like car is having a lean miss. its not lean cause plugs are slightly black. I have timing at 36 deg all in by 3000 rpm. I have a 2800 stall on a 355 sbc. carb is an edelbrock 1405. I only hear the noise when cruising at them speeds. any other speed below is perfectly fine. what gives? any ideas?

skinny z

It's difficult to tell from the plugs the AFR at cruise unless after extended cruising (say 50 miles or so) you shut the engine off and coast to a stop.,Then read them. Even that is a dubious proposition.
Best bet if you are going to tune any carb is to invest in a wide band O2 sensor and gauge. Then you'll have instantaneous readings.

billybob6110

I don't kno if its carb related. if I go above the 65mph at a steady pace it goes away. its only at the 55-65 mph... im not sure what else to check.. some say its muffler resonance but im not so sure if its only at that mph and rpm

skinny z

Yes. Resonance could be the cause. Keep in mind that the state of tune will cause variations in the exhaust note as well. Lean may sound one way, rich another, advanced or retarded timing, something else.
Where does you exhaust exit?

billybob6110

it exits behind the front seats and turn downs toward the side of car

skinny z

There's a lot to be said for that exit location. I've heard plenty of people complain about it.

billybob6110

as in same thing i experience? noise? smell? I do mini smell fumes a little. im going to go back farther so it doesn't come in cabin no more

skinny z

Moving the exit as far back as you can will make a difference. If it's possible, try to get the tips to the rocker panel.
I'm guessing you have a muffler that's near the front as well? Try moving it/them as far back as possible too. That will definitely make a difference in how it sounds inside the cabin.

billybob6110

ya ill deff try to move them back. side exit only looks good with boom tubes imo