I've known that I have been leaving some HP on the table with my exhaust system so I finally started doing something about it. I had dual 2.5" dynomax super turbo mufflers which have a flow rating of 410 cfm. Good, but not great. I also had cutouts in the exhaust system about 36" to 42" back from the header collectors (really too far back).
I removed a removable section between my header collectors and mufflers...about 48" long. I then put some 12" collector extensions on.
I took the car for a drive and it was cutting out like crazy above 4500...WTF? Long story short, it turned out to be my platimum plugs could not handle the open exhaust...ditch those suckers! I also rejetted the carb from 73/82 to 77/86 (engine was a tad lean from dyno data 2 years ago, plus open exhaust usually requires more jetting).
How does it run?...OMG...it's on the verge of chaos and sounds great (i'll have to post an exhaust sound on the other post I saw). :yah
The engine is clearly putting out significantly more HP and torque. It was 360 rear wheel HP before and now I would estimate that it is approaching 400 rear wheel HP.
I found a great article about zero loss exhaust. Basically, if the pipe diameter suddenly increases significantly, the engine sees a sudden drop in pressure just like the exhaust was open at that point. If mufflers are put downstream that have adequate flow (about 550 cfm in my case), the exhaust system will be very near or at zero loss.
So my future plans are to put 3.5" resonators on right after the collectors (1" increase in diameter and 2x the area) and better flowing mufflers.
Have to say though, driving around with open exhaust is FUN! :thu I figure it's no louder than 4 harleys (and sounds a lot better)...so what the heck.
I removed a removable section between my header collectors and mufflers...about 48" long. I then put some 12" collector extensions on.
I took the car for a drive and it was cutting out like crazy above 4500...WTF? Long story short, it turned out to be my platimum plugs could not handle the open exhaust...ditch those suckers! I also rejetted the carb from 73/82 to 77/86 (engine was a tad lean from dyno data 2 years ago, plus open exhaust usually requires more jetting).
How does it run?...OMG...it's on the verge of chaos and sounds great (i'll have to post an exhaust sound on the other post I saw). :yah
The engine is clearly putting out significantly more HP and torque. It was 360 rear wheel HP before and now I would estimate that it is approaching 400 rear wheel HP.
I found a great article about zero loss exhaust. Basically, if the pipe diameter suddenly increases significantly, the engine sees a sudden drop in pressure just like the exhaust was open at that point. If mufflers are put downstream that have adequate flow (about 550 cfm in my case), the exhaust system will be very near or at zero loss.
So my future plans are to put 3.5" resonators on right after the collectors (1" increase in diameter and 2x the area) and better flowing mufflers.
Have to say though, driving around with open exhaust is FUN! :thu I figure it's no louder than 4 harleys (and sounds a lot better)...so what the heck.
