yup. I see it all the time on the dyno. The torque band tends to move up a little. When I had my 90 'stang I put 1 5/8" long tubes on, ace'd the cats and installed two chambers. The car picked two tenths but felt a little laggy out of the gate.
I had basically the same setup. Victor Jrs on a 393 with 3" exhaust dumped at the axle. One of the mufflers came off at the track (during the burnout) and I took the other one off as well...picked up .4 and 3 mph.
i think there will be more of a difference , with bigger hp cars....if your making 500+ hp w/ exhaust and take it off i can see getting a good bit of time...but if your basicly stock and uncap it you may not gain anything.....
I have 302 with GT40P heads, Torker 289 intake, and 6901 with dumps. I do HORRIBLY at the track with the dumps open. My car runs much better capped off and running through the glasspacks. First off, my carb is "tuned" to the glasspacks. When I open the headers, it sounds really good, but takes off with spit and sputter (I guess it is too lean). I have not spent much time trying to rich it up and test it, but plan on doing exactly that. I would like to know which rods/jets work with the open headers, now that I know what works with the 'packs. It will spin the street tires (3.80 gears with spool) with the caps on or off, but it just doesn't accelerate as fast with the open exhaust. On one trip where I used both open and closed exhaust... with caps ON--9.4961 1/8 ET at 73.76, 2.19 60' with caps OPEN--9.7355 ET at 69.62, 2.15 60' I am pretty sure I could "tune" some of this out, and maybe make improvements with open exhaust...but I wouldn't know for sure until I tried it.
I haven't seen any improvement with or without my header mufflers and pipes. I can run almost the same time, so since I'm getting older I keep them on. I can hear motor problems easier (loose rocker arm) and most any other problems that might make noise. One of the guys I race with put a X pipe on his 351W and pick up .25 and that was all he did. I don't know if this helps but I think ShadowMaster has a very good point about the X pipe. If you have a little back pressure it will help your bottem end. As always JM.02 Terry
Trust me on this one.....put an X-Pipe on it. Or....change the whole damned thing to 2 1/2" with an x-pipe on it. That'll wake it up.
