Not too be difficult but, I would tend to think opening the dp would result in some sort of gain, theres alot less piping to go thru this way.
havent actually tested this theory but hope to remember come this spring, and will post results,
unless one of the lucky ones who live near a year open track can try it out???
The normal dump opening is a side outlet. When you pull the cap off, an insignificant amount of flow is diverted and most takes the straight route past the opening rather than exiting. If there is a large amount of back pressure in the exhaust system down stream, some may back out the side door, so to speak.
There is a so called Jersey version of the pipe where the cap is in the straight line and the exhaust is more in the diversion path. This should work, except that most of our exhausts are quite free flowing and little benefit is often noted when dropping the exhaust all together.
I have a hooker 2.5 with dynomaxx mufflers. I think thats the best way to go for a street car. I disconnected my exhaust to see if there was a difference. All I got was turbo lag at midrange. It wasn't even consistant and didn't happen everytime. But I was tooling down the road at 40 and a beater Trans-Am came up and I floored it and sat there. I heard my engine go but had major turbo lag, evntually I passed him. But was embarrassed for a momment. I went home and bolted my exaust back on immediatly. It sounds mean! But I'd rather be fast