MazdaRx7Power

is that the right way? everything i'm doing sound good? collecting dual header into 1, 2 1/2in straight pipe into the ypipe. and then from the y-pipe into 2 1/2 in mufflers.

MazdaRx7Power

anyone?

mazdaspeed7

Bad idea. Scrap the y-pipe. The whole point of true dual is to not converge the 2 pipes. Each pipe goes straight off the engine, to its muffler.

First, doing it like you said, the collector, then splitter would create a lot of restriction, especially if you chop up the stock y-pipe. That combined with your overly big pipes, would leave you with too much pipe to have a bottom end, and too much restriction to have a top end.

Go with true dual. It has a nice powerband, and is not sensative to tuning, like collected systems are. And I still stand by my numbers I posted before. The pipes you want are simply too big for a n/a rotary. Youre not gaining any power from bigger pipes, while also making your powerband much narrower, and killing your bottom end.

MazdaRx7Power

i thought it would be the bigger the pipe the more power you gonna get? never heard anything about velocity!!! is there really a big difference if you do just put it one size the whole way?

Scott 89t2

why are you using the y-pipe if you have dual header you just run one pipe from each hole at the header to each muffler, you don't want to join them. that is going to be VERY loud

mazdaspeed7

That is very wrong. Exhaust design will always be a compromise. Big pipes and having the collector very close the engine will make the most power, but at the expense of low end. Smaller pipes, and having the collector far fromt he engine will give an impressive bottom end, but at the expense of top end power. The idea is to find a compromise that suits you. But there are still limits, where the negatives start seriously outweighing the positives of a given setup.

Theres a point where when you go to a bigger pipe, you lose more bottom end, but start gaining less and less top end. Theres a lower limit, where going smaller starts to gain less bottom end, in proportion to the top end you lose. Generally speaking, the biggest pipe you could use on a street ported highly modded n/a would be dual 2.25" pipes. Anything bigger, the loss of low end would outweigh the minimal gain in the top end. For a stock ported engine, even 2.25 is a little too big. 2" is the best choice if you dont have a ported motor that was built for 9K rpm. That is for true dual, it gets more complicated with a collected exhaust. There is only so much power that could be had from bigger pipes, and I think theres less than 5 hp difference between dual 2" pipes and dual 2.5" pipes in peak hp, but the 2" pipes will have a better power curve and better bottom end.

Bottom line, unless you have a built and ported motor, stick with dual 2" pipes. Thats what I have on my car, true dual, 2" all the way to the mufflers. Since you have(or are getting) 2.5" mufflers, you might want to experiment with stepping the pipes some. If you go too big too close to the engine, you'll lose lots of bottom end, and not gain any top end. you cant really go too far from the engine. At worst, you wont be optimizing the flow perfectly, but will still have a good powerband. My recommendation ont he stepping is in a previous post.