megaphone-->4+ inch dp?
 

Say one was running a t51r (3.25 in outlet). would running a megaphone to a 4 inch or bigger dp (and rest of exhaust) help the turbo spool and enhance top end flow any or is it just a waste?

thats what i will be running with my 60-1

YES !

The lower the pressure on the turbine exit (exhaust system pressure) the faster the spool will be on the turbo.

You cannot make the turbine DP too large or too short, this is the general rule and nothing else realy applies. Only thing that will hold you back is available room and legal, local tolerance, restrictions to noise and other issues :D

This same rule applies obviously to the rest of the exhaust system, the larger the better, twin 3" systems can be a bit easier to fit than a single 4".

4" system on a street car (13B TO4) tends to "boom" a bit. Whatever you do just keep the pressure as low as you can in the exhaust system.

In case I did not make it clear.

Remember Turbine exit pressure (say 4" from turbine exit) is a function of resistance int he DP, mid pipe, CAT (if applicable), and rear muffler.

Anyone of these items is undersized or power flowing it will have an increase in turbine exit pressure and thus have a negative effect on the turbo inlet pressure (back pressure on engine) which will reduce spool, increase stress on the turbo, not to mention lower your power if its sensitive to back pressure (which rotaries are).

BIGGER IS BETTER when it comes to post turbine exhausts.

my question: with a 3" dp, is dual 3" after the mp overkill? would 2x60mm piping work just as well? i'm not going any higher with the DP (already purchased, heh), but i haven't decided on the catback yet.

Just my take on the situation.
I have a Catback 3 inch, and a 3 inch cutout, and I believe that you need some back pressure. Also the flow of the exhaust helps to pull out exhaust gases from the chamber after reving hard in a previous gear.
Free Flowing exhaust and open DP are different as I have discovered. The 4inch exhaust might slow down the air travel/flow within the exhaust system, and actually hurt you in the mid range.
Again just a guess, but from my Seat of the pants feeling, the Catback feels stronger than the open DP.

After the turbo, exhaust velocity doesnt matter. That's why - rice racing

I was thinking about this for a while. And I do believe that the Bigger is better rule is good to a certain respect. I think I'm going with a tunable Exhaust next though, because I think that Backpressure really plays a part in the Area under the HP Dyno curve between gears.

i tend to believe 3' would be about all u would need.

Re: megaphone-->4+ inch dp?
 

Anyone wanna' swap a DP for an HKS T51 R KAI turbo kit or a 4" DP for the same turbo-->> for a JSPEC LIM ???