question: SO what about the HKS dp? It's a 3" pipe that bottlenecks down to 2.75" ...is that any good...or does it not matter becasue it's still 3"?

 

I have yet to see a dyno of a 2.75" DP car vs one with a 3". This would make this pretty conclusive.

 

i really dont think makes anydifferents, under 400 whp.

 

2.75 espelir and i have over 400whp

must be very restrictive huh?

 

its a waste of money to pay 300 or more for a damn pipe

get the espelir for 150 and call it a day

 

how much is the HKS Carbon Ti muffler then?

I cant find just the muffler, I can only find it in a package with the downpipe of $699

 

i did not say restrictive. But over 400 whp you might get more with 3" with the same set up. close to 500 whp i think thats for sure. You can sqees alot out of 2.75" for sure. But if you buy one, and you can do more for the same price why not?
I didn't know the espiril only $150 to your door ,that is awsome deal.Well, if knew then ,i would get one of those.

 

2.75" will probably have a little more lowend than a 3" and a little less power up top. Check the Dyno plots and you'll see some have more power down low but less power on top. Here's an old magazine test w/Dyno that includes the BR, HKS, Works, and some other catbacks.

http://www.tprmag.com/issue/5/5_turbo_exhausts.shtml

Here's a recent Dyno with the Tanabe Concept G Blue TBE

http://www.importtuner.com/tech/powe...e_exhaust.html

the HKS necks down at the cat to 2.75" and has a resonator. It's pretty quiet.

The Tanabe DP is 70mm, catback and test pipe are 80mm - no resonators.

 

I have similar goals also. More midrange, quick spool, more low end torque. How is that setup around the track? What ECU tune?

 

that would be a cat-back system and not a downpipe. and for reference, the carbon-ti muffler isn't 3".

 

I'm planning to track the car this summer so until then it's all conjecture but my mods and my tune are done with the sole goal of a reliable track car. The tune is with ECUflash. Andy at Speed Element got about 320whp out of the car (on their dyno people are going into the 11's after 300whp) but could have got another 20-25whp if I had insisted. In the end we got a setup that spools up very quickly and pulls like a raped ape through redline. EGT's and AFR's are all excellent and conservative. All I need is some aftermarket head-studs and this should make for a strong and reliable track day powerplant.

 

The HKS down pipe is not 3" it's 2.75 all the way.

The HKS catback does neck down where it meets the cat.

 

 

A turbo vehicle unlike a NA vehicle will NOT reap any benefits from a smaller exhaust. The reason is quite simple, exhaust on a NA vehicle pulses straight out of the head into the exhaust pipe by choosing a specific diameter of pipe which will give you a certain velocity at flow you can effectively scavenge exhaust gases out of the cylinder long after the release period. This scavenging is why smaller exhausts appear to give you low end, high velocity at low rpms, compared to larger exhausts which give the same effect at higher rpm where more flow is required to truly reap the scavenging effects.

Turbo cars on the other hand have considerable back pressure in the manifold due to the turbine blades so no benefits from scavenging will ever be seen. That said the perfect exhaust for a turbo is simply directly out into atmosphere, of course thats illegal... so we can only satisfy our turbo vehicles with large diameter piping to minimize any back pressure.

Have a nice day

 

Well said.. there is no need to even consider anything less than 3 inches.