To your point, the neck down of cross sectional area anywhere in the exhaust system isnt a good idea.
If you havea full 3" exhaust and it necks down anywhere even for an inch of the run it can cause your HP output to be compromised. Alot of people take exhaust flow for granted but it is important.

Sean

 

when they say neck down they mean that at the flange it is say 2.5" then it goes to 3". so basically if your running a 3" downpipe and test pipe then you run a catback that reduces to 2.5 them goes back to 3 it just restricts the flow.

don't know which rs-r you have but i have the ex mag gt2 and it does not neck down. full 3" and one bend.

that magnaflow is way overpriced. i think they're ti one is like 1200 bucks and to have it neck down like that is a waste.

 

That is the easiest place for me to loose weight for sure. sadly I spent 10 hours this weekend working on the car to shave 6 lbs off the car. A waste of time

 

just an FYI, but whoever told you all that about titanium knows nothing about it. one thing that metal is most definitely not is brittle. in fact think total opposite of that. it has amazing fatigue resistance.

EDIT: i left my statement above the same, but just double checked my sources. i don't know why i blanked on this, but titanium does indeed form "brittle compounds" when being welded to disimilar metals. so as long as that thing's fully ti, all the pros of ti should be there (including great flexibility). http://www.azom.com/Details.asp?ArticleID=1245 my source


on another note does anyone else not really like the blue tip? i mean i know its a great way to tell everyone that at least the tip is titanium, but i think bare ti is much cleaner and sexier.

 

I wish they had an award for dumbest post of the day... you could be a winnAr!

Sorry to get OT, but ingnorance like this just drives me nuts

 

I remember one time I went to E-Town in November of 04. When i got there, i forgot to remove the slincer in my Apexi GT exhaust. I made the run down the track and ran a 13.7 i believe. When i finished, I immediately pulled the silencer out of the car and made no other changes. I pulled the exact same 1.8 60' and ran a 13.1. That should give you some sort of idea of how Necking Down would effect performance. The timeslips were basically identical, the only significant change was the silencer. I know that is alittle more dramatic but the same effects apply.

 

Greddy Ti. It necks down to 76mm or 3" The rest of the piping is 80mm or 3.15"

 

So Dave, should i cut off the reducer in my catback and weld a 3inch flange? Is it worth it. I dont want to go through the hassle of selling my catback and getting a new one

 

wow i can't believe nobody brought this up...Tuner Performance Magazine Test

 

Thanks for the info. As i was comparing the dyno numbers from Bushur racing catback and the Hks Hi-power, there was not a big difference at all . As you can see the dyo sheet

Bushur Racing catback
247hp-stock
263hp-with catback

Hks Hi-Power
247hp-stock
261hp-with Catback

There is NO 5-8whp difference like Al claims usually is the difference betweent exhausts. Its clearly shown on the dyno sheet.And another thing, the hks turbo kit has the hi-power catback, which has the reducer, then why does the kit make so much hp with that catback?

 

I'd like to see more of the testing methodology (i.e. how repeatable are the results) to see how statistically signficant these results are. There were a few stinkers in the pile who were in the 250 hp range.

 

i agree, i don't think they really say...if you look on that site there are also awesome write-ups for cams, grounding systems and others...(great for us amateurs)

 

Was this done on the same dyno same day same car?

 

I think we are forgetting something here. The neck-down isnt really hurting in this comparison because this a a CATBACK TEST. They probably bolted the exhausts on with the stock cat/downpipe... What Al and David are saying is that when there is a full 3" exhaust then a 1inch neckdown then back to 3inch, its a restriction and yes it does effect power. Its simply physics.

 

i have a helix cat back which is 3" all the way through, very cheap and sounds good too.