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View Full Version : How Big is TOO BIG??



zenetti
06-08-2007, 09:05 AM
I am looking at removing the cat and mufflers except the final muffler and was wondering whether to run a 2 1/2" or 3" pipe. The onlyy reason that I ask is that I was talking to Ohlsen Developments (Mitsubishi gods in NZ) and they recommended a 2 1/2". The reasons given were that with the twin small turbos (as they described them) they need some back pressure to stop them from 'free spooling', and from what I could gather stop themselves from spinning to death.

I was also told to leave the stock turbo downpipes and run the new exhaust from where the pipes join at the flexi.

What do you guys (and gals) think? Any help greatly appreciated.

bradc
06-08-2007, 09:24 AM
the wastegates are there to stop the turbos from spinning too fast, thats their job!

I'm running a 3" pipe on mine and I haven't had any problems. My turbos spool up very quickly as well :)

Nick Mann
06-08-2007, 10:25 AM
Never heard that argument before. Every theory I have heard for turbo'd cars says the easier the gasses get out the better!

You See
06-08-2007, 11:05 AM
When getting my exhaust done at Beyond2 I got the same advice, hence why I settled for the 2.5" catback. Tho others have had positive results with downpipes and a larger diameter exhaust...guess this doesn't help your situation huh? :P

zenetti
06-08-2007, 09:45 PM
I am not going to do too many mods, just want to help it breathe a bit better. I guess if 2 reputable shops have said 2.5", it should be the way to go. apparently 3" makes them spool up TOO quickly and puts unnecessary strain on the turbos so 12-18mths down the track you are up for new turbos.

Nick Mann
06-08-2007, 10:13 PM
My current turbos have been running for 18 months now. With 2.5" downpipes and 3" after the join, with the boost controller set at 1.3 bar and get there as quick as you can. (It can't! /pan )

They aren't broke yet!!

Nutter_John
06-08-2007, 10:23 PM
think lots of myths are being given to you Zen as Nick says he has been driving his hard for that lenght of time and pushing them beyond 1 bar with no issues

Kieran
06-08-2007, 10:43 PM
.... apparently 3" makes them spool up TOO quickly and puts unnecessary strain on the turbos so 12-18mths down the track you are up for new turbos.

I know what you're getting at, and without access to a compressor map for the TD03 turbos on our car it's impossible to say, but I would be very surprised if a 3" exhaust along allowed the turbos to operate beyond their surge line or exceed their maximum turbine speed. Certainly I don't think Nick's turbos would have lasted 18months if this was the case.

zenetti
07-08-2007, 05:10 AM
sweet, thanks for all the help guys - just one more question, I am going to run it from the flexi back ( bye bye cat - gotta love NZ rules!!!) will one muffler at the rear be enough, it won't be too droney?

SHOWVR
07-08-2007, 07:37 AM
i just had a custom 3" mandrel system made up - it feels and sounds awesome.....

Subaru ETA
07-08-2007, 09:40 AM
i got 2 resos and the cat. 1 rreso was abit too droney. and the rules will be changing soon so you will need a cat

VR4 MAD
07-08-2007, 11:14 PM
......... and the rules will be changing soon so you will need a cat

Are the rules changes for emissions going to be retrospective..........I thought not.

Though having said that, I've heard talk that the wording for the new rules could be something like....'if the vehicle came ex-factory with a catalytic converter, it must retain one', ie can't run without a cat as many here do with de-cat pipe sections.

Anyone know any more????

/toycar

Subaru ETA
09-08-2007, 08:00 AM
yup, if thje car left factory with a CAT it will need to retain one to pass a WOF, however, they also wanted to make it that you couldnt alter your exhaust from factory but that didnt get anywhere.

thing is tho they WILL be bringing in emission testing and i doubt very much a vr4 would pass without a cat

Gly
09-08-2007, 08:18 AM
but untill that day comes, i wont have one :P