Restriction In The Exhaust

[rondofj]

Hey guys, a little dilemma...

R34GTT, Precision 5558 / 0.63 a/r, 40mm gate off housing, plumb-back 3" exhaust system, Power FC, usual support mods, stock coils, stock BOV, 100 cell Lobokka metal high flow cat, 100% street car. 286rwkw at 18-16psi by JEM with old Nistune. Changed to Power FC I picked up cheap to get retune and 'better' ecu / tunability.

Unigroup say there is a restriction in my exhaust system - the cat itself because it wouldn't make any more power going from 20psi to 23psi on 98 fuel. Power actually dropped, made a crappy 270rwkw at 20psi and very retarded timing! Recommended to change cat/ de cat with a stock shell outside etc; Current state is a very safe but very retarded tune (timing) on power FC till I get cat sorted.

Options:

http://justjap.com/index.php/engine/exhaust/catco-3-high-flow-catalytic-converter-nissan-type-3.html - highflow cat

http://justjap.com/index.php/engine/exhaust/x-force-3-stainless-high-flow-cat-nissan-type-3.html - highflow cat

http://justjap.com/index.php/engine/exhaust/jjr-stainless-racing-de-cat-pipe-nissan-r34-gt-gt-t-skyline.html - decat pipe / illegal

Please advise what to do, I already have a eGay 100 cell Loboka metal cat fitted (3" entry/exit) and that's a restriction I'm told? What is the most cost-effective way, second hand is ok.

Have read most of the cat threads, too many mixed opinions to decide, my current cat was actually bought based on these forums..

Edited March 21, 2014 by rondofj

[KiwiRS4T]

Most recommended as far as my reading goes is the Venom 100cell metal 5in which I have. But you will definitely get better flow with a decat look alike if you are prepared to take the risk. I am making 314 AWKW with a GT3540 and a three inch exhaust right through. Are you sure your muffler doesn't step down to 2.5in as a lot of big brand Jap ones do? Can you get comparative flow numbers for the Loboka (never heard of it TBH) and the Venom?

[rondofj]

Don't know the flow numbers mate, and its got two names Bokka and Loboka if you ebay it..so dodgy as, but surprisingly good build quality and the metal internals have held 2 years of hard driving. Exhaust system is 3" all the way with stock looking oval mid muffler but that is seemingly 3" as well.

[zebra]

Did yavus drop the exhaust on the dyno?

[rondofj]

nope..

[scotty nm35]

Did yavus drop the exhaust on the dyno?

^^ this. How can they say the cat is a restriction without dropping the exhaust in sections?

I ran 310kw with the same cat, I don't think it would be holding you back too much, but who knows...

[KiwiRS4T]

The difference "could" be down to the different dynos. Does your car feel slower?

Strange because Unigroup seems to have a very good reputation (although anyone can have an off day).

Maybe your second hand PFC is defective?

Did you measure the back pressure? I did a rough measure on mine by making a fitting to go in the O2 sensor hole connected to my boost gauge (not running an O2 sensor).

[rondofj]

Lol I dont even know how to measure back pressure, and no, my PFC is sweet, as confirmed by Mark from Unigroup. He said mine was one of not many cars to be very clean with no issues apart from the bloody exhaust. And they're adamant it is the exhaust because it has so many variables and most cars they've tuned which were down on power was found to have a restrictive exhaust, notably the cat etc;

Mine was overheating and just wouldnt make power even with higher boost, power actually dropped, and according to Yavuz thats an exhaust restriction- intercoolers doin a brilliant job, confirmed..

And yes it does feel significantly slower/retarded timing from driving feel. Yavuz confirmed that timing has been retarded a fair bit by Mark.

[R31Nismoid]

The cat might also just be failing? Depending on how hot etc, not all CATs last forever.

I mean one brand had a LOT of failures in the latter half of last year, so anything could've happened... But you kinda do need to drop the exhaust to work that out

Hell it might even be the exhaust itself, all that gets confirmed by taking a couple bolts off - Is it a Jap one?

[wolverine]

Overheating...would also spend some time sorting that out before returning to the dyno.

[scotty nm35]

Sounds like the cas issues Tony was having in his 34gtt. Why randomly pick the exhaust to be at fault without testing it?

[rondofj]

Ok my exhaust- custom 3' dump from back of turbo to cat, wastegate welded to turbine housing and plumbed back to dump just before cat. 100 cell gay metal cat 3' in/out and 5' body/ bokka brand. 3' pipe from cat to oval mid-muffler. 3' pipe from mid-muffler to X-force 3' straight through

oval muffler.

[scotty nm35]

Gay bokka. lol.

It is a 100 cell cat with a 5 inch body, the metal cats are all much the same construction wise, there is no way it would be a restriction unless the core has shifted, which would be fairly obvious if you dropped two bolts.

I still think it's the cas, but out of interest, do you have a pic of the gate etc?

[Manuel Kasko]

Get them to run it again without the exhaust and don't waste time chasing the "I think it's the cat"

It's a no brainer

[rondofj]

Ok pics from my phone- pic of the cat by itself is an indication of what it is

[scotty nm35]

Well the zorst looks fine, as long as the rear muffler isn't stepped down to 2.5 inch. Can you shine a torch up there and make sure?

[rondofj]

Yeh gotta try that tomorrow- see the joint at the rear of mid muffler -looks like a step down to me? More pics - now you guys can see my whole setup lol

[rondofj]

Muffler on my car: maybe this isthe problem cos its offset not straight- Mark mentioned offset mufflers create significant power loss- its nice n quiet though

[rondofj]

So now you can almost see my whole setup- does it still look like the gay cat or the offset oval muffler - its 3' entry/exit, didnt realize it was offset when I bought it years ago

[rondofj]

Yes I took the cat out last week, insides intact strong as ..