Magnaflow Cat Converter Issue

[Brezza]

hey guys,

i was just wanting to know from any of your experiences whether i need to replace my cat converter or whether it is still okay?

my problem is i had my car dyno tuned by a reputable tuner here in Adelaide, and the car fell short of what we were expecting powerwise. the car is a 89 R32 GTR and has the following mods,

Prior to TUNE

fully rebuilt engine

2860-5's

full 3inch exhaust incl front and dump pipes

3in cat (magnaflow) metal core

K&N pannel filter in stock air box

PARTS ADDED ON WHEN TUNED

Nistune ECU

Walbro fuel pump

660cc injectors

Bleed Valve

it was running 250rwkw runing 13psi boost prior to the tune.

the tune was done on my birthday in early february and it was a 37 degree day, i didnt think it would be too bad, tune the car in the worst conditions then i wouldnt have any issues with the engine detonating in hot weather.

the tuner was only able to have the car make 285rwkw runing 17psi boost, which still does feel pretty damn fast.

but he did say that when he tried to up the boost a little more to 18psi there was no difference in power, he thought that there might've been a flow issue, so he opened up the stock airbox, and did a run to see if the air filter was contributing and it made no difference.

he suggested that the cat converter might be blocked or not flowing very well. he couldn't check the cat on the day as it was hot from the dyno runs.

i took the car to an exhaust shop shortly after and had the cat dropped out and checked, the inside was all covered in carbon but it still looked to be in one piece, the metal core looked to be in good condition, the only thing was that the core was moving around in the cat, the part that attached the core to the casing had either broken or melted, so the core moves a couple millimetres within the cat.

i am just wondering whether anyone has experienced similar things with their metal cats.

i know the ceramic ones tend to breakup or melt but the metal ones are much more sturdy.

i've attached the dyno sheets of the 2 different tunes, is the wavy line in the 285rwkw one due to flow in top end?

_250rwkw____13psi.pdf

_285rwkw____17psi.pdf

[Harey]

such a pity he couldnt drop the cat or exhaust and put it back on the dyno! that would reveal everything.

to me a 3" cat and 3" catback sounds a bit small for -5s but I am no gtr expert.

[sickr33]

BLEED VALVE!!!!!

i doubt you are holding boost very stable

get a Greddy Profect B II or something along those lines

Decat pipe or take the center out of the one you got (MAKES A BIG DIFFERENCE)

3 inch does seem a bit small but is not the cause in this case but will take affect when you get up around the 300-350kw mark.

[R31Nismoid]

3" exhaust - too small.

3" cat - too small

Drop the exhaust from before the cat and i would be very surprised if you don't see major increases.

The turbos you have are 400rwkw on around 20-24psi with a proper motor.

[R31Nismoid]

BLEED VALVE!!!!!

i doubt you are holding boost very stable

get a Greddy Profect B II or something along those lines

Decat pipe or take the center out of the one you got (MAKES A BIG DIFFERENCE)

3 inch does seem a bit small but is not the cause in this case but will take affect when you get up around the 300-350kw mark.

What does a bleed valve have to do with it?

I've never used a EBC and run over 350rwkw/24psi.

[Brezza]

i've got the car booked in for a couple weeks time to be tested on the dyno again!

we're planning on doing another run with the cat on to see if there is any difference because of the weather.

then another run without the cat.

should know for sure then what is wrong.

i have also bought a Decat pipe for cheap to replace the cat if its stuffed.

just to clarify a 3in exhaust should flow enough to get within the 300-350rwkw mark?

i'm also looking at getting an EBC in the future as my mechanic told me that he wouldnt want to run much more boost without a proper controller in place to hold the boost level steady.

another side note, what will my std R32 GTR AFM's max out at?

[Harey]

i've got the car booked in for a couple weeks time to be tested on the dyno again!

we're planning on doing another run with the cat on to see if there is any difference because of the weather.

then another run without the cat.

should know for sure then what is wrong.

i have also bought a Decat pipe for cheap to replace the cat if its stuffed.

just to clarify a 3in exhaust should flow enough to get within the 300-350rwkw mark?

i'm also looking at getting an EBC in the future as my mechanic told me that he wouldnt want to run much more boost without a proper controller in place to hold the boost level steady.

another side note, what will my std R32 GTR AFM's max out at?

Quick look through the RB26 dyno thread showed me few guys running stock GTR afms at 280rwkw, but everyone I saw over 300rwkw had upgraded theirs.

I think for your goal power you should definitely upgrade them.

Is there any reason why you are sticking with the 3" exhaust?

Ignore the comment from your tuner about a proper EBC, spend the money on a bigger exhaust and some upgraded afms. $28 turbotech boost valve is all you need.

[Brezza]

i got the 3 inch exhaust done when i first bought the car. the old one needed replacing because it had holes, i got a 3inch stainless chucked on.

i was told by the guys at the exhaust place that even if i had a 3.5 cat back it would still only flow as much as the front pipe would let it.

and if the front pipe when the two connect only is a 3 inch it would only flow as much as the smallest diameter in the exhaust.

[Harey]

yeah you need a bigger front pipe then as well. from what i have read on this forum the 34 gtr dump pipes are a great upgrade too.

you have chosen some very hardcore turbos and it seems strange to limit them so much.

theres a thread on here with an article from a garrett engineer about how important it is to have a big enough exhaust for your turbos. also that exhaust after the turbo cannot be too big performance wise, although there are obviously size restrictions and minimal gains once you go above a certain size.

there is a lot of info here, first thing I would do is read through the rb26 dyno thread and see what exhaust people are running for each power level. there is a lot of info there. that will also tell you whether you need larger afms, whether an EBC is required etc etc.

[MrStabby]

another side note, what will my std R32 GTR AFM's max out at?

They max out of resolution at around 280kw or so, but they can flow much more. If you tune past that point it can be risky, so you'd want to be much more conservative in the tune. Since -5s go way past 280 you should upgrade AFMs (after the exhaust is sorted).

[R31Nismoid]

3" is not big enough for -5's.

As i said, -5's are a ~400rwkw turbo on a good motor, you need ideally a 2.5" front pipes that merge into a 4" exhaust to allow sufficient flow.

If you only want 300-350rwkw then you've chosen the wrong turbos for a start...

Also putting it back on without dropping the exhaust because it "might be the weather" is pointless.

Drop the exhaust from the front pipe (where the CAT would attach) and give it a run. Sounds like you should see markedly improved results given your description thus far.

[Brezza]

hey guys!

i got the car dyno'd yesterday.

we took the cat off and replaced with a decat.

the car made less power initially because the tune was out,

it made 260rwkw instead of 285rwkw

then after a little bit of tweaking to the fuel maps the car was back on 285rwkw with better turbo response.

but we noticed the smell of fuel from the engine, we noticed that the injector o-rings were being blown out by the boost, so we had to put some spacers on the injectors to hold the o-rings in there tighter, after that the tune was out again.

but with more fiddling the car made over 300rwkw.

the boost was turned up and it peaked at 19psi then came down and hovered around 18psi. i'm runing a bleed valve.

it is now making consistently over 300rwkw with better response.

the best run hit 319rwkw.

very happy with it.

thanks for your help guys.

the car is very fast now,

[R31Nismoid]

18-19psi should be seeing much closer to 340-350rwkw mate.

On a built motor as much as 380rwkw.

Hell my lowly GT-SS's (smaller) are making 280rwkw on 1bar.

[Harey]

hey guys!

i got the car dyno'd yesterday.

we took the cat off and replaced with a decat.

the car made less power initially because the tune was out,

it made 260rwkw instead of 285rwkw

then after a little bit of tweaking to the fuel maps the car was back on 285rwkw with better turbo response.

but we noticed the smell of fuel from the engine, we noticed that the injector o-rings were being blown out by the boost, so we had to put some spacers on the injectors to hold the o-rings in there tighter, after that the tune was out again.

but with more fiddling the car made over 300rwkw.

the boost was turned up and it peaked at 19psi then came down and hovered around 18psi. i'm runing a bleed valve.

it is now making consistently over 300rwkw with better response.

the best run hit 319rwkw.

very happy with it.

thanks for your help guys.

the car is very fast now,

Nice work! Sounds like your happy with it.

If you ever do want more power you know that just changing your exhaust and a retune will net some big results. Not just peak power either as you discovered, as well as increased peak power you will also get less lag!

Edited March 31, 2010 by Harey

[Brezza]

Nice work! Sounds like your happy with it.

If you ever do want more power you know that just changing your exhaust and a retune will net some big results. Not just peak power either as you discovered, as well as increased peak power you will also get less lag!

thanks!!

yeah, i know there are things i can do to gain more power.

GTR's are an awesome car to mod, and huge power can be achieved.

but i am at a point now where i wanted to be since i first got the car, and that was to build a 300rwkw street car. now i have it, but its come at a pretty big cost. motor rebuild, turbos, ecu, injectors, fuel pump, etc

the list goes on, i've spent a lot of money and to finally achieve the power level i wanted is great. and i also have upgraded tyres, rims and suspension.

who know's maybe down the track i might still want to empty my wallet into the car, but for now i am going to enjoy it.

and i just gotta say it, horay for Nissans!! GTR's really do deliver on being an awesome car from stock that has potential to become a real serious street machine.

i f ing love my GTR!!