17 replies to this topic

[t5ftw]

I am considering exhaust mod. I am not sure if I will get ECU upgrade afterward because I don't like to run rich. Anyway, I already have a EST catback waiting to be installed. But I am wondering whether I should do 3" downpipe at the same time or not. If I do, can I keep the stock Cat. I guess this will require cutting and welding. The reason that I am reluctant to use highflow aftermarket cat is because I may move into a State where CARB regulation applies, and I don't want to get into any trouble unless it is worthwhile. So, my questions are, will it be worthwhile to upgrade truboback without following ECU upgrade or to upgrade downpipe and leaving the stock cat on, should I just enjoy the sound of catback and be done with it. Or will Catback actually gives some performance benefit?
What is the least rich ECU tune?

[98-v70-t5-m]

The downpipe with stock cat is very restrictive. The biggest gains on flow in a new downpipe are the removal or replace of the stock cat with a more efficient one. A good name brand cat will be ok; as long as you do your homework you shouldn’t have any issues. Crawl under your car and look at the size of the stock cat it is HUGE. When I had my turboback made I used a high flow magnaflow cat and have had no issues with passing emissions.

^^ edit

I dont believe keeping the stock cat would be an option in a new downpipe it would kind of negate the install of a new downpipe.

[Che'_Moderator]

OEM CAT has huge flow numbers at very low resistance. Its not going to be a bottle neck like the DP or flex joint

[850wagonT5]

You're worried about installing a non-OEM cat? Non-issue. Out of probably 20 or so "hi flow" cats, I've had 1 problem, and they all passed smog fine.

And a 3" aftermarket cat will most certainly out-flow the OEM cat, no question there.

Do it.

[mdlimy]

OEM CAT has huge flow numbers at very low resistance. Its not going to be a bottle neck like the DP or flex joint

i beg to difer, the stock cat is quite restrictive and will cause the rest of the exhaust to get much more hot, i have dyno experience of this, that is with a full turbo back 3" with the stock cat welded in for one day of emmision testing, decided to do a couple dyno pulls before i pulled it, needless to say i saw 9whp dissapear with the cat on then reapear when i removed the cat. I was running a standalone ems so it may not be so extreme with the stock motronic system but it goes to show the restriction of the cat.

[krn]

Second and third paragraphs of the Bosch ME7 section might help answer your questions:

http://www.wothrline...performance.htm

So no major performance gain without a tune since boost pressure might actually drop if
the exhaust is less restrictive (same as motronic 4.3 and 4.4). A tune really is the best
bang for the buck.

I'd put the EST on then look for a stage 1 tune since that is going to be the biggest
bang for the buck (cat back and off the shelf tune has made many Volvo drivers very happy).
Next the downpipe/cat if you think you need more.

A local muffler shop only charged me $50 to do my EST. No need to wait on that

[Che'_Moderator]

i beg to difer, the stock cat is quite restrictive and will cause the rest of the exhaust to get much more hot, i have dyno experience of this, that is with a full turbo back 3" with the stock cat welded in for one day of emmision testing, decided to do a couple dyno pulls before i pulled it, needless to say i saw 9whp dissapear with the cat on then reapear when i removed the cat. I was running a standalone ems so it may not be so extreme with the stock motronic system but it goes to show the restriction of the cat.

What was stock whp with a NEW OEM cat?
What was it with a new after market one?

[mdlimy]

What was stock whp with a NEW OEM cat?
What was it with a new after market one?

no idea stock numbers. this was without a cat and with a low mile oem cat on a 00r motor with a td05 hrc 20g, just to give an idea of how restrictive it was.

[Che'_Moderator]

no idea stock numbers. this was without a cat and with a low mile oem cat on a 00r motor with a td05 hrc 20g, just to give an idea of how restrictive it was.

A used cat vs no cat is nothing like a race cat vs a new cat.

[mdlimy]

A used cat vs no cat is nothing like a race cat vs a new cat.

it still shows the restrictiveness of a used low mile oem cat as opposed to no cat which is very similar to a high flow cat. Yes a brand new oem cat may have high flow numbers at low resistance but it doesnt stay brand new for ever, and from my experience the oem cat was robbing me of 9whp which tells me that after he gets some miles on that brand new cat it will eventually do the same thing. i vote high flow cat if you are opposed to going catless, other wise i recommend catless.

[850wagonT5]

Second and third paragraphs of the Bosch ME7 section might help answer your questions:

http://www.wothrline...performance.htm

So no major performance gain without a tune since boost pressure might actually drop if
the exhaust is less restrictive (same as motronic 4.3 and 4.4). A tune really is the best
bang for the buck.

Completely incorrect if you use external boost control (the factory setup is fine for soccer moms but completely unnecessary for any of us).

Set the actuator to your desired boost level at WOT, and bypass the solenoid (or install an MBC).

I removed the OEM cat (exhaust was already 3") and I picked up a full 3psi on my gauge.

[krn]

Completely incorrect if you use external boost control (the factory setup is fine for soccer moms but completely unnecessary for any of us).

Set the actuator to your desired boost level at WOT, and bypass the solenoid (or install an MBC).

I removed the OEM cat (exhaust was already 3") and I picked up a full 3psi on my gauge.

Does that approach work on a model year 99 with an ME7 ECU?

[mdlimy]

Does that approach work on a model year 99 with an ME7 ECU?

Yes and no, mainly no. short answer is to leave the stock boost controller and wait for ard to sort out me7 tunes and buy one when they are ready, that will net you the most gains for what mods have been done to your car. Or u could just buy an ipd tune right now but I think that's kind of a waste of money. But me7 doesn't like you to alter its boost pressure.

[t5ftw]

Thanks for so many good inputs here. After reading that wothrline article, it seems to me that exhaust alone would not do much with ME7 system. So, I guess I am putting the catback first, and get stage 1 tune. Sill, it is so tempting to get downpipe and highflow cat at the same time, because from what I can see it will requires less cutting and welding and labor costs. Apparently, I can't pay for all these at the same time. So, it has to be either a tune or downpipe and cat.

[scandalo]

With these cars oem cat=oem downpipe. They are a package deal. I see no reason to buy a new oem cat. The downpipes are not very good at all as has been stated and all together they are like 300 dollars.

Couple this with the fact that the downpipe goes in to the cat at essentially a straight down angle there is no reason to weld oem used cat on to an OBX downpipe (OBX for example). Another reason is that I have had several cats simply break from rust at the back before the straight pipe.

Which brings me to my next point. I just got done welding a straight pipe to replace the cat on a 98 XC (for the reason stated above) and the consensus was that the metal there is just too thin. The exhaust will rot out.

In short, don't reuse anything and go aftermarket. And scrap your stock cat. They gave me like seventy bucks the last time.

[t5ftw]

Ok, for downpipe, OBX sounds like a good deal. How is the quality?
For the cat, I found Magnaflow 46005 listed for my 99 S70 T5.
However, the diameter is 2.25" just exactly like the stock pipe.
So, if I am getting 3" downpipe should I get a cat with 3" inlet, such as Magnaflow 41409?
Do you recommendation for cat or downpipe?

[scandalo]

Catless here.

My OBX doesn't want to seal properly on the flange but I feel I may be one of the few. Many others didn't seem to share my problem and were fine.

Keep in mind it is probably the cheapest option unless your are a moderately skilled welder or have friends that can help.

[Abundant Meat]

What about if he uses a boost controller? Wouldn't that ensure he has good gains?