Just bought my Z last night and the guy has Invidia test pipes on it. He's including the stock cats in the purchase. It's a bit too loud for my taste with the test pipes, so I plan to put cats back on it.

This car is my daily driver. I'm not planning on racing it or taking it to the track (well, maybe once or twice just for the hell of it). I'm wondering if the performance gain with high flow cats versus the stock cats is worth the $350 I'd pay for the high flows.

Any opinions?

 

If your running the stock ecu and it hasn't been remapped (ie UpRev)for the test pipes then there will be little or no change in power.

 

With high flow catalytic converters vs OEM catalytic converters you might see a 1 percent gain in peak horsepower. Is that worth $350 to you?

 

my test pipes made quite a difference ( pure butt dyno of course) over the stock cats.. , but from what i hear and read here, stock cats vs hfcs are a very close mix.. not much difference.

Sounds like you jsut dont like the test pipes.. in that case id jsut put the normal cats back on.

But give it a month, you may end up liking the sound better than you do now..... i hated mine the first week, now not so bad.

 

Butt dyno is just you feeling the weight reduction of a lighter wallet. I'd be surprised if almost any of the NA bolt ons made a measurable difference on a real dyno without a tune. I'm more sceptical that it would make a difference that you could actually feel when driving the car.

Without tuning for the change, I look at NA bolt ons as "sound/tone" upgrades and not as "performance" upgrades.

OP, if you don't like the sound, change back out. You won't notice a difference.

 

I don't think the previous owner touched the ECU. I sent him a text to confirm though. Waiting to hear back.

$350 isn't worth the minimal, if any, power increase to me. The test pipes are just so loud they make the inside of my head throb....lol

Stock cats it is then. Thanks for the responses.

 

It's worth checking to see if he flashed the ecu with a tune, just to make sure. This is only because if he went through the trouble of a tune specific to the setup with the TP's you may end up running very rich by switching back to the factory cats.

If he never touched the ECU, you have zero to worry about. Swap back out, pocket the money, and enjoy the sound you're looking for.

 

Indeed. I want to take off the 20's he has on it and put 18's on instead. The $350 sounds like it's much better spent there.

 

Funny thing is that you may pick up more performance by dropping to a lighter wheel and tire by going from 20's to 18's than you'd ever pick up from the TP's vs stock cats (especially if they are heavy/blingy/chrome 20's).

Post em both up on the private classifieds on here. You may even want to post the wheels/tires up in your local region as a FT (for trade). Do you know what brand/style/size the wheels & tires are?

 

The tires are Falkens. That's all I know at this point. I pick the car up tomorrow. I'll post the deets once I get it.

Edit: I think these are the rims: http://www.wheelsnext.com/wheels-tir...ed%20Blue.html

 

Cool. Congrats, man. You're lucky that you're in CA. There are always crazy good deals on used stuff out there. Keep your eyes out on the Private Marketplace and you can get some great deals if you're patient.

The vendors on here are also great and are always helpful when it comes to questions, etc. - so I try to pay them back by sending them my business as well.

Welcome to the community!

 

Thanks! I'll keep my eye out for deals.

Just heard back. No ECU changes, so it's probably running rich with the test pipes.

 

Please explain the running lean comment? Thanks.

 

No expert on this but if he re-mapped the ECU for the TP's more than likely he made it run a little leaner. Lean means that your engine is getting less fuel but more air. In combination with the TP I am guessing that that made an increase a little in power. However, running an engine too lean or even lean for that matter can be damaging. One reason is that it would run hotter.
If he did re-tune the ecu then you don't want to go and throw OEM setup on there and have it stay lean as this could be damaging.
On the other hand, a car can run rich which would mean its using too much fuel which can clog it up I believe. (i.e Bogging down etc etc....)
I think I hit that on a real broad, general level. Hopefully someone can confirm/add to what I said.

 

The man stated that switching to a more restrictive exhaust would induce a lean condition. This is what I would like to understand.

Thanks.

 

I corrected my statement above & this one - my bad.

If tuned, it would have been tuned to a richer AFR with the Test Pipes. This is because the TP are less restriction, which means more airflow, which means without a tune, test pipes would run lean. If you tune it richer to make up for the TP, when you put it back to stock cats, the tune would be much richer than it was originally. (You get more power tuning on the leaner side which was made possible reducing restriction.) I'm not going to get into the details of stoich and air fuel ratios.

However, the car was not tuned for the TPs. So it is probably currently running a little lean because there are test pipes in place, which means less restriction, but no tune for the change. Luckily, the stock tune is somewhat on the rich side. Switching back to the stock cats (which the factory tune expects) will bring the car's setup back in line with the stock tune.

Stock Tune
-----------
Stock Cats = Good AFR
Test Pipes = Lean AFR


Lean Tune for TPs
------------------
Test Pipes = Good AFR
Stock Cats = Rich AFR

 

Corrected. It would actually be running lean right now.

 

Thanks for the correction. I edited my post.

 

Isn't the above incorrect?

Wouldn't a stock tune with test pipes cause engine to run lean and tuned for test pipes then switching to stock cats cause you to run rich?

 

I'm basing what I said off of the Cipher logs that I've seen on my car with test pipes, but I'm no pro tuner either. I'm fairly new to tuning. Maybe the stock tune is just so naturally rich that I was still rich even after the swap?

I went back and corrected my post above. Adding TP's will push you to the lean side, but in my case, the stock tune was so rich that I was still seeing rich AFR numbers in areas of my tune even with the TP's.