Test pipes on NA questons

[Foosblood24]

First question, do test pipes help gas mileage any?

Second, is it even a good idea for an NA?

Third, will a header and catback kit bolt up to the existing cat-converters?

[DCaff300ZX]

Not sure about gas mileage help as opening up the exhaust does not help the engine work easier, at least enough to improve economy.
As for a good idea or not, I myself went with a 2 1/2" system in my NA that was as open as possible, and it ran like crap and sounded worse unless you like a Honda fart can sound. As the shop went to work making it work right, we eventually ended up with only high-flow cats as an upgrade and went back to resonators and Magnaflow mufflers. It ran great then, made maybe a little better power it seemed and definitely was smoother and sounded really good and with no drone. The drone was the hardest thing to get rid of with the larger exhaust and took a couple of better pipe bends and putting the resonators back in.
So basically I'm saying from my own experience that the best route is probably just a 2 1/2" pipe upgrade and hi flow cats with OEM resonators and arrangement.
As for the cats and headers/catback bolting right up I'd say probably not, unless the headers and catback have OEM flanges and dimensions and if so, probably will but need a little tweaking.

[NolimitZ32]

1. Probably not, I don't have the collection of information required to properly dissect this issue and verify.
2. For a street driven daily, no, it will make your car produce noises that are not particularly pleasant as D just explained above.
3. Searching around, it looks like the majority of the ebay headers are made to fit and bolt on to the factory cats.

[Foosblood24]

The catbacks and headers I'm looking at are 2.25

If I keep the stock cats, would that work for an NA?

[NolimitZ32]

It should, operative word is should. I have never done any exhaust work using any standard bits so I can't tell you from experience. Essentially yes everything should fit together however you need to make sure that the flange angles and connection types are compatible.

[Foosblood24]

I'm really just looking for the mods that provide simultaneous HP/MPG gain. I don't really care about the sound. I already have the Cold Air Intake installed and wanted to put a simple header/catback combo to go along with it. She's a 93 so I won't really be able to experiment with test pipes in place of cats till 2018. (25+ year-olds don't need emissions in GA)

[NolimitZ32]

There is too much that goes into sizing exhaust components like with everything else on the car. In short putting headers and a catback on a NA Z32 may yield 3BHP or may yield nada. the gains and general effects of the components you are talking about are so small that its not worth mentioning. Ig you really want to chase the extra couple HP or that 0.72 MPG increase than there is quite a bit of CFD you will need to master to truly be able to theorize on the subject.

[DCaff300ZX]

There is too much that goes into sizing exhaust components like with everything else on the car. In short putting headers and a catback on a NA Z32 may yield 3BHP or may yield nada. the gains and general effects of the components you are talking about are so small that its not worth mentioning. Ig you really want to chase the extra couple HP or that 0.72 MPG increase than there is quite a bit of CFD you will need to master to truly be able to theorize on the subject.

Your mistake is coming at the exhaust for a stock vehicle as if it is something that one or another thing will do this or that, which really isn't exactly the case because each engine has different amounts of exhaust to move due to it's configuration (power/speed, economy/reliability).
As NoLimit says tuning an exhaust system is more or less trial and error as there are too many factors for the average person or shop to compute, and wouldn't even try as moving too far from OEM requires that the engine needs and would need and use any modification...in this case, produce more exhaust to pass and therefore the engine benefit somehow from more room for exhaust to maneuver, or the passage of more exhaust.
The NA VG30DE does not suffer from this problem, and is difficult and expensive to even get near the duty range of truly needing upgrading strictly for improvement of performance so opening up my own NA exhaust to even 2 1/2" with high flow cats in OEM configuration did very little for it other than produce more noise from a bad rasp when accelerating ANY, and a bad drone at freeway speed. The car also really didn't work better, actually it ran worse. Test pipes would be even worse because of even less restriction.
Since this wasn't what I wanted but what I now had, as agreed the shop went about making the new system work with the engine. Putting on different more restrictive mufflers helped the rasp some and the drone very little eventually, then rebending a few tight spots and using smaller dual tips for each muffler took away most of the rasp. Finally re-adding resonators fixed all noise complaints and left it slightly louder, NO rasp and almost no drone.
So basically all that occurred was getting a slightly better sound and , SLIGHTLY better acceleration from stop and definitely better freeway acceleration, but no gas mileage difference whatsoever.
Doing what you are asking about would in effect do the same thing as I did originally (open up the exhaust system more than needed), and would require you to "plug up" the exhaust system in order to make the car run right and sound reasonable.

[Foosblood24]

Very much understood and very much appreciated! Thanks for all the great advice guys!

[Z-owned]

I have headers and test pipes...

[DCaff300ZX]

I have headers and test pipes...

True. I have always wondered how you have gotten away with that, perhaps it's your catback plus you do run cats, correct?

[Z-owned]

Nope test pipes got rid of cats. Also got rid of the egr and any other emissions stuff long ago.

[DCaff300ZX]

Didn't you also get the 60mm throttlebodies?

[Z-owned]

I have the RoboZ bored out stock tb's think they are 54mm can't remember off the top of my head.

[DCaff300ZX]

Gotcha, I thought I remembered you had upgraded tb's...probably why you get away with the exhaust changes with your NA, there's balance to the system with more intake volume to balance the more exhaust volume. Not to mention some parasitic losses eliminated with your many deletes and amazingly excellent condition you keep your Z in...