Let's talks turbo exhausts...
 

I almost have everything in the garage for the turbo build...

BEGI Shanghai w/Chinese turbo similar to the 2854
TDR Intercooler
Megasquirt, AIT and WBO2
Still need injectors
Still need exhaust
Still need clutch

My question is about just how important is a really big pipe? ;)

Seriously... back when I had my 1993 with the Greddy turbo and I was running about 10psi and had about 190rwhp I had an OBX dual exhaust. It was 2.25" diameter. It was cheap. It had a great sound. It has good build quality and it was a very nice looking exhaust. I am seriously considering one for this 1994 Miata build. At only $300 shipped it ain't bad.

There is also that Tsudo exhaust for $160...

I can also get a 2.75 Enthuza Budget Turbo racer for about $100 more. The fact that it is aluminized pipe is of no concern since the car stays in the garage and I usually drive my Mazda 3 as a commuter.

I could use that extra $100 for a high flow cat. I have always heard that the cat is the highest restriction point.

Is there a big difference between a 2.75 and a 2.25 exhaust? All other things being equal?

By the way, I have been to a couple of muffler shops in town and my best price so far has been $325 for a 2.5" exhaust. And that is without mandrel bends or stainless pipe. I am going by another place today and see what kind of price I can get. Most of those guys are clueless. The first thing they usually say is... "Why do you want a 3" exhaust on that little bitty car?" "3" exhaust pipe won't fit in that little thing." I think all they do around here is put dual exhaust on pick-up trucks that exit out under the step bumper.

I guess the 4th option is to buy some mandrel bent pipe, a muffler off ebay, and a Harbor Freight welder and DIY the damn thing.

i bought a 3" for my kit for 300 from a member on one of the forums,
what about the "rsr inspired" one on cr.net

Yes, exhaust makes all the difference in the world. Go big. The minimal difference in cost to get a bigger exhaust is the cheapest hp per dollar you can spend, and the gains are huge.

I have one of those cheap ($140 shipped back in the day) ebay stainless 2.25" exhausts. I got it because it was better than the stocker, was cheap, and would get me by for a while. However, if I had had the dough, I would have gone bigger. Just my two cents.

Are you talking about the Magnaflow in the for sale section on CR.net?

we just talked turbo exhausts.

big and high flow and straight thruuuuuuuu = win.

Well... This is one of those deals where in all honesty I really knew the answer, and that is "Go big or go home." But sometimes you second guess yourself and you kind of hope there is some guy making 225rwhp on a 2.25" eBay exhaust at 10 psi and he will chime on to the thread. ;)

I made 219whp, @10.25 with 2-1/4 exhaust, upgraded to 2-1/2

You can get it done cheaper if you buy your own parts and the shop only has to bend pipe and weld some flanges.

I was given a turbo muffler $0

Got a good deal on a 200 cell per inch metalcat $100

Local shop is doing pipe and flanges from downpipe back $150

$250 for a full 2.5in exhaust with one of the highest flowing cats on the market and a cheapy muffler that passes the golf ball test

PRICELESS

I would do this but in 3in.

Please get 3" with a high flow cat. My spool (14psi target) went down from 4100rpm to 3300rpm going from stock-ish sport exhaust with oem cat to full 3" Enthuza setup. I have yet to verify new torque and power output on a dyno but I added 10 points of fuel at 212kpa already.

Either way get a badass cat.

That was the point of my post. I can settle for 2.5" for my goals, but I recommend going to 3" although I know guys that have run both and not hardly seen a difference as long as they had a real high flowing cat and a straight through muffler.

If you really want to be baller you would have a test pipe section after your downpipe with a 15* taper from downpipe diameter to 3" with a Metalcat 100cpi right behind it, and a huge magnaflow out back.

Either way, don't cheap out on the cat.

+1 on the CAT and see my build thread *sig* for recent vids of my 3" setup.

Well, of all things, this afternoon I go to the shop that is closest to my house of all of them and talk to their "Exhaust guy" Tim. Of course he knows all about turbo cars and turbo Miatas, etc...

We put the car up on the lift, and I explain that I want a 3" pipe. He says "No problem." I ask about mufflers, and he recomends a glass pack, I said "Na", and ask about a "turbo muffler". He said that he didn't recommend that, and then I asked about a Magnaflow straight through design. He thought that would be a good idea.

So I was going to buy a metal core 3" cat off eBay, he was going to weld flanges and extra pipe on it to fit in the stock location, he was going to furnish the Magnaflow muffler, and the 3" aluminized pipe and a stainless steel finisher and all of the fabrication... Everything installed for $180.

I was like... DEAL! :laugh: I don't know about you guys, but that sounds like a hell of a deal to me.

Score!

Wow, helluva price!

I agree with him about the "turbo" muffler...

turbo muffler:
http://www.yearone.com/images/parts/...rbomuffler.jpg

straight-through:
http://image.off-roadweb.com/f/tech/...er_cutaway.jpg

One outflows the other...

all those for signing a petition to ban the name "turbo muffler" say aye.

Just be careful about the bends he is planning. Sounds like he might be planning on some crush-bending.

Yeah... I thought about that. But still wouldn't a 3" exhaust with a crush bend be better than a 2.25 exhaust with mandrel bends?

I ask him about mandrel bends and he said that he could order some and said that it wouldnt cost extra.

I may just go back down there and let's make a list, go ahead and pay for the stuff up front and then it will be there when I get ready to bring the car down there.

Yes, get mandrel bent piping, especially if it's a free upgrade. No brainer.

that is cheap as hell...

go back, double check everything (mandrel, 3", muffler, etc) and if it is in fact agreed throw the money down before they change their price upon your return.

And shit while you're at it, tell him to make a jig and start punching these babies out

I had a local place do a deal on 4 or 5 exhausts for a few of us when I was in FL.
3" exhaust, straight (no cat) and magnaflow, and was around $320 iirc

^just for reference

"Truth-If you have 3" tubing that is press bent it will smash 1/2 inch at
the center of the bend. At that point you have 21/2" flow instead of
3". It doesn't matter if you have one bend or five bends you still have
21/2" flow."

source Mandrel Myths-Mandrel Bending vs Pressure Bending

only crush bent pipe flows worse than 2-1/2 because the flow restriction increases as area changes occur.

It's already too late as I already have this midpipe/cat/resonator setup on my car. Anyone know if these cats are any good? http://www.flyinmiata.com/index.php?...umber=06-58200 doesn't say much about them in the description. I figured I couldn't go wrong for $100.

Make absolutely sure you get a cat that is the lowest restriction possible, or have a test pipe. You could have a 4" exhaust and if you have a tight-celled cat it won't help one bit.
I had a 2.25" cat-back exhaust with a high-flow cat and when I went from the stock greddy downpipe to the BEGI downpipe spool went from 4600 to 3900.
Then, I yanked the whole cat and exhaust and did a 3" cat with a 3" glasspack on the end of it and then it dumps by the rear axle. You'd think that would flow super well - no bends, only ~ 3ft. of 3" piping after the cat...
Wrong, the cat I used was a cheaper 'catco' one. Now it spools at 4500. I guarantee when I do give this cat the ol' hammer and chisel port job, spool will drop well below 4k.
Moral of the story - anything after the cat is wasted money/effort if the cat restricts it, and no matter how free flowing the rest of it is, the motor can't flow any better than the cat allows. Get a good 200 cell cat or a testpipe.
-Ryan

If you run a small turbo, say like the 2560, is it still advisable to get a full 3" system? I was thinking about building a downpipe (not sure what diameter yet), then just hooking it up to a 2.5" decat pipe and then the cat-back system I am using at the moment is 2.25". Does running a 2.25" backbox render the earlier larger exhaust parts useless? Was just thinking about doing that setup to get me going quicker.

I have a 2560 an spool went down from 4100rpm to 3300rpm with the OEM to 3" upgrade. That is with a high flow 3" cat.

That's awesome, I wonder how much lower it would go with a 3" decat. :D By the looks of it, it will be worth the extra effort making a full 3" system. Out of interest are you running EBC?

@saitrix: I was running EBC with a 7psi wg actuator can and it sucked due to cold weather overboosting. Then I ran MBC which was ok and not run a 14psi wg actuator can and nog mbc/ebc at all.

AKA: A bottleneck is a bottleneck. The exhaust only flows as much as the most restricted point.

no, it flows less than that.

Thanks again for that Tony

Even though they may have mandrel bent sections, any muffler shop will still crush bend when necessary. They will not spend the time on a chop saw getting the perfect angle when they can just tweak it on their hydraulic crush bender.

You get what you pay for; a $180 exhaust is probably fine for you. Chinese price exhaust for the chinese turbo. :)

FWIW I ran a 2.5" crush-bent exhaust with a metallic cat and a straight through magnaflow. It still worked much better than the stock exhaust and was really not much louder if at all. The spool improvement was obvious. So a 3" even with some crush-bent sections will still be much better than your stock exhaust, and at $180 that is damn cheap so I say go for it.

But to reinforce what others say above, an all-mandrel bent 3" would probably still be an improvement over that. However it will be louder, and a lot more expensive. I have a 3" enthuza now, but only because I bought it used at a good price.