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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 04-23-2009, 03:31 PM   #1
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Default 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.
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Old 04-23-2009, 04:03 PM   #2
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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
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Old 04-23-2009, 04:07 PM   #3
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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.
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Old 04-23-2009, 04:32 PM   #4
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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.
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Old 04-23-2009, 04:38 PM   #5
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Quote:
Originally Posted by tyson87 View Post
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
Are you talking about the Magnaflow in the for sale section on CR.net?
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Old 04-23-2009, 04:39 PM   #6
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we just talked turbo exhausts.

big and high flow and straight thruuuuuuuu = win.
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Old 04-23-2009, 04:44 PM   #7
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Quote:
Originally Posted by Ben View Post
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.
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.
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Old 04-23-2009, 05:11 PM   #8
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I made 219whp, @10.25 with 2-1/4 exhaust, upgraded to 2-1/2
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Old 04-23-2009, 05:17 PM   #9
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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.
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Old 04-23-2009, 05:28 PM   #10
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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.
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Old 04-23-2009, 05:33 PM   #11
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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.
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Old 04-23-2009, 06:04 PM   #12
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+1 on the CAT and see my build thread *sig* for recent vids of my 3" setup.
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Old 04-23-2009, 07:17 PM   #13
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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! I don't know about you guys, but that sounds like a hell of a deal to me.
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Old 04-23-2009, 08:34 PM   #14
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Score!
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Old 04-23-2009, 08:51 PM   #15
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Wow, helluva price!

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

turbo muffler:


straight-through:


One outflows the other...
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Old 04-23-2009, 09:31 PM   #16
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all those for signing a petition to ban the name "turbo muffler" say aye.
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Old 04-23-2009, 09:34 PM   #17
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Just be careful about the bends he is planning. Sounds like he might be planning on some crush-bending.
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Old 04-23-2009, 10:29 PM   #18
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Quote:
Originally Posted by Atlanta93LE View Post
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.
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Old 04-23-2009, 10:38 PM   #19
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Yes, get mandrel bent piping, especially if it's a free upgrade. No brainer.
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Old 04-23-2009, 11:01 PM   #20
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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 **** 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
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