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so if 2" is too big, how about 1 3/4? 1 7/8?
Topic Started: Aug 9 2014, 01:20 PM (1,789 Views)
Robertfrank
Member
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Ok guys I have a question. My exhaust on my 94 is rotten. The previous owner deleted the resonator and added a piece of rusty flexpipe. So I've been poking around here and have seen many mixed reviews for 2" pipe. From the looks of it my stock pipe is 1.50. So what would you guys think of 1 3/4 or 1 7/8 inch pipe? My driving mostly consists of highway and hills. I live in Utah lol. One more thing. I have checked out the SRD header and truthfully I can't see spending that much on it when i can easily build my own. How about porting the stock manifold? Not hogging it out but making it more stream lined.
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Metromightymouse
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Powdercoat Wizard

In my uneducated opinion, the size of the factory exhaust pipe is not a problem, it's the tiny outlet on the muffler. If your cat is not restricted and you put a muffler with less restriction on it you should see some performance gains. The Mullet has a unique set up that he likes where you replace the resonator with a turbo muffler. Single post here http://geometroforum.com/single/?p=852297&t=5103491 You can search for other posts or read his project thread for more info. He has videos of it running as well.
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Justahoby
Unqualified informant

I use 2" on the bends from the ex manifold into 1 7/8" I.D. after that ( no cat) into a long straight pipe into those bends into the muffler. I made my own 9.5 degree advance gear . Stock cam. It has power gain all the way through .
Way I understand 1 7/8 " is perfect for up to redline , maintains good velocity , and honestly as Metromightymouse has stated about the stock pipe is true as it is not much smaller.
I only went to 2" on the bends as the cheap pre bent pipes are partly kinked.

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Justahoby
Unqualified informant

Justahoby
Aug 9 2014, 02:30 PM
I use 2" on the bends from the ex manifold into 1 7/8" I.D. after that ( no cat) into a long straight pipe into those bends into the muffler. I made my own 9.5 degree advance gear . Stock cam. It has power gain all the way through .
Way I understand 1 7/8 " is perfect for up to redline , maintains good velocity , and honestly as Metromightymouse has stated about the stock pipe is true as it is not much smaller.
I only went to 2" on the bends as the cheap pre bent pipes are partly kinked.

http://tinypic.com/usermedia.php?uo=fNkd6hpTbcNQAjRyZPboVIh4l5k2TGxc#.U-Z5Gn-9KSM
Not sure how to put the photo, but here's a link
The first big bend was 2" I think the last one over the sway bar was less drastic, so I went 1 7/8"
Edited by Justahoby, Aug 9 2014, 02:43 PM.
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davegran
Old Fart w/Wrenches

Just copy and paste from the box with [IMG] in it and you get this:

Posted Image
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Justahoby
Unqualified informant

Thanks :thumb
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Robertfrank
Member
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Are they 2" crush bends into the 1 7/8 pipe?
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Robertfrank
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Enlighten me on this 9.5 gear lol
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perfesser
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Elite Member - Former Metro owner

Stock size for my '91 is 1-1/4". When I installed the new engine, I put a complete Walker system in. The exit from the muffler is the same size as everything else. It has a very civil note to it, and I am definitely not lacking in power. I thought of going larger, but then I asked my self "why?" :hmm :hmm and couldn't come up with a good answer! :dunno :dunno
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Justahoby
Unqualified informant

Robertfrank
Aug 9 2014, 10:39 PM
Enlighten me on this 9.5 gear lol
I put the gear in the vise on my mill so two teeth were on the back of my vise.Made it concentric with the shaft. Used my 3/16 end mill made a slot opposite of the two teeth. One of these two teeth is advanced one is retarded, I mark the one that throws it ahead.. 40 teeth divided into 360 is 9 cam degrees or 18 crank degrees. Half that in between teeth as I had done t is 9.5 crank degrees..
Edited by Justahoby, Aug 10 2014, 11:48 AM.
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Justahoby
Unqualified informant

Robertfrank
Aug 9 2014, 10:39 PM
Are they 2" crush bends into the 1 7/8 pipe?
Yes, I need a little bit tighter so I sliced and welded a few spots in the turn.
Mind you I also set my initial spark timing more than stock also, and have a seriously milled head
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Hanuman
"The Almighty Grounds Cleaner"

MWEBB uses a much smaller pipe to INCREASE exhaust flow.
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Justahoby
Unqualified informant

You mean to increase velocity at lower speeds?
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t3ragtop
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Turbo3 and Twincam Tweaker

i started using 2" pipe on normally aspirated 3 bangers a long time ago. it's just right, especially if you run the engine the way it was designed to run - in the upper rpm range.

for my twincam engines i run 2 1/4" pipe and on my turbo3 engines i run 2 1/2" pipe.

using a smaller diameter pipe as a method for maintaining flow velocity is not the way to go about it. exhaust gas velocity slows as it cools. you need to have a pipe diameter that will move the volume of expanding cooler gas or the wxhaust gas starts stacking up before it can exit to atmosphere.

as it is, the exhaust gas peeks out the tailpipe, sees the big world, and then turns around and tries to get back up the pipe. the stacking increases as the pipe diameter decreases.

what you will find is that there is a small increase in engine torque in the low rev range with a smaller pipe and a decrease of power at the upper rev range. if the exhaust diameter is larger you lose the small bump in torque just off idle and some guys interpret that as a loss of power. those guys shift before 3000 rpm and lug around at 2000 rpm.

the 2" diameter pipe lets the engine run better between 3000 and 6000 rpm. from an operational standpoint, the engine runs better up there which frees the hamsters.

my suggestion is always to run a short, wide high flow air filter and a 2" exhaust front to rear. then drive the little car like you are racing. :D
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Robertfrank
Member
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Nice. I can pick up some 2"inch pipe locally for $4.99 at 7.5 feet. I'd still need a little more but thats no biggy. I did for giggles cut off the rusted out muffler and did notice a small decrease in bottom end torque. I know I can make that up by freeing up some by bumping up the timing. How do i do that on this little guy?
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