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EA81 Exhaust Question?


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17 replies to this topic

#1 Dante

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Posted 23 October 2003 - 05:50 PM

I've been reading up on ea81 preformance modifications. http://www.subspeed.com/FAQ.htm says "A properly designed header and low restriction exhaust system of the appropriate diameter will go a long way toward performance."

I searched the "Older Sube" forum for "header" and related terms and saw one reference to a custom header or y-pipe. It looks like most people are running the stock y-pipe/catalytic converter combination. It looks like a few people have cut the cat of the stock y-pipe and replaced the cat with pipe. A few people have made up dual exhausts, but I understand the y-pipe helps torque...

Are these all the options for the normally aspirated ea81?

Is there any compelling reason to replace the stock y-pipe with a custom header/y-pipe?

Or, is it best to cut the front cat off the stock y-pipe and replace the back cat with a better flowing 3-way (which I understand is legal everywhere except california)?

Thanks in advance for any info you can give me.

#2 PHATBRAT

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Posted 23 October 2003 - 08:45 PM

Going True Dual's will be expensive. What I did on my old BRAT was cut the Y-pipe and re-welded it so that the exhaust flowed more freely. The stock pipe meets at a 90 degree bend which if you think of it full of water, when it hits there it will cause sort of a back up. I re welded mine so that both sides came in at 45 degrees and I had 2 1/4 inch with a glasspack and split in the rear for dummy duals. It worked spectacular. A definate notice in power and sound. I had people believing I had a small block 327 in there. I also got rid of the CAT. Where I come from it's corn bread and chicken, Whoops, I mean where I come from, we don't worry about emissions. A definite kick rump roast mod.

#3 bbbs53

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Posted 23 October 2003 - 09:44 PM

I'm with Phat, only difference was I went bigger, 2 1/2" pipe. A while back, someone, McBrat maybe, made a x pipe then into duals. The two pipes came from the manifold together in the x and out the back, it was a Brat mod and looked real good. There was a real good picture on the old board, the cat is out if you don't live where the smog nazi's are. Go with the least restrictive muffler you can get.:burnout:

#4 Dante

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Posted 24 October 2003 - 11:59 AM

Akira had the ea82 (or maybe ea82T) y-pipe on his ea81 performance mod wish list. What does that do?

Sounds like rewelding the stock y-pipe like you two did and replacing both cats with a better flowing 3-way cat and muffler(I'm in an emissions testing arrea) might be the way to go for me.

#5 Dante

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Posted 28 October 2003 - 12:49 PM

Here's what one ea81 builder I spoke with said:

"Header primary length is critical to this engine, you need 1.625 od tubing (1.5 id) off the head 28" long into a collector from there on your 2" will work."

#6 JonOfScio

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Posted 28 October 2003 - 12:55 PM

but, doesn't exhaust diameters change depending on the breathability of the engine and the power increase? I think he's quoting a STOCK engine.

#7 Dante

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Posted 28 October 2003 - 01:08 PM

I'm sure the first part of your post is right, but I don't know about the second. The guy's statement was in the context of a bunch of performance mods (see my ea81 "bang for the buck" thread).

Remember, the 1.5" ID is for the primaries. The 2" from there back was my idea based on other stuff I had read. I am way out of my depth here, but a lot of the stuff I have read says not to go too big too soon or you hurt scavenging. those sources say to run 1 7/8" or 2" to the muffler (a better one) and 2" or larger from there back.

OTOH, I've read the stock exhaust is so poor it really doesn't scavenge very well at all anyway, so maybe better designed larger primaries would work better on a built car.

I'm looking for answers, not answering them... :cornfuzz:

#8 JonOfScio

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Posted 28 October 2003 - 01:19 PM

I've talked to people, and what seems popular is 1 7/8" ID from the heads down, to a Y, then 2" from there on out. this sounds reasonable to me.

#9 VaporTrail

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Posted 28 October 2003 - 01:38 PM

my former Mountain GRizzly wagon had 2" at head, then 90 deg Y to keep the backpressure for low-end, then 2.5" all the way back to a MagnaFlow muffler... a bit too loud, especially for the 2000 mile trip to Washington twice :)

my new GRizzly Brat has 1 7/8" at heads to 90 deg 'Y' and then 2.25" to same Magnaflow muffler. a bit quieter as well, as a little better low end...

Jerry (Bratrus1) had the dual exhaust on his 86 Brat. better for higher RPM's

The place I go to is a 1 owner shop that specializes in exhaust for all kinds of vehicles (mostly American muscle cars) but the do all kinds of work as well... they did a real nice job on this last y pipe. tucked up nicely for less chance of getting knocked off while off-roading (plus I put a big skid plate on it that covers the exhaust....)

#10 Dante

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Posted 04 November 2003 - 04:41 PM

Well, I think what I'd like to do is something like McBrat did--primaries of an appropriate length and I.D. coming together at an appropriate angle at a collector. Since I have to deal with "smog nazis" I'll replace the two stock two-way cats with one three-way cat at the collector where it will heat up quick and work best and then out via a 2.25 to 2.5" pipe and low restriction muffler (or an adjustable restriction muffler like a Supertrapp).

Now all I need to do is find a good shop near Seattle to design and fabricate the system

#11 GeneralDisorder

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Posted 04 November 2003 - 06:28 PM

Yeah - you don't want too big of a pipe comming off the heads - as McBrat noted. You'll lose your scavenging effect if the exhaust is too large. After a certain point (like after the Y pipe), you can go to a larger pipe for better flow without impacting the scavenging effect. Of course the size of the initial Y pipe will depend on how many performance mods you have done to the engine - the more air you are moving the larger your Y pipe ID should be.

GD

#12 Skip

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Posted 04 November 2003 - 07:12 PM

here is what I did, cut factory head pipes short of the "Y"
more low end and more top end
have a Weber 32/36 feeding it
Posted Image

offered to make complete (minus "Y" pipe) systems for 200 green backs, no one was interested so I quenched the project sorry
Am working on turbo down pipes now
Posted Image

#13 AKIRA

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Posted 04 November 2003 - 10:11 PM

I screwed up about the y-pipe, I thought it was catless, it does have a cat.

#14 Dante

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Posted 05 November 2003 - 01:02 PM

Thanks for all the info. everyone! :-)

Can anyone recommend a person or shop in the Seattle area?

They need to be able to design the header or y-pipe mods for my purposes (maximize towards low-end torque while preserving ability to do the speed limit on the freeway), fabricate the header or do the y-pipe mods and do the rest of the system.

#15 NoahDL88

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Posted 05 November 2003 - 08:15 PM

If your car is stock only go one or two sizes bigger on the exhaust. i calculated it all out last year in my high performance class, 1 5/8 to 1 3/4 is a good size off the head and two may be too big for the way out to the tailpipe. not only is scavenging important but so is the feet per second that the air is traveling, a good range is 240-260 any faster and that creates back pressure, any slower and it becomes stagnant an looses flow.

#16 Dante

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Posted 06 November 2003 - 04:23 PM

Thanks! I think I'll be doing my mods in two stages for financial reasons (the wife gets twitchy if I try to spend too much all at once ;) ):

Stage 1: Intake, ignition and exhaust cat back.

Stage 2: Port heads, regrind cam, deck block and the rest of the exhaust (header/y-pipe, collector and single three-way cat). If I have to re-do the whole exhaust when I get around to the internal engine mods, so be it...

#17 Dante

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Posted 20 November 2003 - 06:39 PM

Bump--Anyone know of a Seattle area shop that can build me a custom y-pipe? Anyone know if Stratus does exhausts?

#18 carfreak85

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Posted 20 November 2003 - 11:47 PM

what about sizes for a turbo motor? i heard as big as you can get, but within reason. Skip, what do you have on your turbo wagon?




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