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Homemade exhaust, any rules?
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KalgoorlieGreg
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PostPosted: Sun Mar 19, 2017 3:06 am    Post subject: Homemade exhaust, any rules? Reply with quote

Hi all,

I'd like to make my own exhaust for a fairly standard 1600DP because I want the exhaust tips set wide, not in the standard position.

It's a big topic, I have looked and come up dry. Are there any rules to what you can or can't do to get a decent exhaust system without causing more issues for myself?

Cheers, Greg.
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FreeBug
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PostPosted: Sun Mar 19, 2017 3:38 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

Exhaust design is always a compromise. Where are you willing to compromise? Noise? Power? Torque? Money?

Your best solution might be to route pies from where the pea-shooters enter the silencer to wherever you want them to exit.

Otherwise, you could become an exhaust engineer, work ten or twenty years in the industry, and still not know everything there is to know about the "perfect" exhaust. There's a lot of litterature and a few calculators out there on the web to help.

Without more info, I can't say more, and anyways, I don't know that much on the subject. If I had to build one from scratch, I would try to build a stepped tri-Y setup with sequential mufflers, but it's a pipe dream (geddit, pipe dream?).
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KalgoorlieGreg
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PostPosted: Sun Mar 19, 2017 5:39 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

I've seen 4 into 1 exhausts, and seen dual unmerged (one for each bank) exhausts. Would a dual exhaust merging the rear cylinder from one bank and the front cylinder from the other bank (with the idea of keeping header lengths similar), and a balance pipe joining each side, be feasible?
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catahoula lou
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PostPosted: Sun Mar 19, 2017 6:35 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

The way I understand it, make sure that it's "tuned", meaning that the individual tube lengths are correct and that each burst of exhaust from the individual cylinders do not "hit" each other.

In other words, each burst should come out between the other bursts, at the same intervals, so that the exhaust is extracted(?) smoothly and efficiently.

This is for single 4/1 or dual 2/1 systems. I was told by a qualified mechanic that the dual 2/1 systems do not provide sufficient back pressure(?), may cause problems over the long haul, and that he strongly recommended the single 4/1 systems for that reason.

You may want to measure an existing tuned exhaust (along the tube center lines, for accuracy) to get a good start on lengths/ratios...

Best,
Thom
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Last edited by catahoula lou on Sun Mar 19, 2017 6:42 am; edited 1 time in total
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Q-Dog
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PostPosted: Sun Mar 19, 2017 6:36 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

KalgoorlieGreg wrote:
I've seen 4 into 1 exhausts, and seen dual unmerged (one for each bank) exhausts. Would a dual exhaust merging the rear cylinder from one bank and the front cylinder from the other bank (with the idea of keeping header lengths similar), and a balance pipe joining each side, be feasible?


Feasible? In what regard? Looks? Noise? Performance?

If you are looking for better performance then no, your proposed design would not be optimal.

The 4 into 1 merged is popular because it works. If you want to do 2 and 2, optimal would be to pair the fronts to each other and the rears to each other.
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PostPosted: Sun Mar 19, 2017 7:29 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

You have a stock 1600. You dont have that much to gain or lose. If you make something worse then a $80 header then you must try really hard to mess up.
Why not start with a done header, and fab your own exhaust AFTER the flange? I would not be anxious to fab a custom header for a stock 1600. There isnt enough to gain. Cause if you want more power, your gonna need to go up on your primary tube size anyhow later.

If you would like some ideas on custom after flange exhaust, I did a short how-to:
https://www.thesamba.com/vw/forum/viewtopic.php?t=641441&highlight=
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PostPosted: Sun Mar 19, 2017 8:37 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

jpaull wrote:
Why not start with a done header, and fab your own exhaust AFTER the flange?


I would do this. Buy one of those 4-1 headers that you can still use your heater boxes with, and then just by a three bolt flange and weld it on whatever type of muffler you want to create. Thats what a lot of people have been doing to create their turbo exhaust on the cheap.
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PostPosted: Sun Mar 19, 2017 2:37 pm    Post subject: Re: Homemade exhaust, any rules? Reply with quote

dont go too small dont go too big. IMHO a 2" is bigenough for a street 2386. and a 2.5 inch is too big for a street 2276.
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Casting Timmy
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PostPosted: Mon Mar 20, 2017 4:05 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

Most important....hide all your receipts from the wife
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yamaducci
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PostPosted: Mon Mar 20, 2017 9:23 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

Rule#1 Make all tubes the same length. Then make it a 4 to 1.
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Boolean
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PostPosted: Mon Mar 20, 2017 9:23 pm    Post subject: Re: Homemade exhaust, any rules? Reply with quote

Tube primary diameter: 2" for 9000 rpm/4 cylinder, 500 cc/ cylinder engines. Decrease or increase linearly with rpm and volume. Look for primary length on the net.
Use supporting hardware like heads accordingly.
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PostPosted: Tue Mar 21, 2017 4:36 am    Post subject: Re: Homemade exhaust, any rules? Reply with quote

kangaboy wrote:
jpaull wrote:
Why not start with a done header, and fab your own exhaust AFTER the flange?


I would do this. Buy one of those 4-1 headers that you can still use your heater boxes with, and then just by a three bolt flange and weld it on whatever type of muffler you want to create. Thats what a lot of people have been doing to create their turbo exhaust on the cheap.


That makes the most sense....Then you can do whatever you want with mufflers and tailpipes. Try to keep the bends as gentle as you can and look at existing systems for ideas on tubing diameters. as mentioned, since its stock, you dont need massive flow. OH - dont get a big tube header - stay 1 3/8" It will perform better and will make your life easier.
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earthquake
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PostPosted: Tue Mar 21, 2017 9:59 pm    Post subject: Re: Homemade exhaust, any rules? Reply with quote

Check out these guys for bends...

http://www.mandrelbends.com/mandrel-bends.html

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