Bad_Idea exhaust taking shape

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Bad_Idea exhaust taking shape

Post by Piledriver » Sat Nov 02, 2013 6:47 pm

Had a half baked idea awhile back for a super simple/low cost to fab T4 exhaust, flat, hangs under trans.
(kinda intended for a 914, but will probably see service on a T4 converted Squareback first)

Decided to waste an hour and a cutoff wheel to rough it out and see how it worked out in meatspace.
4 straight pipes doesn't allow the proper length secondary IMHO, think of as a tri-Y with a single bidirectional secondary.

The painters tape is not part of the final concept, haven't made stubs etc:
BadIdea-side.JPG
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helowrench
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Re: Bad_Idea exhaust taking shape

Post by helowrench » Sat Nov 02, 2013 6:56 pm

It will sure smell interesting if you leave the tape on.

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Re: Bad_Idea exhaust taking shape

Post by Piledriver » Sat Nov 02, 2013 6:59 pm

helowrench wrote:It will sure smell interesting if you leave the tape on.
Sure would...
I tried to PM this to you but apparently you cannot PM w/pictures.

Call me, I lost your #, or at least can't find it on this silly iThing.
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Re: Bad_Idea exhaust taking shape

Post by sideshow » Sat Nov 02, 2013 7:18 pm

So an equal length into a muffler box, like a stock beetle system (pre FI)? How do you plan to defrost the windshield?
Yeah some may call it overkill, but you can't have too much overkill.

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Re: Bad_Idea exhaust taking shape

Post by Piledriver » Sat Nov 02, 2013 7:28 pm

sideshow wrote:So an equal length into a muffler box, like a stock beetle system (pre FI)? How do you plan to defrost the windshield?
I visualize that functioning as a traditional tri-Y, just using much less tubing and far fewer bends.

Performance T4 exhaust systems typically have no provisions for heat.

The squareback has a BN4 in the trunk: Heat is No Problem.(it can actually be too much)

With the planned cooling system for the 914, there should be plenty of room to do similar in front of the engine and connect to the factory heat ducts..
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Re: Bad_Idea exhaust taking shape

Post by helowrench » Sat Nov 02, 2013 10:27 pm

Piledriver wrote:
helowrench wrote:It will sure smell interesting if you leave the tape on.
Sure would...
I tried to PM this to you but apparently you cannot PM w/pictures.

Call me, I lost your #, or at least can't find it on this silly iThing.
Pm'd with direct email and phonage.

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Re: Bad_Idea exhaust taking shape

Post by Ol'fogasaurus » Sat Nov 02, 2013 10:43 pm

http://www.ehow.com/how_7679737_calcula ... -size.html

http://www.ehow.com/facts_7806971_formu ... ength.html

Couldn't you do a 4-into one with a collector doing the gathering. That looks like a lot of stuff not working together Pile'.

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Re: Bad_Idea exhaust taking shape

Post by Piledriver » Sat Nov 02, 2013 11:06 pm

Ol'fogasaurus wrote:http://www.ehow.com/how_7679737_calcula ... -size.html

http://www.ehow.com/facts_7806971_formu ... ength.html

Couldn't you do a 4-into one with a collector doing the gathering. That looks like a lot of stuff not working together Pile'.
The object of the exercise was a low profile, inexpensive and easy to make system with short pipe and a minimum number of bends. It should not be lower than the engines sump under the car. It will probably also work well.

It isn't for a T1 so forget what those look like and look at how it works...
I could do a flat 4>1 collector but the pipes will not be equal length, plus the pipes would be too short tuning wise.
Probably only good for a turbo header.

Ehow.com should never be a reference for designing anything, ever. The supplied tidbit is correct but context-free, and does not apply to a tri-y as it would to a 4>1. On a tri-Y the primary tuned length would be (for example) from #1 to #3s exhaust valve, or 2>4 pair, 180 degrees out.

Just because it looks unconventional does not mean it works any different.
It doesn't violate any rules of designing an exhaust system--- in fact, it relies on the fact the rules are true.

The reflected waves don't really care which way the gas is flowing, so it should function ~exactly like a traditional tri-Y. The lack of extra bends and short runs should allow it to flow just fine with good velocity, while retaining the tyi-Ys "long pipe" tuning.

We shall see, hopefully soon.
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Re: Bad_Idea exhaust taking shape

Post by Ol'fogasaurus » Sat Nov 02, 2013 11:20 pm

(As an attachment I can't snag your picture to talk about Pile")

Forget the T1 (wasn't fair to say that Pile), I wasn't trying to duplicate what can be done on a T1 much easier. You are running two into one then three into one with the two collectors being the same diameter. I hung around a speed shop/muffler shop quite a bit and did pick up some information on exhaust there. I can't argue the no and amount of bends; but I think we both agree it would be better if the tubes were closer to the same length. You do very good work and I think you could do better here. They do make 2 into one collectors and I think, with a little imagination the tri-Y headers were similar to what you are after.

http://www.bing.com/images/search?q=tri ... &FORM=IGRE Not all these are true Tri-Y headers but the concept is there.

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Re: Bad_Idea exhaust taking shape

Post by Piledriver » Sat Nov 02, 2013 11:27 pm

I suspect this will work ~exactly the same with one less tube, far fewer bends, and ~2" more ground clearance.
That's the point.
Bad_idea-bottom.JPG
A 4:1 on a T4 can be done like this:
Image

Compare vs. a Tangerine header for a T4 (true tri-Y).
He cannot make his primaries shorter and keep them the same length.
(I ignored that relying on the fact the 4-2-1 tuned length is not the individual tubes length, plus I'm not making a $2K exhaust)
Image

I'm going for simple, cheap AND effective, while attempting to use the std design rules in an unusual way to get there.
(There will be a 1 5/8" tapered collector immediately after the 1/3 pair enter, so there will be 2x 3 way connections with a 17" or so 2" secondary as far as the system//math is concerned)

There is one school of exhaust design that says "all it wants is OUT", absolute minimum bends, don't worry about tuning...
Another suggests precisely equal tuned lengths/diameters vs. cam profile etc.

I'm trying to headshot both by relying on the fact that the laws of physics are true and properly understood..
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Re: Bad_Idea exhaust taking shape

Post by Ol'fogasaurus » Sat Nov 02, 2013 11:51 pm

Conceivably, if you really wanted to (and it sounds like you don't), you could still put the two pipes on each side into one collector then join those two collectors a bit farther back and still stay on or close to the center line like you are doing now. I wasn't trying to make is overly complicated but simpler to maybe work better. I saw a lot of headers being built back then and it is easy once you have done it several hundred times. :wink:

I'm though! :wink:

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Re: Bad_Idea exhaust taking shape

Post by Piledriver » Sun Nov 03, 2013 12:03 am

Ol'fogasaurus wrote:Conceivably, if you really wanted to (and it sounds like you don't), you could still put the two pipes on each side into one collector then join those two collectors a bit farther back and still stay on or close to the center line like you are doing now. I wasn't trying to make is overly complicated but simpler to maybe work better. I saw a lot of headers being built back then and it is easy once you have done it several hundred times. :wink:

I'm though! :wink:
The original idea actually used just those commercially made 2>1 and 3>1 collectors with essentially the same layout.
I---
A: don't have those handy, nor
B:can I justify the extra ~$75 they would cost, PLUS requiring another ~$100 worth of bends to allow their use. AFAICT they would likely provide exactly zero performance gain, and ~double the amount of welding, increasing cost and reducing reliability. They would make this look less weird..

This is an experiment.

Note the two systems pictured have a tiny bit more ground clearannce due to the layout, perhaps 1/2".
Also note the offset to the "wrong" side to clear the trans shifter console on a sideshifter, pictured trans is a tailshifter.
Ignoring that I could have made everything perfect equal lengths (also useless on a 914) but I suspect as long as the 1/3 and 2/4 lengths are equal, it's OK.

Also note I'm aiming for full 304 SS for <$200 materials. (retail) I'm only short ~8 flanges and some .100 sheet stock at this point (to make stubs) and am about $25 into it. (4x 90, 2x 45 and some straight stock in 1.5" and 2", most was scrap)
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Re: Bad_Idea exhaust taking shape

Post by E_bug » Sun Nov 03, 2013 2:05 am

I like it !
Great stuff.
Diy experimentation is the way to do it. Love the low budget factor too.

Now if i only had a 914. :D
My welding sucks .

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Re: Bad_Idea exhaust taking shape

Post by Piledriver » Sun Nov 03, 2013 2:51 pm

This will probably be used as a turbo header in the Squareback, turbos over the trans.
It can easily be made to clear framehorns and used on a T1/early T3, I just don't have any... yet.

I'll be ordering the tubular framehorns from Berrien this afternoon unless I figure out how to get a different crossbar setup to work. (Clearance issues for the drysump setup)

I'm actually resisting the tubular framehorns as I'm not sure I can space them wide enough to clear an automatic.(~13.5")
I have all the junk to do the 300++ HP motor but lack a transmission that would take it other than an automatic.
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Re: Bad_Idea exhaust taking shape

Post by aircooledtechguy » Sun Nov 03, 2013 4:07 pm

A dyno will tell you if it works or not no matter how hair-brained it looks.

I'm getting ready to begin making me a custom one-off header for my Squareback. Mine will be a 1 5/8" primary going into a 2.5" collector. I'm doing a 4into1 as that's more compact and I have no spare room to fart around with 2 extra collectors. ground clearance is paramount as well, so it's gonna be close fitting and not hang down below the stock sump. I plan to dyno tune mine when it's all in and done.

Of course I'll post pics when it's done but it will be a while. . . :wink:

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