Question about custom (turbo) exhaust collector design

[Komissar]

Hello,

I am currently fabricating a custom exhaust for my '72 Type 3 Squareback. 1600 dp engine with dual stock PSDIT carbs.
This exhaust is sort of an experiment, I intend to use it for a blowthrough turbo in the end.
The turbo itself will be a small one, (for example one from a 1.5L diesel donor car) and I intend it to use it for bottom end boost, rather than high rpm boost.

The steel pipes I have used for fabricating the header have an ID slightly smaller than the ones used on the stock muffler system which is about the same diameter of the inlet opening of the turbo (the exhaust inlet) - I have chosen this diameter to get good exhaust gas velocity.

Now, regarding the collector header - should the "outlet" of the collector be slightly larger than the diameter of the incoming merging pipes (and incidentally larger than the inlet of the turbo) or should it be the same diameter?

Thanks in advance.
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1965 Sunroof Beetle
1972 Type 3 Squareback
1978 Skoda 105S

[jpaull]

I suggest you include "Turbo" in your thread title. That way all the Turbo Junkies will get all excited and give you some input.

Such as:

Question about Turbo custom exhaust collector design

[Komissar]

Thank you I have just done that.
_________________
1965 Sunroof Beetle
1972 Type 3 Squareback
1978 Skoda 105S

[clonebug]

In my personal experience.......I found it doesn't matter much what you have for a exhaust as long as it pushes it through the turbo.

I've been running a cheap......actually free......sedan header with a 2 inch outlet flange up to my turbo for quite a few years. It performs pretty well.

I suppose if you had a race car and were trying to extract every once of performance out of it you could do better if you wanted to spend big bucks on a professionally built header or build one yourself out of many bends but I doubt the the difference would be worth the money unless a couple tenths of a second would make or break your reputation.
Here is my header...... A cheapa** sedan header with thin flanges.....

This is what I started with in 2011....

Here is the same header with a new up-pipe for my third turbo upgrade.

Here is the same header 7 years later supporting 24 lbs. boost and over 200 whp.

My turbine inlet is 1 7/8ths inch and my turbo up-pipe is 2 inch......the inside diameter of the 2 inch up-pipe pretty well matches the turbos turbine inlet.....I would try to keep it the same. or flare it up or down into the inlet to match.
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[theKbStockpiler]

You should use a Merge Collector if possible or use an actual Collector which is going to be significantly larger than your primaries. Otherwise you will not have a scavenging effect.
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My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[tripicana]

I cut up and used a S&S type 3 header.
Had to add a few bends I got from an exhaust shop.
More pics in my gallery.

_________________
foam cowboy hats aren't good helmets.

[modok]

I don't really understand the question.
It should be obvious that steps, sharp corners, and sudden changes in cross-section, and mismatches ect, should be avoided. The center line of the primaries should be aimed at the inlet of the turbo. It isn't highly critical, but if you can get the details right...it will help slightly.

What taper to use exactly, I don't really know. I'd lean towards about 7 degrees, (about a 1/4 inch per inch) but not totally sure. Maybe a little sharper?

[FreeBug]

From what I understand (or maybe don't), SHORT trumps over equal length.

[theKbStockpiler]

If the primaries are not close to equal length it is not a header and IS a tubular exhaust manifold.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[modok]

The term does not seem to have a specific definition in American english.
Example: Zoomie header, is a OLD term for a streamlined tubular manifold.

[oprn]

[theKbStockpiler]

[oprn]

[theKbStockpiler]

If pressure was just all the same type you could block off the exhaust intentionally but the exhaust gas has to be moving to spin a turbine. The scavenging effect creates two separate pressure zones in the exhaust.

When the cylinder 'blows down' it removes the spent fuel charge which is helped with a tuned exhaust and or a header with a collector/merger-collector. With a turbo engine this is going to be worse because the spent fuel charge is going to be greater and have more mass.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[oprn]

So your theory then is that a tuned system is more important in a turbo application than an N/A one?

[theKbStockpiler]

No because power is made or wasted in more than one way.

My theory is that an exhaust should not be like plumbing. If you want a low cost/performance turbo exhaust for many people that is fine because they can turn up the boost. Cutting a 90 degree fitting in 1/2 , making it a 45 degree and welding them together at an angle does not create a smooth transition for example but did not have to be custom bent. The separate pieces are just being connected at this point.
_________________
My beetle is not competing with your beetle. I have the yellow beetle in my town. There is a red one, a green one ......
Use all safety devices including a mask.

[Coyotemutt]

[clonebug]

[oprn]

I agree with clonebug, the difference in exhaust systems with turbos is small and hard to quantify without controlled conditions. Boost pressures and intake temps are the biggest bang for your buck. You can feel that any time of the day!

I didn't have an intercooler on mine and on a hot summer day it would get into detonation at 8 psi while in the winter at -30 it would go well over 15 psi with no issues.

[Komissar]

Thank you all for your input and the useful information provided.


Regarding the above mentioned intake temps, i guess that other then keeping boost levels as down as necessary, for a type 3 Squareback water injection might be a solution, since there is no room for an intercooler back there.
_________________
1965 Sunroof Beetle
1972 Type 3 Squareback
1978 Skoda 105S