Duk
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Secondary Pipe Tuning???

Post by Duk »

On a 60* V6 like our Alfa's are, with 120 crankshaft degrees between left-right firing, are secondary pipes after a set of long primary extractors going to have any tuning effect on the system as a whole?

I'm still not settled on extractor design for my road going 3ltr.
Either have a shorter set of primary pipes around the 20-22"(508-559mm) long and a pair of secondary pipes at about 40"(1000mm) long. Or have a set of extractors that are 34-36"(864-915mm) long with virtually no secondary pipe before the cat.
Either design will use 1 5/8" (external) for the extractor pipes.

Previously I had standard manifolds and made equal length 2" diameter secondary pipes that used small flares to go from the manifold diameter out to 2" diameter at the manifold flanges. That 'felt' like it gave some better mid-range performance, but that could have been the lovely placebo effect.
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Re: Secondary Pipe Tuning???

Post by gran turismo »

I have been using pipemax ($40 at http://www.maxracesoftware.com) to design some headers for my 3.0 and here is what I have found:

1. The secondary pipe that you are referring to is commonly known as a collector. The collector length and diameter apparently has a big impact on the performance.

2. With our engines the common idea is that we need big 1.625" primary pipes. I was suprised when the program output gave much smaller primary dia so I asked (http://maxracesoftware.com/bulletinboar ... f=11&t=372).
Basically 1.625" primaries might be necessary for a standard engine with 9.5:1 compression and low 90's VE. However as you increase compression ratio and VE, exhaust temp is lowered which allows you to decrease the primary diameter and length. I have a set of Shankle headers that I thought were too small but now I think the primary dia. may be just right. My plan is to modify them for the proper length and with flat collectors for better ground clearance.

To back this up I asked PS Schultz a while back and their Alfa V6 headers are about 1.3" OD and they told me that their headers are used on many 3.0 and larger race engines.

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Re: Secondary Pipe Tuning???

Post by Zamani »

JimK ran his software and it said 1.625" + very long primaries. My factory SZs are 1.5" OD shorties. Secondaries are around 20" long 2" OD with Burnsstainless merge collector.
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Re: Secondary Pipe Tuning???

Post by gran turismo »

My software came up with 1.303" dia and 26" long. Has anyone found the smaller primaries to be restrictive?
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Re: Secondary Pipe Tuning???

Post by MD »

DUK,

Advice from a mechanic mate that used to run a tuning shop.

Exhaust headers for a V6 3 litre road car.

Primaries

1.5" OD x 20.76" long, less port length.
The volume of the merge collector should be equal to twice the volume of one cylinder ie. 1 litre

Secondaries

2.25" OD x 26-28" but no longer. At this point the pipes need to see an end to the tuned length and should go into an expansion chamber of some sort.eg. resonator or cat.

The balance of the exhaust system can be twin 2.25" OD or single 1x3.25"OD.

These specs will make good early and mid range torque which is what you want from a road car.
As you can see this is a progressively expanding gas progression.

Foot note

Old school rule of thumb
The shorter and bigger the pipes are for a naturally aspirated engine the higher up the power band will the torque be delivered. However for every HP gain at the top, you loose 2 at the bottom. So the logic of that is for a street car bottom torque is preferrable so small and long pipes are the go.
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Re: Secondary Pipe Tuning???

Post by Mats »

Hang on a minute now... a street 3.0 motor needs 3.25" exhaust? That is MASSIVE and there is no way it needs to be that large. What kind of power are you basing those calculations on?

I remember what I read about manifolds for the DFV engine in F1 back in the days. There was a short fat pipe in one corner and a long slim in the other, very obvious differance in design yet in the end they delivered the same amounts of Hp.
There seems to be a shift towards the fat and short verison nowadays in favour of the long and slim (in the racing world).

Are you all basing your calculations on stock cams?
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Re: Secondary Pipe Tuning???

Post by gran turismo »

Mats,

You can see what my calculations are based on here, they are not stock cams:
http://maxracesoftware.com/bulletinboar ... f=11&t=372

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Re: Secondary Pipe Tuning???

Post by Mats »

gran turismo wrote:Mats,

You can see what my calculations are based on here, they are not stock cams:
http://maxracesoftware.com/bulletinboar ... f=11&t=372

Jeff
Hmm, you input duration for intake and exhaust, lobe separation and then where the intake is timed? Very focused on single cam engines, but I guess it works fine.
Is all the data output as raw data in rows and columns? I can't find a single graph on that site. :?

Is it worth the money?
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Re: Secondary Pipe Tuning???

Post by gran turismo »

Is all the data output as raw data in rows and columns? I can't find a single graph on that site.

Is it worth the money?
Yea, all of the output is in rows and columns.

It it worth the money? Well it gives you dimensions for several different styles of exhaust header and for the entire exhaust system. It also gives you intake runner lengths and diameters. It also gives you an ineresting rudimentary analysis of your engine design including horsepower and rpm ranges for various components and a bunch of other stuff. I don't personally know anyone else who has used it but there seems to be lots of evidence on the internet :roll: that it gives good results.

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Re: Secondary Pipe Tuning???

Post by Mats »

No graph option? :shock:
Is it possible to export the data then? Comma separated or excel or something?

Hmm, I really should learn to use GT-Power. :roll:
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Re: Secondary Pipe Tuning???

Post by Duk »

Cheers for your input guys :D

Gran Turismo (my favorite game 8) ), you refer to the secondary pipe as the the collector. I can see why this is so, but have never heard of it referred to like that.

MD, I am seeing your points about smaller rather than larger diameter primary pipes, that are shorter than what I'm intending to use.
Your comments about the collector being twice the volume of 1 cylinder (1 litre) has me referring back to GT's comment about the whole secondary pipe being considered the collector. Is that your interpretation?
Twin 2.25" secondary pipes seem a bit big, but I'm here to learn and want all the info I can get.
But a 3.25" exhaust pipe after the cat is positively massive for such a modest power output. Keeping it at a sane noise level would be a challenge.

I am in a sort of pickle at the moment. I bought a heap of 1 5/8" 180* mandrel bends and machined up straight pipes to make a proper merge collector, so I'm semi stuck with making extractors from that. However, I can make a jig from my standard manifolds and make another set in the future that have smaller, shorter primary pipes and larger secondaries.

That is the real challenge with automotive part design. How many variation of 1 part or system of parts do you design and build for testing?
Anybody who builds 1 design and then starts categorically stating that "that design" is the be all and end all of, in this example, extractors and secondary pipes, is utterly full of it. Especially for road cars where the compromise is the greatest............
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Re: Secondary Pipe Tuning???

Post by MD »

Duk,

Just to clarify.
3.25" final pipe sizing is about a continuosly expanding gas on its way out idea bearing in mind you are starting out with 1.5" headers.If in practice this produces good power but shithouse noise suppression(which it will) peg it back to 2.5 or there abouts. I dont think the "tertiary" stages of a road car system are as critical as the primary stages on an NA engine.

As for terms like collectors,well the whole exhaust system is a collector but I don't think that's what you mean. When I say a MERGE collector, I mean typically where the ends of the primaries are gathered together in a coupling housing that will allow two, three, four or more pipes to be introduced into the next tuned section which is the secondary pipe, this thing is called a merge collector. The secondary pipe is NOT the collector however it continues to have influence over the tuning resonance until it sees another chamber like a resonator signifying the end of its resonance length.

Here's everything you ever need to know about merge collectors

http://www.spdexhaust.com/pdfs/02-11_Me ... rs.pdf[url][/url]
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Re: Secondary Pipe Tuning???

Post by Duk »

Cheers MD.
Yeah, the merge collectors that I machined were the same design as the slip on ones in that PDF file (tho not quite as sexy :P ) and have the 'goilet' center, but are based on straight pipes so that I could hold them in the indexing head to machine the correct amount at the correct angle.

There are so many schools of thought about extractor system designs.

Do I think of the engine as 2 individual 3 cylinder engines and base extractors around that method? Or do I try and take advantage of the potential scavenging effect of all 6 cylinders?

At this stage it will be 2 x 3 cylinder engines with long primaries and short secondaries into the cat.

If the indexing head just happens to find it's way back onto the mill again, and I just happen to have some 1.5" pipe, then the beginnings of second shorter primary design may start...........

But I have to much on the plate already to get to carried away :oops:
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Re: Secondary Pipe Tuning???

Post by Mats »

Oh, you're talking about megaphones. That explains a bit.
Seems like one of those magic contraptions that everybody talks about but no-one ever use except on bikes with zero noise restrictions.

To be honest, "secondary tuning" to me is really the pipe after the complete manifold/header. But that's depending on naming conventions I guess.
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Re: Secondary Pipe Tuning???

Post by Duk »

Mats wrote:To be honest, "secondary tuning" to me is really the pipe after the complete manifold/header. But that's depending on naming conventions I guess.
That has always been my interpretation as well.
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