Stainless Steel Headers

[Jerosmith]

So, long story short, I used to be a welder. I have the utmost confidence in myself when it comes to fabricating things out of steel as long as I don't have to do any machining. haha

So, I'm gonna be building my own equal length headers for my spider and one other person.

I've got a pretty good idea of how to accomplish all this, but I figured I'd as you guys this easy question:

"If you had a machinist and a welder and all the materials needed, what would you make your headers out of, what size would the primary and final tubes be? Why?

The first step has even yet to be done; the flange is being made from 1/2 inch stainless and my friend is gonna do all that machining, cuz I'm just a welder, nothing special. ha.

So, there's still lots of time for you guys to chime in on this matter.

Let me know! Thanks! Jer.

[vandor]

> what size would the primary and final tubes be? Why?

The Guy Croft book covers this, has sizes, lengths, etc. IIRC it says 4-2-1 is better than 4-1. I talked to him about it, and he said that for it to work right it has to be equal length down to the mm. I figured I'd never find a fabricator good enough to pull that off, or if I did, I could not afford him

[TimpanogosSlim]

down to the mm?

begs credulity. thermal expansion rate will vary from the front to rear most cylinders due to, well, the rear one being far from the grille and close to the firewall. Probably alters the flow characteristics more than 1mm of length.

[Jerosmith]

I gotta say, to have all the tubes equal length down to the mm actually, truly, isn't all that accurate when you're considering air flow. Air should be measured in volume no? So to be completely, perfectly accurate, what would have to be done is the measuring of volume in each tube. That is assuming the exact same amount of exhaust comes out of each cylinder. As long as you could have the air flow thru the bends of the tubes of equal restrictions, that should actually be the most equal in air flow in my eyes...

That is something I just don't understand about the science behind some of these performance headers... Equal length sometimes means having to make insane bends and corkscrews where I would personally think this would be more restrictive of another more "direct" tube. If you catch what I'm saying...

Can anyone shed some dynoed light on this matter?

Looking at the performance headers you can get from allisons automotive, they are twisted all around. That, if I decide to do, is gonna be one hell of a build from scratch... Why are they so twisted? What does this help?

Can anyone say they've tried different headers on the same car and gotten different results? Truth be told, I'm fabricating my own just so I can be proud I made something beautiful from scratch in my engine compartment.

Also, I have to ask where you got the information of 4-2-1 being better than 4-1. I thought I had read somewhere that 4-1 is the way to go with performance headers. Can someone just tell me what to build please? Lol explain to me why longer headers are better or worse, I can understand the equal length bit would surely help. If any of you guys can link me to resources for measurements with tried and tested headers, that would actually just save me a lot of time.

If someone comes back here and gives me clear reasoning, I can start my build... Otherwise, once the flange is done, I'm just fonds take the "easy" way out, and make each tube as close to equal length as I can and have as little bends in them as I can muster. Just because to me, this has to make for more equal airflow to the collector.

Help? Haha

[Jerosmith]

OK, so, google helped me out when I was super specific with my search field. And I found this very informative thread: Haha

http://www.guy-croft.com/viewtopic.php?t=1917

Here is a link with Guy Croft stating that 4-2-1 is USUALLY best option with 4cyl engines. So, unless someone has some proof otherwise for my 1800 1978 spider, that is what I'm gonna be doing.

Also, it's stated in this forum thread that long primaries and short secondaries are best for performance.

So, as long as I can find the room (I'm sure I will) this is also what I'll be doing.

I'm seriously considering doing mock up out of pvc piping just to see what different shapes and characteristics will look/work best before I go wasting 304 stainless.

If I do this, I'll likely take pictures and post to this thread to maybe show you guys. Once I'm happy with the mock up, I'll put clamps around as many places as I can around the pvc, and talk weld them in place so I can make a jig out of it and fabricating with stainless will be (almost) as easy as just placing tube where they need to be, making appropriate cuts, and welding them up after everything is all tacked into place.

I'm being super thorough about my plans so that if there's anyone out there with more expertise, that might know a better way, by all means I'm all ears!

I must say, to the gentleman who said 4-2-1 is better that 4-1, in thank you, it was your post that led me to the very specific search criteria that led me to this post that has been so informative.

[engineerted]

Attached is a good article that explains the science behind header designs. Also did you know that you can get the flange form one of the tubing suppliers. Columbia river I believe.
http://www.mandrel-bends.com/catalog/fl ... /fiat-210/

Http://www.epi-eng.com/piston_engine_te ... nology.htm

[engineerted]

Here is some formulas that may help, Truth be told, all engine react different so use this as a guide only.
I run a 4 into 1 on the race car, 17-21inch primary length 1.5' primary dia to a 2-1/4" merge collector. usable torque and power for my engine is 5-8 rpm not really for the street unless you like to buy $8/gal fuel.

Exhaust Tuning Theory and System Design

Exhaust tuning theory is actually fairly simple; it�s all about getting the negative (and, hence, scavenging) pressure pulse to arrive at the exhaust valve as it is opening. To do this we have to set the pipe lengths and diameters correctly.

The formula for Primary pipe length is:

P = [(850 x ED) / RPM] - 3

Where:
RPM is the engine speed to which the exhaust is being tuned.
ED = 180� plus the number of degrees the exhaust valve opens before BDC.
P = Primary pipe length (on a 4-1 manifold), or Primary pipe length plus Secondary pipe length (on a 4-2-1 manifold), in inches.

Generally road engines will require the manifold to be tuned to the max torque rpm whereas race engines will be tuned to work either at max bhp rpm or a speed midway between the max bhp rpm and max torque rpm.

4 -1 manifolds restrict the power band, whereas 4-2-1 manifolds give better mid-range power but reduce top end power by as much as 5-7%.

Generally speaking with a 4-2-1 manifold the starting point for Primary pipe length is 15 inches, thus Secondary pipe length is P - 15 inches. Changing the length of the Primary pipe tends to rock the power curve around the point of max torque. Shorter Primaries gives more top end power but less mid-range, and vice-versa. There is, however, little change in the peak torque or the rpm where this occurs.

Ideally the Primaries should come off the cylinder head in a straight line for around 4 inches before any turns occur.

Inside diameter of the pipe can be gained from:

ID = sq root [cc / {25 x (P + 3)}] x 2.1

Where:
cc = cylinder volume in cc.
P = Primary length in inches.

In some engines it can be useful to have a 'step' between the exhaust port and the Primary (ie the Primary bore is greater than that of the exhaust port). This tends to be the case in engines with rectilinear exhaust ports.

For a 4-2-1 system then, Primary pipe diameter is calculated as above. Secondary pipe diameter is given by:

IDS = sq root (ID x ID x 2) x 0.93

Where:
ID = calculated inside diameter of the primary pipes.

The pipe diameter can be used to change the peak torque rpm � a reduction in diameter of 0.125 inches will drop the peak torque rpm by 500-600 rpm in engines over 2 litres and by 650-800 rpm in smaller engines. Increasing the pipe diameter by 0.125 rpm has approximately the opposite effect.

The total length of the Collector and Tailpipe (to the front of the silencer) should be equal to P + 3 inches (or any full multiple of P + 3 for a road car).

Tailpipe internal diameter is given by:
IDT = sq root [(cc x 2) / (P + 3) x 25] x 2

Where P is calculated as above.

Collector length is given by:

CL = [(ID2 � ID3) / 2] x CotA

Where:
ID2 = diameter of Collector inlet
ID3 = diameter of Collector outlet.
CotA = Cotangent of angle of Collector taper (which ideally should be around 7-8� (certainly less than 10�).

The design of the collector should be such that the inlet pipes terminate abruptly otherwise the tuned exhaust pressure wave will carry on into the tailpipe and the calculations done to get the negative scavenging wave back to the exhaust valve on time will all be wrong.

[Jerosmith]

Here is some formulas that may help, Truth be told, all engine react different so use this as a guide only.
I run a 4 into 1 on the race car, 17-21inch primary length 1.5' primary dia to a 2-1/4" merge collector. usable torque and power for my engine is 5-8 rpm not really for the street unless you like to buy $8/gal fuel.

Exhaust Tuning Theory and System Design

Exhaust tuning theory is actually fairly simple; it�s all about getting the negative (and, hence, scavenging) pressure pulse to arrive at the exhaust valve as it is opening. To do this we have to set the pipe lengths and diameters correctly.

The formula for Primary pipe length is:

P = [(850 x ED) / RPM] - 3

Where:
RPM is the engine speed to which the exhaust is being tuned.

Ummmm, wow. Thank you so much for the very thorough lesson my friend. I'm driving in new Hampshire right now, so i have to keep this short. But I definitely want to discuss this more with you.

To be completely honest, I have no idea where to even get 100+ octane in Canada, so that's out of the question I think. Haha. Executable to, I do want to be able to smoke my tires off if I want.

I can't stress enough how grateful I am that you've taken this much time and effort to respond to my questions. You sir, are a gentleman and a scholar. Truly.

Talk soon! Also, if you have Facebook, add me up. Name is Jeremy Gregory Raymond Brisebois. Cheers!
ED = 180� plus the number of degrees the exhaust valve opens before BDC.
P = Primary pipe length (on a 4-1 manifold), or Primary pipe length plus Secondary pipe length (on a 4-2-1 manifold), in inches.

Generally road engines will require the manifold to be tuned to the max torque rpm whereas race engines will be tuned to work either at max bhp rpm or a speed midway between the max bhp rpm and max torque rpm.

4 -1 manifolds restrict the power band, whereas 4-2-1 manifolds give better mid-range power but reduce top end power by as much as 5-7%.

Generally speaking with a 4-2-1 manifold the starting point for Primary pipe length is 15 inches, thus Secondary pipe length is P - 15 inches. Changing the length of the Primary pipe tends to rock the power curve around the point of max torque. Shorter Primaries gives more top end power but less mid-range, and vice-versa. There is, however, little change in the peak torque or the rpm where this occurs.

Ideally the Primaries should come off the cylinder head in a straight line for around 4 inches before any turns occur.

Inside diameter of the pipe can be gained from:

ID = sq root [cc / {25 x (P + 3)}] x 2.1

Where:
cc = cylinder volume in cc.
P = Primary length in inches.

In some engines it can be useful to have a 'step' between the exhaust port and the Primary (ie the Primary bore is greater than that of the exhaust port). This tends to be the case in engines with rectilinear exhaust ports.

For a 4-2-1 system then, Primary pipe diameter is calculated as above. Secondary pipe diameter is given by:

IDS = sq root (ID x ID x 2) x 0.93

Where:
ID = calculated inside diameter of the primary pipes.

The pipe diameter can be used to change the peak torque rpm � a reduction in diameter of 0.125 inches will drop the peak torque rpm by 500-600 rpm in engines over 2 litres and by 650-800 rpm in smaller engines. Increasing the pipe diameter by 0.125 rpm has approximately the opposite effect.

The total length of the Collector and Tailpipe (to the front of the silencer) should be equal to P + 3 inches (or any full multiple of P + 3 for a road car).

Tailpipe internal diameter is given by:
IDT = sq root [(cc x 2) / (P + 3) x 25] x 2

Where P is calculated as above.

Collector length is given by:

CL = [(ID2 � ID3) / 2] x CotA

Where:
ID2 = diameter of Collector inlet
ID3 = diameter of Collector outlet.
CotA = Cotangent of angle of Collector taper (which ideally should be around 7-8� (certainly less than 10�).

The design of the collector should be such that the inlet pipes terminate abruptly otherwise the tuned exhaust pressure wave will carry on into the tailpipe and the calculations done to get the negative scavenging wave back to the exhaust valve on time will all be wrong.

[Jerosmith]

Lol, my message is halfway thru that last quote in that last post... My mistake, like I said, I'm driving. Lol

[Nanonevol]

You're driving? Don't text and drive!

[timinator]

For stainless header materials try these folks.

http://www.burnsstainless.com/

As far as what style of header to build there is no right answer. Lots of math available if you search. Good header fabricators could build your 4 cyl. header in 10 to 12 hours. More power to you if you want to build your own header. I have built several headers because no off the shelf headers were suitable. The Fiat header is a tight fit so compromises are unavoidable. I have seen what Mark's header can do for the performance of an engine. The common complaint about the "twisted bunch of tubes" being bad for horsepower is a myth.

Don't be disappointed if you have to cut everything off the flange and start over because you didn't allow for something. It just happens. The thing to remember about a header on a 4 cyl. is that they vibrate like nobodies business. You just can't get away with welding a tail pipe to it and supporting it with a cheap hanger. The header will crack to pieces in no time.

Everyone has an opinion on what primary tube length to run. If it is stepped once or twice, merged 4-2-1, merged collector, or megaphoned there are even more opinions. I use PipeMax for those calculations as do a lot of other people. You might look into this as your source for header requirements.

[Jerosmith]

Thanks much Tim! I did not know about that violent rattle. Very good to know. I'll make sure it's good an secured then.

As far as steel goes, I live in a big city, I'm sure I'll be able to find mandrel stainless and material for the flange as well... I don't see a point in paying for shipping. I don't know if it's hard to find that stuff in the states, but in Canada it's fairly easy to find any kind of steel you could think of. Plus, I still have a lot of connections since my time being a welder/fabricator.

That being said, this really is going to be a challenge for me, especially now with all the information you guys gave me. So much more to think about now. I'm actually thinking maybe I'll get the opinion of one of you guys on what to go for.

If anyone ever wants to give me a call or chat with me on Facebook about these fun little cars, here's my info.

Jeremy Gregory Raymond Brisebois
Vancouver, BC, Canada
705-493-6111

Thanks again guys! You've been super helpful!

[fiatfactory]

.

[Jerosmith]

Where most people get it wrong (and a few of the off the shelf vendor items suffer from this too) is the exit angle from the cylinder head... it is NOT at 90 degrees to the header flange, pay careful attention to this as it make an appreciable difference.

SteveC

What is the best angle then good sir? And if I were to make it on an angle, I'm either going to need to start off right away with a bentpart of the mandrel, or the hole in the flange will need to be slightly oval to match up with the angle-cut tubing, no? Where have you gotten this information and what's the reasoning behind having an angle straight-away?

[Jerosmith]

Where most people get it wrong (and a few of the off the shelf vendor items suffer from this too) is the exit angle from the cylinder head... it is NOT at 90 degrees to the header flange, pay careful attention to this as it make an appreciable difference.

SteveC

You sure you're not talking about the intake manifold? Because I can clearly see from the gasket alone for the intake manifold that the holes are oval so as to match up with the angle the tubes would have to be cut. I ordered the EXHAUST manifold gasket from napa for my machinist friend to fab my flange for me. He lives 3000 miles away from me, but I go there probably twice a month. So, when he picks up that gasket I'm gonna have him take a picture for me and the shape of the gasket should dictate the angle at which my tubes need to be cut at.

IF the exhaust ports are at a different angle than 90 degrees to the head, this all makes sense.

So, thank you for bringing this to my attention. I will be doing some more digging.... If anyone has the engine kicking around without an exhaust manifold on, could you be so kind to tell me if the above is true? Or just take a picture of the exhaust port and we can get a better look? I would take the manifold off my own car to check mussels, but my spider is my daily driver and my only car, so i didn't wanna go ripping it apart before I'm ready to install my new headers