ok, lets talk about headers

[trfourtune]

ok,
i hope to make some clarifications about headers (4-cylinder, 4/1) -basics only-no theory (not much anyways). first,larger diameter (primary pipe)=higher rpm power,smaller diameter (primary pipe)=lower rpm power. stop.
now, take a particular primary pipe diameter and increase or decrease its' length= rocks the torque curve for this diameter- longer= towards lower rpm, shorter=towards higher rpm.collectors 4-1. longer=wider power transition, flatter torque curve, shorter or none= shorter power transition, sharper,shorter torque curve.
headers WITH mufflers need big exhaust after headers. some newer designed headers go through a venturi after the collector then up in size for the remainder of the exhaust & through to the muffler. i will save the 4-2-1 header for another day. BUT A 4-1 HEADER CAN BE MADE TO PRODUCE HIGH OR LOW POWER DEPENDING ON ITS' DESIGN.
rob

 

[swift6]

Okay. Didn't see much of anything there to initially disagree with. Was there a point to yelling the last part?

 

[foxtrapper]

"longer= towards lower rpm, shorter=towards higher rpm"

That's probably one of the most common mistakes made regarding header pipe length.

It would be sorta true if the header ended out at the rear bumper. Then we would be dealing with a first octave acoustical wave.

But since headers are so short, we are dealing with fractions of wave lengths, and you're as likely to get close to one frequency as another with just about any pipe length.

It ends up with the pipe length being a minor factor (including keeping them equal length), and the collector design being the important factor.

"headers WITH mufflers need big exhaust after headers"

What's your basis for this? For depending on where the muffler is, it's inlet diameter, and its flow characteristics, a large pipe between it and the header can kill flow, not help it.

"some newer designed headers go through a venturi after the
collector then up in size for the remainder of the exhaust & through to the muffler."

It's a gimic. A venturi doesn't gain you anything in flow. Quite the opposite actually, as it's a restriction. Unless you want to suck in water or something, you don't want a venturi in your exhaust.

 

[ALLAN]

OK----All the above made everything completly clear, header science is now put to rest.

 

[Alan_Myers]

Hi all,

I agree there are a lot of factors that go into a well-tuned exhaust header/exhaust system.

However...

Isn't it fair to say that most people won't be designing, bending and welding up a set of carefully tuned headers for their street car? I'd expect most will simply shop among what's available and buy a ready-made set from one or the other of the major vendors. And, besides, just how precisely can we expect a street car's exhaust tuning to be, or is even worthwhile in terms of expense/effort in relation to real performance gains?

Sure, a few really talented individuals may want to go through a design exercise, make up their own header and experiment with the various tuning characteristics. But, I'm guessing that the rest of us will be buying from among what's available off-the-shelf.

There's a limited selection of ready-made headers out there, both for the 4-cyl. and for the 6 cyl. TRs. But, there is some real possibility of buying a header that's less than suitable for street use. I've done it myself and seen an awful lot of 4 cyl. cars, in particular, using the "wrong" type header simply because these are what's been most common and are often cheapest.

Below are three pictures of header types for 4-cyl. TRs. (Photos are borrowed from www.cambridgepotorsport.com's online catalog, the only webisite I could find with good illustrations of the various header types). You'll find similar variations in header design for the 6-cyl. engine.

In general terms, when buying TR headers off-the-shelf we don't get much choice of primary tube diameter, so that leaves primary length to consider (plus construction, finish and materials: see below).

Short primary:

This type are similar to what was fitted to the 12-Hour Sebring TRs (a Kastner design) and might be expected to give the best street performance, i.e., reasonable flexibility for low- to mid-rpm work (and peak HP at approx. 5000 rpm). In fact, among the choices, this design is closest to the original cast manifolds in it's dimensions.

Long primary:

These headers are more for pure road race, appear to be based upon SAH/Kastner designs for for high rpm work with improved production class motors (peak HP at approx. 6000-6200 rpm). At one point this was about the only type available, and there are alot of them around, from several different manufacturers.

Really long primary (less common):

These really long primary headers are most intended for ultra high performance with more highly modified motors (peaking up and over 7000 rpm).

In this and previous posts I've expressed concern that the second type - the long primary - is what's very often sold to TR owners for installation on their street cars. It's the only design some vendors offer. Installing a set won't ruin a car, by any means, but I think a better off-the-shelf solution for most street cars is the first type: the shorter primary design. Those are becoming more widely available and should provide better manners in most street driving situations.

Another major consideration when shopping is header materials. The choices are essentially two: mild steel or stainless steel. Mild steel is cheaper, easier to work with and might be just fine for a long time in a car that's driven frequently (this helps keep the exhaust system clear and dry). Stainless is more expensive, but can last indefinitely, might be the best choice for infrequently driven cars. By the way, stainless are usually the preferred chioce when wrapping a header to help reduce heat under the hood, while mild steel might be the choice if ceramic coatings will be used. Both wrapping and ceramic coating can improve gas flow, too.

Whatever design, finish and materials are used, the actual construction of the header is also important. It should have solid welds of course, but also nice, smooth mandrel bends (no "crushing" on the inside of the bend), roughly equal length primary tubes and nice, thick mounting flanges. Nearly all headers require some fine tuning for best fit and seal, too. /ubbthreads/images/graemlins/hammer.gif

Finally, yes, what comes before and after the header are also important. A good header might be mandatory with certain other modifications (i.e., Weber sidedraft carbs), and is usually part of any overall engine improvement plan. A freer flowing exhaust will make most effective use of a header, but that's a whole 'nother topic!

/ubbthreads/images/graemlins/cheers.gif

 

[trfourtune]

alan,
the more important factor is diameter first, then the length so you have to be careful when you compare the apples and oranges. i am no expert, i'm still trying to sort it out. there are 2 theories at work at the same time, the sound wave and the physical pressure pulse of matter and i have yet to find anyone who has put the balance on paper for anyone to read. i have discussed this with a f1 guy and he will only say what works but not how he gets there (he's a acoustical sound engineer-i have his design and it does not look like anything else out there-i'm building two headers-his and another).oh and yes i have the book on scientific design of exhaust systems (old but valid).
rob

 

[foxtrapper]

Rob,
There's a lot of good information about exhaust flow designs, especially headers, hiding on the web. I say hiding because you want to do a Google search on "expansion chamber" and start reading. It's quite fascinating.

Vizard tucked a good bit of information away in his first generic hot-rod book. I think it was titled something like "how to build and tune high performance engines" or something like that.

Vizard also wrote an excellent article several years ago for Circle-Track magazine on setting up exhaust sytems.

 

[Jon80spit]

Hi Rob. I am also going to build headers. Using stainless in a 4-2-1 design looking like Alans #1. I cut the 3/8 stainless plate on a plasma cutter. I will use mandrell bent pipe cut and fit. Am very interested in how yours work out.

 

[Simon TR4a]

A couple of minor points about the photos Alan posted:

The first one shows a continuous flange cut from one sheet of metal, which is likely to fit nice and flat, also the pipes are more likely to line up accurately with the ports.

The second appears to have a nicely designed collector with the pipes blending gradually, not at a sharp angle.

The other point is that a 4-2-1 arrangement might also work well for a road car, but I guess that's off topic as the thread deals with 4-1 headers.

Thanks to all who posted; useful information.
Simon.

 

[Alan_Myers]

Hi Simon,

Actually, I don't think 4-2-1 is at all off-topic (for the 4 cyl. cars, of course), although all three examples shown above are 4-1 style.

Here's a 4-2-1 design that's very similar to #1 above:

(Copyright, Alan Myers)

Obviously these are wrapped, but I think will still give you a good idea of the configuration. These are Falcon stainless steel headers currently on my TR4.

Unseen in this photo is the collector that gathers the two header outlets together into a single large pipe, right below the starter. That in turn feeds a single 2" pipe, slightly larger than stock, and a single muffler near the rear (Falcon stainless steel "Sport" system).

Your point about the single, thick flange is a good one, but I'm not sure it will always hold true. I suspect either type will often still need some fine fitting work. Even if a good accurate jig is used and care is taken, the heat from welding usually causes some twist or warping. That's less likely with a nice heavy flange (1/2" thick on these Falcon headers, but as thin as 1/4" on another mild steel set I've got). Besides the obvious need for a nice, flat surface to mate up to the head, another concern is that the ports line up very well, and/or that there is enough material around them to do some careful port matching by hand.

In some repspects, a two-piece design like these Falcons might be easier to tweak and adjust slightly for a good fit. The outer pair are completely separate from the inner pair, and can be adjusted independently from one another.

I have to add that these Falcons impressed me in terms of workmanship. The bends are obviously made with mandrels, so there is no "choking" on the inside radius (the same can't be said for the rest of the exahust system, also Falcon, but not mandrel bent). And, the bends are about as minimal possible to work with all the various intake manifold possiblities. (Actually could have been a bit straighter or larger radiused, and further from the port, on my car. But that's with a Weber/Warneford manifold that allows more room than some other Weber or the stock intake manifolds.) The primary lengths are close to equal and diameters seem reasonable. Some day I'll get the car running and tell you how well it all works, which is really the final proof in the end.

Interestingly, Falcon's stainless steel headers for the 6-cyl. TRs are instead a long primary design, a choice of 6-3-2 or 6-3-2-1 (said to be based on the Group 44 TR6 header) and similar to the second type shown above. These are a two-piece header design, with a choice of outlets that feeding into either a dual or single pipe exhaust system. www.the-roadster-factory.com offers them and has both types illustrated on their website (the two-piece headers themselves appear to be the same in both dual or single exhaust configurations, it's the separate collectors that differ).

I don't know of a source for a shorter primary design for the 6-cyl. cars. Perhaps someone else does.

/ubbthreads/images/graemlins/cheers.gif

p.s. Oh, and I gotta tip my hat to Rob and Jon, who are planning to build their own headers. You are more ambitious than me! But, that's the ultimate solution, in the end, if you want to really control all the tuning factors such as primary diameter, equal primary length, etc., etc. Best of luck to you guys! Be sure to let us know how it works out on your cars.