The great header debate - simplified?

Mguar, thank you for the offer! However, considering the space constraints I'm dealing with I think it would honestly be more headache than its worth.
I had a feeling trying to make this a 'simplified' discussion would be an exercise in futility due to the large number of extremely knowledgeable members on here, but that's why I come here. :D
Scmidlap, yes I was a member of the boards and a good friend of mine had those exact headers but I don't remember any actual hard dyno numbers. I think for the sake of cost and packaging I'm going with the MSDS headers.

In reply to mguar05:

THAT is exactly what I was looking for. Should I be more concerned with maximizing high rpm hp for the track or more low end torque to compensate for drivetrain losses due to the AWD and automatic transmission setup?

In reply to chknhwk:

Now that you've stated it a second time, I'm curious as to why you view low-RPM torque as a specific answer to drivetrain losses?

The weight and parasitic losses will be with you in all applications... Answering where you want/need the power seems to me to be more a matter of appliation than of specific AWD/auto issues (apart, of course, from your increased ability to use more torque at lower speeds before wheelspin).

I'm not viewing it as an answer to drivetrain loss but more of a question of which has the better bang for the buck? Do I want to focus on low-end torque or high-end hp as a dailydrive/road race vehicle, taking into consideration my drivetrain? Or am I over-thinking matching header design to this specific vehicle? Like I said, I was looking for a more simplified discussion on the benefits of each.

your over thinking it. throw some modified msds or nautilous headers on her and be happy. you will see between 13 and 20 hp and 11 and 19 tq gain at the wheels. the power takeoff is your biggest hurtle with the awd but as i said not insurmountable.

You can cheat a little bit and use larger diameter to compensate for shorter tubes.

In reply to chknhwk:

Tell me how you use the car and where on the RPM scale you want an improvement..

Here's something to consider.. you will see the losest gain at lower RPM but added power over a wider band will gain you more than more power over a narrow band..

I'll try to put some fictional numbers to that so you can understand what I'm saying.. The assumption is as a daily driver with a extremely low back pressure muffler/exhaust system.. (stock exhaust systems have sufficent back pressure so potential gains from headers can be pretty well negated)

Let us assume for discussion purposes the headers gain either 4 horsepower from 2500rpm up or 12 hp at peak rpm.

Consider how long you will be at peak rpm as compared to how long you will spend from 2500 up to redline.. One of the things I've learned the expensive way is that power gained at peak RPM can actually make the car slower whereas power at a wide band yields serious improvement even when realtively small.

Keith wrote: You can cheat a little bit and use larger diameter to compensate for shorter tubes.

Kieth; It really doesn't work that way.. This is going to be confusing and likely I'll explain it completely wrong but I will try.

Let us assume that an exhaust pulse is 180 crankshaft degrees long (to vastly oversimplify things) The speed that pulse travels is a constant so it's length at a given RPM is say 28 inches long. Increase the tube size from an inch and a half to an inch and 3/4 and the pulse will still be 28 inches long. However with a larger pipe the exhaust will no longer have the same velocity.

It would be like trying to make a larger clarinet in order to compensate for a horn player with less lung capacity. (pretty miserable but maybe someone else can explain it better)

Check out rotary header lengths. They go through fads. It was 92-98" primaries, then it was 22-24" primaries, then it was 10-12" primaries, and it all goes around in cycles. None really "seems" any better than any other, but if you're running long tubes and you got beat by someone with 12" tubes, you're going to try them out, you know?

Mazda has all sorts of SAE papers on the subject. They tested header lengths from 4" and beyond. The effectiveness curves were bizarre, to say the least. Over an actual powerband, it doesn't really look like one is better than the other.

I have the 90+ inch length option, because I acquired a Racing Beat exhaust system. But it doesn't seem to make any more or less power anywhere in the range than my old 24" primary exhaust system, and I'm using an engine with "high overlap"...

In reply to Knurled:

I have absolutely zero experiance with rotaries (other than getting a few running for friends) I'm guessing the whole issue with rotaries is a matter of noise. Trading off a little power for an acceptable noise level.. Then again it could be that the various porting techniques determine effective length? (much like camshafts affect primary and collector lengths in valved engines)..

mguar05 wrote:

Keith wrote: You can cheat a little bit and use larger diameter to compensate for shorter tubes.

Kieth; It really doesn't work that way.. This is going to be confusing and likely I'll explain it completely wrong but I will try. Let us assume that an exhaust pulse is 180 crankshaft degrees long (to vastly oversimplify things) The speed that pulse travels is a constant so it's length at a given RPM is say 28 inches long. Increase the tube size from an inch and a half to an inch and 3/4 and the pulse will still be 28 inches long. However with a larger pipe the exhaust will no longer have the same velocity. It would be like trying to make a larger clarinet in order to compensate for a horn player with less lung capacity. (pretty miserable but maybe someone else can explain it better)

That's why I called it cheating, and said "a little bit". It's not ideal, but if you simply can't fit a 30" primary on the car then you have to go to other options.

My brain is saying "if you're slowing down the velocity, then you'll have a shorter wavelength and thus you'll hit the same resonant frequency with a shorter pipe", but I'm pretty sure that's assuming a constant that's no longer constant. I'm packing for a long tow to Laguna Seca, I'll mull over it as I drive.

mguar05 wrote: Why not build the correct headers.. send me the bore stroke #cylinders and camshaft timing events Duration, intake opens intake closes, exhaust opens exhaust closes and I'll run the formulas to get you correct size, primary length and collector length.. Once you know that you can either select something close or make something correct.

81.5mm bore 77mm stroke 4 cylinders 252 total / 226@ .050" IVO - 1BTDC IVC - 45ABDC EVO - 45BBDC EVC - 1 ATDC

The equation, for the curious, is as follows:
Header pipe length (inches) = ((850*(360-EVO))/RPM) – 3
Header diameter ( inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1

EVO is exhaust valve opening.

mguar wrote:

Osterkraut wrote: The equation, for the curious, is as follows: Header pipe length (inches) = ((850*(360-EVO))/RPM) – 3 Header diameter ( inches) = ((cylinder. disp. * 16.38 / ((hdr len + 3) * 25))) * 2.1 EVO is exhaust valve opening.

That formula is OK except it doesn't take into account the effects of the camshaft. A camshaft with 252 duration is going to need more length than a camshaft with 305 duration or the reverse 220 duration will need more length.. Diameter too is affected by horsepower per cylinder.. with very high horsepower engines needed bigger pipe diameters and lower horsepower engines needing smaller diameter tubes. I used to do this long hand but now I've gotten lazy and throw the numbers on the computer.. To be spot on I'd need other information such as compression ratio, valve sizes, port flow numbers etc.. But I can guess in this case given what has been written so far I suspect he's going to use that information to purchase a header rather than get spot on.. Street driven, does it really matter? It's mainly about bragging rights, not real performance. You'd be amazed at the numbers of headers I see hooked up to restrictive exhaust systems.

He did ask for simplified. How far into the weeds do you want to go for a header on a streetcar? Though if you've got all that info, smoke 'um if you've got 'um: http://www.wallaceracing.com/header_length.php

mguar wrote: OK based on those numbers (which differ from the OP's) and guessing a lot of important data. I come up with 34 inch primaries, of 1&5/8ths with a 10 inch collector..

engine builder recommended 1.5" primaries 28" long... I never did get a collector size.

Osterkraut wrote: http://www.wallaceracing.com/header_length.php

Hmmmmmm,

Your Primary Tube Length is 27.59 Your Primary Tube Diameter is 1.40 inches Your Collector Diameter is 2.43 inches One Collector .

.

. . I'm currently running a 4/2/1 type
Primaries - 38mm(1.5") x 406mm(16") Secondaries - 45mm(1.8") x 406mm(16") Collector - 66mm(2.6") x 350mm(14") - length is to 1st "cake" of cat

.

mguar wrote: . To be spot on I'd need other information such as compression ratio, valve sizes, port flow numbers etc..

10.75 to 1, intake valves 30.5mm x2, exh valves 25.5mm x2.

As far as port flow @ how many points do you want?

mguar wrote: read exhaustively

He's got jokes!

I'm not sure the equation for Tri-Ys, you got me there.

mguar wrote: OK those are tri-Y type I understand they're supposed to help at lower RPM than 4into 1 collector type but I don't have the formula handy.

Nope. A 4 into 1 beats a tri-Y at whatever frequency it's designed for. Be it high or low.

The tri-Y has more harmonic frequency possibilities, and as such tends to work across a broader range and be less peaky than a 4 into 1 header.

That's why the tri-Y is more flexible than the 4 into 1 header, giving a fatter but less high powerband range.