M50B25 exhausts

[Jacko 2084]

Anyone got, or found, any real world numbers on M50 exhausts. What works, what doesnt, recommended diameters and header lengths?

Im thinking two equal length 1" branches of 3 into 2 then a single 2 1/2" pipe to a single muffler, and likely a resonator in the middle to quieten it down.

Thoughts?

Edited September 6, 2010 by Jacko

[Jacko 2084]

Found some equations, did some maths, and some assumptions

Tuned for 5500 rpm peak, pipe sizes rounded up

6-2-1 (better mid range)

Primary 16" of 1.5" ID

Secondary 14.2" of 2 ID"

6-1 (better high rpm)

Primary 30.2" of 1.5" ID

2.25 to 2.5" single exhaust (depends which theory you use..)

Edited September 7, 2010 by Jacko

[pureboiracer 0]

where did you find these theorys and formulas?

[Jacko 2084]

where did you find these theorys and formulas?

Random volvo forum for the equations, theres references to them everywhere but this makes the most sense

-

Ok, on with the calc's

By the looks of it most people have different NA power goals to one another. So with that in mind I'll start things off by posting up the equations used so anyone can play around with them, plugging in some numbers and what not.

We'll concentrate on the pipe length and ID's to start with and get into collectors and exhaust pipe diameters another time.

a few notes to start off:

* all formulae used are pre-derived by A.Graham Bell

* length of the secondary pipe are measured from the start of the first collector.

* all results are in inches ( ")

* TB's needs an equation editor because writing them like this looks rubbish.

Primary pipe length

P=((850*ED)/rpm)-3

- ED refers to the sum of 180 degrees plus the number of degrees the exhaust valve opens before BDC.

- rpm as mentioned in a previous post. But more specifically is the engine rpm to which the header is being tuned.

Internal diameter - primary pipe

IDP=sqt(cc/((P+3)*25))*2.1

- sqt Taking the square root of bracketed equation.

- cc The cylinder volume.

- P Primary pipe length calculated earlier.

That's all the calculations needed for a 4-1 header but for a 4-2-1 we'll need:

Internal diameter - secondary pipe

IDS=sqt(IDP^2*2)*0.93

- sqt as before

- IDP ID of primary pipe

So now we have the primary pipe length, its ID and if we're building a 4-2-1 header, an ID for the secondary pipes as well.

Secondary pipe length

Now this is where the literature gets a little vague in regards to using a formula to calculate the length of the primary pipes. So I'll just quote a section from the text:

"The length of the primary pipe (P1) should always be at least 15". Adding length to the primary will favour top-end power, while adding it to the secondaries helps the mid-range. The length of the secondary pipes (P2) can be found by simple subtraction: P2=P-P1."

Example

Theoretical motor spec's:

cylinder volume = 575cc

tuned rpm = 6000-7000rpm (I'll show the difference in results between these two points)

Exhaust valve opening degrees before BDC = 60 degrees (just an example as I do not have any hot NA volvo cam data on hand. Plus as you may see once put into the first equation, 180+60 = 240 so thats gota be a good starting point) (240! it's a sign )

From this data we get:

Primary pipe length (4-1 style header) = 31" (26.143")

Primary pipe length (4-2-1 style header) = 15" (just using the texts suggested minimum for this example)

Primary pipe internal diameter = 1.727" (1.866")

Secondary pipe length = 16" (11.143")

Secondary pipe internal diameter = 2.27" (2.45")

*note: results in orange are for the 7000rpm tuned area.

As you can see calc's give out some rather large diameters for the secondary pipes but remember the tuned rpm is high, a lot higher than the standard NA manifold (header).

Also the length of the secondary pipes also appear to be shorter (visually, not numerically confirmed) than those commonly seen on NA redblock rally and rallycross headers (maybe they're onto something ).

Another point to note is that by increasing the number of degrees the exhaust valve opens before BDC reduces the ID and increases the length of the pipe required.

Finally, these results aren't exact. They're not even exact from a theoretical point of view. They do however give a rather good approximation of pipe lengths and diameters. So for their simplicity these few equations are very handy tools to have.

Theres about 5 different exhaust diameter calcs from googling.

Rethinking mine I should probably re do it for a peak of 5900 RPM to work with stock max power.

[Jacko 2084]

Found this too, but havent played with it yet -

http://dairally.net/daihard/chas/MiscCalcu...rs/DaiPipes.htm

[Jacko 2084]

Found this too, but havent played with it yet -

http://dairally.net/daihard/chas/MiscCalcu...rs/DaiPipes.htm

^Seems to have a bug with 6 cylinder engines.

[thorburn 120]

Are you building the headers yourself?

If you are I found this to be quite a good read. http://www.burnsstainless.com/techarticles.aspx

[Jacko 2084]

Are you building the headers yourself?

If you are I found this to be quite a good read. http://www.burnsstainless.com/techarticles.aspx

Nope, a mate is (I cant weld for shed) im just working it all out so he can build em

Nice find! Got some reading to do.

[Jacko 2084]

Think I might have cocked the above formula up, equation is for a 4 cylinder engine so the equation for the secondary diameter is only taking the diameter of two primaries, whereas Ive got 2 lots of 3.

Not 100% but I think it should be something like this -

Internal diameter - secondary pipe

IDS=sqt(IDP^2*3)*0.93

- sqt as before

- IDP ID of primary pipe

So now we have the primary pipe length, its ID and if we're building a 4-2-1 header, an ID for the secondary pipes as well.

Which works out, 6x2x1 tuned for M50B25 at 6k rpm with stock cam -

1.55" ID 15" Primaries

2.5" ID 12.5" Secondaries