close to 300 hp wanted

[geoffinbc]

Both are equally important. With higher horsepower you are usually getting more torque or moving torque up high.

Having the abiity ro rev the motor way out gomes in real handy. The longer you can hold a low gear the more you can take advantage of the torque multiplication the gear offers.

All in all it still comes down to AVERAGE horsepower.

[DarkKnight]

Ed from headersbyed firmly held that 40"+is better. He said he doesn't know why companies even make smaller for he'd rather have manifolds But he said go as long as possible, but fitting them sometimes is mor eimportant. I chose 30' becuz they'd fit, plus totally maximize high end. And he said with the 4 valve/cyl design and the high redline, 30" should be about right, but maybe a little short. Now the guys over at Mymonte.com, they chose an 8" primary, and they aren't equal lengh and they have a larger diameter than the headers on Winston Cup cars.

If you look at the info brad put up about making headers and you do the math you get the following for a 3.1L with exh valve size 1.42" (assumes an exh. valve open period of 206 degrees) If I missed something sorry, just correct me.

Length of primary pipe (in feet) P = (ASD^2)/1,400 d^2

A = exhaust valve opening period in degrees of crankshaft rotation
S = stroke length in inches
D = cylinder bore in inches
d = exhaust valve port diameter in inches


P=(206*3.3122*3.503^2)/1400*1.47^2

P=(206*3.3122*12.271009)/1400*2.1609

P=(8372.67141/(1400*2.1609)

P=(8372.67141/(3025.26)

P=2.768FT=33.211"

So going on those numbers we can assume for a streetable cam in a stock engine the primary tube length should be 33.2" I didn't have the info I needed to get the diameter, but I'm sure someone already knows. Now if we're talking about a dohc motor, would var. "d" need to be multiplied by 2 first then squared or what? How do you sompensate for the second exh. valve? In either case it seems that the length would definatly need to be shorter for a DOHC motor.

[v6h.o.]

Now if we're talking about a dohc motor, would var. "d" need to be multiplied by 2 first then squared or what? How do you sompensate for the second exh. valve? In either case it seems that the length would definatly need to be shorter for a DOHC motor.

you'd take the Total or combined area of both valves.

[DarkKnight]

Let's think about this. When are you "using horsepower" and when are you "using torque".

Torque is rotational force, and we feel that in our backsides. Horsepower is the rate you can apply this force, and it gives us our top speeds. How much of our enjoyment comes from a big fat kick in our backsides and how much of our enjoyment comes from seeing the fenceposts get blurry?

Umm.. Your understanding of HP and TQ are wrong. HP and TQ are *not* exactly seperate things. HP numbers are a calulation of Torque from the following formula.

HP = rpm x TQ
5252

Your only talking about lowend and highend power, HP is just a measurement of overall power. Now if you look at a TQ curve on a dyno sheet and you pick two of the same TQ points on the curve (one before the peak, one after) and compare the HP numbers, you'll see that HP is higher after the TQ peak. That's because the motor is making the exact same amount of TQ, but at a higher RPM, thus making more over all power. TQ is a mesurement of the twisting force the motor generates. HP is a measurement of the work an enigne does with that force.

[DarkKnight]

you'd take the Total or combined area of both valves.

I'm a little confused. Total area or diameter? The formula calls for diameter, not area. For instance the area would be

(3.14*(.735^2))*2

(1.696)*2=3.39 inches Sq.

Diamter would be

1.47*2=2.94 inches.

That's a big difference.

[SappySE107]

I wrote that headers page....but brad put it back up when we lost everything. Damn software:P hahaha!

I will update that page once I start making some headers (when my heart is in it).

[v6h.o.]

you'd take the Total or combined area of both valves.

I'm a little confused. Total area or diameter? The formula calls for diameter, not area. For instance the area would be

(3.14*(.735^2))*2

(1.696)*2=3.39 inches Sq.

Diamter would be

1.47*2=2.94 inches.

That's a big difference.

sorry wrong word used in the sentance.
it would be total diameter would it not?

[Guest]

Ok, here's my idea on the diameter vs area deal in that equasion, which is missing the actually diamter of the tube BTW, which is needed to find length, so I'm unsure how that equasion can be used with any confidance. (I'll get back to this).

now, if you add the 2 diameters of the exhaust valves (which are what? 1.1" in 3.4 DOHC?) Let's use 1.1" you get 2.2", easy, but this is not an accurate indication of area, which is also important. I.E.

a circle with a 2.2" D = 0.7853982x(2.2x2.2)=3.80"
BUT
2 valves with diameters of 1.1 = 0.7853982x(1.1x1.1)=.95" then there's 2 valves so .95x2=1.9"

Big difference.

(BTW 0.785392 = pi/4)

Every calculation I have seen for header primary tube length also includes diamter of teh primary tube, never have I seen the exhaust valve as part of the equation. So maybe the diameter in that equation is actually primary tube diameter not exhaust valve diameter?

[SappySE107]

Length is powerband, diameter is power (summed up). That equation is taken from a 30 year old book. Like I said, it needs to be updated but I lost interest in headers since I wasn't actually making a set at the time. The headers by ed papers explain diameter as a figure based on power. Length of the tube is a figure of the powerband.

It is a figure of the exhaust valve. I hadn't figured it out for DOHC either, as the whole book talked about 2 valves per cylinder.

[smilinguy99]

Let's think about this. When are you "using horsepower" and when are you "using torque".

Torque is rotational force, and we feel that in our backsides. Horsepower is the rate you can apply this force, and it gives us our top speeds. How much of our enjoyment comes from a big fat kick in our backsides and how much of our enjoyment comes from seeing the fenceposts get blurry?

Umm.. Your understanding of HP and TQ are wrong. HP and TQ are *not* exactly seperate things. HP numbers are a calulation of Torque from the following formula.

HP = rpm x TQ
5252

No, I'm sorry your formula is correct, but it appears you really don't understand it. Focus on the sentence "Horsepower is the rate you can apply this force..."

What is this force? Torque.

What is rpm? It is a rate at which a certain event occurs. That event is the single rotation of a shaft. Torque is rotational force independent of the rpm at which it is produced.

RPM provides the rate to the formula. Horsepower (in this case) is computed from measured values--torque and the speed at which it is produced.

No where did I say they were completely separate.

What we often refer to as "torque" is the area of the torque curve some distance above and below peak.

What we often refer to as "horsepower" is the area of the horsepower curve some distance above and below the peak.

sg99

[Anonymous]

Here is what I would do on a 3.1L that is near stock.

45" long primaries
1 1/2" diameter
Collect the 3 from each side into a 2" pipe, collect the 2s into a single 2 1/4".

Check out the thread about my headers in the DOHC Perforamnce section.