Headers for a B3 (found some, your thoughts?)

[bhearts]

I want to make a ss dae knockoff header. I also really want to make allot of stuff. Lol. I personally think the runners needed to be a little smaller than 1.375. Considering factory aspire manifold o.d.was like 1.2" primaries

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[rmoltis]

I want to make a ss dae knockoff header. I also really want to make allot of stuff. Lol. I personally think the runners needed to be a little smaller than 1.375. Considering factory aspire manifold o.d.was like 1.2" primaries

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The point of a performance header is usually power gains.
To improve power you need a higher volume of air flowing through the engine.

This will require a tube that flows a higher capacity.

His goal wasn't to increase stock efficiency.
It was to create more power.

He put the torque peak between 4,000-4,200rpm.
But power starts to pick up around 2,000-2,500 rpm rather that right from idle.

If I recall I measured 1.25" i.d. primaries on my oem aspire manifold.


I did actually want a header designed around increasing oem efficiency.
For more torque and better mpgs.

But this one is also fun in its own performance oriented way.

[bhearts]

But by that logic the best exhaust would be no exhaust. It's not really about tube capacity more it's about tube velocity. That's how the merge collector works.

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[bhearts]

I have to admit though. 1.375 id mandrel pipe is the cheapest by far. And it's nearly impossible to find anything in that step between 1.375 and 1.125 id.

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[bhearts]

Ace race offers 1.375id pipe for 5 dollars per 90 degree bend. All the other sizes are double that price. That's the size of pipe the bigger displacement engines run, and in bigger I mean 2.0l plus. It's the common 4 cylinder header piping size because cheap. But you can hardly get one size pipe to cover the entire spectrum of displacement from 350cc per cylinder to 600cc per cylinder.

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[rmoltis]

But by that logic the best exhaust would be no exhaust. It's not really about tube capacity more it's about tube velocity. That's how the merge collector works

I think you interpreted it wrong.

I said more air into the engine Not less.
I also said it needed a tube that could flow a higher capacity.
Not a lack therof

Your torque peak is the point of maximum airflow into the engine.
I also stated either oem efficiency (which would be tuning the pipes to create a torque peak at 3000 rpms) and any header maker knows the torque peak is the point of highest velocity.


Or performance which the torque peak (highest velocity) is raised to a higher rpm.
Why? Because the more rpms= more strokes of the piston per second which processes a higher volume of air over less time which requires a larger tube. The larger tube will change the velocity peak to a higher rpm.

Which equals more airflow into the engine which equals more power

If you think logic dictates more air into the engine doesn't equal more power I'd like to see the results.

You need more air for more power.
No exhaust would create less air into the engine. Which equals less power.

The peak velocity of air into an engine can only go so fast I don't think people understand this.

You can't continuously increase velocity infinitely for more gains.

But you can increase the density of the charge

Which is also more air=more power.

I define quantity of air by the amount of molecules that make up the air and in what size space it is contained.


I could do what you did and say logically a smaller tube would flow a higher velocity and could make more power.

But the tube size would limit the volume of air allowed through once it hit peak velocity.

Now if you wanted more power at a lower rpm this reduced tube size would flow a reduced amount of air.
Which means it hits its torque peak sooner (highest velocity) Which would give peak efficiency at that point by raising the volumetric efficiency to its highest point at that specific rpm.

That total power number at a lower rpm with peak velocity. will be less
Than the total power made from that same engine with its torque peak (highest velocity) at a higher rpm.

This is because more air into the engine means more power.

When you design a header you pick the rpm you want it to peak at which is (highest velocity). Its the air flow choke point.

You would calculate the cfm of airflow required to fill those cylinders at that rpm. (Taking into account volumetric efficiency yada, yada, yada,)

So you would select a tube size which would accomodate exactly that much air and no more.

Because yet again torque peak is highest velocity of flow tied also with max airflow through the tube.

And the merge collector is the point where the high pressure wave hits a larger (low pressure) area. High pressure flows easier into a place where low pressure exists.

This in turn slows down the velocity but still keeps the air moving forward which creates a low pressure zone behind it as it continues forward.

This low pressure area behind the moving mass of air creates a flow path of less resistance to the next cylinders high pressure wave coming.

Because high pressure air seeks out the low pressure environment.
Energy travels more efficiently trough the path of least resistance
This is also how wind works.

The point of this post is to compare headers for the op to determine which is best.
Which means pointing out the differences in power delivery and how they would turn out relative to each other.

I didn't expect we would be diving headfirst into header theory.

[bhearts]

If you have no valve overlap, can you engine actually breathe in more air with a header compared to a factory exhaust? Can you gain by having an exhaust primary bigger than your exhaust port at the mating surface?

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[TominMO]

If you have no valve overlap, can you engine actually breathe in more air with a header compared to a factory exhaust? Can you gain by having an exhaust primary bigger than your exhaust port at the mating surface?

The Aspire exhaust manifolds are notoriously inefficient at pulling the air thru them. Dickmeyer did a test on one, and found that the airflow from the different ports actually interfered with itself, because of how badly the manifold was designed. Diameter of the ports and tubes is only one factor.

By moving downstream the location where the air from the different cylinders converges, efficiency is increased if the header is designed properly. For example, when the cyl 1 air passes thru the collector, it creates a negative pressure environment that then pulls the air toward the collector from cyl 4, as it comes out its own exhaust pipe. This is my non-technical understanding of what's going on, fluid-dynamics-wise.

When the converging is too close to the cylinder head, it's like trying to run while only taking very shallow breaths.

In the 4-2-1 eBay header in post 1, notice that cylinders 1 and 4 are connected, and cylinders 2 and 3 are connected. Because the firing order is 1-3-4-2, I'm thinking that efficiency of flow would go up as RPM increases, because the air pulses from the individual cylinders would come closer together. With 1 and 4 connected, 1 fires and creates the negative atmosphere for 4 to be pulled downstream; but after 1 fires, next is 3, then 4, then 2; so there is a delay for 4, and the scavenging effect from 1 diminishes. Since an internal combustion engine can be considered a glorified air pump, this alone may explain why power increases with RPM, within design limitations.

With a 4-1 header, this issue of the delay is no longer critical since they all dump into the same collector at the same location. Every exhaust pipe contributes to scavenging of every other pipe. Exhaust 1 comes down and contributes to 3, which contributes to 4, etc.

Your comments and corrections Charlie.

[errjam]

I want to make a ss dae knockoff header. I also really want to make allot of stuff. Lol. I personally think the runners needed to be a little smaller than 1.375. Considering factory aspire manifold o.d.was like 1.2" primaries

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interested...

[errjam]

interested...

His goal wasn't to increase stock efficiency.
It was to create more power.
in one the increases stock efficiency ...

[rmoltis]

If you have no valve overlap, can you engine actually breathe in more air with a header compared to a factory exhaust? Can you gain by having an exhaust primary bigger than your exhaust port at the mating surface?

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You're thinking too narrow.
You can change valve overlap
Modyfying a car isn't about changing only 1 variable.
If you are really into it multiple things need to be changed/updated/altered to maximize your gains.

Also the header is ideal to be slightly larger than the exhaust port.
High pressure seeks low pressure for easier flow.
Since the cross sectional area is higher. Air expansion will occur helping draw air from the engine. It keeps the air more easily moving in one that direction .

To test scavenging i took the aspire manifold.
Covered 3 of the oem "primaries" where they met the head.
Then used a hair dryer blowing through the open one.

I found out like Tom said that the firing of the pulses interfere with
The exiting of other cylinders gasses.
It would blow back and blow the paper off the manifold.
This was disturbing to me.

Then I did the same test on the DAE header.
But this time no matter which primary I blew air through.
The paper was "vacuumed" onto the flange.
This was my first experience understanding the benefit of scavenging.

The secondary advantage/gain of a performance header.
Is since the air exits easier. The piston on the exhaust stroke sees less pressure/resistance trying to press the air through the exhaust.

You will feel like your engine isn't working as hard.
This frees up ponies used up in the oem action.

[bhearts]

https://www.youtube.com/watch?v=c7PfOXP2Vf0

according to this guys formula. even a 1.25 id pipe would create a torque peak at 5400 rpm. which is so terribly high for a stock b3. youd have to be revving to 7k to take advantage of that. that next size pipe that i find common is that 1.1 inch id pipe. but according to this guys formula, it would put the torque peak at 4200 rpm. which i think would be perfect for street driving and fuel economy b3. maybe not ideal for a ported head b3.