turbo header

[DomWoo]

whats a good size pipe to be used on a turbo header

i was thinking 2" and can get really good deal on it so.. what do you guys think

i would be going 2" - turbo - 2.5

[Stefan]

Well it seems to me most manifolds are around 1.5" - 1.75" diameter. I think 2" would be way too big. For street use go for the smaller size or slightly larger than the exhaust port in the cylinder head. Again, if for street use, keep the primary length short but with minimum bends. I worked out that for my engine a primary length of ~9" would keep it short and allow for equal length primaries with just one 90 degree bend for cylinders 2&3 and one 90 degree bend and one 45 degree bend for cylinders 1&4.
Flanges need to be 0.5" thick to help prevent warping. Tube thickness 1/8" thick for mild steel and possibly 1/16" for stainless, though I'd go a bit thicker.
Look here for a 'How To' on building a turbo header
http://www.sdsefi.com/techheader.htm

2.5"-3" would be fine for the rest of the system.

Stef

[PrecisionBoost]

The smaller the pipe the more restriction.... but the faster the exhaust velocity.

There are very complex calculations to do with RPM,Displacement,Engine Efficency, and heat transfer coefficents (among other things) which allow you to calculate the optimum size of tubing but most of these things are tested in a laboratory and then put into computer simulations to find the best looking power band.

Most people think bigger is allways better but it's an "urban legend"

Realisticly you have a trade off....

smaller pipes causes slightly more restriction which results in a small power loss due to the pistons having a harder time pushing it out of the cylinder.

but smaller pipes will also create a much faster flowing exhaust which not only spools up the turbo quicker, it makes it more efficent if the header is well designed. (equal length tubes are very important)

Think of a water hose.... put your finger on it and it you get a sharp fast moving stream of water that goes out 20 feet..... remove your finger and you get a big fat stream of water going out just a couple of feet.

With both your finger on and off you get the exact same amount of water coming out of the nozzle.... one has lots of volume but very little pressure while the other has tonnes of pressure but not as much volume.\

P1 X V1 = P2 X V2

Anyways... too small is bad and too large is bad.... I agree that 1.5" is probably the best bet.... and 2.5 should be good on the back end.

You could probably even go to 3" after the turbo and drop it back down to 2.5" with a smooth transition fitting a few feet after the turbo.

[DomWoo]

cool, im going to go buy some stainless 1.5" monday and see what i can bend up

then after i get it all bent the way i want it i will get some 1/2 flat stock and plasma cut it to the shape i want, weld everything up, fit it. hook up my turbo (oil lines and everything, and see how it spools for a few seconds, then start welding up the intercooler core and hooking that up,

the car is sitting untile i get the timeing belt changed, and i have all winter so im in no hurry

[bluesheepbrian]

This maybe a dumb question but what is a turbo header?
And what is it for?

[Corbis]

Basically a turbo header is just used to connect a turbocharger to the engine:
See Exhaust Manifold / Headers

[Audacity Racing]

in response to the smaller pipe = more volume idea... that's not at all true... i'm a mechanical engineering student in a dynamics class right now. the bigger pipe is less restrictive... therefore the air flows faster. the exhaust volume remains the same regardless of the pipe size, so the bigger the pipe the more gas flows through. anything with increases pressure along exhaust while altering volume creates drag within the pipe. a bigger pipe also allows the total surface area of the fins on the turbo to be utilized. it's far more effecient to have larger pipes. remember... higher pressure doesn't mean higher velocity flow... not at all.[/quote]

[damian007vk]

yeah but it is also known that hotter exhaust gases moves quicker out of the exhaust than does colder gases, and thus the bigger the pipes the more time and space the exhaust gases have to cool down and scavange......mention that 2 your teacher, see what he says.

[PrecisionBoost]

the bigger pipe is less restrictive... therefore the air flows faster.

I hope this doesn't offend you but I think your a little mixed up.... I went through Engineering as well and I have to say I don't agree with your statement.

You seem confused about what I said... and perhaps I didn't go about it the way it should have...... I really shouldn't have used pressure in this example... it's actually density that I'm refering to (although they are directly related)..... most people don't really understand density but pressure is something they know about..... so I used this in my half truthfull explaination.

These are the key points I was trying to make....

1) Smaller pipes will have a faster exhaust velocity
2) Larger pipes will have a slower exhaust velocity
3) Slower exhaust velocity allows the exhaust gas to cool down quicker which increases the density and decreases the velocity (which makes it cool down even further an loose more energy )

It's all about conservation of energy..... if the exhaust is going too slow it looses energy to the surrounding air outside of the header and therefore decreases the energy transfer to the turbine.



Ok.... most of you are going to want to skip this next part but I feel I must explain myself to another engineering type person who seems to be confused...

I hope you (Audacityracing) read this carefully because your going to fail your dynamics class if you don't understand the first law of Thermodyanamics (better know as the "conservation of mass principle")



What we should really be talking about is "mass flow rate" and "Volume flow rate"

The mass flow rate of a gas flowing in a pipe is proportional to the cross-sectional area of the pipe, the density and velocity of the gas.

The density of the exhaust flowing in the pipe is typically fairly constant accross the cross section of the pipe.

The velocity at the outside next to the pipe aproaches zero while the maximum velocity is in the center of the pipe..... but we can simply call it "average velocity"

(good link... http://hyperphysics.phy-astr.gsu.edu/hbase/pfric.html )

mass flow rate = density X average velocity X cross-sectional area

Volume flow rate is the volume of fluid flowing through a cross section per unit time. ( so make a straight line accross the pipe and imagine the amount of gas passing that line during a given time interval )

Volume flow rate = average velocity X Cross-sectional area

Given that the Volume flow rates (as dictated by the output of the engine) are the same in both pipes so the average exhaust velocity must decrease with a larger Cross-Sectional area.

Therefore a larger pipe will have a slower exhaust velocity

As well since they are directly proportional.... if you decrease the cross-sectional area by going with a smaller pipe the average velocity must increase

There are a billion and one other factors....that make this not exactly true...

For example.... the slower exhaust velocity allows the gas to loose more energy (cool down) which increases the density

If density increases and both the mass flow rate and the cross-sectional area are constant then the only change that can happen is that the average velocity must decrease

So again.....

cross-sectional area (pipe diameter) is directly proportional to exhaust velocity

decrease one and the other must increase

So although smaller pipes cause more restriction they will make the turbo spool up quicker and transfer more energy than the larger pipes.

The backpressure caused by the smaller diameter pipes is offset by the piston compression..... which is to say that the piston forces a set amount of exhaust mass no matter what kind of backpressure is on the system.

This force decreases mechanical energy from the engine but increases the energy of the exhaust. (conservation of energy)

So lets say the backpressure causes a loss of 1hp because the piston has a harder time forcing the exhaust mass down the smaller pipe.

This 1hp taken away from the piston must be transfered to the energy in the exhaust...which will actually increase the temperature of the exhaust (due to compression)..... which will transfer more power to the turbo.... which will transfer more power to the compressor..... which will force more air into the combustion chamber which will make more power than you lost in the first place due to backpressure.

So it's a closed loop cycle..... you will not make more power with a huge exhaust pipe.... it looses too much energy due to slow exhaust velocity.

Having said that...... if you use an insulating wrap on the exhaust the larger pipe won't loose as much energy so it could make as much or more power than the smaller pipe.

When it comes down to it...... it's all about heat loss...... you want to have a high exhaust velocity so that it gets to the turbo without cooling down but at the same time you don't want to create huge amounts of back pressure.

Hopefully you understand what I'm saying.... and I'm not trying to say your totally wrong..... a larger pipe has less resistance to the flow but it's not an open system.... the piston forces it down no matter how much backpressure there is..

( this is true up until a point where by which the backpressure force approaches the force the piston is putting out.... which will then stall the engine )

Ideally the only way to find the perfect header is to test out different diameters with different coatings and insulation.... calculating all the variables is work for a supercomputer.... there are just way too many variables.... even turbulance of the exhaust exiting the exhaust port will play a role on how much power is transfered to the turbo.

[Nubira2.2]

then can you figure out the better pipe lenght and diammeter for each engine volume?

For that you would need (as an example) the volume of the exhaust that is coming out from a 2.0L engine each second ? Something like that.

For that it would also have to be considered the density of the fuel when exploted in the engine, the outside temp, the engine temp, the atmosfier pressure ... etc

[PrecisionBoost]

Here is some more stuff to think about.

I would say that the cross sectional area of the four pipes coming from the exhaust port should be roughly equal to the total cross area of the merge pipe before the turbo.

Think about it this way.... if you have four one inch tubes feeding into a 2" tube you would have the following...

Primary tubes = 1"
Cross sectional area = 0.785 square inches X 4 tubes = 3.14 square inches total.

Merge tube = 2"
Cross sectional area = 3.14 square inches

So the 2" merge tube has the same cross sectional area as all four primary tubes..... so therefore there is no restriction.

Next example... four 1.5" tubes merging into a 3" tube

Primary tubes= 1.5"
Cross sectional area = 1.766 square inches X 4 tubes =7.065 square inches total

Merge tube = 3"
Cross sectional area = 7.065 square inches.

So again we have a perfect match.

So your general rule of thumb is that the merge tube should be twice the diameter of the other four primary tubes.

If your merge tube was only 2.5" and you had four 1.5" pipes leading into it you would have a problem... since the cross sectional area of the 2.5" tube is significantly smaller than the 1.5" primary tubes you will end up with a restriction.

The problem with this is that you will increase the likelyhood of something called reversion where the exhaust pulse from one of the tubes ends up going up another tube instead of into the turbo.

Reversion decreases the efficency of the turbo system and causes backpressure in the tube before the turbo.

Going from four 1.5" tubes into a 4" tube will have less backpressure than the 3" tube but you will be changing the velocity of the exhaust gas... which will result in a slower turbo spool speed and slightly less efficency.

[PrecisionBoost]

Ok... so now we know about the merge tube vs primary tubes.

Next thing is to calculate the cross sectional area of the turbo's input flange.

On a T3 the flange the cross sectional area is about 4.5 square inches

The smaller T25 flange is about 3.5 square inches.

Ideally you want to keep a steady consistant velocity so you should ideally match your primary pipe sizes to the flange cross section.

So if you using a T3 then the merge tube should have a cross sectional area of about 4.5 square inches and each of the primary tubes should have a cross sectional area of 1.125 square inches.

A merge tube of exactly 2.39" in diameter will have a cross sectional area of 4.5 square inches.

So each primary tube should have an inner diameter of 1.195"

So ideally you would like to run 1 1/4" tubing with an 0.065" wall thickness for the primary tubes and a 2.5" tube with a wall thickness of about 0.11"

For a T25 flange your matched merge tube would have a cross sectional area of 3.5" so the merge tube should have an inner diameter of about 2.11"

So 2 1/4" OD pipe with a wall thickness of roughly 0.14" would be ideal.

The ideal inner diameter of the primary tubes should be about 1 1/8" on the inner diameter.... so again 1 1/4" tubing would probably be the closest pipe ( with a 0.125" wall thickness )

[PrecisionBoost]

So here is the breakdown....

T3 flange --> 1 1/4" primary tubes leading into a 2 1/2" merge tube

T25 flange --> 1 1/4" primary tubes leading into a 2 1/4" merge tube

Going smaller than this will cause restrictions

Going larger than this will not help since the turbo inlet is will become a bottleneck and cause backpressure and reversion.