Best turbo manifold design

[Neutrino]

So in your guys opinion which is the best turbo manifold design?

I see on most stock turbo cars the turbo placed as close as posible to the exaust ports with the justification that the closer you are to the original point of the excaping gases the hotter they are and the faster they move so turbo lag is minimised....in this case the design of the tubes is unequal


But i see some aftermarket manifolds that will twist the tubes quite a bit in order to get them to be of equal lenght also I notice them to be of very different design - i guess because of the airflow they are suposed to have or engine bay clearances....

and other companies i see making the tubes quite long and placing the turbo father from the exaust ports


so what are the advantages and disadvantages of the different designs and which do you like the most?

[SaabJohan]

With short exhaust tubes the exhaust will be hotter which means a higher efficiency of the turbine, the higher temperature also means higher enthalpy in the exhaust which means that we can get more power out from the turbine or decrease the exhaust pressure before the turbine and still produce the same power. Since the volume in the tubes are small the turbochargers will also have good response.

For most standard turbo cars the camshafts are too mild to offer any real disadvantage by the non equal length tubes. For hotter camshafts the tubes can be made equal.

Long tubes are sometimes used, this is mainly used on racingengines when exhaust-temperature is a problem. Due to the hotter camshafts the powerloss from non equal tubes will be larger, but there will also be a powerloss from the reduced exhaust temperature. The engine will however work better when not under boost compared with one fitted with short tubes.

To keep the exhaust energy as high as possible the tubes should keep a straight, smooth and simple way to the turbocharger. The tubes should be made of thin material with poor conductivity like inconel or stainless. Mild steel or titanium should not be used.

Heat isolation is a good idea, carboncloth can for example be used.

Peugeot inline 4 racing engine with heat isolated exhaust/turbo, the tubes seems to be quite short:
http://www.mulsannescorner.com/WR-JK5.jpg

Cadillac Northstar V8 with carboncloth/metalfoil heat isolated exhaust/turbo:
http://www.mulsannescorner.com/CadGC-4.jpg

Honda F1 engine with short straight pipes:
http://hem.bredband.net/b132378/annat/honda.jpg

[Sluttypatton]

Well put. Also, log style manifolds are subject to more heat stress as the pulses group together and create hot spots in the manifold. This can reduce the life of the manifold, as they are subject to far more thermal expansion than 4 into 1 designs. A 4 into 1 design allows the pulses to stay seperate much longer, creating a low expansion manifold. Shorter manifolds do allow quicker turbine response as the exhaust reaches the turbo much quicker. SaabJohan, I tend to disagree slightly with you on mild steel, while it is not the ideal material, it does have a place in certain applications. Mild steel is cheap, extremely abundant, and easy to work with, although it may require some sort of plating to resist corrosion. I would say mild steel is a good material to practice building ones own manifold with, although stainless is probably the material of choice. Mild steel can be used effectively as long as one takes into account it's high conductivity when designing the manifold. Make sure to cut the flange, separating each runner, to allow for expansion, and drill the flange bolt holes slightly larger than needed. Heat loss will become an issue if you use long, or large diameter, runners (large diameter runners also decrease velocity of the exhaust). This is because the larger the surface area, the easier it will be for heat to escape (heat transfer is related to the surface area of the material...less area, less heat transfer). So in short, keep the runners short, and prepare for expansion if you use mild steel.

In my opinion, a short runner, stainless steel, 4 into 1 manifold is ideal. But that is only my opinion. Again, well said SaabJohan.

[SaabJohan]

Mild steel can not handle the exhaust temperature, it will anneal and give a deposit on the inside of the tubes. This deposit can then follow with the exhaust flow and destroy the turbine. This will soon be noticed if the engine is runned with high temperature for a longer time.

Carmanufacturers had problems with exhaust material (both manifold and turbine house) in the early years of turbocharging, mainly because of cracks. Today they use a cast iron with a high nickel content.

316L (ASTM) is a prefered material choice for tubes if inconel is too expensive.

The type of exhaust manifold we have discussed is called a impulse system, there is also a system working with constant pressure. With that system there is a chamber before the turbine where the pulses are smoothen out, that system does increase the turbine efficiency but have poor response.

[Neutrino]

thanks both of you guys for the info this is really informative..its nice to have a FI forum that its only visited by serious people and not have the bitching that goes on in the honda acura FI forum


but anyway....so the general agreement is that on regular engines the closer the turbo is to the exaust ports the more efficient will run and the faster it will spool even if the tubes are inequal lenght....
so this would be the best design for most turbo cars?:



so what is the deal with all those manifold designs that look very convoluted like this:

what are they trying to acomplish with a design like this? equal lenght? or something else? to me they just seem unecesserally complicated and restrictring airflow with all the bends


and about the materials used what about using ceramic manifolds...todays ceramics are very cheap very strong(heck they use them in tanks) and they can whistand insane temperatures

or another ideea that just came in my mind what about coating the inside if the manifold with carbon carbon

[FYRHWK1]

the nice thing about equal length headers (or manifolds, whichever) is that each pulse has the same distance to travel to the turbine. That keeps the turbine fed with a steady flow, although once you start filling the manifold up with gas it really doesn't matter.

IMO, a seperate tube for each cylinder should be used so that overall pressure of the exhaust system isn't fighting the piston or trying to push gas into it as the piston reaches TDC and back down. A twin scroll system can work well too, that way pulses don't run into each other and slow down, they're free to feed the turbine nozzle without being slowed. Equal length doesn't matter so much, just so long as it doesnt effect the pulses.

[Sluttypatton]

Another way to help prevent reversion is through the use of "reversion cones" (I think that is what they are called). Reversion cones are built into manifolds, just after the flange, into each runner. These cones slightly increase backpressure, but help reduce reversion.

Please elaborate on mild steel, I hadn't heard of that before, and a friend of mine is currently running a custom mild steel manifold. So far it has worked just fine. Also, a number of authorities on forced induction have recommended mild steel as a material for manifolds.

Neutrino, without knowing what car that manifold came from it is hard to tell what they were trying to accomplish. The doubled over design may have to do with placement. The number one consideration when designing a manifold is "will it fit", because if it doesn't, it wont matter how good the manifold is, you wont be able to use it.

[SaabJohan]

To use carbon-carbon is impossible since the manufacturing process require heating to over 2000 degrees C, which the metal won't handle. It should however be possible to coat the inside of the pipe with a thermal barrier coating (TBC) like the onces used in gasturbines. It have been used in F1 to coat the exhaustport in the cylinderhead.

My guess is that the strange looking exhaust manifold on the picture is just complicating things.

Also, on a I4 engine cylinder #1 and #4, #2 and #3 should be paired together.

Mild steel can't handle the exhaust temperature, but most people building their own systems in this material usually don't notice this. Mainly this is because they aren't using as high exhaust temperatures as one could, or doesn't load the engine under enought time so the heat can be built up. But it has happend that turbochargers have lost their turbineblades, mild steel in the exhaust manifold can be one of the reasons for that.

[ales]

Is it possible to ceramic-coat or teflon-coat the inside of a mild steel manifold? If so, will it help it to withstand the temperatures?

And could someone comment on this setup?

[Neutrino]

Originally Posted by SaabJohan

To use carbon-carbon is impossible since the manufacturing process require heating to over 2000 degrees C, which the metal won't handle. It should however be possible to coat the inside of the pipe with a thermal barrier coating (TBC) like the onces used in gasturbines. It have been used in F1 to coat the exhaustport in the cylinderhead.

My guess is that the strange looking exhaust manifold on the picture is just complicating things.

Also, on a I4 engine cylinder #1 and #4, #2 and #3 should be paired together.

isn't there any other process that would alow that....like a chemical bonding.....

ans what about certain aloys that can handle 2000 degrees C those paired up with a carbon-carbon coating would whistand insane temperatures....of course this might be redundant since if the gases ever reach that temperature the engine would be melted already

but what about the use of ceramic (not just coating, the entire manifold made of ceramics)

Originally Posted by Sluttypatton

Neutrino, without knowing what car that manifold came from it is hard to tell what they were trying to accomplish. The doubled over design may have to do with placement. The number one consideration when designing a manifold is "will it fit", because if it doesn't, it wont matter how good the manifold is, you wont be able to use it.

both those manifolds in my pics are aftermaket manifolds for hondas...i've gotten them of the web....the first pic is much closer to the standard stock manifold design for I4's and seems better since the turbo is very close to the exaust....the second manifold however is a very common (aftermarket) design i've seen for many cars and i don't think its main purpose its for clearance since it does not acomplish more in the turbo position that the firts design



and ales i know quite a few headers are ceramic coated so i don't see why you could not coat mild steel...how much it will help however i don't know

[SaabJohan]

Polytetrafluoroethylene (Teflon) can only handle temperature up to around 260 degrees C.

Ceramic coating can be used, but it is expensive. Also if the coating is done on mild steel the deposit could build up under the coating causing it fall off. When ceramic coating is used the bonding layer is very important, since it must protect the coated material and even out the differences in thermal elongation.
In any way, to spend money on an expensive coating and then use it on mild steel is just a waste of money, it's much better to spend it on inconel tubing.

Carbon/Carbon is made from carbon fibre and a special polymer matrix. Then the part is heated so only the carbon atoms will be left in the material.

Ceramics are brittle, have poor tensile strengths and are usually sensitive against thermoshock. In other words, to make an exhaust manifold in this material will be difficult.

[Neutrino]

Originally Posted by SaabJohan

Ceramics are brittle, have poor tensile strengths and are usually sensitive against thermoshock. In other words, to make an exhaust manifold in this material will be difficult.

latelly the ceramics are getting way better....heck even tanks use ceramics nowadays for armor....the brits have a ceramic tank that is suposed to be tougher even than the depleted uranium M1 Abraham


so something that is designed to take eplosive penetrating missiles is for sure not brittle or sensitive against termoshock.....


also if i'm not wrong there are some ceramic turbos out there right?

so i don't see why not use a material that can be way cheaper but even more resistant than iconel for manifolds

[SaabJohan]

Originally Posted by Neutrino

latelly the ceramics are getting way better....heck even tanks use ceramics nowadays for armor....the brits have a ceramic tank that is suposed to be tougher even than the depleted uranium M1 Abraham


so something that is designed to take eplosive penetrating missiles is for sure not brittle or sensitive against termoshock.....


also if i'm not wrong there are some ceramic turbos out there right?

so i don't see why not use a material that can be way cheaper but even more resistant than iconel for manifolds

The tank is using steel reinforced with ceramics (MMC) and tungsten rods (could be tungsten carbide, I'm not sure). Since steel is used it will help against the downsides of the ceramics, also, in a tank the most important properties are hardness and toughness and ceramics have the first.

Ceramics have become better but they are still more or less sensitive against thermoshocks. They are also brittle and have low tensile strengths and toughness. Ceramics have a diffrent atomic structure than metals and this will give them some drawbacks that we can't get rid off.
The low heat conductivity of some ceramics are also one of the reasons to the sensitivity against thermoshocks, but some caramics have a high heat conductivity like SiC and those are suitable as high temp. engineering materials.

Engineering ceramics are not cheap and to manufacture a manifold from ceramics will be very expensive and difficult since we'll have to sintering a very complex shape. The finished result may also weight more than a manifold of inconel.

There are some turbos that use ceramics in the turbine, probably SiC, but as it seems now these have not become a success, the same thing goes with ceramic turbine blades in gasturbines which still use ceramic coated nickel based superalloys. Even tho the superalloys starts to melt at 1300 degrees C, gastemperatures over 1600 degrees C are used.

[peeface]

Ceramics are used as tank armor BECAUSE they are brittle. The ceramic shatters, thus absorbing the energy from a bullet, missile, etc. If the tank was hit repeatedly in the same spot, it would become vulnerable. Likewise, if you made a ceramic egg for yourself, crawled in and rolled off a building, the egg would shatter, absorbing the impact and you would (hopefully) be OK. That said, when that mani got hot, it'd be real delicate. Stick to steel with a ceramic coating.

[Steel]

how good are the thermoshock proterties of zirconia? I've been seeing knives made out of them, but I don't know if they'd be a good material to make a manifold out of.