Manifold tuned lengths for turbo.
Discussion
How critical is this?
Looking to do a custom turbo install one day and i got thinking about this.
Now on a N/A engine a lot of care is taken to get the 'pulse length' right for power yet a lot of turbo cars dont seem to have equal length pipes, is this on purpose or just being lazy in the design? ones that imedeatly spring to mind are Subaru and the R5 GT turbo. I know you can get equal length pipes for an Impreza and you get a good gain out of it although you do lose that burble, but the turbo still performs well as standard. Now the Impreza is a bit of an extreme example due to its design but the little R5 is different, this is offset to over the gearbox due to lack of space resulting in the pipe length of No.1 being almost twice that of No.4 yet i do not remember it being as 'burbly' as that of the scoob.
So with me wanting to do something similair to a transverse mounted I4 with little room how much attention should be paid to the tuned lengths? for what little extra i could gain should i just go straight out and in to the turbo?
Mike
Looking to do a custom turbo install one day and i got thinking about this.
Now on a N/A engine a lot of care is taken to get the 'pulse length' right for power yet a lot of turbo cars dont seem to have equal length pipes, is this on purpose or just being lazy in the design? ones that imedeatly spring to mind are Subaru and the R5 GT turbo. I know you can get equal length pipes for an Impreza and you get a good gain out of it although you do lose that burble, but the turbo still performs well as standard. Now the Impreza is a bit of an extreme example due to its design but the little R5 is different, this is offset to over the gearbox due to lack of space resulting in the pipe length of No.1 being almost twice that of No.4 yet i do not remember it being as 'burbly' as that of the scoob.
So with me wanting to do something similair to a transverse mounted I4 with little room how much attention should be paid to the tuned lengths? for what little extra i could gain should i just go straight out and in to the turbo?
Mike
If seeking huge amounts of power, then it really can make a difference, but for about 85% of applications, a simple log design works, and is much cheaper and less complicated to make.
And nearly all of the Subaru manifolds are not equal length, they are just of tubular design.
There are a couple of equal length designs on the market that have appeared recently, but I dont know of any results from these.
The tubular design is free flowing, and will produce less EGBP which will give good returns esp for a higher revving engine.
But unless you are aiming for over 150bhp/litre then simple works in most cases.
And nearly all of the Subaru manifolds are not equal length, they are just of tubular design.
There are a couple of equal length designs on the market that have appeared recently, but I dont know of any results from these.
The tubular design is free flowing, and will produce less EGBP which will give good returns esp for a higher revving engine.
But unless you are aiming for over 150bhp/litre then simple works in most cases.
If you could time them to get for even pulses at the turbo, then it probably would be ideal, but thats unlikely to happen often.
Reducing restriction is always worth doing if possible, but space and cost limitations mean it doesnt always happen.
log manifolds work, as the runners are short, good heat energy is kept, exh gas velocities are high, so spool time is good too. Generally speaking despite looking very restrictive, they just work.
Going to larger bores, longer pipes albeit smpoother will usually mean more spool time, slight loss of low down power, but huge gains mid-top end.
Reducing restriction is always worth doing if possible, but space and cost limitations mean it doesnt always happen.
log manifolds work, as the runners are short, good heat energy is kept, exh gas velocities are high, so spool time is good too. Generally speaking despite looking very restrictive, they just work.
Going to larger bores, longer pipes albeit smpoother will usually mean more spool time, slight loss of low down power, but huge gains mid-top end.
Equal lengths are important but only to maximise the pulsing (maximum dP in the manifold) this would be an ultimate design. Obviously to give maximum pulse, the pipes should be as narrow as possible (for the required flow) this favours well flowing designs. Resonance does not apply as there is no reflection. Also the point about heat transfer applies, I imagine, probably not for a performance consideration but a cooling one. The massive surface area would radiate a massive amount of heat which is a snag under most bonnets anyway.
That's just off the top of my head.
That's just off the top of my head.
Oops, I was talking about inlet manifolds!
For the exhaust manifold I'd keep it compact and short so all the energy reaches the turbo and keeps the pressure up. You often see different runner lengths and the turbo can be mounted anywhere as the pressure is probably fairly constant. In an ideal world I would want the turbo somewhere central with all the runners being the same or a similar length, short.
A log manifold is where the exhaust runners enter into a tube at individual points. A bit like some plenums on 4 cylinder engines.
Boosted.
For the exhaust manifold I'd keep it compact and short so all the energy reaches the turbo and keeps the pressure up. You often see different runner lengths and the turbo can be mounted anywhere as the pressure is probably fairly constant. In an ideal world I would want the turbo somewhere central with all the runners being the same or a similar length, short.
A log manifold is where the exhaust runners enter into a tube at individual points. A bit like some plenums on 4 cylinder engines.
Boosted.
boosted ls1 said:
Oops, I was talking about inlet manifolds!
For the exhaust manifold I'd keep it compact and short so all the energy reaches the turbo and keeps the pressure up. You often see different runner lengths and the turbo can be mounted anywhere as the pressure is probably fairly constant. In an ideal world I would want the turbo somewhere central with all the runners being the same or a similar length, short.
A log manifold is where the exhaust runners enter into a tube at individual points. A bit like some plenums on 4 cylinder engines.
Boosted.
From my knowledge, log manifolds are used to create abrupt turns and keep the fuel in suspension (higher saturation/separation) I suppose there would be resonant effects in the inlet but these would be made more complex by the varied pressure. You'd have to look at the ends of the port to figure whether it had resonance designed in, or whether it was merely to equalise ramming properties (inertial filling). I would expect the latter to be true, particularly as a lot of modern stuff have the injectors virtually in the port.
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