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Twin turbo with one bigger than the other.


HadeS

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I have an idea of making a turbo setup but never seen it before.

 

Any informations will be welcome.

 

http://img24.imageshack.us/img24/7317/twinsetup.jpg

 

What your thoughts?

 

I don't think it'll work very well and here's why:

The exhaust gas coming out of the first three cylinders will reach turbo #1 (the little one) and start to spin it up. It will then be cooler by a couple of hundred degC and will be moving a lot slower, whereupon it reaches the collector of turbo #2's manifold. Here it meets the exhaust gas coming out of cylinders 4, 5, and 6, moving hotter and faster than it. The 4/5/6 exhaust gas will fight the 1/2/3 exhaust gas and start reversing/pressurising it, as it's either that or go through turbo #2, and physics loves the path of least resistance.

 

So, backpressure goes right up on turbo #1 and spool is significantly affected. EGTs could also go up because of this. Gas flow reversal would probably be poor and start contaminating the intake charges in 1/2/3.

 

Eventually the gas goes out of turbo #2 but the velocity is all over the place so it won't spin up #2 very well either. Due to the exhaust gas going all over the place and meeting different resistances and fighting itself, the VE of each individual cylinder will vary and the engine will run like a lumpy bag of spanners.

 

This doesn't cover firing order issues or the simple fact that 3 cylinders feeding one small turbo is just as laggy as 6 cylinders feeding a big one. You need all 6 cylinders feeding the little one to start with to get the instant response you are after.

 

Also, the design gives runaway boost to turbo #1 as it has no wastegate control, so if you do ever make it to high rpms it'll overspeed and go pop :)

 

And, any boosted air from #1 will just exit through the intake of #2, again, path of least resistance. I appreciate you may have simplified the diagram by leaving out such things like a reed valve or so forth, but as I think there is a wastegate on #2 I'm not sure.

 

A simple parallel twin like a Skyline or a 1JZ would knock this design into a cocked hat for spool, power production, and smoothness. I think I see what you're shooting for but I don't think this would achieve it.

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Here it meets the exhaust gas coming out of cylinders 4, 5, and 6, moving hotter and faster than it. The 4/5/6 exhaust gas will fight the 1/2/3 exhaust gas and start reversing/pressurising it, as it's either that or go through turbo #2, and physics loves the path of least resistance.

 

Didn't think of it, but can that happend on the twinscroll?

 

But I see what you are saing. Thanks for the feedback Ian.

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Didn't think of it, but can that happend on the twinscroll?

 

But I see what you are saing. Thanks for the feedback Ian.

 

No, it doesn't, as each pulse is at the same velocity and temperature, going the same direction, and they only meet inside the turbo :)

 

I'm not saying this is gospel, by the way, it's just what I think from looking at it and thinking it through :)

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