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Tubular Turbo Manifolds, tube diameters and effects

 
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Vic Dyno Hire



Joined: 30 Sep 2009
Posts: 82
Location: Melbourne(Ballarat), Victoria

PostPosted: Wed Mar 03, 2010 5:30 pm    Post subject: Tubular Turbo Manifolds, tube diameters and effects Reply with quote

Im curious to hear peoples experience with using tube smaller than the exhaust port to assist with botom end torque.

The dilema i have is the availability of tube sizes to match the port area.

Here is an overview:

Tube sizes-
One size i have has an area of 551mm2(26.5mm diam.)
The other has 961mm2 (35mm diam.)

The port at the flange face of the head measures 728mm2(26x28)
and the area inside the exhust valve seat is 551mm2(the same as the small tube i have).

The turbo is also a little large for for the application and im prepared to give up a little top end to improve the bottom end. Im using the stock NA cam.


Will going smaller than port size with the tubing assist with spooling/bottom end without too much detriment to the top end?

Thanks
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Vic Dyno Hire



Joined: 30 Sep 2009
Posts: 82
Location: Melbourne(Ballarat), Victoria

PostPosted: Sat Mar 06, 2010 3:10 pm    Post subject: Reply with quote

My theories are,

Higher gas speed, less time for gasses to cool before the turbine
and less surface area exposed to the air, less heat loss.
The obvious one would be stronger pulses to the turbine to help it along.

The question is, would the higher pumping losses at higher rpm outweigh the benefits? Would the turbine housing be the bigger restriction ultimately.

I understand that the only real way to know would be to build two manifolds and test them or build one and test pressures at the turbine inlet and an average of the runner inlets.

Does anyone have any experience or theories on this?
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Gadgeroonie



Joined: 24 Aug 2004
Posts: 1726
Location: UK

PostPosted: Sat Mar 06, 2010 3:35 pm    Post subject: Reply with quote

having ports larger than your exhaust manifold dia is going to create restrictions, not something we tuners like !

the best way to do this would be a split design where the system opens up under higher boost / power

however its a lot of work - some manufacturers do have variable length intakes but i'm not aware of a variable dia exhaust manifold

i'm pretty sure a manufacturer would just design a cylinder head with smaller ports for a punchy engine

it would probably be easier to build an engine that uses a variable exhaust housing and use that to help build boost
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Vic Dyno Hire



Joined: 30 Sep 2009
Posts: 82
Location: Melbourne(Ballarat), Victoria

PostPosted: Mon Mar 08, 2010 12:55 am    Post subject: Reply with quote

What about if i tapered the runners down to the smaller size over the first couple of inches, starting the same size or slightly larger than the port?
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Smokey Burnout



Joined: 28 Jul 2008
Posts: 61

PostPosted: Tue Mar 09, 2010 12:31 pm    Post subject: Reply with quote

The inlet to the tubes should match or be bigger than the exhaust port. If it is smaller and sudden, an effect know as vena contracta will begin robbing you of energy available to the turbo. If it is larger then it should be by only about 5-10% based on cross-sectional area, and the transition to asmaller size downstream should be tapered.

The taper, if you do want to reduce tube size should be a least 3 units of length (or more) for each unit in reduction of tube size, but probably no more than 5 units. Longer taper tend to cause packaging issues among other things. For example going from a 3" to 2" the transition length should be a minimum of 3" long. Doing it this way will minimize the pumping losses.

The taper if you are trying to increase gas velocity to the turbo should ideally occur at the turbo entrance to minimize losses and maximize gas velocity into the turbo. The port here should match or be only slightly smaller than the turbo entrance. I would say off the top of my head that the tube area (not diameter) should be not less that 90% of the turbo inlet port. That said, you could build an insert that reaches into the turbo inlet to direct the gas into the volute without the a sudden expansion.

Ultimately, how much gas volume and pressure that you produce at a given engine speed will dictate what the turbo is capable of doing.

The reduction in size will not necessarily reduce heat loss because the velocity will increase in the tube enhancing heat loss. Also, at a given instant, the mass of gas is smaller so it is easier to cool from that point of view as well. I have done heat transfer analysis on systems that we were trying to remove heat from and it is increasing difficult as the pipe size gets larger. The reverse is true when reducing the diameter, but each set of parameters is unique.

There are other factors however, so it is difficult to say. To keep the heat in use exhaust wrap or ceramic coating.
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Vic Dyno Hire



Joined: 30 Sep 2009
Posts: 82
Location: Melbourne(Ballarat), Victoria

PostPosted: Wed Mar 10, 2010 3:38 am    Post subject: Reply with quote

Thanks Smokey. Based on that, i got it a bit wrong regarding heat loss.

The larger tube/ bends i have are 25% larger in cross sectional area.
That would have ruled them out.

I ended up using the smaller tube that is about 23% smaller in cross sectional area than the port and made some tapers about 2" long to bring them up to port size. after just reading your post i see that idealy i would have a gradual taper just before the turbine inlet and not at the head face.

When i cut the tubes to form a collector (left with 1/3 of each tube) they match the turbine inlet in area. so probably not too bad.

I`ll wrap them, to keep the heat in.

This is only a practice/setup engine, im only wanting about 150Hp/ Ltr. The race engine will be more like 300HP/Ltr using the same turbo.
It`s a different head and manifold for that one.
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