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Scott said:
The trumpets do need to be rolled back further to smooth the flow out into them, but the area behind them will have no bearing on turbulence.
I'm sorry but where did you come up with this conclusion? from computer software prediction?

When a moving gas meets a surface that is opposite or not along the direction of the initial flow you will get a change of direction of the gas. When a gas reaches the corners of each trumpet, you will see turbulence, the gas will not sit there, the flow willl change to a pattern similar to a swirl.

Every read out of wind tunnel measurements (NOT CFD software predictions) show gas will behave that way when it is forced to change direction against acute angles such as corners or surface gradients exceeding 11-15% of the original direction of flow
 

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Any photos of internal trumpeted plenums used in a real competitive racing application?
OK so it's not 99% (Not even near to be fair), but that's because of money and not design.

Ferrari F430:



E46 M3


Ferrari F1, photographed by DCD:


1971 Tyrell F1 (Usually housed in plenum)


To a much smaller extent - this is the insode of the Nismo GTR plenum:

The inlet for #6 is NOT bellmouthed in order to reduce the airflow into it - showing that they think that the bellmouthing increses flow.

There's loads more examples, in loads of different formulas and high performance cars.

I'd also agree with Scott's comments that the trumpets need to be rolled back more.
 

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.... I've often wondered what a tubular type inlet manifold would be like ? (Leaving the IC, the charge pipes splits into 6 and goes off to each cylinder with an equal tuned length of pipe.)
You would then end up with what the engine sees as very long, (albeit equal), tracks. Good for torque up until a point, but to get them all equal they would probably be too long for that even.


I just think that the end of each trumpet should be flush mounted to the airbox/chamber, and not just intruding in..
This would only reduce the volume in the plenum. Something you do not want to do. :(


I'm sorry but where did you come up with this conclusion? from computer software prediction?
I have been designing Air Induction Systems and intake manifolds for 12 years and work with CFD software every day to help our designs.


When a moving gas meets a surface that is opposite or not along the direction of the initial flow you will get a change of direction of the gas. When a gas reaches the corners of each trumpet, you will see turbulence, the gas will not sit there, the flow willl change to a pattern similar to a swirl.

Every read out of wind tunnel measurements (NOT CFD software predictions) show gas will behave that way when it is forced to change direction against acute angles such as corners or surface gradients exceeding 11-15% of the original direction of flow

I am very aware of this, but in this application it does not work that way. Look at the pictures kindly posted above and any F1 engine, and you will see what I mean.:)

The ideal trumpet will have a 180 degree entrance of 1/2 - 1/3 d, then a 12 degree, (inclusive), taper into the throttle. The trumpet length will depend on the torque curve you are after.


I have concidered the RB26 log plenum a few times over the years, and not seen any real area for impovement that the likes of Nismo have not addressed already. :)
 

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Discussion Starter #24
DESIGN MODS

I have changed the velocity stacks, the volume per plenium is: 1872cc's that's just a bit less that 1,5 times the displacement.





 

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That is looking better. :)

Now try tapering the tracks with side walls of 6 Deg if you can.
If you look under the bonnet, you should be able to grow them plenum top and bottom to gain the extra volume and allow a bigger Dia on the bellmouth radii. ;)

I would also increase the Dia of the entrance to each plenum if you can.
Mind you, you may have a problem with clearance between the back chamber and the shock tower. Get your tape measure out. ;)
 

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I would be very interested if someone can make this, not for a skyline but a twin setup like that would be very interesting to replace the 300zx plenum design as its crap and all the high power ones have a custom twin plenum design which looks very much like the one you have designed but instead of inline there seperate feeding each side




Mike
 

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The 300ZX plenum has tuned runners and it seems to me had quite a bit of work put into it, ok for massive power you might not care about low load/rpm gas speeds and runner lengths and want more out and out power but for a driveable road car it's pretty good.
 

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A big pro for twin plenum!!!!!

if you have a twin plenum, and a twin intercooler setup that completely seperate both turbo chargers, you will be able to run both turbo chargers at absolute maximum capacity.
A gtr already has 2 afm so its nearly there.:chuckle:
 

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Why will you have "absolute maximum capacity" with two plenums?:confused: :confused:

There will be nothing will control the balance between the two of them.
It will be very unlikely they will have identical efficiency.
 

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Discussion Starter #33
I could understand that a completely divided setup would have some advantages, and a sharper response could be one of them, and the possiblility that one turbo disturbs the airflow of the other turbo is eliminated.
But you should realy make the system as equal as the other.
 

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I'm a senior in mechanical engineering and luckily have every software program at my disposal plus several profs for questions. fabianGTR34 you mind loading up the file that you made for the plenium and what software you used and i'll give it a crack too. Also just cuz nissan spent maybe a mil on research and design could just mean that they figured out the best plenium design so that they don't have to service the engine on warranty not that its the optimal performance design.
 

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Discussion Starter #40
First CFD result

I have ran the first analysis on the plenum design. I let the computer flow a mass of 30kg/min trough one plenum, (roughly 600 HP) so a 1200hp total situation. This is nowhere near the conclusion yet, since I have to test it on volume flow, speed, etc.. and a lot of different load points. But at least it is a start. I think the pressure distribution is quite good so far, there are differences, but the scale is pretty small..

 
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