Unable to find answer to plenum question despite search...

[CosRush]

Before I post this question, i'd like to say that I have serached through the forums using many different keywords to try and get an answer to my question.

I apologise in advance if the answer is somewhere on here and that I have just missed it.

Information preceeding my question:-

My stock Ford Cosworth Turbo inlet plenum has an incredibly restictive elbow.

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Whilst this restriction still does not limit the power able to be produced (upto 500Bhp), and improvements to the restriction in its design can only possibly yield better flow i.e. less friction on the air thereby requiring less Turbo boost pressure for the same volume of air.
I hope that makes sense what im trying tosay.
The incoming air does enter the plenum from the underside just off central so does give a relatively equal flow to all inlet runners.

So.....have things moved on since this original design?

Yes they have. In Sweden where the engines have been extensively used for racing a new design plenum was divised (termed a 'swedish plenum').

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The inlet was at one end of the chamber at right angles to the inlets.
The volume was tapered to the rear (i believe in order to maintain the velocity of the air to the furthest inlet ports away from the Throttle, by virtue of the taper increasing the airflow velocity)

The plenum volume itself is also increased. Testing has shown that these flow very well on 500Bhp+ engine but show a slight throttle response drop on lesser engines. I put this down to the increase in volume over the standard.

Now my question........

I have here one of the Swedish Plenums, so if any more information is required in the form of measuremments thats not a problem.

However, this plenum is too big for my particular application. I am looking at having a new one made and would like ot know what factors determine the Taper rate from front to rear???
Taking this top view how would I work the taper required???

I realise that perhaps Maths aside, the best solution would be to make a prototype and test it, make adjustments and retest until a satisfactory result was achieved, but this would be very time consuming and also costly (hence why major manufactures spend a vast amount of money on the designs). Ive seen many 'Homemade' ones and some have shown really very good results far better than the stock item, but I will be straight and say that unless the maths are very simple to calulate the taper, no thought was given to any airflow differences between the inlet runners.
I base this on the very uncomplicated design of those ive seen.

Thanks in advance to anybody who can help

 

[CosRush]

quote]patprimmer
You can then easily experiment with volume by using spacers at the split line.[/quote]

This has been done for about 2 years now, but nobody has any decent testing information with regards to the overall effects, other than to say it improved throttle response........

While flow benches can be a useful tool, they are constant flow and therefore do not tell the full story, like variations in adjacent cylinders due to charge robbing due to firing order. They also do not give any help re plenum volume so long as the plenum CSA is enough to supply steady state flow to the furthest cylinder. Flow benches do not help predict the effect of pulses in the manifold and do not help in predicting the effect of volume on the magnitude of these pulses or oscillations.

I also agree with pat over this very important issue Pulse induction tuning.
In the standard plenum you can see how the pulse length is equal between the cylinders by virtue of the plenum face being at right angles to it, im sure Cosworth tested the pulse range and adjusted the plenum face to add the induction pulse at around the turbo on spool area for added torque.
However, utilising a tapered plenum the face is in a different region for each runner, so I can only assume the pulse tuning would be not only unequal, but you could find that the pulse of one runner matched the frequency at an unsuitable time and caused that partiular cylinder to go lean.......

My recommended method would be to make a plenum in 2 pieces so it can be split for internal access. Take your best shot with the volume on the small side.

I too have my own ideas of how I would design the plenum, but ultimately it still boils down to lots of fabrication of individual sections and joining them in a way the same as for the final piece, testing adjusting, more fabrication etc etc. Which if you have access to Time, Spare materials and tooling would not be too much of a problem. But now I myself am out of the Aerospace business, I do not have such facilities, therefore all of the above would have to be paid for by me :-(

As an example (I realise it need not be.....) but the Swedish style inlet plenum I had here until recently which was built deasinged and tested on HP cars (upto 700BHP) was made from stainless steel, hence it cost of £350.
Aluminium is obviously much cheaper in the form of materials, but still requires Tig welding (something which seems to be expensive in itself).
Add this to the addtional equipment needed for any testing as I stated previuosly (Egt probes,WB Lambda etc) an it does work out expensive IMO.
Certainly for me at this time :-(

 

[kitabel]

Slight improvement on slot shape, use 3/8" radius on all 4 surfaces.