calculating plenum size on 2.3l turbo? 1

Hi My name is also Mark and I'm ALSO messing with a 2.3 Turbo Ford. How strange we should bump noggons here. To my knowledge the plenum size is not as important with forced induction. Taking the original plenum as a example, and considering most tuning effects hold true for both NA and pressurized intakes, I would say the existing plenum is fine, or something about that size. Check out for his custom intake, it incorporates a nice size plenum. Mark

There are many factors to consider, there is not really any perfectly "correct" size.

First each runner must have enough volume to draw from so each cylinder is not going to rob the next, so bigger is better in that regard.

Also the plenum entry must not flow at high velocity directly across the face of some particular runners. If it does it can starve those cylinders of air, and they will run rich, while others further from the plenum entry will have excess air and run lean. A symmetrical plenum is going to be better than an end fed plenum as far as air distribution goes, all other factors remaining equal.

If you only have a single throttle body at the plenum entry, a large plenum is not going to help with throttle response or lag. A smaller plenum might be better in that regard. However, if you are planning on individual throttle bodies in each runner, it is going to have crisper throttle response with even a humongous plenum.

In practice you will always be limited by the available space and layout.

When tuning the induction on an n/a engine there are three tuning variables. The first is runner cross sectional flow area. This will be the strongest tuning variable and will effect the torque peak. The second variable is runner length. This can introduce tuning peaks and hollows into the torque curve, but the effect is not as strong as diameter. Plenum volume is a third variable that may (sometimes) be used to create an additional low speed tuning hump in the torque curve. The runner VOLUME, that is length x area, can combine with the air volume in the plenum to create Helmholtz resonance at a particular (usually low) frequency. Its a bit like the tuned port in your loudspeaker box. The volume of air in the runner, combined with the springiness of the air in the plenum causes the air in the runner to bounce like a spring.

This is not the same as tuned runner length which relies on the speed of sound. If you blow into a beer bottle you can get a low frequency droning sound which has a wavelength far longer than the size of the bottle. Look up "Helmholtz" in google for some formulas.

See if this is interesting:

That's a good summary, I particularly like page 38.

I HATE it when they use electrical analogies for systems modelling - would the electrical professor have accepted my turning his tuned circuits into springs and dampers?



Cheers

Greg Locock

I have heard that a plenum including runners should be roughly the same volume as your engine capacity. 2.3L in your case. I am in the process of building one for a turbo small block ford so I will know how it works soon. Hope this helps.

Hi Buddy
I never designed an intake plenum for a turbo engine. For NA, we should get the volumetric efficiency of the engine. Once we have that, as a rule of thumb we multiply the number by the engine displacement. There you go, the plenum should be smaller than that number.
Bear in mind that the bigger the plenum is, the slower the response of the engine will be. For turbocharger, I would expect it to be much more important.

As a start you might take a look at a production induction system from a factory 2.3l Ford turbocharged motor.

(t-Bird super coupe etc).....these were pretty good pieces off the shelf and take to modifications. Its unclear whether you want to fab up a sheet metal inlet plenum system, or use off the shelf pieces.....the latter probably will be the best case.

You will be moving dry flow air so think that way.

What would I do? Use as many off the shelf pieces as I can. Size the turbo (s), injectors and the throttle body correctly....fuel management will be /must be an important part. To maximize the effort you need to set up a proper fuel curve..especially at boost pressures over 8 psi or so. this will necessitate an aftermarket ECU such as Motec or Electromotive. Many people have gone before you and have done the drill.....see if you can find articles/specifics on the needed parameters so as to save yourself hours/months of trial and error. Good luck.