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Negative Boost

If you have written the 'eliminating the negative boost' series of articles, I would like to let you know that as you describe it you only measure the static pressure with the tubes connected at the side of the passages. As the inlet air speed is increased (when passing in smaller diameter passage or other airflow meter etc) the dynamic pressure having the direction of the moving air mass is actually increased. It is proportional to the square of the inlet speed and density. So as the static pressure measured from the side is lowered, the dynamic pressure pushing the air is increased, so up to a point (connected with the mach index of the incoming mass) these are actually helping the inlet pressure (and mixture). This is why multiple technologies exist to narrow/(close by flaps) or make longer intake passages at lower speeds. This is done to increase the air speed and the dynamic pressure which helps a lot in these conditions.

So as in the articles if you measure the dynamic pressure you would see it is higher at the locations described. To measure it the best way is to use the static/dynamic pressure differential via some tubes one of which is placed in direction of the moving air, as any moving gas has a direction of movement and at that direction there is a pressure acting coming from the movement. As a garden hose when squeezed squirts further away as the force in that direction is increased when the speed of the water is increased as a result of the narrower outcome area.

I hope this information would help you when some mods are suggested in the articles. For example if some of these engineered restrictions are removed, the effect would be that at lower rpm the inlet air speed would just drop, the dynamic pressure would decrease and the net effect be opposite as suggested in the article. And please see the decrease is not linear but quadratic (^2) with speed of the air.

Some systems like BMW DISA and many others use it with good results. Also it is even used in static manifolds, intake runner length-diameters. (Like BMW M52/M50 intake manifold design differences, etc).


Putting Pitot tubes in at each measuring point would be better than measuring just static wall pressure, but that’s a pretty well impossible approach. The quoted technique works very well in practice, whatever its theoretical shortcomings.

The Loremo

If you haven't come across it yet, the Loremo, a very economical car, may be worth an article:


See The Loremo!.


I'm a stooge and have been reading the beginning of your articles for a few years now (no subscription) and now I'm excited say that I'm no longer missing out and wish to thank you for sharing your full articles with us non subscribers. I believe if you continue to do this and also continue to keep the standard of your articles high you will not fall short but instead your following will grow and your advertising revenue will quickly surpass your subscription fees. Keep up the fantastic work!!! By the way, have you considered a composite construction HPV. You'd be saving weight and designing something more easily mass produced for consumers.


As you have noted, we are moving towards a non subscription model. Re an HPV made from composites: such a design is of course possible but it does not lend itself very well to prototypes.

Closed Loop Monitor

I decided to try out your "Closed Loop Monitor" Project. Bought the parts, soldered them to the board, checked for unexpected shorts and cold solder joints with an ohm-meter, and went on to try it on my car. It's been a whole day trying to figure out what I did wrong. Double, triple and quadruple checked the drawings, inside and out, top view and bottom view. It stays either completely lit or completely off, no matter idling or under load. Measured the output of my oxy sensor with a voltmeter – perfectly fluctuating between 0,2 and 0,6 V at idle, going up to 0,8V at load. Are you sure the pot has to be wired in this way? If the LM311 has to compare between the oxy output and a corresponding reference, I think   the pot has to be a voltage divider with a coefficient of 20 to create a reference voltage of 0,6V from the 12V supply. Can you please help me solve this dilemma?

Stanislav Randjev

The circuit is the simplest possible and so it is not protected against voltage spikes, etc. If you are continually having problems we suggest that you instead build the Smart Mixture Meter Smart Mixture Meter, Part 1 and if required mount just one of the orange display LEDs on the dashboard.

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