tech question

[J4MES]

cold air induction (CAI) is a common mod for MX-5s/Roadsters, supposedly freeing up a few BHP...


the question relates to the air flow meter/efficiency subsequent to this mod - how does the AFM affect the engine management - surely more (& colder) air means a requirement for more fuel from the injectors? also, if i include ram air into the equation (i'm routing cold air being scooped from a large oil/fuel funnel (on it's side) into the air box)? also, will i have to free up the exhaust system to cope? hmm...

[Moby-Dick]

cold air compresses more so I'd imagine you can put more fuel in each engine cycle. ( same principle as a turbo )

thats about my limit for the moment

thought I'd guess reducing exhaust backpressue would help

[J4MES]

granted - will the air flow meter recognise this and tell the ecu to tell the injectors to inject more fuel???

[Moby-Dick]

pass all I know is that I have to change mine for big power!

[Lowe]

With normally aspirated engines reducing backpressure isn't always wise - you can actually reduce power if you mess around with it. Best left to exhaust designers.

[Event Horizon]

Cold air is denser, so has more oxygen molecules to use in combustion, so the ecu would compensate by supplying more injector time to each injector. As for ram air systems, the map sensor adjusts fuelling by reading the pressure in the plenum chamber.

If you used ram air on carbs, you would get into problems. The float bowel has to be linked to the induction system to enable the carb to adapt to the changing air pressures.

[Richie]

AFM - most modern AFM's are "hot wire" or "hot film" types.

The ECU will attempt to keep this wire or film at a set temperature whilst the incoming air tries to cool it down therefore the ECU determines the density and flow of air going to the engine by the current it needs to supply to the AFM to keep the wire/film at a set temp - the codler the air, the more current is needed to heat it up.

[J4MES]

cool, where's the plenum chamber????

[Zak33]

Cooler and mass rammed air will be sorted by your ECU matey It makes a big difference....what you are attemting to do is LOWER the INLET TEMPERATURE. Run your car for an hour...then stick your hand, CAUTIOUSLY, onto the inlet manifolds.....where the air finally goes into the cylinders....they get WARM cos they are bolted to the head, which is hot.

Dropping the temperature of that bit of metal is a very good plan. Even a few degrees gives more power and more torque.

If you see the long and tortuous route that the manufacturer makes the air flow before going into the engine itself, it makes you realise just how good a home made kit can be.

I have access to a laser temp probe.....its quite cheap...point it at summit, pull the trigger and the laser beam tells you how hot summit is. My mate Robster put a ram air kit of our own design onto his Nova GTE and the inlet temp dropped by many degrees....quite amazing. That car is now noticably sharper

so its not the actual ramming of the air that is creating more power by forcing air in.....when the piston drops and SUCKS air in it is far more powerfull that your driving fast and forcing it in.....no ...what happens is the air itself is cooler and less obstructed, its less restricted and literally fans the metal cool on its way in.Which means it gets into your engine faster AND colder

brrrum brrrm