Re-Profiled Cams

[shaunw]

Very interesting, thanks Peter

Shaun

[DavidOliver]

I am looking for a candidate to try putting a variable speed electrical (12 volts) air fan on a non-turbo engine, better Low Compression.
This has the function of removing the problems of hot air turbos, chargecoolers,, and to use modern electronic speed control with pressure sensors,
rev sensors, and the recently developed air turbines as used in model aircraft.
It also avoids the elephant aspects of mechanical blowers.
The cams would of course be L14 and low rev torque problems would be solved.

Here in Spain there is no readily available sources of equipment or electronic control whizkids in love with cars.

Any comments?

Dave the cog

[TrevorK]

I would expect a fan that shifted a decent amount of air to draw significant power and, with 12V, need a big current. I think commercial applications use 48V. If you are pressurising the air, it will heat it up. Wouldn't it be better to take the engine to 2.5l?

[DavidOliver]

The fans I refer to are used in model aircraft which do not carry heavy batteries and fly for several minutes.
The 912 engine at 6000 rpm uses 6.6M3/minute of air, not a lot.
A Revotec radiator fan, at 12 volts and 8amps current delivers 38m3/minute of air.
We are looking for only 0.6bar extra pressure to be equivalent to a turbo. We are not creating high pressure and will not be heating up the air from compression. The turbo air heat comes from the exhaust temperature of the Turbo.

I am stuck for getting the fan electronic speed control to relate to engine power demand. I do believe the standard turbo is only power on or off by wastegate maximum pressure control.

The reason for considering an electric fan is no hot Turbo and airduct plumbing, and a blower is a very heavy piece of gear.

If my calculations are wrong I would be pleased to be corrected.

Dave the cog.

[rbgosling]

If you know of this (using a fan to improve performance) being done before, and making a measurable difference, then maybe it can work. But I am skeptical. In general terms, pumps (as in anything used to move fluid) tend to fall into two categories - those that primarily shift volume, and those that primarily increase pressure.

A fan is very firmly in the first category - it can shift a lot of volume, but only if there is no significant pressure increase downstream. If it is trying to fight (or even just to build) a pressure differential, the volume flow rate will drop very quickly.

To get more air into an engine you need to increase pressure, since you are trying to squeeze more air into the same volume. That's what a turbo- and supercharger are designed to do, and the shape of the rotor and the speed it spins at reflect that task.

What would work instead is an electric supercharger - which uses an electric motor as you mention, rather than being driven by the exhaust (turbocharger) or off the crankshaft (supercharger). But this will have the appropriate speed and rotor profile to achieve the pressure increase required to increase performance.

As Trevor mentioned, this would require a significant amount of electricity to achieve a useful benefit.

It's not an area I've looked into in any detail, but the briefest Google search suggests that most (if not all) electric supercharger kits on sale achieve next to nothing. Wikipedia agrees. If automotive aftermarket manufacturers cannot design and build an e-charger that works, it is even less likely that any home mechanic would be able to do so with off-the-shelf items.

[bash]

Theres stuff on utube that shows multiple leaf blowers being tried, they dont work because they move lots of air but dont generate much pressure.

Bash

[bash]

On the other hand, rotrex use a belt driven turbo/supercharger so the heat generated is very much reduced.
https://www.tts-performance.co.uk/copy- ... onversions

Bash

[Pete Boole]

You simply cannot compress gas without the temperature rising - basic thermodynamics. How hot can you get the end of a bicycle pump?!?

Pete

[bash]

Correct, I suppose the reduced heat comes from not using the exhaust.

Bash

[rbgosling]

Correct, I suppose the reduced heat comes from not using the exhaust.

Bash

That's one reason the Mercedes F1 engine has the exhaust turbine at the back of the engine, and the compressor at the front (with the MGU-H motor in-between). Eventually Honda and Renault decided to copy the design, Ferrari are still stubbornly ignoring this particular benefit.

[Pete Boole]

What's the MGU-H motor Richard?

Pete

[rbgosling]

What's the MGU-H motor Richard?

Pete

The MGU-H (Motor Generator Unit - Heat) is a cunning device to improve both efficiency and power. It's an electric motor/generator that's attached to the turbocharger. When you are not on full power (which to be fair isn't often, particularly at the upcoming race at Monza this weekend), it uses the pressure and heat of the exhaust gases to spin the turbine, and acts as a generator to collect electricity. When you want extra power, it acts as a motor, combining with the torque from the exhaust turbine to send even more power to the compressor to pump more air into the engine. Also useful to avoid turbo lag when coming onto the throttle, since it can provide additional boost in advance of there being a significant contribution from the exhaust gas turbine.

So, really, the unit on an F1 engine is a combined turbocharger and e-charger. And it's one of the main reasons an F1 engine converts more than 50% of the chemical energy in the fuel into motive power, while even the best road-based petrol engines get little more than 30%.

[Pete Boole]

I'll have two please!!

Pete

[TrevorK]

You may have to sell your house to buy them, Pete.

[Pete Boole]

You may have to sell your house to buy them, Pete.

Best not mention that to SWMBO then

Pete