10 replies to this topic

[sonscar]

I read of people flowing parts,radiusing things,bellmouths etc and testing on flow benches.Has anybody actually measured the airflow in a running motor actually in a car?Academic interest only,Steve..

[BEN99W]

It's definitely been done. It's a science in itself. The length of the inlet tract from valve to mouth and indeed around the mouth has an impact on airflow. As air is sucked in the airflow is interrupted as the valve closes and the airflow effectively bounces back out. This results in a pulsing effect which is sensitive to length and shape. Apparently 17 inches is optimal, but of course the inlet dimensions are also bound by hardware availability and packaging in the limited confines of the mini engine bay.

I experienced noticeable improvements changing trumpets and increasing inlet length to outside of the engine bay on a westfield, but was wondering about this in a post I made 8 minutes before yours regarding using the elbow that the airbox fits on.

I'm sure Vizard would have the definitive answers but it's an interesting topic.

Ben

[sonikk4]

I know back in the day Dave Walker of Emerald fame did quite a bit of work on this subject albeit on Ford’s when I was heavily into the Ford scene back then. ( late 80’s early 90’s)

I think on the open rd it will be a variable due to ram air flow depending on how things are set up. If you have a plenum for example, then the shape of this how it directs the airflow over bellmouths etc plays a major part. But again different speeds will have differing effects.

It’s very much like our air intakes into Air conditioning packs on large civil A/C. We have a controllable ramp at the very beginning of the intake, processor controlled which opens / closes at various angles depending on speed, pack requirements etc

Aircraft speed, height all play a part and utilises numerous sensors to enable this to function and provide the right amount of air into the pack assembly.

Same thing for a car, so many different variables which a fuel injected car, ecu controlled will fair much better than a normal carb installed car will.

Again it is an interesting subject if you are into aerodynamics etc and so many things that affect how engines react to the design of air intakes, plenums, length of bellmouths etc.

[sonscar]

I suppose what I am thinking is,does an engine ever get near to using all the air that has been lovingly made available to it?Steve..

[Shooter63]

Jesus you guys over complicate things all you need to work out how much air your engine is consuming is an AFR gauge and an accurate fuel flow meter, the AFR tells you the ratio, the fuel flow meter tells you the amount of fuel,then a bit of simple maths and bingo, that's now much air the engine is consuming. Or if you can't be arsed with that, bhp x 2.2ish = air consumed ( if you don't agree with that have a chat with a certain Mr Vizard and put him right)

Shooter

[Spider]

Jesus you guys over complicate things all you need to work out how much air your engine is consuming is an AFR gauge and an accurate fuel flow meter, the AFR tells you the ratio, the fuel flow meter tells you the amount of fuel,then a bit of simple maths and bingo, that's now much air the engine is consuming. Or if you can't be arsed with that, bhp x 2.2ish = air consumed ( if you don't agree with that have a chat with a certain Mr Vizard and put him right)

Shooter

 

I was going to post much the same.

CFM is directly proportional to BMEP in the cylinders, which if you put a fudge factor to for losses, it's pretty much proportional to Flywheel HP.

[mini13]

or rig up a generic hot wire airflow meter and a voltage meter on the the output

[PoolGuy]

In a Mini, getting enough air to the engine isn't difficult, what's important is getting enough cool air.

[sonscar]

My point was possibly badly made.Say you flowbench tested your head and induction and for arguments sake it flowed 200cfm at 30 inches vacuum,would your engine ever use this amount?I know how things work and know about AFR and fuelling calculations etc,ram effect and bmep.I was thinking about this as I was looking at data from my MGBV8.100% map at 70% throttle so I wondered if it was capable of flowing more air than it could ever use?Just curious,Steve..

[Turbo Phil]

The limiting factor in making power with the A-series is the restrictive cylinder head. That’s why the K head etc conversions work so well. Improving the engines ability to breath at higher RPM will support higher power outputs.

Phil.

[Spider]

My point was possibly badly made.Say you flowbench tested your head and induction and for arguments sake it flowed 200cfm at 30 inches vacuum,would your engine ever use this amount?I know how things work and know about AFR and fuelling calculations etc,ram effect and bmep.I was thinking about this as I was looking at data from my MGBV8.100% map at 70% throttle so I wondered if it was capable of flowing more air than it could ever use?Just curious,Steve..

 

'Reverse' calculate it based on the car's flywheel HP.