Ram air effects

[Porridgewog]

So most of us have dyno'd our bikes and are very pleased with the numbers but if you were to actually go that ridiculously fast on a road what effects is the ram air likely to have?

Over to you boffins!

[mikef4uk]

Originally Posted by Porridgewog

So most of us have dyno'd our bikes and are very pleased with the numbers but if you were to actually go that ridiculously fast on a road what effects is the ram air likely to have?

Over to you boffins!

Likely to make you need a change of underwear

[Porridgewog]

Originally Posted by mikef4uk

Likely to make you need a change of underwear

That's so True

[YELLOPER1L]

Allegedly, at 155mph the ram air generates 7bhp.
I thought dynos simulated the ram air effect but I've never had a bike dyno'd so can't confirm that.

[Depths_of_Mind]

Every Dyno I've been to has a HUGE fan that blows both onto the radiator/oil cooler (to assist in cooling the bike) AND also the ram air intake.

[wedge]

Fans are good for cooling but unless its a weed Blower right to the front I'm not sure its going to "charge" the ram air

[Depths_of_Mind]

Originally Posted by wedge

Fans are good for cooling but unless its a weed Blower right to the front I'm not sure its going to "charge" the ram air

I'm not talking about a "box fan".. Eyeroll all ya want, the type of fan I'm talking about looks like it came from house furnace or aircon unit. So was pushing out ALOT of air at quite a high rate of speed.

[H-2 CHARLIE]

The fan your thinking about are called Air movers /looks like a snail fan , unless its 2-3 feet in front of the intake it wont help down on the ground .

[Depths_of_Mind]

Originally Posted by H-2 CHARLIE

The fan your thinking about are called Air movers /looks like a snail fan , unless its 2-3 feet in front of the intake it wont help down on the ground .

Yea.. them are what I was thinking.. .had one like 1' infront of the air intake and one pointed at the Rad/Oil cooler about 2' away (just a little infront of the front hugger) ... This has been at 2 different dyno locations in 2 different states.

[markjenn]

Originally Posted by YELLOPER1L

Allegedly, at 155mph the ram air generates 7bhp.

This sounds a little high to me. There is a relatively simple equation that relates speed to ram air pressure:

ram air pressure = 1/2 x air density x airspeed squared

For english units,

ram air pressure in psi = mph squared x .0000176

Plug in 155 mph and you get .42 psi.

Atmospheric pressure is about 14.7 psi so if you're doing 155 mph your engine should be seeing about 15.1 psi, or about equivalent to a turbo with a 3% boost. If the engine doesn't experience any extra loses due to the boost then power should increase about 3%. On a 180-hp engine, that would be about 5 extra hp, pretty close to the number above.

Because of the velocity-squared term, things do heat up when you're going seriously fast. At 200 mph, you could theoretically expect a 9-hp boost, and if you could go 250 mph, it works out to 13 hp. By the same token, the effect is negligible at sane speeds - at 75 mph, its 1 hp.

This all assumes the ram air system works absolutely perfectly, recovers absolutely 100% of the air's velocity as increased pressure, and there are no losses in the intake or engine due to the boost. In reality, I don't think any of this is true, so you'd expect to get less boost, perhaps much less boost. And the S1000RR's ram air system doesn't really seem to me to be very well designed to capture the ram air effect - I think its main purpose is simply to feed cool air to the intake. In reality, the boost you get is probably a few hp at the bike's top end and not much else.

It would be very interesting to instrument the pressure at the S1000RR's throttle bodies and ride the bike at various speeds with different intakes. Without such data, its pretty much speculation. But the above numbers determine the theoretical limits of what is possible. And it ain't that much.

- Mark