TR6 rolling road results

[DRD]

3 hours ago, john.r.davies said:

An air box has two functions; 1/ to collect and direct cool air from outside the under-bonnet area to the intakes, and 2/ to provide a large volume, relative to the intake duct, to allow the air to slow down.   By Bernouille, this raises the dynamic pressure and promotes flow into the bores.

I can't see how Webers can avoid the need for both of those.

John

The change in pressure due to that is negligible at the speed a car goes!

[Motorsport Mickey]

1 hour ago, DRD said:

The change in pressure due to that is negligible at the speed a car goes!

Yeah…just don’t do it with a sealed airbox, it’s still enough to mess with the fuel flow erratically. As per Kastner ( and me, I don’t always trust effects until I try them myself).

Mick Richards

[john.r.davies]

2 hours ago, DRD said:

The change in pressure due to that is negligible at the speed a car goes!

It not the car's speed, it's the velocity of the air in the ducts.

At (say) 4000 rpm, the engine will entrain 5000 litres/min of air ( (2.5/2) x 4000)  OR 300,000 Liters/hour

300,000 Liters = 300,000,000 cubic cms (per hour)

The intake area of a Pi Plenum is 50cms^2  (Pi x 4^2), so this volume will pass at 6,000,000cms/hour = 60,000meter/hour = 60kph (40mph)

The numbers are attractively parallel, so at 6000k the air will pass at 60mph.   The dynamic pressure will be about 0.07psi

  In a plenum twice the size the velocity will be a half of that, so the pressure will be a quarter of that.     Small, but significant. 

But why aren't Webers sensitive to dynamic pressure?

John

[Tim D.]

It's interesting that Colin Chapman fitted a large plenum on the webbers on his elan. Perhaps he knew something. 

Tim

[Motorsport Mickey]

3 hours ago, Tim D. said:

It's interesting that Colin Chapman fitted a large plenum on the webbers on his elan. Perhaps he knew something. 

Tim

Yeah...he knew he had a bloody big space he could put a big airbox in...not the confined area we have on TRs.

Mick Richards

[BlueTR3A-5EKT]

On 9/30/2022 at 4:34 PM, john.r.davies said:

It not the car's speed, it's the velocity of the air in the ducts.

At (say) 4000 rpm, the engine will entrain 5000 litres/min of air ( (2.5/2) x 4000)  OR 300,000 Liters/hour

300,000 Liters = 300,000,000 cubic cms (per hour)

The intake area of a Pi Plenum is 50cms^2  (Pi x 4^2), so this volume will pass at 6,000,000cms/hour = 60,000meter/hour = 60kph (40mph)

The numbers are attractively parallel, so at 6000k the air will pass at 60mph.   The dynamic pressure will be about 0.07psi

  In a plenum twice the size the velocity will be a half of that, so the pressure will be a quarter of that.     Small, but significant. 

But why aren't Webers sensitive to dynamic pressure?

John

You probably just hit on why Triumph specified an air filter element with an internal wire frame, to stop it collapsing and being sucked up into the plenum.  There were two identically sized filters available that fitted the Triumph carb and the PI saloon cars.  The difference was the wire internal reinforcement of the PI filter compared to the unsupported plain paper element for Carb cars.