It's the XJR to Mark 2 transplant again. Are there any engineers out there who are up on their fluid dynamics? I'm using the complete XJR HVAC system in the Mark 2, including left and right blowers which will be housed in the sides of the footwells. I was looking for the best way to duct fresh air to the units (there's no room for a plenum in the scuttle area) when I ran across the recently completed Callum Mark 2. They use the side louvers to exhaust hot air from the engine compartment, and I'm wondering if I can use them to pull in fresh air. I know louvers accelerate the passing air creating a low pressure area, and my concern is that at high speed the blowers may not move enough air. The XJR fans are 6" diameter centrifugal units which I understand move a lot of air but develop little pressure. I'd hate to invest in a custom louver die set and do all that sheet metal work only to discover I have no fresh air when cruising down the highway. Most cars pull air from the base of the windshield which I assume is also a low pressure area, but then I really don't know what I'm talking about. Appreciate any thoughts out there.

 

I know it is many years ago now, but the Daimler V8 250 I used to own had a scuttle vent that could be opened or closed from inside for ventilation.
As they use the same body as the MK 2, I would think the Jag has as well.

 

Hi again

Two points.

The original vehicle had to get fresh air from somewhere. So would that be a suitable source?

There are articles at autospeed.com that show the high and low pressure points in the air envelope around the body of a vehicle. Those pictures may be helpful in finding a suitable spot.

That site also has many articles on intake pressure which show a technique for measuring dynamic air pressure at any point on the surface of a car using clear tubing, a teabag, a ruler and a big pop bottle. The alternative is a Magnehelic differential pressure gauge of the right scale. You can find those used on ebay.

 

Plums, the Mark 2 scuttle intake and plenum had to go to make room for the evaporator/heater/damper unit from the XJR. Thanks for the link - looking at some of the data it looks like plus or minus .2 to .4 inches of water are typical high/low pressure areas around a vehicle. If my math is correct this translates to about .005 to .01 psi, which I can't imagine impeding airflow to these blowers. I also doubt a few 7/16" tall louvers will have much if any impact on airflow around this brick. Hey, if nothing else they'll look good. Thanks again.

 

As little as that?

Anyways, heres the psi converter:

Inches Of Water to Pounds Per Square Inch | Kyle's Converter

A couple of random thoughts:

a pair of scuttle vents to the side instead of a central scuttle vent might be something to consider, the air will still benefit from pressurisation as it hits the windshield and wants a path out of there.

other vehicles of the period had opening scuttle vents just behind the wheelwell. i think? studebaker was one example and 50'is ford sedans.

the magnehelic gauge is usually employed in hvac situations, so the low differentials must have some bearing. one use was to measure whether a filter is clogged.