Works rally side vents...more than meets the eye

[AUSMHLY]

Hi guys,.

Was any other modifications done to the car to help the rally side vents perform?

Any truth that some modification was also done to the front wheel wells, by venting them too?

Was my source correct, or is this how rumors start.
There was this guy Roger, we found out he was the one who started ALL the Healey rumors :cooler:

Cheers,
The rumor starter.

 

[HealeyPassion]

Roger,
Well interesting that you would ask... I happened to visit JME's shop in Leamington Spa, UK when URX727 was being restored (the last time as it's been restored before). URX727, number 76 shown in your picture, was the car that Pat Moss won the September 1960 Liege-Rome-Liege overall (beat everyone not just the Ladies class). I've got a pic of the vin plate that shows the 8446 number which was URX727.

As you can see there were no mods to the inner fenders (fender wells) or structure to enhance the air flow to the rally vents. So I would say your "source" was incorrect.

Cheers,
Steve
https://stevesaustinhealey.com

 

[Cottontop]

I happened to visit JME's shop in Leamington Spa, UK when URX727 was being restored

I always thought that the "Real/Original" rally vents had a slight (~1/4") bump/rise or "air dam" along the straight portion of the front edge.

Air dams cause a high pressure area in front of them and a low pressure area behind them.

The purpose was to cause the flowing air to slightly move away from the fender, creating a low presssure area behind the front edge of the vent and facilitating the flow of engine compartment air out and into the moving air stream.

Air dams are not visible on the picture that you posted, but did you notice that on the fenders of the car(s) that you saw or have you ever seen that on any vented fenders ?

I have seen air dams on only one of the many vented wings that I have seen.

IF I build fender vents, I will build in a slight dam for that reason.

I'm hoping that I don't need fender vents, but time will tell.

Tim

 

[GregW]

I always thought that the "Real/Original" rally vents had a slight (~1/4") bump/rise or "air dam" along the straight portion of the front edge.

Air dams cause a high pressure area in front of them and a low pressure area behind them.

Hi Tim,
It would be interesting to see if adding an air dam there would make any difference. The fender bead stands proud about a quarter inch too and it is only an inch or so in front of the vent.

 

[Cottontop]

It would be interesting to see if adding an air dam there would make any difference.

Yes it would. I think that it would be a very easy thing to test if a guy had access to a car with fender vents.

Adding a dam is in my design IF (BIG IF) I ever have to build the fender vents. I hope that my 24" radiator and dual 12" fans offer enough coolant volume and airflow that I don't need them.

The fender bead stands proud about a quarter inch too and it is only an inch or so in front of the vent.

What fender bead are you referring to ?


In the early 2000s, I was trying some things to eek out some more cooling for my V8. Years previously, alongside the road, I found what was obvioulsy a front air dam for some car. It was about 3" tall, 60" wide and at the ends curved around for about 4 inches so as to extend to the front wheel opening.

I cut it down to 2" and narrowed enough to mount to the front frame cross member (behind the radiator) and to extend rearwards down the frame rails.

The without-to-with temperature change was about 4o-5o. The dam was indeed piling up the "frontal" air so that it would be sucked through the radiator and sucking the "after" radiator air groundwards to flow out under the car.

Airflow is sometimes difficult to understand, but on a Healey, it is a major component of the engine cooling process.

I don't know if I am correct or not, but I maintain that improving the car and engine compartment airflow is why Geoff added wing vents instead of a larger radiator. A larger radiator would only yeild MORE hot air to have to deal with. Vents increase the outflow of hot air that is already in there.

In my latest cooling mods, I am re-adding a dam to the bottom of the radiator and ducting the radiator outflow groundwards and will be adding a belly pan to smooth the airflow out the back.

Tim

 

[GregW]

What fender bead are you referring to ?

If I may steal Steve's photo, this is the area I'm referring to. In my mind, the fender bead has already separated the air from the fender before an air dam has a chance to be effective.

 

[Cottontop]

Hi Greg,

To me, that is "the Cove" and is put there for "looks" instead of airflow efficiency. If the cove actually does enhance airflow it is a BIG accident.

All of the below is just the way I see things. I am not an areodynamics guy, but I know one who is. I'm gonna check with him, but I see the front 1/2 of the wheel well as a negative pressure area caused by the Bernoulli effect of the air breaking around the front under the headlight. That explains to me why so much disc brake dust accumulates on the (spoked) wheels (my wife's Jag gets FILTHY!). The dust is being sucked from the rotor & pads OUT through the spokes and into the laminar flow around the fender.

When I visualize the airflow in the circled area, I see the flow coming out of the rear most portion of the wheel well and hitting the front edge of the wheel arch. Just as the air comes around the corner and is sucked in towards the fender, the cove moves inward. This creates a large circular "burble" (like a vertical mini-tornado) in the front corner of the cove. Think of the circular back-flow around a post stiuck in a water flow or the circular back flow at the rear corners of the transom of a boat.

This burble upsets the boundry layer and creates a condition where a tiny portion of the air trying to exit the vent is actually sucked forward into the cove before being spun off into the rearward laminar flow.

The big problem with the shape and placement of the cove is that it wreaks havoc with the airflow over the face of the vent.

Regardless of what is happening in the boundry layer, I think that a slight dam (~1/2" X ~1/2" X the height of the vent) at the front edge of the vent would push the laminar air away from the fender after it comes out of the wheel well and before it actually gets to the vent.

This push-out would create a low pressure at the face of the vent gills and help to suck air out of the engine bay.

Does ANY of that make ANY sense?

I know a couple of guys with cars with vented fenders. I'll see if I can glom onto one of them for a test run.

Tim

 

[Keoke]

Yep Tim, seems to me that all the air flow over the vent is turbulent and the velocity gradient is unpredictable. Similarly, when the airflow gets back to a laminar condition if it ever was is also unpredictable.---Keoke- :confuse:

 

[HealeyPassion]

Guys,
If I may get back to the original hypothesis, that Geoff and the boys put a lip on the leading edge of the vents to create a draw on the vent air flow... in a word no. My vents are most likely as close as one gets to the factory vents... I took a rubbing off of Pat Moss's SMO745 car when it was at JME some years before the URX727 picture I included. Then I modified the Kilmartin vents to match the factory car rubbing (Kilmartin's were about 1" larger). Additionally, I've taken detail pictures of the vents on the original factory car at the British History Motor Centre in Gaydon, one of which is included in my Project Paper on my works side vent. Project Paper on works side vents Not only did the vents not have an air darn on the leading edge, the vents extraction volume was marginalized because the factory didn't bevel the edge of the footwell to maximize the vent size... this can be seen in this picture. On mine, I did bevel the footwell. Clearly the vents are intended to excavate the hot underhood air... beyond that I don't think think Geoff and the boys had to much understanding of aerodynamics. JMHO

Cheers, Steve

 

[Keoke]

-May be more Thermodynamics than Aerodynamics here me thinks--Keoke-- :laugh:

 

[Cottontop]

in a word no.

Steve,

Thanks for clearing that up. Since I had only seen one yes dam fender and more than a dozen no dam fenders, I was pretty sure that was the case.

I am still going to try to mock up a fender and test it with and without a dam in order to try to find out just how effective a dam would be.

I know that a dam under my radiator was VERY very effective.

Tim

 

[HealeyPassion]

Tim, I think what you are saying makes sense, i.e. putting a dam on the leading edge of the side vent. It'll be interesting to see if you can find a way to test the theory. I'm all for doing everything possible to excavate air from under the bonnet. The other benefit is that front end lift is exacerbated by high underhood pressures, so giving the air a clean exit helps keep the front end down at higher speeds. Of course, a front facia air spoiler would also help that a bunch. I wonder if Jim Hockert will do that to keep the front end down on his BJ8 at Pikes Peak Hill Climb. I know that when I put one on my old Corvette (a 1966) I photographed the front end at speed and could easily see how much lower the front end was... you may recall that the first time they went to LeMans they had their front tires come off the ground at about 150mph. As I recall, they cut holes in their hoods to reduce the under hood pressures and got the wheels back on the ground... just.

Cheers,
Steve

 

[Cottontop]

Steve,

I did not run ANY thermostat while I was testing different ideas and evaluating temp. drop. The most significant drop I got averaged about 15F one day when I drove around with the hood totally OFF. All the hot air got out and none was captured anywhere in the engine bay.

THAT convinced me that cooling a Healey was more about airflow than radiators. That and that DMH put in wing vents, not bigger radiators.

The other big help was when I installed a wide Yamaha motorcycle radiator immediately behind the grille. That gave me more coolant capacity plus direct contact with incoming grille air.

The PO of one of the newer modified owners did THIS to the hood of his Chev-Healey.

I can't wait to see how it works in action. He WILL be running a hardtop so the hot air exiting and over the windshield will not be a problem.

Jim Hockert's first order of business is to get ready for the PPIC where maximum speeds are 60-70.

I'll ask him what he'll do about front end lift. He does not intend to park it after the PPIHC.

Charles Matthews has a NASCAR Chevy powered 100-4 built by Pete Farmer and an original (oval grille) 100S rebuilt by Pete. Charles has oval tracked both cars and says that the 100-4 starts to come up at about 155 and the 100S gets "loose" slightly lower.

Personally, that won't be a problem for me.

Most people keep their front ends down with ground effects, aka. dams & spoilers....

I wish I had paid more attention to the underhood airflow in the green Endurance car as it had neither vents nor louvers.

I think that i've got a way to test my "dam-B4-the-vent" theory, but I've got to find a car.

By the way, to miminize the air to deal with under the hood, block off the hood scoop. Fresh air in there only compounds the problem.

Tim

 

[HealeyPassion]

Tim, I'm not sure the modified hood in the pic will work. You may recall that the Chevelles in the mid-60's used pivoting cowl ducts (back edge near the windshield) to get more air to the carbs... they said the area in front of the windshield was a high pressure area that would force more air into the engine (carbs in this case). If that is true of Healeys then the air in the engine compartment won't be excavated at all. But, maybe the air flow is different on AH's... it'll be interesting to see. When the car is not in motion it will provide an exit point for hot air and that's a good thing when you get caught in traffic.

Steve

 

[ModifiedBJ7]

With great interest I've been following the Works Rally side vent conversation. There is an ex-Works Rally car (SMO 74?) that has duel exit vents at the rear of the bonnet versus the long single vent on my car (above photo from Tim). What I find interesting about this setup is they also have the traditional Works cockpit vent directly behind/center the the duel exit vents. Looks like a sure fire way of bringing the heat directly into the cockpit.

Right now I'm looking at the Rally Giants book "Austin Healey 100-6 & 3000" by Graham Robson. There are a several photos of the SMO 744, 745 & 746 Factory Rally cars. One is a rare color photo showing a frontal image of the SMO 744 & SMO 745. I *think* the SMO 745 car has the duel rear bonnet vents. Hard to be 100% certain, but sure looks like it. If that is the case it must of been a trial test and wasn't successful since they didn't extend that idea to later Rally cars??

Idea I; Tim, once you get your car on the road why don't you install my bonnet to see if there truly is a difference in heat exit?

Idea II; What about a small electric fan mounted on each wing vent to help push hot air out at speed and at a stand still?

Charlie

 

[Cottontop]

Mornin' Steve,

Note that the rise in the back of the pictured hood is IN THE hood, not the cowl.

'Tis, for the most part, true that the cowl is a high pressure area. Moving air generally creates a low pressure area. Still air generally ceates what is called a high pressure area although that "High Pressure" is rarely above atmospheric.

As the air moves up over the hood and makes the transition to move up the windsheild, a relatively still air "zone" is created somewhere in the cowl area.

What we don't know is WHERE that zone starts and where that zone ends. Many factors affect that start line, including the air splitter behind the front bumper. Frontal air dams are often used to lower that split line and move the still zone at the cowl.

Lacking a wind tunnel and smoke wand, discovering air flows can usually only be investigated by taping short lengths yarn (or light string) to the body and driving the car.

On the Healey, the rear edge of the hood is about 16" from the base of the windsheild. What remains to be seen is whether or not the rear edge of the hood is in a moving or still air zone. The PO of that hood was betting that it was in the moving. Pete Farmer is betting that it is in the still.

Right now, probably none of us really know. It'll be interesting to find out.

Here in Dallas, we have a Chev/Healey with the radiator in the trunk.. Richard and I did a lot of "yarning" of the whole car to discover the airflow patterns in order to optimize the airflow into the trunk for maximum cooling.

There is a whole 'nuther topic for a White Paper.

If I can get hold of a car, I plan to "yarn" the hood/cowl and fender vent areas to find out both.

Tim

PS - Whether people like what Richard has done with his Healey or not, most people would have "crunched" what he started with. He has put one more Healey back on the road.

 

[HealeyPassion]

Tim, very interesting. I'll be interested to see how those tests pan out.

Roger, you may think your question about the works side vents has gotten highjacked but I think this is all about the same core issue... AH airflow.

Cheers,
Steve

 

[HealeyPassion]

Charlie,
Yes I'm familiar with those raised rear bonnet vents on a few works cars but they didn't seem to ever become a staple addition to the cars as the side vents, etc.., so one would conclude they weren't very effective (the ultimate works version built in 1967 has about every trick in their play book and it didn't include them.) When I saw SMO745 it didn't have the rear hood vents... which doesn't mean it didn't have them before as they frequently changed body items during the evolution of these cars. In fact, some URX727 versions didn't have side vents... and I think some of the pictures of the SMO745 in the Rally Giants book didn't have side vents, and the one I inspected at JME's shop did have side vents. These cars were working rally cars and they frequently got modified as the rules allowed and experience lead them.

Cheers,
Steve

 

[AUSMHLY]

Tim, very interesting. I'll be interested to see how those tests pan out.

Roger, you may think your question about the works side vents has gotten highjacked but I think this is all about the same core issue... AH airflow.

Cheers,
Steve

No worries Steve. No highjacking.
It's all good, as they say.
Cheers,
r