C3 front end lift (aero) question.

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The Artist formerly known as Turbo84
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Clinging to my guns and religion in KCMO.
I was going to post this in the tech section, but that area doesn't look like it gets much attention.
A fellow VM member (I'll let him identify himself if he wishes) mentioned that the lift at speed on his car is due to the bodywork area in front of the radiator. While I don't have any actual data myself, it seems reasonable that this area would contribute to the front end lift. Given that this area (actually, a volume) in front of the radiator is a diffuser, changing high velocity air into pressure (to increase efficiency of airflow through all the radiator fins), the slight pressure gain over a large surface area would create a "measurable" force of lift. The reason for the lift, in my estimation, is more than just the possibility of a negative pressure on top of the bodywork (the shiny part) ahead of the hood, but the fact that the diffuser volume is not symmetrical top and bottom. The top is sealed, while the bottom is partially open due to the "bottom feeder" slots (which would be at ambient pressure). Does this make sense?
If so, I'm inclined to do an A-B comparison in the future, blocking off these slots (while monitoring the temp gauge, of course LOL) and do some higher speed runs. I'm unclear at the moment how I'll actually measure the lift, or change in suspension travel, though.
Just kicking around some ideas.
 
If I am following you correctly, you are describing a high presssure area in front of the radiator and the underside of the hood and nose (directly in front of the radiator). Also a corresponding low pressure area on the other side of this?

I think that makes sense. Seems like you might want to barge the air going under the car with some going to the outside and some up into the radiator and close off some of the grill area. The top side might be more difficult to do something with. Look at pictures of the old Grand Sports. They had vents in the hood and some had a vertical strip at the front uf the hood that stood upright a couple of inches. Maybe that was a "fix" for what you describe.
 
I am convinced that our C3s beg and scream for vents on our hoods. The side vents aren't getting the job done. If we provide a place for underhood presurized air to escape thru a vent, more air in front of the radiator will get thru the radiator, reducing the pressure in front of the radiator. The pressure in front of my radiator is so great now with my license plate grill, that my headlights pop up at 140mph with the low vacuum of WOT. I have no data to back this up, just my hunches.
Bee Jay
 
I am convinced that our C3s beg and scream for vents on our hoods. The side vents aren't getting the job done. If we provide a place for underhood presurized air to escape thru a vent, more air in front of the radiator will get thru the radiator, reducing the pressure in front of the radiator. The pressure in front of my radiator is so great now with my license plate grill, that my headlights pop up at 140mph with the low vacuum of WOT. I have no data to back this up, just my hunches.
Bee Jay

I have no technical data to back this up either, but I can see the hot air (heat waves) come out of my BB hood vents that I cut open. So there is pressure being relieved AFTER the radiator through the hood. Its probably not enough of a pressure release to equalize pressure in the nose, but it has to help some.
 
If I am following you correctly, you are describing a high presssure area in front of the radiator and the underside of the hood and nose (directly in front of the radiator). Correct. Also a corresponding low pressure area on the other side of this?
I think that makes sense. Seems like you might want to barge the air going under the car I'm not following what you mean here. with some going to the outside and some up into the radiator and close off some of the grill area. I don't believe the grill area is an issue, unless there is more air entering than is necessary for cooling. Then blocking off the grill would be good for drag reduction. The top side might be more difficult to do something with. Look at pictures of the old Grand Sports. They had vents in the hood and some had a vertical strip at the front uf the hood that stood upright a couple of inches. Maybe that was a "fix" for what you describe.

My main focus at the moment is the area ahead of the radiator. While I agree that it is a good idea to vent pressure and hot air out of the engine compartment for cooling purposes, the lower underhood pressures do lower the pressure that actually pushes the air/fuel mixture into the cylinders on engines with open air filter elements. But that's a topic for another thread. :)
My main interest is balancing the pressure "vectors" in the diffuser area ahead of the radiator. It seems to me (without actually looking at the car at the moment) that if sufficient air (for cooling) enters the actual grill area, while not allowing any to enter the bottom area (just ahead of the spoiler) by blocking off these slots with additional "floor" area, then this floor area in the diffuser will have a pressure vector in the downward direction, partially nulling out the upward pressure vector causing the front end lift.
I'm wondering if putting a manometer in the diffuser volume to measure the actual pressure, and then multiplying the pressure and the added floor area (covering the inlets) would give the amount of force pushing the front end down, partially negating the inherent forces pushing the front end up.
Ideally, (and this is just wishful thinking), in addition to the diffuser inlet shape change, it would be nice to have a thermostatically controlled air inlet/dump that would either restrict how much air was let into the diffuser, or was dumped out. This would keep the diffuser pressure from ever going higher than was absolutely necessary for proper radiator operation. This should reduce the lift that this area causes.
I believe a few old aircraft used a thermostatic system somewhat similar to this for their cooling issues and to reduce drag. (So obviously I'm not inventing anything new here.)
 
OP, Mike, was referring to me on that one, due to some thread elsewhere, everyone kept saying there was bad front end lift on these sharks....

now wether is was going 150 mph or not is NOT the issue here, I admit I was not, apparently, due to instrumentation errors, as I choose to believe Garmin, and fuck all the tach/speedo/tire diameter crapola I was using before....

so anyway, in that time period, I was doing a couple tests, my car is a '72 vert, with some front end modifications, nothing drastic, as removing headlights on any of these sharks MAY affect lift at speeds, honestly, I dunno about that, but certainly getting them stock operating headlights outta the way wether UP or DOWN, will assist airflow ....

I have a BB grafted on hood with the stock SB hood cut out underneath, so it's just one huge open area, I stuck pennies on tape in 3 spots on the rear opening, went 100 mph, the pennies just fluttered...no real indication of any great airflow....guys insisted there was.....so I repeated it with fuzzy yarn same 3 spots on the hood opening, and a couple over the rear hood/grill area....yarn just laying there.....

yarn hanging at speed did a bit of inward flutter towards the engine compartment, the one laying flat hardly moved at all.....I would have to say the flow from the windshield to the engine compartment area is not all that much, really....that yarn was not being blown all that hard, hell I could huff at it through a straw and get better reaction....still not enough to make a penny move inward when hung with 2" wide tape....

All this shit was done about a year ago, before my infamous 'paint' job.....

so having the hood hinges off I goofed and did not put the pins through the front edge...(I hinged my hood from the cowling, not the front due to up and over air induction....reverse hinged, for a vette) I fucked up royally, and so when pulling out on the commercial road, some 200' back was some traffic, I accelerate quickly, the the entire primered/prepped hood flew off the car with great speed and force, cleared my car entirely, as well as anyone behind......I picked it up and was greatly pissed.....:crap:

so that happening told ME that all the lift is in front of the radiator, I was only doing maybe 35 at most when it flew off.....obviously when it got vertical at 35 mph, that thing was like a spinnaker on a sailboat, oops....:eek:

I never thought there was all that much air resistance to the flow through the condenser and radiator, obviously there IS, LOTS of it....hence lifting that hood so good and proper at a mere 35 mph....:twitch::suicide:

I never did any tests up front, as I can't see without a vid cam mounted, I don't own one....too much hassle anyway....


The above experiences tell me, there is no pressure in the engine compartment, those side gills pass almost no air, I would suppose if they did, there would be pressure under the hood, there is a mild vacuum under there even at good speeds....BTW, it is 13" to the hood opening edge from w/s base, and 8" to the back edge of the hood....

:surrender::smash:
 
I am convinced that our C3s beg and scream for vents on our hoods. The side vents aren't getting the job done. If we provide a place for underhood presurized air to escape thru a vent, more air in front of the radiator will get thru the radiator, reducing the pressure in front of the radiator. The pressure in front of my radiator is so great now with my license plate grill, that my headlights pop up at 140mph with the low vacuum of WOT. I have no data to back this up, just my hunches.
Bee Jay

MY only comment is that if the vents are forward of the top rad edge, that the airflow through that rad assy will be greatly reduced, and high speed/freeway cooling will suffer badly....or your fans will be on a LOT, and maybe not enough to cool the engine....maybe a SB and the rad from HELL could do it...maybe....:nuts:

vents behind that rad will do nothing.....

BTW, BJ, my vacuum headlights used to pop up a lot due to operational defects/design/parts? at lo speeds in traffic, sometimes.....even the WSW door did it, there is a cure for it, but another thread.....
 
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Hey Gene,

If those side gills aren't passing much air, were does all the air thats coming in through the radiator go?? I suggest it must go down and out, some passing through the gills. I saw a video posted on the site somewhere of a guy doing the silly string (yarn) test and it showed the side vents working pretty well at 100mph. I only have my car to look at and it has an air dam in the front that sits pretty low to the ground that's used to direct the air to the radiator. It's a triangle shapped piece (pointy end front!) and it's made of the same rubber stuff the front and rear ends are so it's flexible. It's only mounted along the back and held by one bracket in the middle of the front (wonder how that'll hold at 140mph....). The point is that as the air hits it, wouldn't it produce down force before it's directed to the radiator, and if other cars have some arrangment to direct the air to the radiator wouldn't they also get the down force?? Maybe with some strengthening and modification, you could pick up down force there that would be multiplied as the speed increases?
 
Hey Gene,

If those side gills aren't passing much air, were does all the air thats coming in through the radiator go?? I suggest it must go down and out, some passing through the gills. I saw a video posted on the site somewhere of a guy doing the silly string (yarn) test and it showed the side vents working pretty well at 100mph. I only have my car to look at and it has an air dam in the front that sits pretty low to the ground that's used to direct the air to the radiator. It's a triangle shapped piece (pointy end front!) and it's made of the same rubber stuff the front and rear ends are so it's flexible. It's only mounted along the back and held by one bracket in the middle of the front (wonder how that'll hold at 140mph....). The point is that as the air hits it, wouldn't it produce down force before it's directed to the radiator, and if other cars have some arrangment to direct the air to the radiator wouldn't they also get the down force?? Maybe with some strengthening and modification, you could pick up down force there that would be multiplied as the speed increases?

Well, maybe they do, it was just a guess on my part....can't see as it's a whole lot of pressure there or something would be coming OUT of the hood opening, not INTO it.....I have to assume the fans and rad all angled back would blast air down in front of the engine...., where it skips up again??

I still think any factory 'spoiler' is more the 'effects' than 'affects' if you get my drift....

PM me with your phone # I got time today, I just shot some black paint on the camper, so it dries in what sun we get....

:waxer:
 
Walk up to your car and pull up on one of the front fenders. It doesn't take much of a pull to lift the front end up 1". The air that comes into the front of the car, thru the grills or thru the bottom openings in front of the spoiler has a lot of area to come into the engine compartment, but only the side vents to go out. The rest is forced to the bottom of the engine compartment and out the back under the chassis, where our also infamous rear bumper parachute catches air again. The high pressure under the hood is what makes the front end lift at speed and give that light non-steerable feeling. My red Italian car does 171mph easy with only 300hp. But when you look at the bottom of the car, it's flat. Any intake for air, water cooling, and oil cooling, is more than matched with outlet vents. My entire engine cover is vents and in between the rear lights are more vents. Look at the C6R, that hood has more vents than I've ever seen on a stock based car since the Grand Sport Vettes of the 60s.
Bee Jay
50thBirthdayParty186.jpg
 
Walk up to your car and pull up on one of the front fenders. It doesn't take much of a pull to lift the front end up 1". The air that comes into the front of the car, thru the grills or thru the bottom openings in front of the spoiler has a lot of area to come into the engine compartment, but only the side vents to go out. The rest is forced to the bottom of the engine compartment and out the back under the chassis, where our also infamous rear bumper parachute catches air again. The high pressure under the hood is what makes the front end lift at speed and give that light non-steerable feeling. My red Italian car does 171mph easy with only 300hp. But when you look at the bottom of the car, it's flat. Any intake for air, water cooling, and oil cooling, is more than matched with outlet vents. My entire engine cover is vents and in between the rear lights are more vents. Look at the C6R, that hood has more vents than I've ever seen on a stock based car since the Grand Sport Vettes of the 60s.
Bee Jay
50thBirthdayParty186.jpg

Good looking car! Is it a front radiator? If so, what does the inlet/outlet look like?
 
Walk up to your car and pull up on one of the front fenders. It doesn't take much of a pull to lift the front end up 1". The air that comes into the front of the car, thru the grills or thru the bottom openings in front of the spoiler has a lot of area to come into the engine compartment, but only the side vents to go out. The rest is forced to the bottom of the engine compartment and out the back under the chassis, where our also infamous rear bumper parachute catches air again. The high pressure under the hood is what makes the front end lift at speed and give that light non-steerable feeling. My red Italian car does 171mph easy with only 300hp. But when you look at the bottom of the car, it's flat. Any intake for air, water cooling, and oil cooling, is more than matched with outlet vents. My entire engine cover is vents and in between the rear lights are more vents. Look at the C6R, that hood has more vents than I've ever seen on a stock based car since the Grand Sport Vettes of the 60s.
Bee Jay
50thBirthdayParty186.jpg

Good looking car! Is it a front radiator? If so, what does the inlet/outlet look like?

No. The oil and water radiators are just behind the doors. The side strakes guide air to those radiators. The engine lid has tons of vents to let air out of the engine compartment. There is a vent between the tailights also.
Bee Jay
 
Walk up to your car and pull up on one of the front fenders. It doesn't take much of a pull to lift the front end up 1". The air that comes into the front of the car, thru the grills or thru the bottom openings in front of the spoiler has a lot of area to come into the engine compartment, but only the side vents to go out. The rest is forced to the bottom of the engine compartment and out the back under the chassis, where our also infamous rear bumper parachute catches air again. The high pressure under the hood is what makes the front end lift at speed and give that light non-steerable feeling. My red Italian car does 171mph easy with only 300hp. But when you look at the bottom of the car, it's flat. Any intake for air, water cooling, and oil cooling, is more than matched with outlet vents. My entire engine cover is vents and in between the rear lights are more vents. Look at the C6R, that hood has more vents than I've ever seen on a stock based car since the Grand Sport Vettes of the 60s.
Bee Jay

Still no upward pressure on the vast majority of our hoods, it would have to come out that back section opening if it was much, instead it's flowing into/on top of the engine....and not by much....

I been thinking of doing holes in the back plane, ala' GS racers...but had no confidence I could pull it off, enough with the body work already....

I think it's because our rads are angled back so much that the air is forced downward in front of the engine....

Those flat panels are a funny item as in my wife's '99 Escort had them under neath refered to as 'fairing'....by some guys in the past....anyway, leaving it off has not affected fuel economy one bit....so there can't be much windage reasons for it to be there on THAT car anyway....

That little italian thing, looks likw a C4 in front/windshield, the back looks like a Fiero with Trans Am tail lights on it.....:rofl::smash: must be some lo production custom job....
 
Walk up to your car and pull up on one of the front fenders. It doesn't take much of a pull to lift the front end up 1". The air that comes into the front of the car, thru the grills or thru the bottom openings in front of the spoiler has a lot of area to come into the engine compartment, but only the side vents to go out. The rest is forced to the bottom of the engine compartment and out the back under the chassis, where our also infamous rear bumper parachute catches air again. The high pressure under the hood is what makes the front end lift at speed and give that light non-steerable feeling. My red Italian car does 171mph easy with only 300hp. But when you look at the bottom of the car, it's flat. Any intake for air, water cooling, and oil cooling, is more than matched with outlet vents. My entire engine cover is vents and in between the rear lights are more vents. Look at the C6R, that hood has more vents than I've ever seen on a stock based car since the Grand Sport Vettes of the 60s.
Bee Jay

Still no upward pressure on the vast majority of our hoods, it would have to come out that back section opening if it was much, instead it's flowing into/on top of the engine....and not by much....

I been thinking of doing holes in the back plane, ala' GS racers...but had no confidence I could pull it off, enough with the body work already....

I think it's because our rads are angled back so much that the air is forced downward in front of the engine....

Those flat panels are a funny item as in my wife's '99 Escort had them under neath refered to as 'fairing'....by some guys in the past....anyway, leaving it off has not affected fuel economy one bit....so there can't be much windage reasons for it to be there on THAT car anyway....

That little italian thing, looks likw a C4 in front/windshield, the back looks like a Fiero with Trans Am tail lights on it.....:rofl::smash: must be some lo production custom job....
The base of the windshield is a high presure area. The air flow over the hood is met by a brick wall windshield and causes higher pressure there. That is why the Vette, Camaro, and Chevelles have Cowl Induction. I have the back of my hood opened up, and it definitely does not vent the engine compartment. If it did, I'd have oil film on my windshield and occasionally some smoke from oil leaks hitting the headers. When I build my modded hood, it will have vents and a cold air cowl induction system.
Bee Jay
 
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Took a break from working on the rear suspension to take a look at the front bodywork. There's significantly less surface area in the bottom portion in front of the radiator compared to the top. If this diffuser volume is even remotely efficient (at converting air velocity into air pressure), then there's going to be a decent amount of force pushing the front bodywork upward.
This has got me curious enough to start thinking about constructing a manometer to measure this pressure.
 
I sealed the three cooling holes in the lower valance and reduced my outer grill openings to about zero but the biggest improvement came from adding the little plastic factory spoiler...I could honestly feel that difference....
 
I have been saying this for a while now on other forums but its like nobody believed me,i was one of the fellas that claimed he went 150 mph according to my speedo,which probably isnt right,but the fact is at that speed my hood started to pry off from the hinges,i seen it lift about an 1 to 1 1/2 inches ,then i started to slow down,plus the front end got lite .
I have a question to somebody who might know here when the 68 to what ever vettes that read 160 mph on the speedo,would the cars do 160 mph when they were new?If so ,why cant they run that fast now ?.
 
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The radiator airflow/downforce on these cars worked really well.
Some of the C6R cars had this idea adapted to them.

006.jpg

Here are a couple pics of a front engine design, forgot what they are, don't even know if they worked, but the effort looks good.

radiatorducting2f.jpg

headertank1.jpg
 
Bee Jay, try putting some manly springs under your frame rails and you won't be able to lift the front so easily.

My car is stable at 140mph, don't feel any lift. Now when my car was stock, I felt lift at any speed past 80mph.

The front end of a C3 is like a big spoiler, if you drop the car low enough with enough of a rake, she'll stabilize. The bottom of your oil pan might get all scraped up like mine, but it's worth it to turn your snazzy looking muscle car into a sports car. IMO.

I installed the 550 coils, with 3/4 of a coil cut and some low profile tires. I also cut out a wide opening behind the cowl on the hood.
 
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