Tudz, I like the L88 hood, but I'm on a path to modding mine, with what I've got going, because anything has got to be an improvement over what's going on now. Also have money invested in the hood vents that I've had made up, gotta get something out of the investment, that's for sure!

I also agree on the C6R style and I think I see the same front hood venting on the new C7 as well (correct me if I'm wrong!) and you're right, it would take some serious modding of the radiator angle, adding a splitter with two separate air paths, etc and whew, that's some serious work.

So we'll try this first and to 79CalShark, yes, I thought of finer or thinner gaps and I think that would look too, but I wanted to go a little 'beefy' structurally (more aluminum than holes) for the first iteration to see how it holds up. I will be painting them this weekend and hopefully mounting them by the end of next week, and then a testing we will go!

 

Just to comment on this, I would be slightly worried that as you increase in speed you open the vent more which increases the forces, and since aerodynamic forces scale with velocity squared, at high speed the forces could be pretty intense and make the car harder to control at high speeds or start incurring a drag penalty at high speeds (if you care about such things!).

Of course, C3's are horribly unbalanced aerodynamically, so you probably can't make it worse

Though I guess it depends if you are trying to just vent air at highway speeds and low RPM/power for street purposes, or vent air and reduce front end aero lift at high RPM/power for race purposes.

 

Happy to have your input as an Engineer here! Thanks so much for participating, your lines of thinking are great and I enjoyed the read on some of the difficulties encountered with fluid dynamics and computer modeling.

You've got a good point! It was a thought that crossed mind, because I thought I could utilize the laminar flow under the car, to go up and into the engine compartment at speed, but I can see what you mean, by the penalty at high speed and the drag effect is certainly something to think about.

I think I'll stick to the ram-air, because that's relatively neutral (I hope) and from what I've see, the front of the vehicle at speed has a surplus of high pressure across the front and that forced into the intakes, I'm envisioning on the inside of the turn signals would work just as well, without the penalty of the 'scoops' and push air out of the engine compartment, from the front to the back.

I'd bet two two inch pipes, hard lines or tubes would have a pretty good amount of air coming through them at 65 mph! This is going to be the Phase II of the Thermal Management system I'm thinking of for the C3.

Phase I: Extract The Heat (Hood Vents or Grills)

Phase II: Keep it moving (Ram Air System from outer front grills to forward part of Fender Liners, behind radiator).

Phase III: Reflective and Insulation materials (multilayer technology, using reflective film and insulation to ward off what heat is left).

 

When it comes to fluid flow, it's less "engineering" and more "wild guessing" The last couple of times I was in a wind tunnel (a couple of years ago now) for an open wheel race car, we did several hundred runs just testing lots of little devices we thought would make improvement, device we'd designed ourselves, devices we'd seen on other cars where we had the theory behind it... of those several hundred runs, only a fraction made it on to our testing short list and only a handful actually made it on to the car So often what you think a device will do, it doesn't do it as you thought it would, or it does it but then buggers up the flow somewhere else, and that's with a room of guys who have been doing race car aero for years So treat any suggestions anyone makes as wild guesses regardless of how qualified they might be And if anyone sounds confident that something will do something, assume they are too ignorant to know better

Are you worried about front end aero lift at all? If not, it simplifies things a bit. I come from more of a race car background, so I deal more in downforce and when the engine people tell me the car is going too slow, I start to look at drag as well. You could definitely mount a splitter, even a retractable one as you mention, down low which scoops are up in to the engine bay, but you need to make sure you have sufficient venting in the hood (not just "some" venting, but you need to make sure you can vent air as fast or faster than it wants to come in). If you don't, you'll end up with even more front end lift than the car had to begin with. My inclination would be to not try and scoop too much air behind the radiator though, as when you scoop air up behind the radiator rather than in front of it, you'll raise the pressure behind the radiator which will impede cooling.

Of course, you won't know how much it'll impede cooling until you do it and test it. It may not even register on your temperature gauge... or it might... no real way of knowing without testing it (you could CAD up a model of the car and CFD it, but it'd probably be faster just to build something and test it ). I'm sure it won't impede cooling anymore than the tiny engine bay did to begin with and probably won't be a problem unless you're running at high RPM with your foot to the floor for long periods. Some of the C3's would overheat even out of the factory when you were pushing it. I've read some of the old magazine reviews of the LS5, complaining if you gunned it on the highway for any length of time it would overheat even when the car was new and not 40 years old.

Yeah, I'd love to know up much air would actually come through them. Maybe you could bend up the pipe to the shape you want (turns in the pipe will reduce flow, so you want to test the same shape as you intend to use) and just get someone to drive at 65mph, hold it out the window and see how much air comes through it

I would be interested to see the air speed behind the radiator just in regular running as well, and what temperature it is. The electric fans on my radiator seem to pull a decent amount of air, if they had enough venting through the hood I'd hazard a guess at saying any ram air that I could get through a 2" pipe wouldn't make a lot of difference. But as always, the only way to find out is to do some testing.

 

As far as front end lift, it's something that I never considered, because the test vehicle (my street driven '74, is far from being an all out race car, but that may come into consideration, if the test results show a significant drop in engine bay temps and the possibility that it gets used in a race car.

LOL on the ram air experiment, by holding a pipe out of the window! Why, I might do, just that this weekend with some scrap 2" PVC pipe! And my thinking, is that the ram air would provide cold air directly into the engine compartment, versus the hot air coming out of the back of the radiator, and please correct me if I'm wrong here, as you have way more experience in this subject, than I do!

I will build and install square scoops behind the outer turn signal grills, that the two inch pipe will mate with. They would have a significantly larger cross section, than the two inch pipes they're mated to. I roughly estimate at least 4" tall, by 5" wide, with a four sided taper and into the two inch pipe(s).

Thanks again!

 

My 79 L-82 has an air scoop underneath the car right behind the radiator which is mounted on hinges. I believe it opens at speed to bring in cool air into the engine compartment...does anyone else have this? You can see in the pics below...

I also found my cold air intake had closed up from heat thru the years such that it wasn't really getting any air, so I put in a couple of spacers which opened this up a few inches which really helps scoop the cold air from the high pressure area right in front of the radiator...in pic just under hood with two wood dowels holding it open

 

Wow, that's intriguing! Was this stock on your '79? And it's below the car, right? Any other '79 owners want to chime in on this?

 

As far as I know, it's stock, it sits right behind the front cross member and opens in front of the fan
, you can see in the 3rd pic looking down into the fan shroud, I have a dowel stuck
Down into the vent holding it open. I know the second owner recored the radiator
And there's an electric fan, which I didn't think was stock, so maybe he installed
It...not really sure when it opens but it only takes a slight push. I was guessing
It would open at high speed due to low pressure buildup as air flows under the car
But I just got the car a few weeks ago and haven't seen anything like it on the boards.
Anyone else have this bottom vent under the fan shroud? It's just above the front sway
Bar and behind the front cross member.

 

Wow... That's what I was thinking too. I even thought, that you might incorporate a lightly spring loaded 'flap', which would release at higher speeds and all you have to do is cut a rectangle in the center of the scoop, hinge it ,spring load it and there's a 'release' for your high velocity air.

Or conversely, you could counterweight it, or make it driven against a counterwound flat spring, that would allow fold back, on deceleration and point straight back at speed. I'm just thinking aloud, here.

 

Yeah, when it comes to aero, what is completely fine on the street at 70mph could send you in to a wall if a butterfly farts at 140mph on a track.

I'm not a powertrain guy, I'm an aerodynamics guy. But my understanding, if you're holding the car at a certain power and a certain RPM, the waste heat should be pretty much constant. So whether you suck in air from outside and through the radiator or suck cold air in behind the radiator, the same amount of heat needs to be vented either way.

Again, I'm not a powertrain guy, but my understand is that it's an energy thing more than a temperature thing. So if the engine is dumping 5hp of heat in to the engine bay, it will still dump 5hp in to the engine bay regardless of whether you suck air through the radiator or whether you suck it through a cold air intake (the difference will be engine temperature will rise and more heat will radiate from the engine itself if you aren't sucking it through the radiator, but the heat dumped in to the air would be the same).

The amount of heat can obviously change depending on the engine and depending on the tune of the engine, but for a given engine and a given tune at a given RPM and power (like cruising down the highway), I can't imagine the waste heat changes much.

Sooooo, if you suck in 3000CFM per minute and vent it out, it will exit the car at the same temperature regardless of whether it was sucked in through the radiator or whether it was sucked in through a cold air intake (the difference will be engine temperature, not vented air temp).

That's not to say your ram air idea is bad, I guess I'm just saying that you need to think more about the total air coming through from the front of the car and whether your ram air intakes would increase that appreciably... I'm not going to advise on that unless I have some numbers so I can actually make an educated guess (I once tested radiators and fans in a wind tunnel for someone which would help... however I don't have those numbers on hand).

The time that a cold air intake vent would really help vs. just sucking more air through the radiator, IMO, is if you were trying to reduce cabin temperature and you could get the vent to dump air on the firewall. That way, you are cooling a localised area rather than simply trying to cool the whole engine bay (the same applies to ducting aimed at cooling brakes, you're trying to cool a very local area).

BUT, if the ram air intake can appreciably increase the CFM of air through the engine bay, I agree that it will help reduce engine bay temps... I'm just not sure it will and can't really advise on it without some numbers to back it up (I can tell you what tests you need to do if you want, but I don't really have the time or equipment to do them on my own car ).

I'm not really trying to push you one way or the other on your design and think you have the right idea, just offering my opinion on the physics of what is happening

 

The Chevy engineers claimed a 5hp increase with the cold air intake. I don't know if its true, but they were engineers who were responsible for the vettes performance nbrs, But you may be right, who are they after all? It could be a bunch of BS ������������

 

Oh if you can suck cold air straight in to the engine intake, yeah, totally. I'm talking more about overall engine bay temps and using a cold air intake to cool the engine bay as a whole.

If you can get the engine bay temps down, that will improve performance because the engine is sucking cooler air from the engine bay, in which case a cold air vent or simply increasing radiator flow and ensuring it has proper exhaust venting achieve the same result. If you can't get engine bay temps down but just suck cold air straight in to the engine's intake, bypassing the engine bay as a whole, you'll improve performance as well (won't improve cabin temps, though).

That's kind of what I was implying with localised cooling vs overall engine bay temps. Cold air vents work for localised cooling, but if you're simply trying to bring the whole engine bay temp down (to simultaneously improve performance, reduce cabin temps and reduce wear on components that are being cooked in the engine bay) then your goal should be net inflow and net outflow. Then if you're trying to reduce front end lift as well for race purposes, you also need to make sure you aren't increasing pressure in the engine bay by ramming more air in to it than can be easily vented. It's a pretty complicated system of heating/cooling/air flow/air forces, hence why the race team that can spend 1 million dollars on improving aerodynamics is a lot better off than the team that can only afford $100k.

EDIT: edited for clarity.

 

I'm really interested in the outcome to this experimentation! In regards to cabin temps, how much air flows into the cabin when the kick panel vents are open? My coupe is an air con one but it has been completely removed, I was wondering whether it was worth opening up the kick panel vents and adding a couple of axial fans there as well.

 

Good one! That would certainly be an option to consider in the heat managementbscheme, so call me a dummy, but I never really tracked down what feeda air to the kick panel? Because mine didn't make much difference! Maybe different routing?

Also, am I correct, Hagis, that an axial fan is more jet turbine like? That would make it easy to install, in-line and part of the ducting, itself?

A lot of really great thinking by everyone here and the last round of thoughts by,Tudz, our resident Aero guy, gave us some great technical thinking and a peek into the highly turbulent world of Aerodynamics! Thanks, both of you, for your contribution!

 

Yes axial fan could go in the duct, but as I suspected it sounds like there is very little air flow to the kick vents,perhaps getting more air into the plenum from somewhere would be a start? Anybody got any suggestions?

 

I'm going to look at my C3 when I get to the shop. Now I've got to know, from where those panels blow?

 

I believe those kick panel vents are fed by the openings on the ends of the windshield wiper trough. The Chadwick link I sent previously discussed these and stated that a huge amount of heat came in from there and recommended resealing the seams you could reach.

John

 

Thanks! I'll check it out in the morning. Was supposed to do that, but took the '74 out to the Gene Winfield car show, rod meet, custom and rat rod event. They had gassers and T-buckets, side by side with slammed 60's Eldorado's.

 

Update: 11 pm, PST and we're still at the Shop. We just got done measuring the hood and figuring out where and what to cut tommorow. Got a lot of the wide blue painters tape, along with an outline of each vent.

Tomorrow, we cut the hood. We also decided to paint the aluminum vents, satin black. The body color idea won't be as distinct, as it will blend and may not show up satisfactorily in pictures. Also, if this works, I want our prototype work, visible, but don't want to go the bright shiny route either.

With luck, I'll be testing this tomorrow. Must go home now!

 

At the Shop and we're applying the last reference lines on the blue tape template. The hardest part was getting it 'just right'! The sides of the hood taper differently, than the cowl hood. Also we're respecting the understructure, and shaving only a sliver on each side. The restrictions on the underside of the hood are very tight!

That 5" width is the max! You're going to be chewing a whole lot of critical structure, going beyond that. S Also, the hood latches, on the underside, push the first available space, a full 12" plus, from the rear edge of the hood.

Gotta help John, surgery is happening soon, we put a lot of thinking, studying and all of you, contributed mightily to this thread. Thank you, to us, the C3 Corvette community! Will report on the patient, later on this afternoon.