mrvette

GM had a formed rubber gasket across the top of the rad support, that met the hood snug and secure when hood was down as well as doing the same thing on the sides and under...I think all the front end lift comes in front of the radiator on that large flat triangle area of the hood forward of the 'gasket'.....

So the curiosity is, with a stock fan shroud, the air is redirected horizontally into the front of the engine, no matter the fan being electric or mechanical....but I have dual spals, mounted to the lower and upper rad U channels, so fans are parallel to the radiator...and direct the air down and under , no matter if fans are on or not....the air is aimed at the harmonica balancer...

which is why there is no pressure under the hood on the ENGINE side of the radiator, on MY car...

IF I remove the gasket and let that incoming air up and over, I wonder about cooling at moderate speeds, with all the pressure relieved the air is not forced through the radiator, ....can't win...

another-user

thats exactly what i had in mind.

TheSkunkWorks

Fact is, at the most basic level this whole issue is one of aerodynamic pressure differentials. Since we're dealing with a body in ground effect rather than one in free air, generally the less air is allowed under the nose relative to that flowing above it, the easier it is to generate downforce rather than lift at speed. Among other things, unless vented elsewhere so as to divert it from ultimately ending up beneath the nose of the car, radiator exit flow adversely affects pressure differentials towards or into the lift side of the equation.

At speed, aero becomes a first order factor. That isn't really a concern worth stressing over for the vast majority of owners. But, when approaching the upper end of the performance scale, until and unless substantial supporting data clearly shows otherwise for a given vehicle, best IMCO to accept conventional wisdom (as has been established by engineers in the field) and seek to adapt proven methods for managing aerodynamics per those norms.


vette427-sbc, I've been wondering how long it would take someone to bring up that type of C3 hood extraction.

69427

I can't perceive any lift or "steering getting light" issues on my '69. The current configuration is pretty simple, but have a couple additional tweaks planned. I've got the ride height down an inch or so from the stock height. I've got a Pace Car spoiler that helps divert a portion of the air from getting underneath the car, and I've blocked off the two grills (in front of the headlights) to reduce the volume of air entering the pre-radiator plenum. The car never overheats (I credit a good engine tune and a DeWitt radiator), even on 90* track days (like last week) or 100* track days (like last July). I may try to block off some of the center grill too.
I've been working on some aluminum panels to smooth the bottom of the car (particularly in the front before the air gets hopelessly turbulent) and other panels to help direct the air out the side gills instead of letting it collect under the car. Once I get this finished I need to do some wool tuft testing to see if it would be productive to lower the bottom edge of the underdoor rocker moldings. If it looks like air is actually trying to enter the underside of the car (from the sides) some of this air could be blocked by extending the molding lower edge downward. It looks like an additional two inch drop would be almost visually unnoticeable.

TheSkunkWorks

Sounds like you have a good working plan.

IIRC, Bee Jay experimented at one time with some sheet metal block-off plates behind his grilles without detriment to temps (also has PC dam). I'd think you could keep reducing the inlet area as long as they're OK. Yep, this one's on my list too.

And, side skirts wouldn't seem too hard a project, as long as you can verify they'd be working in your favor at speed.

With my '78 having been off the ground for a while, I've spent more than a few hours underneath it contemplating how to go about the whole splitter/pan/diffuser thing. I've actually found a resource for doing the splitters to my specs, and have started working on the station bucks for molding a prototype diffuser, but just don't have the funds to get either to the finish line just now. Same story with other somewhat hardcore bits I'd like to develop for market...

ToniH

I think I took this pic in 1982 or 1984:

I'm Batman

I've said it before, but I've always been amazed at how much difference even the little stock chin spoiler makes on my 77. It used to start to get noticeably (and frighteningly) light in front even at higher highway speeds. In the 60-70mph range.

roscobbc

I doubt if the stock 'gills' on thier own would allow enough extract air flow to balance air coming in to engine compartment - perhaps removal and adapation of the area where the 'fillet' sheet metal covers over the frame (at rear of engine compartment adjacent to bulkhead/behind wheel tubs) ?

TheSkunkWorks

I'd be afraid that removing the inner covers mentioned above might not have the desired effect, as it depends on which way is the existing Δ above relative to beneath them currently. What you don't want to do is open something up to an immediate area which has higher pressure than that from which you're attempting to extract air; hence the reason to stay away from the base of the windshield, for instance. Unfortunately, while tufts may do a fairly good job of showing flow lines and turbulence, they aren't very good at indicating which side of a closed panel has higher or lower pressure, and not all locations readily lend themselves to practical trial and error. In any event, if I understand where you're talking about, the area in question still opens up beneath the car so I'm not sure what would be gained overall.

pauldana

Saw this at the last car show I went to. Behind the radiator, in front of engine, with a pan/scoop from good to bottom of car

vette427-sbc

Id like to see what you've got going for a diffuser... I started one and got side tracked with finishing other projects. I want to get back on it but I need to get my car running again first.
Not sure if I posted pics of mine on this site but heres one. The rear "parachute" is probably horrible for high speed aero

johnmb

Oh, my eyes, my EYES!

I'm Batman

I would imagine the stock spare tire carrier does at least something to help keep air out of the rear bumper cover.

pauldana

Made a cool mod for this.... and I agree with you on this..


Took out the tire, and put springs in the bolts, the springs hold the carrier down, but if hit will allow it to move up...

damoroso

What about opening the L88 style hood where I have marked in pencil? I realize getting the air out of the engine compartment is all about air pressure, my thought is that the air being diverted up and over this area of the hood would create a low pressure area helping pull air out of the engine bay. Putting the openings here move them to a location that's behind the radiator (though not much, still should pull some hot air) as compared to opening up the vertical area just forward of what's marked. Waste of time, effort and energy?

69427

Here's a couple pictures while I'm still getting the aluminum sheets tweaked to fit on the frame. These pieces just block some of the engine compartment air from dumping under the floorboards and colliding with all the uneven surfaces. The intent is that a higher percentage of the compartment air will be persuaded to exit the side gills instead. Passenger side:



Driver's side:



Depending on how things go at the next track day I might consider riveting a small vane on the bottom of each panel to direct some of the air under the panels outwards, again hopefully reducing the amount of air that tumbles around under the car.
I've also got the pattern cut out in cardboard for the horizontal "belly pan" that fits between the pacecar spoiler and the oilpan sump, but I haven't been able to get to the shop yet where I buy the larger sheets of aluminum (the panels above are just scrap pieces I had left over from previous projects). This belly pan should clean up some of the flow under the first few feet of the car.

damoroso

I like it, it'll be interesting to see if you notice any difference. It also looks like there are panels on the other side of the frame rails just forward of your new pieces. Looks like between the frame rails and the fenders. Is that also something you did? I don't recall those on other vettes...

69427

The other panels are original. They help block off the area between the frame and the rocker molding area. They would work better if they were flush with the bottom of the frame but I understand the manufacturing/assembly constraints and why they were placed where they were. Down the road (if time permits) I might try to put a panel that's level with the bottom of the frame, and block off the front of that area to keep it from catching a lot of air.

SHOWME

Its crazy how much air these cars pack under that tight little hood.I spent two years building and rebuilding a front and hood that would pass air through properly.I gained in cooling alot! and hood and front lift has all but dissappeared.I found that alot of the overheat/high heat problems with these cars has to do with venting more than drawing more in...It must be forced through the rad and released.I know that the high curves on the front fenders also create lift(This is why they were reduced from the macoII to the production vette.)So many ways to go and things to do to aid in the redution of lift. How much you want to do is up to you....


Still have a few changes for the lower front in the works.

69427

Made a little progress today with the front undertray. It's 52" wide by 48" long, and the front edge is positioned under the pacecar spoiler. I still need to make a few more clearance cuts, but it looks like there's plenty of locations to make supporting hanger brackets.



I also recently bought a differential pressure gauge, so once I get the tray installed I'm interested in running some hoses from the gauge down to the front there to make some measurements.