Those are some cool looking cars.

 

I surely have posted about high speed runs before, but here goes again....do not trust your tach and speedo on indications....buy a GPS, that is the truth, not your speedometer, you maybe well find the speedometer is accurate to 80 mph but wildly over indicates above that....I know mine is NOW accurate to 80 which is really 78, but when it says 100, it's only realy 94mph.....ran out of room at that point....
but anything lower is dead nutz on....methinks the factory wanted it that way....


Some time ago, I did some yarn tests on my hood which had a open end on the BB hood scoop which is a repro junk thin glass on the cut out stock hood, open under it....so I hung some yarn on the back edge in 3 spots, and over the no gasket hood rear edge, where it hits the wiper door/cowel vent plate.....

at all sorts of speeds, the yarn did not move with airflow, just sat there, not sucking out or in, that meant to me there was NO airflow pressured up or down under the hood, back in the engine compartment....

the upward pressure on the hood comes from in FRONT of the radiator in the forward triangle area, which makes total sense as the top gasket blocks airflow from up/over the radiator forcing the air through the radiator....

I have fixed Eckler's sugar scoop headlights, due to a accident here in '98, a damn deer wiped out the stock lights.... so I eventually reduced the headlight opening to 1/2 the size and put in lower profile bulbs....

see shutterfly site for pix....

 

...and I've seen where tuft tests tend to confirm flow into the cowl at speeds as low as ~30 mph.

There is some pretty well established and proven theory on managing underhood aero, and one needn't look at very many modern racecars (GT2 and the like) to realize that a significant amount of attention to detail is placed on this area. Based on what I've seen and studied (texts, not wiki), it's hard to imagine the race engineering community doing a 180* turn on the matter. Until/unless that happens, while there might well be exceptions due to certain nonconforming variables, I think I'll stand by my take on what's at play here.

That said, observations which would seem to run to the contrary, along with my own tendancy to geek out on this sort of stuff, are why I'd really like to log some hard data to better document how this all relates to the C3 in general, and to my shark specifically.

 

ok... seems that there are 2 divverent camps on the hood vents...BeeJay and MrVett both did the yarn test... but seem to have 180* different results and thoughts.... the air dam will have to be lowered as it seems everyone is on board........ but the hood vents seem to be a different story....

i can see how the scoop would also raise the front end a bit from all the wind up on the radiator area...but is it significant? anf if it is, the hood vents should help????

 

Ummm...don't nobody take this wrong, we all do what we do.

I'm just curious why are we driving at sustained 130-160 MPH, at least that's what I get from the discussion here.

I can see acceleration to 130MPH (drag racing don't you know) but why more??
And just where can you go to get one of these old dogs up to 160 and not risk collateral damage??

Thanks!

 

Bee Jay's vents are apparently well located and, being well ahead of the cowl area, functioning as might be expected. One of the more significant things many race teams do is to channel rad exhaust out in a way which doesn't contribute to underhood pressure (and resultant lift force), as can be seen in the hood below...





As for why; because it's there and some of us simply must climb that mountain. FWIW, in future I'll attempt to reserve such speeds for the track.

 

:I'm out at willow springs raceway....

So, to vent or not to vent, that is the question..

So let me get this right.. We seal the hell out of the radiator to prevent from overheating.... But doing this gives us more lift..... Dam if you do, dam if ya don't .. At lest it sems

 

Why? - its an excellent natural (healthy?) method to relieve constipation

 

The pressure drop behind a proper front dam should serve to reduce pressures within the nose ahead of the rad sufficiently for most of us to not worry too much about differentials in that particular area until getting pretty far up the performance scale. Besides, isolating rad in-flow wouldn't be all that easy, so of the two I'd focus on dealing with the hot air exiting the rad first.

 

Me and my buddies use the fat chick rule and it really works. If you feel the need for speed over 120 mph, you have to find a really fat chick to take with you. Preferably one who would need a seatbelt extender. If you do this, you'll find that after you find her, the feeling you had for going over 120 will quickly go away. This also serves the purpose of keeping you and your Vette safe at all times.
Duane

 

I did some yarn testing on a BB/LT1 hood with the vents opened up and no seal from the rad support to the hood. Airflow was marginal at road speed, but at 100+ I noticed the yarn started to really get pulled out of the vents.


I also did a bit of testing on the side gills for under hood air extraction. I had a 1" wicker in front hoping that would help evacuate more air... but it did not. (I still havent tested it without a wicker though) Air flow through the gills was pretty minimal, relatively speaking for 100+ speeds. If the air is not exiting through the side gills, you can assume that most of the air going through the rad is going right back under the car (not ideal).

 

hummmm.... if i remember correctly, on the stock fan shroud it had an flap on the bottom that opened and closed via a vacuum relay for some reason i am not sure..... i wonder if it had something to do with this....

my setup has 2 spall fans on it, i would think at 120mph+ that with the amount of air forced into the radiator and pulled through by the fans..... would be a lot of air directed under the car.... but then again nothing compared to the 120mph going under the car....

 

The BEST way to prevent high speed lift on the front end of a C3 (at elevated speeds) is to not exceed 120 mph.....

 

 

What's with the negative waves?

 

The forces of the wind at that speed might blow away the tank sticker

 

my brother and I loved that movie!!...

 

 

Well, this will probably get me banned from the forum, but.....



This photo was taken in 1970; the car is a '67 I bought in 69; I'm the great looking guy on the left.

I clocked about 148 (5900 rpm) one afternoon on a long backroad when I was living in Dewitt County, TX. It was a rural area in south central Texas with numerous long, well paved, FM roads all over the place, and I'd regularly cruise 100 - 110 around the countryside. Yea, I know, but I was only 27. And I saw 120 +/- from time to time.

Point is, except for the 148 run which I backed off pretty quickly, the car always felt solid at 100+ mph speeds. But, you'll notice the vents on either side of the hood bubble, and I always thought they contributed to the stability. It'd be nice if someone made a fiberglass vent panel that could be attached to a 'vette hood on either side. It'd be interesting to see how it worked out, and regardless, it'd look cool as heck.

 

I had to punch a hole in my tunnel to fit my 700R4 and the fatass aluminum driveshaft. I drove the car before I plugged that hole. Man, at highway speeds I was getting hurricane force winds, very hot air btw, blowing into the cockpit thru that hole. I guess I could pull up my carpet and fatmat and the aluminum plate I riveted over that hole to see if my hood vents reduced that source of hot air. I've also been told that some Vettes came with a big foam horse collar over the tranny to limit the air in the tunnel. I did the yarn test on the vents. The yarn flowed out of the hood at relativley low speeds. When I put an aluminum spoiler in front of the vents, the yarn really jumped out. I also put some yarn tufts at the base of the windshield and believe the hype, the yarn goes into the engine compartment. That is why I get my cold air from the base of my windshield, actually from the windshield wiper trough. It's fun to open the hood after a long drive to see the cold sweat on my carb hat and carb. That's some cold air.
Bee Jay