Summerfun

If you run the exhausts inside a belly pan, how about two open pipes next to the exhaust pipes for the air to escape through??

Leave the two pipes that you run right next to the exhausts open where they enter the engine compartment and cut them off close to the mufflers in the back.....air can now move freely out the back.

.....even two small extractor fans inside the pipes perhaps??

Summerfun

Will moving air out the back reduce the turbulence around the sides of the car?

I figure that top and side vents make air do a lot of 90 degree turns and that sounds to me like turbulence due to pressure changes.

However, moving air from the engine compartment out the back where air that moves over the top of the car comes down and does all kinds of turbulent things (sounds not too scientific, does it ) would actually aid to normalize pressure differences behind the car and reduce lift??

Budman68

I noticed on alot of the old C3 race cars they had small 90 degree lips mounted on the front of the hood area. Was this to keep the windsheild clean or adjust wind turbulance.

As far as reducing engine compartment pressure, I thought those vents on the side did that. After looking at them, there is no way they can be effective over cruise speed. You have 31" by 18" of radiator surface air flow trying to excape out of two 6" by 3" holes. Maybe they intended for the air to go out the bottom, but that doesn't make sense after adding the air dam. The slits in the hood make the most sense to releave the pressure. I guess the down side would be heat in the cowl area.

rihwoods

This morning I'm trying the yarn trick on the L-88 hood at cowl..I'll get pics..
I think air moving down the side of the vette helps draw air out the gills...more like a "chimny" effect...???

Maybe setting off one of those smoke bombs under the hood at speed...

I know this for sure..when I blew a P/S pressure hose at 75 mph,the smoke was coming out the sides and rear of the 78....none at hood cowl seal...

rihwoods

Ok..My yarn test...

Test set-up...


Engine at idle....


55 MPH..


At speed....


At least I know this much...clear to me now why they vented the Grand Sports adding vertical vanes at front of hood to relieve pressure....
At idle, air from engine fan blew yarn towards windshield...
Rich

Budman68

Wow, I never thought it would vacuum that hard at speed. I bet there is 30 or 40 lbs of vacuum. Get test.

Summerfun

Interesting

rihwoods

Actually,I was surprised getting up to speed....at idle,they stood almost straight out towards the windshield...then just before 30 mph,they reversed into the hood opening and the faster I went,the flatter they got inside the top of opening.......still looking for my vane amenometer..it measures velocity..plus I'll have to figure out how to mount it inside hood at opening...will not tell me anything outside...
Rich

Bee Jay

Wow Rich. That's exactly what we needed to see. Chevy was right with their cowl induction. Positive pressure at the base of the windshield. I guess you couldn't mount some yarn the same way on the side vents, drive, and take pictures. You would need a chase car. I don't see them being too functional with all the crap (charcoal canister, AC thingie) right in front of the exits.

rihwoods

Think I have figured out away to do it...if I tape long pieces of yarn (8")inside side vents, I can do a quick lap down the road ,stop and get out to see if they came out the openings...my wife thinks I'm nuts,but gave me the yarn anyway...

Twin_Turbo

Someone needs to score a magnehalic gauge and do some testing

1969Vette383

Oh Rich baby, keep the shots like this coming! I'm missing my car . Three years of being down for restoration/modification is killing me. I miss my home away from home in the driver's seat of my C3. The view over that hood is what I'm hoping to see sometime around December.

On to the results- that's kindof what I had imagined. It can be concluded, that so long as air is flowing over the car, there is an air induction at the base of the windshield. While stopped, or at low speeds, the low pressure zone hardly exists and thus no sucking occurs.

It's a damn shame my car isn't running. I don't care about the yucky, cracked black paint on it now (was Le Mans Blue which will come back this summer). I would find a way to safely adhere smoke bombs on the nose and hood of my car in order to take stills/video of the smoke pattern.

rihwoods

Test number two.....I realize these are visual tests as I have no means to measure velocity or CFM....the following pictures are from my own thinking and practice:
The first pic shows that the gills do expell air out at speed....you must excuse fact that pics are not in sequence....

The next two pics show air turbulance at rear window...no big surprise here




I took care to ensure yarn was inside gills..I did notice at engine idle air was coming out gills,but not strong enough to push yarn out the openings....after running the vette a few miles,I stopped and found yarn was outside gills which proves air does exit gills at speed..


The rear window pics are just my doing to confirm turbulance at rear window...if you look close, yarn blows towards rear window...none of this is scientific,just a practical means to show a visual persective of air flow....
Before run....at Gills...the last pic shows yarn at engine idle...after run up to 70 mph, I stopped and yarn was outside the gills...I made yarn long enough to be at least 2" below gill openings...

JPhil

Oh, Man, Great Stuff Rich! (I got to spend the day replacing my starter motor, pulling and clearancing my pipes to the tranny, putting the interior back together after my heater core rupture and clearing out a new garden space for the wife...Tomorrow is Dad's day down in Boulder....)
For your manometer, can you use a long piece of tubing to place at various points and keep the manometer itself in the cabin? (I used to have a nice little HVAC draft guage I was going to do this with but I can't find the little bugger any more.)
OK,TT, I give. What's a "magnehalic guage"? Even Webster's New Collegiate Dictionary just said, "Huh? I dunno."
Rolling around under the car today I was scoping out belly pan potential. Boy it would be rough to do, and virtually impossible with undercar exhaust. I think the heat entrapment, even with side pipes, would discount that idea for all but serious racers.
I do believe I will lower the car a bit in the future here--actually my front end is now about 3/8 inch higher than it used to be because of all the weight I've removed. Looks like a Jeep.
Hmmmm...July 4th coming up.....Think I'll buy a gross of smoke bombs....

John

rihwoods

Best of luck to you getting your vette back together...luckily,both of mine are running....my 78 needs suspension work...bushings,etc...but there is no subsitute to driving these C3 Corvettes,,
Rich

Bee Jay

Dear Rich's wife. Rich is the man, he may be nuts to you, but he is the man to us. Give him a big fat hug, kiss, and some more yarn for Father's Day. And thanks from all of us at the Corvette Forum.

rihwoods

I can't adapt my vane anomonmeter as you suggest.as it is digital....heck..I can't even find it...from tests I've done,i'm pleased to know air is sucked into my 69 L-88 cowl opening...as for the rest,I'm convinced that lowering the front end of our C3 vettes makes a big difference in handling and reduction of drag...no question there...I did this on my 78 by cutting half a coil on the front springs..this lowered the front end by 1"....on my 69,I am running 245-60-15's on the front and 255-60-15's on the rear to drop the front by 1/2"..can't go any lower at this point as my 6 qt oil pan is only 3" off the pavement...i'm looking at a different oil pan to allow more clearance..maybe a Moroso..???
Rich

rihwoods

My only knowledge of the
magnehelic zero center pressure drop gauge is for balancing carbs...not familiar with using them to gauge air flow at velocities experienced at 75+ mph......but that is just my own ignorance....

rihwoods

My wife just said..."thats fine,you come and live with him"....
You may not believe this,but my wife used to live in Lompoc back in 1966 or so.......we have not been up there in several years....but it would be neat to meet up sometime.....I'll stay in touch...
Rich

Bee Jay

Come on up. I'll drive the chase car with cameras.