Aero difference between 67/8 and later hoods?

[BigSky71]

When I restored my 71 I installed the early front clip because I wanted the sloped hood. Now that I am driving it again, there seems like there is a lot more wind that hits the windshield with the sloped hood vs my original 71 setup.

I didn't notice this before when the truck had the stock more straight up hood. Now when there is any head wind at all the truck feels like its struggling to power through the wind. I first thought I had some motor issue or a tranny slip, but it runs great on the fresh motor and I had the tranny rebuilt this spring by a reputable local shop and I installed a new torque converter.

Any one else felt this difference between the early and late hoods? The lack of aerodynamics is actually pretty annoying on the highway at speeds above 60 or so... like trying to throw a brick through water, lol

[msgross]

it looks cooler though!

[lowdownstar]

i never would even thought of that. are you glad that you did the change? I am thinking of going that way myself. i have a 69 stock hood. It does look sweet.. good luck to you

Ray

[BigSky71]

Originally Posted by lowdownstar

i never would even thought of that. are you glad that you did the change? I am thinking of going that way myself. i have a 69 stock hood. It does look sweet.. good luck to you

Ray

I am glad I made the change no doubt, but the feeling when driving on the highway is annoying. I don't plan on driving the truck long distance but would like drive it a few hours away to some shows.

I partly wonder if the lack of aerodynamics would be less noticeable if the truck was not lowered and bagged. If more air went under the truck at speed maybe it would get through the air better... not that I intend to raise it up though.

[lowdownstar]

hey bigsky

it's all about looking cool..... the hell with the rest. lol i think you did a great job with your truck. I bet your going to do well at the show. have fun with it, that is what it's all about.

Ray

[Longhorn Man]

I'm willing to bet a punch in the gut that if you were to do a wind tunnel test, the early hood would win... as would a lower vehicle.

The air hitting the windshield means you are only cutting a hole as big as you need in the air. Cutting and deflecting so big that it 'throws the air over the roof' is more than iss needed.

Ever noticed on a late model car or truck, you roll the window down, even just a bit, and it kicks up a whole lotta wind and noise in the car? That's becouse the air is right up against the body, not being deflected around and over it.

Visualize the air as water... hydrodynamics... and you can picture it way easier.

[jay-dawg]

I would think it would be the other way around with the earlier hood being more aerodynamic. but I don't think an inch or two would matter. a brick is still a brick. just my .02

[BigSky71]

Originally Posted by Longhorn Man

I'm willing to bet a punch in the gut that if you were to do a wind tunnel test, the early hood would win... as would a lower vehicle.

The air hitting the windshield means you are only cutting a hole as big as you need in the air. Cutting and deflecting so big that it 'throws the air over the roof' is more than iss needed.

I see your point but I think the difference here is the drip rail on the top of the cab. With the late hood maybe the bulk of the air misses the drip rail and goes over, but with the early hood it hits the windshield then has to deal with the very unaerodynamic drip rail. No way to know without actual testing but if I really get ambious maybe I will stick my old hood back on and go for a drive, lol.

[special-K]

Just get a bug deflector.I hear they`re the rage.

[Mondo]

I think there's something else.... at 60mph I can't imagine there being a difference. You block the air with the flat hood or the top of the windshield with the sloped hood - it should all be neglible.

Too little air pressure in your tires would make a bigger difference.

[whatnow123]

I don't know if there is a difference, but I do know that my windshield/driprail catch a lot of bugs.

[jef5150]

i would think if it was that big a difference prostreet pickups would only run a "specific" year chevy front end .


jeff

[BigSky71]

Originally Posted by special-K

Just get a bug deflector.I hear they`re the rage.

I was thinking of designing a convertible bugshield for trips over say 40 miles... paint it to match, then tell the tuner guys its a front wing, like in World of Outlaws!

[ChevLoRay]

I've used vinyl/fabric hood protectors on a couple vehicles and they have a couple of pieces that serve to deflect the wind...or maybe to help the wind keep the deflector from flapping. Since I was on the interstates, it worked. I just don't know of anyone making one to fit our trucks, though.

I wish mine was back on the road so I could experience some buffeting and wind noise.....

[special-K]

Originally Posted by ChevLoRay

I've used vinyl/fabric hood protectors on a couple vehicles and they have...

C`mon!!You can say it.It`s called a BRA!!!As in brazzier,over the shoulder bould....uh,I guess that don`t apply.

I get mucho bugo between my windshield and gutter with the 69-72s,too.One thing I`ve noticed on the 88-98s is I catch alot more bugs (and more big ones) as well as experienced and seen alot more cracked windshields and I figured it was due to the more aerodynamic design.So...

[69TowRig]

Wind resistance is a function of frontal area, drag coefficient, and speed. Your frontal area has not changed, your speed has not changed, and I'd bet that your drag coefficient barely budged. I think it's just a matter of your mind playing tricks on you.

The flatter, taller late hood does not "throw" the air over the truck, if it did then you would have a vacuum in front of your windshield. What it does deflect (and you have observed) are solid objects like bugs and etc up higher so they don't hit the windshield as much as you drive through the air.

[LONGHAIR]

Originally Posted by 69TowRig

Wind resistance is a function of frontal area, drag coefficient, and speed. Your frontal area has not changed, your speed has not changed, and I'd bet that your drag coefficient barely budged. I think it's just a matter of your mind playing tricks on you.

You frontal area has changed.....it may not have been reduced in size, but it has sloped back quite a bit. (Change)

Originally Posted by 69TowRig

The flatter, taller late hood does not "throw" the air over the truck, if it did then you would have a vacuum in front of your windshield. What it does deflect (and you have observed) are solid objects like bugs and etc up higher so they don't hit the windshield as much as you drive through the air.

Cowl Induction hood? Taking advantage of the "low pressure area" in front of the windshield. (vacuum?)
Deflect objects? in the air....up higher?
That whole statement seems to contradict itself? It may not make it totally over the roof, but it has to be higher.
As pointed out earlier, that is the concept behind a "bug deflector" and why the "sun visor" manufacturers tell you not to use both together.

[BigSky71]

Originally Posted by ChevLoRay

I wish mine was back on the road so I could experience some buffeting and wind noise.....

Well true, at least my truck is back together and I get to drive it...

One test I could do would be to get my buddy to bring out his mostly stock 68, then drive the same section of road in both trucks and see if I can tell the difference.

[texanidiot25]

Give me a day or so, and I will post some stuff that will answer a lot of the questions...

It explains the aerodynamics of blocky vehicles. You'd be surprised what the effects of rounding corners on a brick can be.

[BigSky71]

Originally Posted by texanidiot25

Give me a day or so, and I will post some stuff that will answer a lot of the questions...

It explains the aerodynamics of blocky vehicles. You'd be surprised what the effects of rounding corners on a brick can be.

I look forward to it. I saw a show in recent years that showed how some guy back in the 1930s installed his car body backwards because it was more aero dynamic that way. This was a thirties sedan looking thing with a fairly flat rear [now front] that had rounded corners. The flat but round edged rear was more aero than the long hood, fenders and grille they reported...

[Longhorn Man]

What it does deflect (and you have observed) are solid objects like bugs and etc up higher so they don't hit the windshield as much as you drive through the air.

Unless the stones and bugs are hitting the hood, then the stones and bugs are being carried by the air... which is deflected,... up over the cab a bit better.
Basicly, you just repeated what i said, after saying I was wrong.

[IvelDesigns]

you can notice a difference?? really??

granted, i didn't drive my truck for 3 months between swapping the 69 clip for the 68, but i haven't noticed any difference in how it feels going down the highway. and i take 2 hour drives in it on the interstate fairly often.

I will say that i have noticed more bugs on the bottom side of the drip rail though.

[BigSky71]

Originally Posted by IvelDesigns

you can notice a difference?? really??

granted, i didn't drive my truck for 3 months between swapping the 69 clip for the 68, but i haven't noticed any difference in how it feels going down the highway. and i take 2 hour drives in it on the interstate fairly often.

I will say that i have noticed more bugs on the bottom side of the drip rail though.

I think I can tell a difference, but my truck was apart for almost three years.

I maybe overly sensitive though because I rebuilt the entire truck and thus listen for any noise or symptom that I didn't put it back together right. It bothered me enough that I pulled the tranny and had it rebuilt this spring thinking it was slipping. It drives the same, but shifts better now. Tranny needed to be done anyway, it was the only major mechanical part on truck I didn't rebuild during the resto.

I have put 1,600 miles on it now though and am starting to relax, lol... I just didn't notice the truck slowing down in shifting winds before and the wondering if anyone else felt the that difference between the different hoods. I won't even bring up any aero difference questions about going from long box to short box , but I did that too.

[72-c20]

any change to the rear end ratio?

[BigSky71]

Originally Posted by 72-c20

any change to the rear end ratio?

Yep I am now running 2.75s in my Ford nine inch, but I had the same ratio as stock in there last fall [3.55] and it did the same thing. Maybe I am too far down in the torque curve though with the 2.75s. The motor is the stock 350 rebuilt with the edelbrock stage one or whatever its called, stock iron heads, Performer intake, edelbrock carb, 1-5/8" headers, and two Flowmaster 40s. I figure its shy of 300 hp but that's a guess.