Been reading a few posts re top speed / gearing etc.

And it is suggested that the C3 despite looking as sexy as hell, just ain't very good at slicing through the wind.

Anyone know the typical or individual Cd figures for the C3 range??

And is there ( for road use ) a benefit to the 1" to 2" nose down stance or is it better to travel level ??

My old Ford Granada was better at an inch nose down - was doing 33mpg ( UK gallon ) at 100mph. 2 litre - fuel injected OHC - basically a Pinto engine.

 

The C3 was notorious for nose lift at speed....thats why you see a lot of the vintage racecars with pretty big front spoilers.
A have a very good article in an old Hot Rod magazine about aero and the does and dont's for spoilers and stance...will try and find it and post it.

Nick

 

I just cut my front springs for an expected 1.5" to 2" nose drop. I'm guessing that will help with aero and MPG.

 

I think the C3 had over .5 Cd. For looking so "curvy" and "swoopy" it was a brick. A lot of that came from under the car - suspension, tires, exhaust pipes, etc. You can see a decrease in Cd when they added the spoilers in 78. Extending the front spoiler keeps some of that air from going under the car.

The C2 was really bad for lift. They described it as being like an airplane wing. They didn't do aerodymic testing on the C2 and C3 like they do now. A little lower front end will improve aerodymics and improve handling. That is why the C5 sits a little lower in the front.

 

I personally like the looks of a c3 when they sit level, but, I know from personal experience that the front end on my car would start to wander at around 130 mph. Of course, I don't do that any more.

 

The CD of of Formula 1 race car is around .75....of course they do it with power and downforce....

 

You can "thank" the EPA, for wind tunnel testing done on current cars. Reason for it of course to improve fuel economy

 

Is there any info on the C3's aero numbers and how the level affects the MPG? Like a lower front would get what kind of increase in dynamics and how much of an increase with MPG?

 

If its the underneath causing the problems - is it worth spending some time installing flat sheets of alloy to smooth things out ???

 

So much of the underneath on the C3 is open and catches air, especially the long nose/engine bay creating front end lift. You notice the C6's using front tray/difusers and venting air through the radiator and straight out the hood. There are dozens of things you COULD do, I doubt that any one or two will make major mpg differences.

 

I believe they started wind tunnel testing with the c3 vette I’m under the impression that is the reason they went with the bubble rear window in 78.

Post #15 and 25 for Cd:
http://forums.corvetteforum.com/show....php?t=1501506

I have a 75 with an 80 rear bumper stock FE7 suspension, 550lb front springs and a smaller diameter front tire. My setup rakes the car forward and I have not had a problem with the reported front end lift or light feeling. With this configuration the vehicle has traveled at a speed of 140mph. I also believe that this loose feeling could also be the result of a combination of a quick turning ratio and tolerance stack up in the sloppy factory power steering system. I have converted to manual steering which has slowed the turning ratio down somewhat because the tie rod ends were relocated to the outer holes on the knuckles and I eliminated the slop from the PS control valve.

 

I put a pacecar type spoiler on my '69 and it's behavior at 130mph was markedly improved.

 

According to the greenwood website they adjusted the rake of the body to the frame not changing the chassis angle with suspension.

Aerodynamics is Science, Going fast is Art.

 

I really doubt I'll be exceeding the 100 MPH much, let alone 140, so I am doing my front drop mostly for looks. I like the idea that it may change the aerodynamics and change how it acts at higher speeds. Maybe a little more stable.

 

1970 LT1 aerodynamic forces at 100 mph, Drag 280 lbs(includes tire
drag) lift front 230lbs, rear lift 55 lbs.
1970 Z/28 camaro, aero dynamic forces at 100 mph, Drag 350lbs (includes tire drag) lift front 325lbs, rear lift -40lbs

 

I have experienced the steering going 'light' at around 140mph and beyond so I am in the process of fitting cooil overs with adjustable spring platforms to lower the front end a little and increase teh angle of attack. Apart from all the underside openings, teh very height at which the air is split between over and under the car gives us a clue. All that front end sloping away from the bumper taking the majority of the air underneath the car.

A bigger front spoiler to divert the air round the side of the car helps, but I like the stock appearance, Dr Rebuild has a spoiler extension which will help as well, but they are not internationally friendly for various reasons. I have plans to get another std front spoiler to use as a mould and make an extended one, but thats some way off after the coil overs and new front wishbones, but I will get there.

Graeme

 

Yes, but have you seen the work involved in it? Plus you've got to be careful that the sheeting doesn't start causing lift. I know somebody who works for an F1 team & was talking to him about aerodynamics (the downforce on an F1 car is equivalent to it carrying something like a Rolls Royce on top!) as I was thinking about smoothing out the underside airflow. At first it started off well, by having a sheet that runs to the rear bumper cover while getting higher from the ground, you create downforce at the rear (due to lower air pressure caused by the wedge shape of the air), but then you may need to create a lot more at the front to compensate (or the front may lift). Then the scrappy, messy stuff around the suspension & engine bay could create turbulence/lift & you might not know about it until the car suddenly goes airborne at high speed. And then there's the cooling issues in the engine bay along with the problems of getting the air out of the engine bay that's come in throught the rad, etc, etc, etc, etc. I decided it'd be easier to just boost the power & lose some weight! Other major drag areas, that may be easier to sort, are the lips at the front of the T-tops & the body (whatever it's called) that sticks out at the rear of the side windows.
I'd say that it's better to drop the nose down a bit if you intend to do high speed work. The 80-82 front end creates a lot more downforce than the earlier ones (according to the books), especially if those excrutiatingly expensive rubber spoliers are in place, & I was surprised at how solid mine felt at 130mph. A relative of the wife was killed in an earlier Vette when the front end lifted at 140, causing complete loss of steering control, so I'd drop the front a bit if I was thinking of doing some high speed stuff. Better to scrape the nose on speed bumps than pull wheelies at 140mph


You had me worried with your Granada fuel economy figures for a moment as mine only does 17.9mpg, which is less than the Vette gets. It's the 2.8i V6 version though & it's getting a bit "tired" (& it feels nowhere near as stable at 130mph as the Vette does). Nice car though, it's a pity they don't make 'em like that anymore

 

I get 10-11 MPG right now, or at least teh last time I had it on the road. Can I expect much of a change based on only the 2" drop in the front?

I will also be adding a 200R4 when I do my motor swap this next spring.

 

 

I wouldn't expect a noticable change.