dogfish246

Hey, I was wondering if anyone has ever made or bought a rear diffuser for the C4? I see they have them for the C5s and C6s and thought about making one for the C4.
I was also wondering if anyone had any experience with splitters for the front? Another downforce application...

Anyone know about C4 downforce or aerodynamics for the C4? Does anyone know anything about the correct way to make a diffuser so it will work properly?

Lets see some pics if possible!

Aardwolf

I've been planning to make one for mine, when time allows. I don't expect a big gain but a little help adds up, also partly for filling in the area where the spare tire was. In your first picture you can see how the whole under body is aero. Adding just a diffuser without the rest isn't a complete system.

There was a thread in the C4 ZR1 section with pix of a diffuser being made and several others too IIRC. There was also just a topic in the race section about making a diffuser. Check those threads and also get a decent aero book.

Some pix I saved:

jeffp1167

Used to be a company that made them for C4's that came in a complete body kit. Thought it was sold through ecklers or one of the vette suppliers. Don't remember the company that made them though but was a nice setup.

aci but they refer to it as a tunnel

dogfish246

Thanks for the pics. I was thinking about making my own that would attach to the spare tire carrier. Make it out of fiberglass and paint it black so its not really noticeable. Im not looking for major improvements but I want it to be functional. Your first pic is cool. Did you make that? What did you use?




Yeah, that is the only one I have ever seen for the C4...

tehcarguy

Shouldn't be too hard to make a rear diffuser if you have the right skills. That greenwood kit That jeffp posted up is more for aesthetics than aerodynamics. I've actually seen a splitter for the front of a C4 that bolts in place of the spoiler and had reinforcements bolted to the bottom of the front bumper. However, these aero devices don't really work unless you have them as close to the ground as possible.

Aardwolf

I forgot to comment on the splitter, there was just a topic in the race section on that too.

http://forums.corvetteforum.com/auto...-race-car.html

As for the front end my friend has the mold and he has them made as ordered.
He also got the hood and the wing for me.
He knows his shet when if comes to corvettes.
His name is Mike and runs Mike Poupart Motorsports.
You can contact him at (504)472-0400
He can get you any info on the front end, hood or the wing that you need.

c4cruiser

Greenwood was the company. You could get different levels of the kit; rocker panels alone, spoiler alone, rockers and diffuser, or all of the pieces. IIRC, the Greenwood diffuser fit over the spare tire carrier, but it was a royal PITA to get to the spare. The diffuser used something like Dzus fasteners to hold it in place and you had to remove the entire piece to get to the spare.

astepup

Ok...I really hope I'm not the only one on CF that has no idea what a diffuser is for. I gather it's for a racing application. Does it somehow add downforce to the rear end?

astepup said that

dogfish246

Yeah, here are the basics that I have learned. When comparing air that goes over the car to the air under the car (split at the front of the car), the faster the air moves the more there is going to be a low pressure. So if the air that travels over the car moves faster than the air under the car, this will generate lift (like an airplane wing). This concept is know as bernoulli's principle. What we want for downforce is the air below the car to move faster than the air that goes over the car making it stick to the road (low pressure under the car). The diffuser allows the air under the car to move faster (smoother) and then when it exits near the exhaust the exhaust gasses help pull air from under the car at higher RPMs. Thats the basics...

I dont race my car but I am gonna need something to get me some attention at shows this year so I am thinking of fabricating my own diffuser out of fiberglass. I want to make it a bolt on to the spare carrier so it can be taken off if needed...

Thanks for all the info guys!

tehcarguy

Yes, it is mainly for racing applications. A diffuser works by lowering the pressure underneath the car. In a normal car there's all kinds of stuff just hanging underneath the car which creates pressure. On a race car, people usually cover all this up and add a diffuser. This helps to make a huge amount of downforce.

dogfish246

Do you know if it increases the drag coefficient substantially? I read somewhere that it was the most efficient way to create downforce and not make too much drag.

tehcarguy

If you cover up the entire underside of the car, then yes it reduces drag quite a lot.

dizwiz24

this is a great thread. keep it up. ive enjoyed reading it and learning something new.

dogfish246

OK, so if I start designing my own diffuser what are some key parts of the design?

So far I am thinking 4 or 5 fins that are about 5in high and are the length from the rear differential to the bumper. The diffuser is going to seal pretty much the whole rear so its going to cover the mufflers and gas tank. Im going to use a dynomat or something to prevent excess heat from destroying the diffuser. Its going to slope pretty much the same way the rear tire carrier slopes.

Any other points or ideas? Is it a good idea to cover the mufflers? This is a daily driver and not a track car.

crzydrumer14

I've been planning thinking of doing the same thing lately. Might start this project tomorrow after I wash my car... ha... If its not raining.... I'll keep you posted 'dogfish'

-Will

dogfish246

Definitely keep me posted!!!

School has been keeping me too busy to try and make a cardboard fab but I was thinking of making it go from the cats back to the exhaust so the whole bottom is smooth and helps aerodynamics... Boost my downforce and fuel economy.

blr33439

I have the greenwood on mine. It looks good but probably has minimal airflow effect. Most of the diffusers that have legitimate performance gains go down to the ground which is not good for a street car. Can anyone say pothole.

SuperL98

The effect of a rear diffuser on the Coefficient of Lift (rear) and the Coefficient of Drag, vs the diffuser angle.

JrRifleCoach

Ok.....

hitmanpty

what????