My friend and I are building a rear diffuser for my '93! I know we won't see much of a difference for normal driving, but maybe if we do this right, then I'll see better mpg's (1 or 2 at the most) at speeds over 60mph.

Listen, this is our first time doing something like this. I know it looks pretty bad, but we haven't started trimming it and making it look nice. We are also aware that the fins don't stand up straight, and we'll address that before we start laying glass down later today. And we never had access to really big pieces of cardboard, so we had to make due with what we had.

Apologies for the bad cell phone pictures:

Here's where we'll be mounting the back of the diffuser.


That's where this used to hold the spare tire:


Here's the base of the diffuser:


Here's the "finished" prototype.


So yeah. Any tips? I'm about to head back to the store to get some more fiberglass cloth and hardener. We hope to have this finished by next weekend at the latest. We'll do MPG tests and stuff next month.


-Jay

P.S. If you want to go look at the entire album where I'll be adding all of the pictures, here you go: http://razzi.me/a/22303

 

Props for the effort


Keep us posted on your progress.

 

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Well I made my first stupid mistake today.

After we finished for the day, I took off my glove, which was covered in resin and stray fibers. Then after I had it off I absent-mindedly started cleaning up our mess. During the process of cleaning, I had gotten resin all over my bare hands. Thankfully google is a thing, and my friend was able to google "How to get fiberglass resin off of your skin", because soap and water wasn't working and my hands were burning pretty badly at that point. So after using a full bottle of nail polish remover, I got almost all of it off and it's not burning anymore so I guess that's a good thing. Though I now can't grip anything for too long. If you've seen National Lampoon's Christmas Vacation where Clark's hands are covered in sap, you'll know what I mean.

So I'd say we're off to a good start.

I don't have any pictures of the progress we've made with the glass, but I'll update as we go along. I'm going to do some more work with finishing the glasswork this week, and my friend is coming back over friday and staying for most of the weekend so we can get this finished and painted as soon as possible.

 

Use Dot 3 brake fluid the next time you get resin of your hands, works best if done right away.

 

Cool project and I hope it goes well for you.

 

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Acetone the for resin clean up of hand and tools. Do not use on plastics, they will melt...Keep up the good work....

 

look forward to seeing the progress and especially the MPG reports.... subscribed!

 

Looking forward to seeing the final results.

 

What kind of tape did you use to hold the cardboard up and did you fiberglass over that? What kind and what weight of glass did you use and how many layers? What resin/hardener did you use?

Looks Good! Cant wait to see the results!

 

We used packing tape. And honestly, I couldn't tell you the weight, it's just your standard run-of-the-mill 3M Fiberglass mat and resin. I got it at Home Depot and when I ran out, I got more from my local hardware store. So far I've got about $60 into all of this. That includes resin, brushes, masks, gloves, fiberglass, tape, sandpaper, and paint.

 

Thanks for the info. You can fiberglass over packing tape? Was the fiberglass woven?

 

I'm not sure if you can. I'm doing it though.

I know you can't glass over duct tape.

Oh here's the cloth I used, the stringy stuff (I'm using real technical terms now):


I also have this kind, but I haven't used it, and I'm not sure if I will.

 

Ok cool! Thanks for the info. I have been wanting to make my own diffuser but school got in the way. Now I graduated, and have a job so I want to try and get it done!

FIY the bottom fiberglass pic is woven fiberglass and is used to make the item more stiff. You might need to use it so that your piece doesnt flex with all of the suction from the lower pressure

Here is the link of my thread if you are interested: http://forums.corvetteforum.com/c4-g...-diffuser.html

 

Your thread actually gave me the inspiration to do this! I've been following it since I joined the forum back in September. Crazydrummer14 and VetteDaddy's diffusers really pushed me into wanting to do this.

Funny thing is, I'm actually doing this for school!

 

I thought I'd add something in here about the effects of the undercarriage of the C4 on the efficiency of the diffuser and top speed...

I talked to Tommy Morrison when they were doing Snake Skinner testing...

Adding a belly pan to the car added 15 MPH to their top speed, and added significant stability on the top end.

So, aero is not just one thing or another...it is the entire package working together as a unit.

When I finally get started on my '92 ZR1-bodied race car...I have to replace the entire floor of the car due to rules stating metal MUST be in place under the driver & passenger. I plan to rework the floor and add a full belly pan to it (front to rear) out of aluminum.

I kinda like the looks of this diffuser...



Not very practical for a street car, but plenty good for a real race car.

 

Yeah, a rear diffuser on a street car will be mostly for appearance. I don't expect much, if any real gain in MPG. Note in the photo above, they still have cutouts in the rear bumper for releasing trapped air in the rear bumper, unless there are radiators in there and they are only for cooling.

1991ZO7, does that car have a full belly pan? And that's exactly how I wanted to redo my exhaust, but chickened out (body work).

 

I don't know...I assume it does. It's a Japanese C4 ZR1 that was raced...I found it in one of the other diffuser threads.

Hard to say if it had radiators in there or not...it is entirely possible.

Beauty of their execution is the exhaust is very straight...for maximum power. Not too sure how well those bullet mufflers worked at keeping it "legal" for noise purposes or track restrictions, but it sure looks cool

 

I wanted to make a full belly-pan from the cats back but I didnt know how make it work with the exhaust... My only problem would be that the exhaust gets hot and I am unsure if the fiberglass would be compromised and maybe even catch fire due to that...

I think a full belly-pan would help on the streets... Think about highway driving going 65-70mph... I bet you would see better mpg's and hold the road better especially on windy days...