i am currently working on a flat underbody and rear diffuser and am just wondering what you guys think would be the best material. it needs to be something that can cope with the heat of the exhaust which will be pretty close but will be side exit on the left hand side behind the door. i was thinking 1.5mm aluminium sheeting with NACA ducts to get some cool air to the gearbox exhaust and diff. any thought or suggestions?

 

I think there are some examples in a thread about underbody aero. Search for diffuser and it should pop up in the list.

 

I used ABS but it wasn't a full underbody, just a long front undertray. The rear of it came within ~2" of the downpipe and I never saw any heat damage to it.

 

I'd do sheet aluminum with a skeleton structure.

 

Has anybody done a full flat underbody in a full time racecar for any period of time? If so were there any heat issues and how were they dealt with? This is my main concern, don't really want to cook the diff or gearbox.

PS, I'm Dan's (mr2daj) business partner. We run an MX5 specialists in the UK; AK Automotive. There is very little info on this over here, in fact I think we run the only rturbo'd MX5 racecar in the UK.

 

Have you looked at the undertray of the DB9R? There you can take some hints on how it can be done (sorry, can't find the picture I have in my head).
A complete flat undertray, besides the underside of the tunnel which is a separate peace with various holes (probably several different ones during development or for different conditions).

The Miata is not much different, it's just the tunnel that needs some ventilation, how much depends...
A complete flat bottom with a fully open tunnel would be a real improvement to the stock situation.

 

What race series matey?

 

We run the turbo'd car in the Northern Sports & Saloons, and we also run a successful car in the MA5DA.

I think we've spoke over on MX5Nutz before.

 

Copy what Lotus does on the elise. You might even be able to buy elise parts and cut them to fit the miata. I figure finding elise parts is probably easier on your side of the pond...

 

i think it well be easier and more cost effective to make custom parts. the elise is also rear engined and therefore has no exhaust heat to contend with underneath. i think we are going to go with ally just not sure on weather to use thin stuff with strengtheners or slightly thicker without. may be a little trial and error over the winter to see what works best.

 

Looks like aluminininium.



From this thread:
https://www.miataturbo.net/showthrea...light=diffuser



And this one has a Lotus Elise diffuser:


From this post:https://www.miataturbo.net/showpost....6&postcount=58



And this looks like plastic:


Other pics here:
https://www.miataturbo.net/showpost....7&postcount=98


I used the search button.

And there are many threads on front splitters and materials/design/attachment of them as well. Most come back to the centerline of the front wheels or further.

 

i would say use aluminum. use naca ducts to take the heat away.

 

Damn you, I was going to say that. :I

I don't see why having a few NACA ducts on the undertray along the PPF couldn't hurt.

 

I'm actually really digging this one... If my other plan to use an FC3S diffuser falls through, I might end up going this route.

And to answer the OP's question, as Savington said, sheet aluminum with a skeletal structure. Add some well placed vents. Profit.

 

spoke to my exhaust builder today and he reckons its a bad idea. he suggests leaving gaps along where the exhaust is otherwise the exhaust will overheat. he is no idiot either and builds a lot of exhausts for high end race cars and touring cars. i wonder though how these holes will effect how the air passes under the car and possibly negate any gains that would have been made?

 

Dump the exhaust out of the fender... Problem solved. Haha

 

no can do. MSA rules state the exhaust must exit behind the driver. it already exits just behind the left door (passenger door over here). also i could see noise being an issue lol. limited to 105db.

 

Haha! No worries, I was partly joking. As you said, it really depends on the class you are racing in. If venting were setup properly for this, I don't see it being a real problem with sealing up the underside of the car though.

 

My rear diffuser is aluminum:



Previous owner originally had a full aluminum under body tray, but the heat build up was intense so it was removed. The pieces under the control arms remain:

 

place some NACA ducts in the front section of the underpanel, and place some louvre vents in well located areas to relieve exhaust temps.