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16 Aug 2008, 17:08 (Ref:2270162) | #1 |
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Flat Floor and managing heat
I'm trying to fathom how I can modify a front engined production sportscar with the exhaust routed under the floorpan to a flat floored configuration.
The major obstacle is the heat generated by the exhaust system. I am toying with the idea of constructing an aluminium floor which would be flat but I hope it could serve as a heatsink for the exhaust system. Is this a very silly idea I have had late at night and how could I calculate the coling effect as the underside of the car will hopefully have laminar airflow over it. Does anyone have any experiences how similar problems have been solved? |
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16 Aug 2008, 17:17 (Ref:2270165) | #2 |
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I have used thermal transfer calculations to work out the cooling effect. I am more concerned about exacerbating the heat problem in the cockpit.
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16 Aug 2008, 19:35 (Ref:2270231) | #3 | ||
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Hello Fisher.
Nice topic/discussion point, and a problem I also have to find a solution to. This is obviously a really common thing to come across as a high number of GT1/2/3 cars are front engined and utilise a flat underside. From what I've seen most of those teams have less to worry about as they terminate their exhaust system before the rear wheels. I don't know what car you're running, but maybe you could look at doing that as one option? Failing, or supplementing that solution I've thought of two possible routes we may take outself. The first is to add louvres to the underside, along the length of the exhaust system. You're obviously thinking about adding a flat bottom for aerodynamic reasons, and the louvres option could work well with that. My theory is that by allowing heat to be transferred to the air under the car you're lowering the pressure. That's of it according to the simple fact that higher temperatures = lower pressures. In doing this you will be reducing lift, or increasing downforce depending on how effective your car bodywork is. The second idea I've come up with is to channel air along the tranmission/exhaust tunnel from the front of the car. On our car this could be easily done as the engine is tiny (Mazda RX-7.) If you make sure the air stays neatly ducted to the rear of the car you could be reducing aerodynamic drag by allowing it to escape into a low-pressure area. Although I'd thought about these solutions before you started this topic I hadn't really planned to implement any of them, having given aerodynamic efficiency priority over what is mainly comfort. I will probably put these into practise if exhaust temperature built up proves to be a problem. Our motor is turbocharged so it could be a real possibility.. Last edited by Alex Hodgkinson; 16 Aug 2008 at 19:38. |
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17 Aug 2008, 09:56 (Ref:2270410) | #4 | |
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14 Nov 2008, 21:28 (Ref:2335059) | #5 | |||
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So having hot gases under the car would increase the pressure under the car decreasing the effect of the diffuser. Am i right? |
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15 Nov 2008, 20:46 (Ref:2335435) | #6 | ||
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In a known volume (sealed system), yes. In this case? Who knows! Like you I've only got school physics to fall back on, so I can't decide if the heating of the air will cause it to expand, 'spill' out the sides and thus lower pressure or if the aerodynamic effects will trap it under the car, increasing pressure. Any aero guys around?
In any case, I'm guessing - purely guessing - the effect will be minor. I mean, it will hardly heat the air at all due to the shear volumes involved. |
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16 Nov 2008, 11:16 (Ref:2335723) | #7 | ||
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My experience is with a front engined car that I modified to have a rear radiator. These cars are notorious for excess in-cabin heat, often attributed to the exhaust, but without the front radiator it became quite chilly.
Ultimately, the rear-rad experiment was not a success, but I'd suggest striving to vent the hot air from a front radiator somewhere other than under the car. Then the remaining under-car airflow will be adequate to deal with exhaust pipe heat alone. John |
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16 Nov 2008, 13:45 (Ref:2335794) | #8 | |||
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an Extractor hood to vent the hot air going though the radiator to exit out of the hood. Or buy some plastic or Carbon fiber vents and cut holes in the hood behind the radiator area and put the vents in the hood too allow the hot air to escape. also there is some very good heat shielding matting that you can put under your car or up against your fire wall and transmission tunnel to shield heat. The other thing could be to put new ceramic coated headers on. This helps move the heat out the exhaust pipe vs radiate out from the pipe. Old headers should really not be ceramic coated so new headers would be needed. There are many ways to cut heat in the cabin down. |
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17 Nov 2008, 22:51 (Ref:2336683) | #9 | |||
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14 Jan 2009, 09:02 (Ref:2371182) | #10 | |
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NO! Don't heat wrap the exhaust horrible, useless stuff! I have found recently this coating from Zircotec through Thorney Motorsport which is ceramic and is brilliant! It is only 350 microns thick so for packaging it's brilliant as well. Check out their site to fill you in, don't wrap though you'll only end up doing it in another 6 months or so.
Lots of benefits. |
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14 Jan 2009, 10:45 (Ref:2371230) | #11 | |||
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17 Jan 2009, 21:09 (Ref:2373498) | #12 | ||
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17 Jan 2009, 22:07 (Ref:2373533) | #13 | ||
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Not for different configuration as such. More stuff like (in my case) altering the downpipe angle to miss a revised passenger footwell, adding two extra joints to allow easier assembly, changing the length/angle of the final section before the silencer to accommodate a different silencer box diameter, adding on a boss to fit a lambda sensor. That sort of stuff. But I guess it only really applies if you constantly fiddle and modify like I do, many will get a setup and keep it that way, so ceramic coating would be a better way to go :-))
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