sgraber
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| posted on 20/11/06 at 04:21 PM |
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Progress Report + Rear end advice - Lower valance mockup
Seeing Andy's rear end (ooer!) gave me inspiration to take some time to cover up the gaping hole at the rear of my car.
Over the weekend I was able to mock up a lower panel (in black), install the license plate and re-route the exhaust including the new supertrapp
style muffler, which is only 8" long and mock up the center console.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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RazMan
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| posted on 20/11/06 at 04:35 PM |
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Can't quite see enough detail to get the full effect Steve, but from what I can make out it is looking good.
Regarding the Supertrapp silencer, I am curious as to how you will handle the 'radial' gases without contaminating bodywork. I used a
Supertrapp on one of my trail bikes in the '80's and it made the whole back end rather sooty.
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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DIY Si
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| posted on 20/11/06 at 04:35 PM |
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Are you going to have a rear diffuser at all? If done nicely they fill quite large holes and help you go faster too! Is that super trap silencer the
only thing that fits or that you have to use for some reason? i only ask, as I think they do a good job of silencing, but at the cost of lots of flow.
All the exhaust has to come out of a few small holes rather than 1 large one, and as such they tend to sap power. All from what I've heard/ fond
out for myself, as others may have different experiences.
Oh, otherwise, looking very nice indeed sir! 
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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sgraber
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| posted on 20/11/06 at 06:06 PM |
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The space for exhaust is very limited. This was the only 8" unit that fit the location. I will have to see what happens with the radial gas
outflow.
Also have to experiment with running an open pipe vs the supertrapp as far as power sap goes.
no diffuser at the mo, but a redesign of the rear should allow more room for it.
My picture taking was poor and i'll try to get a better photo today. (edit - see photo attached below)
[Edited on 11/20/06 by sgraber]
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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RazMan
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| posted on 22/11/06 at 12:45 PM |
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Steve, apparently Supertrapp do a kind of shroud to direct gases in the conventional direction.
(Pic on the right)
Hope it helps
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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sgraber
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| posted on 22/11/06 at 03:18 PM |
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quote:
Originally posted by RazMan
Steve, apparently Supertrapp do a kind of shroud to direct gases in the conventional direction. (Pic on the right) Hope it helps
Yes it does. I was thinking about doing a half-shroud above the outlet. Essentially the same idea as the protection-shroud around my angle grinder
except with the properly shaped and sized shroud. Seeing your image validates the thought nicely. Thank you. 
Any opinions about the shape of the lower valance?
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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RazMan
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| posted on 22/11/06 at 03:49 PM |
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Oh I see you put up a pic - sorry I missed that.
The lower valance looks good and covers the chassis well but how about a diffuser in there and some mesh.
My Photoshop skills are pretty crappy but here's a rough idea. Just my personal view of course and not meant as a criticism
 
Rescued attachment Scraber1.jpg
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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DIY Si
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| posted on 22/11/06 at 03:50 PM |
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There's 2 ways, I think, of doing that back centre bit. Either a bit of mesh and a diffuser of some sort (well you might as well fit one), or I
quite like the exposed look, as per the back of the old porsche Le Mans cars, where you can see a fair bit of the internal mechanics/gearbox/chassis,
that kind of thing inside. Could always just design a diffuser that covers the hole up and closes the bottom edge to the rear face, or do you need to
have a hole/mesh part for cooling/air flow issues?
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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sgraber
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| posted on 22/11/06 at 05:36 PM |
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I need to have that back area open for cooling issues. We get pretty toasty here in the Southwest USA during the summer months. But I would like to
have the back finished off nicely so people don't see the frame. I don't think the back end of my frame looks good enough to show off...
The mesh is a good idea and I also like the idea of using the round perforated hole mesh. Think speaker grille cover steel with the little holes. I
think that can be massaged into curved shapes but will still hold its shape well once formed. I have a hi-tech gloss black paint donated by
rust-bullet that I want to use on it.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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DIY Si
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| posted on 22/11/06 at 05:43 PM |
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Should look good. Sounds like it should be fairly discrete, but shiny, so you know it's there. Just had another thought. Would it be possible to
have a diffuser that curls up but leaves a gap between itself and the rear valance? That way you could hide what you to, but still have the air flow
sucking through the engine bay, due to the low pressure created by the diffuser.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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sgraber
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| posted on 22/11/06 at 06:31 PM |
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What length should a diffuser be in order to have any effect at all? Let me tell you what I have done right now so you can advise.
The bottom of the car is flat from the front all the way back to just behind the seats. with 5" ground clearance. Then it slopes gently upward
1.5" over the next 34". That's from behind the seats to the back edge of the frame. with 6.5" ground clearance at the rear of
the chassis. I have a flat bottom panel for this too. From the rear of the chassis to the edge of the valance I just made is an additional 6"
and I have a 45 degree slope over those 6".
Will that do anything noticeable?
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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DIY Si
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| posted on 22/11/06 at 06:43 PM |
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It should work. Any wide enough and flat under tray will help, as long as it slopes up towards the back, so yours should do fine. If you want more
effect, you can put ~4mm rubber strip round the edge of the underside of the car to hold the air in and create a greater suction effect. The diffuser
wants to be right at the back (obvious really) and is supposed to slow the under car air back to a normal (ish) speed to allow what ever spoiler
effect there is to work better. The shape under the car should be something like an arrow shaped wedge, with the back being both higher and wider than
the front, as it needs to be greater in area to lower its pressure.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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gttman
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| posted on 22/11/06 at 07:47 PM |
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Aero is hard to predict unless you are experienced with it.
Having a flat floor may not be the best option as if the engine bay is open it may promote the air to expand underneath the car into the engine
bay.... I'm not saying it will, just that it might.
Personnely I am planning to fit as big a diffuser as possible.... but I still worry.
Andygtt
Please redefine your limits
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DIY Si
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| posted on 22/11/06 at 07:55 PM |
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I assumed from what he said that the bottom of the car is near enough sealed. Or at least has a continuous full width floor.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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gttman
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| posted on 22/11/06 at 08:43 PM |
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I agree completely with all that you said, I'll be adding the lip to keep the air under the car etc......
But sometimes people assume panneling the engine bay in a middie is best and sometimes if its not going 300kph it is the wrong assumption.
As an example an Ultima doesn't have the engine bay pannel'd and it's not a recomended mod either.
Just more stuff to consider.... 
Andygtt
Please redefine your limits
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DIY Si
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| posted on 22/11/06 at 08:50 PM |
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Ah, fair enough, I understand what you meant. True, just panelling stuff in isn't always the way forwards, as the rest of the car, or the shell
shape can make any changes silly or for the worse.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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sgraber
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| posted on 22/11/06 at 09:10 PM |
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Nice one Andy! Way to throw the 'unknown quantity' variable into the mix! 
So I suppose that means I'll just have to test the crap out of the car with and without the engine floor panel, with and without the diffuser,
etc...
Oh shucks, I have to drive the car to do that. How terrible! heeeee heeeee.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
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DIY Si
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| posted on 22/11/06 at 09:14 PM |
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I'd say just fit them and make sure the floor is completely front to back where possible. Have a look at the elise and similar cars for ideas of
what the diffuser should look like. Your car should be fairly similar.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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