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Impact Bumpers
craigt

Front Fogs

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How are front fogs mounted? Is it a special valance with cut outs or are they just bolted through the valance?

Thanks

Craig

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Depending on year. They're either surface mounted or within a recess/cutout.  Eitherway if you remove the valance from the car the fogs come with it.

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This thread is as good as any to ask:-  if you remove the front fogs from the car, what do you need to do to the switch/wiring for the rear fog still to work?  As my rear light will only come on if I turn the front fogs on first (as standard I presume).

Also, is it still good practise to remove those rusty old acro-prop front bumper tubes (as per Davids pics above) and fit lighter 'alloy'? crush tubes ?  They look like they'd need some good heat to get those off!

I'm going RS/RSR front look, hence the questions :)

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I didn’t do anything with my wiring when I put the flat valence on. Just tied the front fog wires out the way.

My bumper tubes came off pretty easily...

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Thanks Doc, did you fit the lighter crash tubes? Are they same length?

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Yes: I had some custom made in aloominum. Took a front and rear original in and said to make lighter ones the same length etc. Saved a chunk of weight per corner :signs118:

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4 hours ago, Dr Rock said:

I didn’t do anything with my wiring when I put the flat valence on. Just tied the front fog wires out the way.

Same here when I put my fg bumpers on

Mark

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Slightly off topic but in order to replace my heat exchangers and relevant exhaust pipe work, I removed my rear bumper complete with shock-absorbers, heat-shield et-all which I had not held in my arms for some years. Bl@@dy hell, wish now that I had weighed it as a matter of interest as I was surprised at how bl@@dy heavy it was! Either I was getting weaker or my rear bumper had put on weight! Easily see why folk go for the fibreglass option, there is a serious weight problem hanging out the rear of the car beyond the engine! Completely unnecessary unless one factors in the car-park cowboy’s and the engine protection from a more serious impact.

David.

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any ideas on where to get the alloy crush tubes? Tried Matts 911 but he only lists the stock versions that I can see.  Think it was SVP used to do them.  Google search drew a blank, unless I am describing them wrong?

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22 minutes ago, MarkJ said:

any ideas on where to get the alloy crush tubes? Tried Matts 911 but he only lists the stock versions that I can see.  Think it was SVP used to do them.  Google search drew a blank, unless I am describing them wrong?

Hi Mark,

Presuming you are going for a fg bumper, why do you want crush tubes?

Your new crumple zone will fail before the crush tubes are used.

Remember me at Brands in the wet a few years ago? :(

IMAG0987.thumb.jpg.c486fc59c74be07b92bbde41109054d4.jpg

It polished out OK

 

Mark

Edited by SilverWT

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26 minutes ago, MarkJ said:

Think it was SVP used to do them. 

That’s why I had mine made.

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but don't the crush tubes act as a shock absorber/ front impact protection to the body? ie they would take up the slack or bounce something off before crumpling the car body (velocity dependant!), I know they can only do that locally to the two front corners but still in my head it feels like a bit more protection to the shell.

My current stock looking fg bumpers front and rear are both connected to the shock tubes. The bodywork place bonded a bracket to the inside of the bumper that connects directly to ends of them, so that's another reason to keep them.  How would you connect the fg front bumper/valance without them? I should have taken a photo when I was underneath just now!  If I can safely junk the front heavy tubes I would happily do so.

Its no deal breaker to be honest, just thought its another of those 'while your in there' jobs to save a bit more weight.

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The steel crush tubes aren’t very heavy. Shocks, yes but the crush tubes aren’t that heavy. What’s the weight saving on alloy ones? Surely it’s no more than 300g a corner is it? 

Here you go 225g difference. http://forums.pelicanparts.com/porsche-911-technical-forum/801697-rear-crush-tubes-bumper-bellows.html

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3 hours ago, MarkJ said:

but don't the crush tubes act as a shock absorber/ front impact protection to the body? ie they would take up the slack or bounce something off before crumpling the car body (velocity dependant!), I know they can only do that locally to the two front corners but still in my head it feels like a bit more protection to the shell. 

Not with a fg bumper, the bumper itself will give some bounce before crumpling. It's all a bit academic when you look at the bumper height of even small modern cars, they will all go straight over the bumper and up the body anyway. Only a concern if you plan on hitting a tree, brick wall, or the pit lane wall.

Mine has "L" shaped ally brackets and they crumple as well as a crush tube, are lighter, easier to make and easier to fit to a bumper. They bolt to the fixings that would have held the half round clamp for the tubes. 

And here is a diagram I prepared earlier....

DSCN4094.thumb.JPG.7bff6f754bb79d3e4df812f6c92b01d7.JPG

 

Mark

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those are the stock items SP.

225g a corner saving for the alloy variants hardly seems worth it, thanks Northy.

Thanks for the bracket diagram Mark, if the bodyshop struggle using the bumper shocks to fix too,  i'll get them to fab up similar to yours :)

 

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FYI

Weight saving over stock front bumper shocks:

Stock front bumper shock : 1392g

Steel crush tube: 650g

Saving over stock: 742g per side

 

 

DSC00361.jpg

DSC00362.jpg

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That's a bit better.  So why would one IB model/variant have an impact pipe instead of an impact absorber? The Pet diagram just shows both as alternatives.

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think mine has absorbers at the front, need to re-look.  Surely by nature of being called impact bumpers, they would all have been fitted with a shock absorber?

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Blame Porsche UK.

The sachs telescopic shock absorbing bumper mounts were a standard default for most UK cars. A box could be ticked to remove these and get the basic crush tube bumper mounts but you had to ask and know what you were asking for - same applies Fuchs wheels and sunroofs - default for the rest of europe was 15 inch an no sunroof.

From '74 onwards Porsche had the idea of making 'world cars' - one car to fit all markets. The impact bumper design was a result of the US 5 mph impact test. 

Other european manufacturers choose to offer different spec cars to suit the designated market. A good example of this would be late 70's BMW's. US cars had awful front and rear ends. UK / euro cars were fitted with slim bumpers. 

 

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USA cars only had the shock absorber type, "impact bumper"

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