Skid guard / sacrificial plate

[WorldClassAccident]

I am getting a bit paranoid after losing the last exhaust so was wondering about fitting an aluminium/steel skid plate / sacrificial plate to protect the exhaust.



It shouldn't be too difficult to make as it is just a couple of simple bends. I probably wont do it as curved but it was the easiest way to draw it.

The idea is that it will get scraped rather than the exhaust. It is not a full on rally solution which is why I thought I might get away with aluminum but I think I would prefer steel as I could use thinner steel and compromise ground clearance less.

I was think 1mm or 2mm steel plate wouldn't compromise the ride height too much and would save the back box getting ripped off if a speed bump or something clipped the front edge.

Advice please on:

1) Steel thickness
2) Attaching it to the bottom of the car
3) Heat issues if there are likely to be any
4) Anything else you think I should know

[IanA]

Had exactly that problem and in the same place on my TVR Taimar V6.

I used 18swg steel but attached via u-bolts to the pipes. 1mm should be ample. Curved front and rear to encourage skidding rather than catching over obstacles.

No reason why you shouldn't add some cut-outs for cooling except curve the trailing edges of the holes so they can't catch either.

Did you know... the actual dimension for a given Standard Wire Gauge number varies with the material. Ally will be different to steel...

[WorldClassAccident]

Thanks Ian. I was planning the front edge sloping and the rear edge open so that should be ok.

Now about a full rear venturi tunnel...

[IanA]

Originally Posted by WorldClassAccident

...Now about a full rear venturi tunnel...

Now that's going to be heavy if done in 1mm steel. Find one on a local boy racer's Scooby, turn it upside down and take a quick splash mould. No need to turn it over when you've finished...

[WorldClassAccident]

if done in 1mm steel

A bit of cardboard and some resin...

...what could possibly go wrong :-)

[IanA]

Use the cardboard (covered in cling film) to laminate your own carbon-fibre reinforced sheet- then make your diffuser out of that. Such fun.

[y cymro]

I'm not sure if this is what Ian did, but rather than a floorpan mounted plate that will lose you more precious ground clearance, what about welding skid plates to the front and rear (if required) of the silencer

[WorldClassAccident]

Lack of welding equipment and ability prevents that option unfortunately.

I can live with 1-2mm loss in clearance as I have probably gained 10mm with the new pipe.

Just being cautious with my shiny new system

[y cymro]

Your exhaust looks good. In fact it's so shiny it's a shame you couldn't run it over the top of the car
Could the chap who fabricated the system weld some plates on in situ at a reasonable cost?

[WorldClassAccident]

Lots of googling and dull teleconferences and rain outside and lack of the new air filter arriving made me think about the aero effect of the bulbous rear end of the Z300S.

I reckon it would be quite easy to get a bit of glass fibre that it reasonably flat and cut it to shape so it bolts to the top of the exhaust brackets near the front and tuck up inside the rear of the car held in place with a few bolts.



Angle the front up a bit so it doesn't act like a parachute and we get a semi-venturi effect but more importantly we don't get the parachute effect we currently have. If you look at the Maserati 300S -450S and they had varying numbers of random looking holes cut into the back end.

This is as well as the steel bash guard.

Thoughts?

[IanA]

Go for it- the most aerodynamically efficient vehicles have flat floors.

[IanA]

Originally Posted by y cymro

...Could the chap who fabricated the system weld some plates on in situ at a reasonable cost?

With such a low car I'm surprised they didn't offer to fit skid plates. Worth asking them?

[Roadster]

I think it will tidy it up Nick
But as for aero benefits - your rear is based on a D type which looked aero but the bulbous rear doesn't let air separate cleanly.
As the decades went on they started cutting the end off blunt to aid the drag (kamm tails)- eg rear of cobra coupe, 250 gto gt40

[WorldClassAccident]

A quite crawl under the car shows a slight scrape at the back of the new box which it probably what I heard the other day.

My current design with dimensions is below.



Do you reckon it would be okay to just screw it direct into the floor pan?

That appears to be what has been done with the heat shield surrounding the exhaust.

Do you reckon I should make oval holes for the fixings so if it hits the ground a squidges sideways the fixings don't get pulled out?

Now off to find some 1mm steel. Does it need to be stainless?

[WorldClassAccident]

I will ask the exhaust place about skid plates before trying to do my own. Just to get an idea on price and how they would fir them.

Aero - Not trying for a Venturi tunnel or proper aero advantage. Just looking to stop all the air that is going under the car getting caught up in the big round empty space behind the rear axle.

I 'could'; do full aero but the shape of the rear does not lend itself and I don't want to ruin the period look with vents, splitters, diffusers etc

If you are interested in proper aero it is worth checking out this guys threads
http://www.bimmerforums.com/forum/sh...g-nomenclature


Cheers

[y cymro]

I agree with Ian. If you want it, why not. Of course, a flat floor to take advantage of the ground effect is a new idea which Maserati didn't employ in period. Here are the holes you mention


The chassis had a flat floor at the centre but not at the front or rear to allow easy access to the mechanicals, and encourage air flow to remove heat



Wouldn't fancy a rear end shunt in that.

Did you know that Mark Knopfler owned a 300S?

[WorldClassAccident]

I could fit vents fed from under the car to exit through the holes in the back




but as I said, I am looking to reduce drag rather than add downforce

[WorldClassAccident]

I picked up a 1000 x 500 x 1mm piece of sheet steel today. I spent some time under the car trying to work out how to get it to fit and how I could bend it to shape.

I discovered that the car floor either side of the centre tunnel is uneven on each side and different heights each side and unless I can bend and flex the steel as easily as paper I was not going to get my original design to fit.

I bottle of wine and a sauna later and I have my new design. This involves fitting a set of Rivnuts into the floor of the car, some threaded bar and a few bolts to hold it all together.



The idea is that the steel sheet stays flat. There are 6 tabs cut into it that can be bent back and bolted to the car. The idea is that the bolt heads will be closer to the car than the skid plate and also can be individually adjusted (bent) to cope with the different floor heights.

There is a side benefit in that the skid plate can be put that little bit lower and if it does scuff the floor the tabs will just bend back a little to raise the plate a bit. Auto-optimisation as I like to call it.

I am a little tempted to turn the edges of the plate down to form a venturi tunnel. This little idea explains why my now flat floor is 1000mm long instead of the original 450mm. By making it that length it can be used as the anchor point for any rear diffuser I fit to guide the air out of the back of the car instead of into the inside of the bodywork.

2 birds, 1 stone.

Let's see what happens tomorrow when I get the extra Rivnuts and threaded bar I need

[WorldClassAccident]

Made a start during my lunch hour.

1) Get some 1mm steel sheet


2) Stick a Rivnut into the floor pan after cocking up the initial drill position.


3) Bolts some threaded bar into the Rivnut. The different bits of threaded bar will be different lengths as the floor is not even. Hopefully this will result in the sheet of metal being flat and level.


4) Use a bit of wood to show that the end of the bolts is actually higher than the bottom of the exhaust box. This is because there will be tabs bent upwards to fix to the bolts. This will mean the nut will not be the first thing to hit the ground. The tabs of metal will also act as a little springing to allow the plat to move slightly if it scrapes the ground.


Four of the six mounting bolts in place when work stopped play. You can probably see the hair and flesh hanging off one of the bolts where I scraped my head. Ow!


More when I get time.

[WorldClassAccident]

All six fixing points are in place and the panel was trial fitted.

I cut the slats so the bolt ends are below skid plate


I have left it with one side painted with POR15 and I will do the other side tomorrow and then hopefully fit it.


I might give it a coat of silver hammerite on the bottom as well so it looks pretty as it gets scraped. Will be raising the front end about 100mm to reduce the amount of scraping