Sump guards

[Carlos]

What material and thickness sump guard should I be using for rallycross. The plate I am using is very thick and heavy but am a little hesitant as to what thickness to go for. Do I stay with steel or is there an alternative which will give the necesary protection. I am on a fairly tight gudget so no F1 type materials.
Thanks for any help

[imull]

just been down and measured the forest sump guard for my rally car. It is 6mm Duralumin (duralloy?)

the other shell I have was a rally cross car and as its a flat floor GRP shell, it was fully skidded with 8mm duralumin with 6mm sump and front suspension skidding again...

[KC]

I think Duralumin is an industry name for T6 Aircraft grade aluminum. It is a hard grade and very tough. Good for high tensile strength and light weight.

[imull]

it is an alloyed aluminium but not sure exactly what its composition is.

Carlos, I know the Alcoa branch near Swansea sell it and would be very surprised if their other depots etc dont sell it...

[boyracer]

We've used ~6mm Aluminum (good stuff) as a sump guard on a Grp A WRX for several years, it's taken a lot of hits but it's still OK.
Keep it as flat as possible to help skid over rocks rather than ram straight into them. And think reasonably careful about the sort of distance you're trying to cover. Too far and the sump guard when hit may flex and damage the sump anyway.

[imull]

also, put a layer of foam/sponge between the sump and the guard. should prevent a stone getting caught and then puncturing the sump...

[C R Box]

6 MM DURAL (Duralaminium)is ideal. It should be 4mm clear of the sump. Turn up the fron edget and drill 25MM air vent holes trough it. Don't drill any holes underneath. Use lubrcant when cutting and the holesaw will cut 3 times as fast. Any oil will do. If possible reccess the bolts so the heads can't be damaged by rocks etc. The sump guard is a good place to fit a tow hook.

[Cameron Winton]

Dural should be a good material. It is an Al - Cu alloy ( copper at pretty low precentage) and I believe (Need to remember back 18 yrs to University) the copper helps with ductility. that should be good for a sumpguard as it should have at least some of the energy absorbing capability of a steel (eg it will stretch when thumped rather than brittle fracture)with less weight.
If you really want to fiddle, I have heard of a cheap alternative to a composite sumpguard where two thin sheets (dont ask me how thick) are bonded either side of a sheet of very good quality plywood. Lighter than the equivalent thickness of Al and close to the same mechanical properties.
The length of guard is very important. I heard a story from when mini's were 1st rallied that the sumpguards did not extend out under the gear linkage. After a few yumps, the shell started to break up where the subframe meets the shell at the bulkhead. The guard stiffened up the subframe so much that all the loads were concentrated into the bulkhead.
T6 Al is heat treated to improve mechanical properties. The T6 defines the heat treat conditions.

[Cameron Winton]

Forgot to mention - cut a hole (round - stress concentration factor will be 3 no matter what size) to help get to the sump plug if a quick oil change is needed

[avsfan733]

Make sure to attach it well!

you don't want to just through a couple bolts on and go ripping parts out of your frame

[zac510]

Should the sump guard be hard bolted to the vehicle or should it have a bracket that will 'give' when hit?

[JimW]

"Dural® - Aluminum/Copper/Magnesium - Material Information Al95/Cu 4/Mg 1"

Jim

[BertMk2]

Originally Posted by zac510

Should the sump guard be hard bolted to the vehicle or should it have a bracket that will 'give' when hit?

I've only ever seen them 'hard bolted' - if it has any 'give' in it then it could end up whacking into the sump

Not sure about the foam/sponge idea - the theory is good but it sounds a bit flammable to me! (Then again I'm probably a bit paranoid - we set fire to the exhaust wrapping on our last car )

[Notso Swift]

Originally Posted by Cameron Winton

If you really want to fiddle, I have heard of a cheap alternative to a composite sump guard where two thin sheets (don’t ask me how thick) are bonded either side of a sheet of very good quality plywood. Lighter than the equivalent thickness of Al and close to the same mechanical properties.

Bolser wood, use a really good epoxy to bond the three layers.
Cost is also down, buying a couple of 2 x 3mm sheets of Alu is a lot cheaper than 1 x 6mm. It is also easy to work with. I am pretty sure they were 3mm, so it would weigh the same as 6mm. (But a lot of other guys use 4mm steel so it is still light

Also it doesn't hurt to have a leading edge of a cheap replaceable material... such as steel, 2mm x 50mm x width, with counter sunk heads. that takes the force and saves the Alu from wearing too much, just drill it out and replace when it shows signs of needing it.
Foam between guard and sump is common with other guys, but I have that overheating and fire reservation that is expressed by others, even if you spil something on it and that causes it to start to burn how do you stop it? Mind you, I used foam on other under body parts (fuel tank)
Rigid mount to chassis, you also need to be careful that the engine mounts don't provide too much movement to stop the sump crashing into the guard