PPF reinforcement

[muzza2]

has anyone installed one of these?

anyone want to give me pro's / con's if you have?

http://www.miatamania.com/Shop/ViewProducts.aspx?PlateIndexID=38927&SortOrder=1

[Alf]

Does not appear to add extra lightness!

Cheers,
Alf

[muzza2]

Does not appear to add extra lightness!

Cheers,
Alf

not all of us are looking for "saving" weight
i would rather have a car that has all of its interior bits which handles rather then a car with every single "extra" bit of weight taken out.
i mean some people go as far as to taking the bonet stay out...
thats just stupid and not me.

extra weight... who cares....

[bruce]

It looks like overkill to me. The Mazda engineers would have spent a lot of time designing the PPF and if it needed a few mill of extra thickness I'm sure they would have done it.

[CT]

They are a good idea in big power cars. The PPF stretches and warps under high power launches. There's been a few break in race car land over the years. I've been meaning to make something up for a while now.

[Garry]

My PPF cracked at the diff mounting points

[Matty]

My PPF cracked at the diff mounting points

The diff end is where the greatest bending moment (torque) is applied. I don't see that this brace will do much as it is attached at the other end...

[Mokesta]

You'd be better off thickening the top and bottom flanges of the C section rather than adding another web if you are trying to increase bending stiffness. I'd say that unit was a waste of time.

[orx626]

Someone do a strand7 stress analysis on it, until then nobody can be certain.

Why? Is fatigue an issue?

[orx626]

Someone do a strand7 stress analysis on it, until then nobody can be certain.

Why? Is fatigue an issue?

no but flex is.

Is deflection an issue with PPF's?

[orx626]

what are you talking about? doesn't it twist with the gb and tries to take the diff with it?

If the PPF is suppose to transfer torque from the gearbox to the diff then why would Mazda have used a torsionally weak section such as a channel?

[Mokesta]

The PPF is meant to react diff torque and hold up the tail of the gearbox. These loads are both effectivly in the vertical plane so the PPF is in bending and shear.

Engine and diff torque about the longitudinal axis are reacted by the engine mounts and diff ears. These react at different rates so the diff and engine need to rotate different amounts. The PPF is therefore flexible in torsion.

The PPF is the ideal section shape to be stiff in bending and shear but flexible in torsion; a "C" section.

Assuming that the diff ears and engine mounts can only move a certain amount until they contact solid stops and there isn't a huge amount of chassis twist, the PPF won't see much more twist as engine power is increased. It will see a lot more bending and shear. If it's limits are reached it may need more capacity in these two modes. The device shown at the start of this thread would be an inefficient way of adding this capacity.

There are some gyroscopic effects that can load the PPF in the horizontal plane on a sharp clutch dump but I expect these would be second order loads.

If Mazda intended the PPF to transmit a torsional load, the unit would be a box or tubular section and the diff wound't need ears, just a simple hanger. That is, the arrangement between a Porsche 928 engine and box.

M

[orx626]

....and here endth the lesson!!!!

'Z'-sections aren't bad either.

[zoomzoom]

Just words, yes, but I am very sure these guys have a fair idea of what they are talking about so I would certainly take their word for it.

[Keith]

I just went to the link at the top of this thread and saw the price. $214 US ( plus freight) for a simple C section !!!Strewth. Im in the wrong business!If I wanted one,( which I dont) Id get it bent up locally for a fraction of the cost.
I reckon Mokesta has nailed it.
Its a cost benefit analysis( leaving aside the $$$). A famous yacht designer, Uffa Fox, said about 70 years ago "Weight is only of use in a steamroller". So the cost is that you lose speed, and particularly acceleration, in a direct proportion to the weight you add to the vehicle- as well as increasing fuel consumption every time you drive it..but there doesnt seem to be much of a benefit to performance.
The other thing Id add its this: Mazda engineers went to a lot of trouble and expense to design & produce a reasonably high tech ( for a mass produced economy car of its day) lightweight alloy ppf. This clumsy bracket is just a bent up mild steel c section.Mazda could have done that for a fration of the cost. Surely you wouold pay to get rid of it, not to add it!!!
Interesting thread!