pd_day

iTrader: (6)

I am just trying to get a discussion going about the thickness of seals to put in when rebuilding a motor. I understand that the stock seals are 2mm while aftermarket seals can be had at 3mm. I've read many message on the board and most ppl claim that 3mm seals are better then 2mm seals because they can handle more boost on turbo cars.
Since 3mm is 1.5x of 2mm, then 3mm seals should be able to handle 1.5x the boost of 2mm seals, rite?

So since 3mm is 1.5x of 2mm, it would also have 1.5x more contact area between the seal and the housings which equate to hotter running temperature from friction because of the extra surface area.

Now that you got more heat in the engine, you'll have to run a lower boost setting then 2mm to avoid detonation.

So doesn't this defeat the whole purpose of putting in thicker seals?

I might be off on all of this, please enlighten me if I am wrong.

Mykl

I'm no specialist, but here's my take on it...


Thicker seals do not allow you to run higher boost, or make more power. If anything they cause more friction and wear down your housings more quickly.

The only good thing is that should you detonate, they're less likely to break because they're thicker and stronger.

A rotary can only run so much boost depending on what octane gas you're running (assuming you have all the necessary equipment to run high boost), increasing seal thickness doesn't affect max boost.

pd_day

iTrader: (6)

So the thicker seals is more like an insurance so that engine is less prone to detonation at the expense of engine life?

If that is correct, then it would be more wise to get 2mm seals when rebuilding and get the car tuned probably so that the maximum power can be obtained while engine life is not comprimise (spelling?).

Now it leaves me wondering why ppl claim more power can be achieved with 3mm?

Mykl

Exactly.

But keep in mind that **** happens, like an injector goes bad, or your fuel pump decides to mysteriously die, or some other problem suddenly arises in your fuel system. It's just insurance, but even with 3mm apex seals if you detonate hard it's still going to do damage. It'll just move on to the next weakest link in the chain.

That's my take on it though, hopefully somebody who knows better will speak up.

dre_2ooo

HHMmmmm........ I think the engineers who designed the engine took this all into consideration to make the fastest, yet most reliable engine tehy could...

Maybe you should do some research into what seals the 787B (2.6L 4-rotor) were, you KNOW that was made for pure speed.

The material make-up of the seal is another factor too. Carbon Vs. Steel etc... I dont think that it will handle 1.5x more boost. It takes a VERY complicated process to figure that number. Plus the coefficient of friction is NOT dependant on the AMOUNT of surface contact. Friction is equal REGUARDLESS of how they contact. Friction is the quotient of the force of the spin/the force being pressed againt the housing. That is how they deveop lubricants for gears etc. If you upgrade the cooling system this would counter the excess heat. 3mm seals will also have more inertia than those of lower mass (assuming its the same material). this will cause a natural centrifugal force to the housing, causing more force in that direction, thus increasing wear. The vibration of the seals in and out of their "homes" will also increase. Add this to the snug fit they have will not give them teh freeplay they need to compensate for unpredictable hishaps tht go on inside an engine. If you can lower the forces acting on teh seals between the housings and thenselves, while increasing the width to seal better, then you will have a much better chance at relaibility. Alas, no such "wonder metal" has been found/created yet. So heavy steel, or low-life carbon it is...