Detonation PSI
 

I understand that detonation is an explosion within the combustion chamber due to a lean condition or other various reasons.

This damages the seals because the explosion causes a higher pressure(psi) within the chamber than the seals can handle(right?).

So does anyone know how much pressure can be in the chamber without damaging the apex seals?

Thanks Justus

RICE RACING listed the peak chamber pressures that can kill the seals, for various different types of seals. It was a year or two ago, but it's here somewhere.

Thanks for the info.

Anyone else know??

Justus

https://www.rx7club.com/showthread.p...threadid=11396 Here's a link with some interesting info about the stock seals... "calculated safe to 1000hp in a 13B"

https://www.rx7club.com/showthread.p...threadid=34156 Has some specifics for you as well!

https://www.rx7club.com/showthread.p...threadid=42795 This is the thread I was thinking of, has limits for CARBON seals as well as standard!

"carbon seals... limit being no more combustion pressure than 2.0MPA"

(followed by neat chart showing max HP levels at a given RPM)

"Ferrous 2mm seals have a BMEP limit of around 4MPA and hence at 4000 rpm you could run up to 430bhp (N/A + NOS) and not break the seal due to excessive combustion pressure."

Thanks for the links ;)
Although, I am not looking for boost psi, I am looking at just the psi inside the chamber that the seals can withstand.
Basically I am wondering at what psi do the seals damage when the engine detonates.
But thanks again for the links :D

Justus

That IS the pressure in the chamber that the seals can withstand.

BMEP = brake mean effective pressure = average (not peak as I erroneously reported earlier) chamber pressure

4 Mpa (4,000,000Pa) = about 40 Bar = about 580 PSI.

Of course this is not PEAK pressure... but when you get beyond natural aspiration, detonation in a rotary can and will destroy any kind of seal you put in there. I've detonated an N/A probably 50-80 times (before I figured out the problem!) but it was nowhere NEAR the kind of initial pressures seen in a turbo motor. Heck since it was happening at mid RPM at part throttle it wasn't even at the kind of pressures you could see in an N/A either!

Wow, sorry I misinturpretted that :(
So, in a 12a engine, the 2mm seals can withstand 4 Mpa before damamge will occur to the seals, correct?

So if the engine was forced inducted would the 4 Mpa BMEP stay the same??

By force induction it just means detonation is much more harmful to the seals due to the already added pressure in the chamber, correct?

Do you happen to know where I can get numbers for the BMEP for other rotaries like the 13-REW??

Thanks and sorry again peejay!!

Justus

12A's never came with 2mm seals.

Damn you are quick to reply :D
Sorry, then with the seals that came with.
(I have a 13-REW I don't know the 12a's very well excuse my ignorance)

Justus

Hey...if PSI determines whether detonation could occur, would varying the compression ratio help in preventing detonation?

https://www.rx7club.com/showthread.p...hreadid=281500

It doesn't determine whether or not it can occur, it occurs from lean fuel mixtures and/or failed cooling systems.
Detonation causes more psi in the chamber. The psi that it generates is greater than the apex seals can withstands and causes damage.

Having a lower compression engine would lower the chances of detonation harming the apex seals as much, as long as the volume of air/fuel mixture doesn't fill up the combustion chamber completly so that when it detonates there is more room for the expansion.
But by making the engine a lower compression and then adjusting the A/F mixture as mentioned above, you would not be making as much power due to the decrease in the amount of A/F being injected into the engine.
The resasons most engines are made lower compression is so they can fit a larger amount of A/F mixture and make more power. These engines are normally force inducted(turbo, supercharger) which forces more air into the chamber than the engine could naturally fit, so by making the engine lower compression it allows for more room so the turbo or superchager can induce more boost.

Hope that helps with your question reza.
Justus