Moon Assad

If its got no outlet because the CAT is clogged it will blow a flame back through the engine across the overlap when both ports are open using whats open on the intake side as the exaust. If the engine intake cant suck the fuel into the engine it will reflux into the intake (BOOM) the ignition of fuel will find the path of least resistance wich was the coupler.

carbonRX8

iTrader: (1)

Um, no


There is no overlap. Try again.

Moon Assad

Ok, what do you think happened.

Moon Assad

Set up an RX8 rotor in a housing you will see that when the rotor is at bottom dead center there is very little but some overlap. Dont try starting a **** storm, im trying to explain what happened, if you have an opinion why not state it.

Moon Assad

If you look into the history of this thread you will see that when Greg clogged his CAT it spiked the boost to I think he said 15 or 16 psi. If you add fuel into that issue and it ignited some how the same thing would have happened.

Moon Assad

Another possibility is that since the exhaust wasn't totally pushed out of the engine it carried to the intake port causing it to ignite.

joff

Oh no, not this again.

Moon is right.

There is a clearance volume thats carried over from exhaust to intake even if the port timing does not overlap. If the cat is clogged (effectively a motor with no exhaust port) -- the entire exploded charge will re-compress into the clearance volume and spit back out the intake as soon as the intake port opens.

Rote8

I got a thought:
Something in the lower intake, intake port, or the rotor itself, got hot.
(could be from a plugged cat, or no oil injection, or something that had fallen in the lower intake)
With our fine factory temperature gauge, we would probably not know this.

When whatever it was finally reached the ignition temperature of the air fuel mix, BOOM.

carbonRX8

iTrader: (1)

That was quite an example of post count increasing there moon.

This speculation is only minimally supported by the example of "overlap" and completely unsupported by any previous example of a clogged cat. Look them up. A clogged cat generally just results in stumbling and loss of power. The SC side of the story throws an interesting, but ultimately misdirecting, aspect into the mix. Besides, what you are describing would have to happen instantaneously between exhaust cycles, otherwise it would have happened on the previous cycle, which leads to the same argument ad nauseum, thus invalidating it.

This certainly sounds like a classic example of a backfire. A real backfire and not what is typically called such (post ignition)

You dont need the cat to be clogged for this. Just fuel, air and a preignition ignition source.

carbonRX8

iTrader: (1)

Looks like someone is thinking.

Bastage

iTrader: (1)

Jeff, is that you?

joff

Renesis specs have exhaust port closing 3 degrees BTDC and intake port opening 3 degrees ATDC. Theres 6 degrees there with no ports open there. (no overlap)

Reference: http://www.tomorrowstechnician.com/C...0000001985.pdf

13B-REW (FD RX7 engine) and other peripheral port rotarys on the other hand do have significant overlap. Unless its been ported or changed recently, I can't understand how any RX8 motors could have overlap.

Brettus

iTrader: (2)

hah - good spotting Bastage

carbonRX8

iTrader: (1)

No, but I appretiate the commentary.

I admit I was feeling like stirring the pot and I apologize.

marsredr100

iTrader: (1)

Apology accepted but just remember to…

joff

By preignition source you mean something like hotter, higher pressure carry-over gas in the clearance volume from a clogged cat? I don't think a clogged cat is as ridiculous a reason for this as you think it is. Moon and Cam may not read forums as much as you but do have a lot of relevant experience.

This is where a turbo is nice: with potentially clogged cat there, backpressure will rise, turbine looses power to generate boost and you know something's wrong in advance. If you get preignition while the intake port is open, the pressure goes backward through all sorts of IC/tubing volume back through a compressor that will gladly flow air backwards.

On a NA car, there is also a path from intake ports back to atmosphere through the throttle. Clogged cat probably just bogs things down there as NA power is very sensitive to backpressure. It also takes a very significant preignition to cause any intake tract damage due to 1) being NA, and 2) having an opened throttle body to atmosphere.

On a positive displacement SC, pressure builds between blower and intake and (IIRC) bypass valve is a type that seats harder as pressure rises -- so no relief there. This would seem to make things worse. Positive displace SC will not flow air backwards as it cannot stall due to being belt-driven. Manifold preignition pressure can rise more catastrophically here. Plus, we have less intake volume and its all cast aluminum!

Moon Assad

If you look closly you can see the ports still open. Yes, im proving to you that what you said is WRONG, buy the way you ow me 50 miles worth of gas) that the ports do overlap. I have the gear inplace in the rotor so also add a few thousants (that was probly miss spelled but I dont give a dam). In these pictures you can see a very slight overlap. And if you dont think a flame can pass over that area if the exaust is plugged you need to leave these cars to the pros.

Moon Assad

Ow, almost forgot here they are. there is also a pic of a 09 motor.

carbonRX8

iTrader: (1)

I think you could show overlap by just placing a rotor on a side iron. Oh, look...

carbonRX8

iTrader: (1)

No. How did all that high pressure hot charge get in there if the cat was clogged? If the cat was clogged enough that you were not getting any flow, how did you get any flow in the first place? It is chicken and egg and therefore cant be the explaination. And besides, it is not clogged at the manifold, there is lots of volume to expand into and cool. It would have to be absolutely completely clogged at the manifold. So far, that hasn't happened.


Ok While I agree that the situation is different, this never happens. Ever.



Again, while you do a fine job of highlighting one of the downsides of a clutch-less belt-driven SC, this does not require backflow of exhaust gas to cause a backfire. What is more likely is some higher temps leading to some ignition source in the intake. If that is indeed what happened.

Moon Assad

How to experiment with combustion.

http://www.youtube.com/watch?v=CpAJOPzKK-M

joff

Ok, whats the exhaust gas temp of a FI rotary at WOT? 1400C a few inches from the manifold maybe? How about if the tuning is off -- perhaps severely retarded by 20degs due to DSC hiccup? Probably even hotter than 1400C then.

Okay, now -- with 1400C measured in the manifold, how about the exhaust gas inside the clearance volume of the rotor tub? Double hotter.

Now, consider that the autoignition point of gasoline is 280C.

What happens when the intake port opens and vaporized fuel starts mixing with remnant >1400C exhaust gases? Surprisingly enough, most of the time nothing catastrophic happens. You might wonder how a motor can avoid autoignition at all -- in reality its a very delicate system -- you depend on a combination of the motor running at an ice-cold (in comparison) 100C and the latent heat of fuel vaporization to keep away preignition each and every cycle. You do not need a 100% clogged cat to upset things -- in reality it doesn't take much. Just running the motor a measly 15C hotter (measly in comparison to combustion temps) can cause autoignition and detonation.

Any rise in backpressure in the exhaust gives rise to more intake charge heating. At some point, you pass the safe threshold and pre-ignite or detonate.


Please tell us the credentials you have and corpus of testing you've done to speak with such authority without needing explain. I hope its nothing along the lines of all the forum posting and reading on the interwebs you do.

Rotr8

iTrader: (2)

Before I went FI, and the reason I ended up getting the RP supercat, my factory cat actually blew up, and my car caught on fire, at the time I was cruising around at about 35mph, came to a stop didnt have any Halon or anything,, Anyway the fire went out on its own after melting the 02 sensor cableand half of the goo holding the heat shield on the car, and shorting the whole sensor. Went to the shop(dealer), core temp was 1680 couldnt touch the damn thing for a whole day, amber red for about 4 hrs...
Anyway sitting there wonder WTF to do the flames went all the way up to the engine bay and at about the hieght of the LIM,,,
What about an electrical fire, that might explain the wierd DSC readings too... Just a feask of nature or like round here those damn squirrels that like to crawl into engine bays and like to chew on the fire blanket, and other wires....

olddragger

iTrader: (3)

i cant believe you guys have never seen a s.c blow at the strip.
? is why did it happen? Right?
Seems to me a sudden clogging of the cat at partial throttle --he was going slow remember--would have been symptomatic before the blow? Clogged cat---yep I can understand that. But other stuff could have happened too---and this pcm WILL pull timing--at least with a fuel starvation episode it will--have it on the efi data logger.
OD

Rote8

<Eddie Murphy voice>
It was the old banana in the tail pipe trick.