GeoFX

iTrader: (1)

I un-installed the Motordyne 5/16" spacer last night on my FX35 (still have the MREV2 on) and noticed that the isothermal plenum post spacers were deformed from what looks like melting. I spoke to Tony (Hydrazine) about this and he said that the melting temps for the spacers are ~500 degrees F and there's no way the air can get that hot in there unless there was something wrong like backfire of the exhaust gases back into the plenum or something. I do have the IsoThermal aramid gasket installed as well.

He remembered that I posted pics of my lower plenum assembly a while back and noticed it was had a lot of brown staining and he's seen it on other VQs where it's possible backfire could cause it. I originally thought this could be from the oil from the blowback valve going back into the plenum causing the staining.

Anyway, any thoughts on why these spacer posts melted and deformed? If it's not oil from the blowback valve, could something else be amiss like backfire?

Here's a pic of the lower plenum assembly. Any ideas would be appreciated.

Wired 24/7

iTrader: (2)

Pics look like normal oil in the plenum. Why don't you post some pics of the deformed pieces...

MustGoFastR

iTrader: (13)

yeah, post pics of the plastic pieces. I'd think you'd notice if you had a backfire problem, as it would take several to raise temps that high in there; it would be loud and you'd feel it. Your upper plenum would be hot as Hell too, and when you were over the other day, I took a temp reading of it and it was only around 120 deg even after it sat and had max heat soak.

GeoFX

iTrader: (1)

Can oil cause that much staining though? That's what I thought initially and actually installed a DIY oil catch coming from the blowback valve into the lower plenum.

The isothermal plenum posts are resistant to melting to 500 degrees F so what can cause plenum temps to be that high? It's definitely not faulty spacer posts.

Anyone else noticed this much staining when taking off their upper plenums?

Yeah MustR, it was sitting at around 120 degrees after around 10 minutes of heat soak.

sq40

iTrader: (4)

Scary.. Why not use Metal Spacer Posts?

GeoFX

iTrader: (1)

Metal spacer posts will conduct even more heat between the lower and upper plenums. You don't want to do that.

Besides, I'm trying to determine a cause for all that hot air blowing inside the plenum...doesn't seem normal.

sq40

iTrader: (4)

Intake valve not sealing possibly on the exhaust stroke?

MustGoFastR

iTrader: (13)

Ok, well, is the MREV 2 lower plenum stained? That first pic is of the stock lower plenum, right? We put in the oil catch with the MREV install, so it's catching all the blow-by. If the MREV plenum is stained, then you should worry about the backfire possibility, if it's clean, then the spacer posts deformed in some other way. If temps were rising to that level in the plenum, you'd have some drivability issues, I'd think, and would notice the the car wasn't running right in a pretty obvious way.

Got pics of the spacer posts yet? How bad are they? remember one end of them was cupped and had thin walls on that cupped area. That part could likely deform with much lower heat (but not really hurt anything).

Oh, and with all the blow-by oil you're catching, I'd say that amount of staining with the milage you have is perfectly normal.

Hydrazine

iTrader: (53)

I was thinking about your description of the top of the cups being deformed.

If this is the case, there must be a significant amount of very hot gas flow to create it. The top of the cups arent in contact with anything but the top of the plenum and the air flowing around it.

The upper plenum certaintly has no natural reason to go above 500'F so the upper plenum can be excluded as being part of the heat source.

The lower plenum is only in contact with the bottom of the spacer and the lower portion of the plenum certaintly can't go anywhere near 500'F. They are injection molded @ 500'F @ 2000 PSI. And at atmospheric pressure, the spacer won't really deform until ~600'F.

My guess is the only source of this magnitude of heat must be from hot combustion gasses flashing back into the plenum.

How could this happen?... There are a few possibilities I can think of.
1) Preignition during the intake stroke. (Potentially hot plugs?)
2) Intake valve leakage during the combustion phase
3) Intake valve leakage during the exhaust phase.
4) Reversion during the overlap phase of the valves. (exhaust mods?)

When you cleaned out the runners of your lower collector were they stained brown? Some? All? Which ones?

As a precationary measure, get a dyno and post your results.

Tony