mcrsr

i've noticed a lite bit of surface rust in the ports, but the valves and combustion chambers were free of any signs of water,i am running stainless marine exhaust with comp cams extreme marine cams,xm 272, in a carbed 454 w/ performer intakes, is this anything to be worried about??? wouldn't raising the idle speed slightlt higher help alleviate the problem?? comp cams swears that these cams will not cause reversion, also, what affect(if any) does ignition timing play??

Panther

Check the gaskets between your manifold and exhaust pipes. Also pressure test the exhaust manifold and tail pipes. If you have a leak you will get reversion.

If you have rust signs on the ports it's probably in places you can't see it.

What timing are you running? In the past I've run run 34-36* in my NA motors.

What are the specs of the cam?

Rage

"If you have a [exhaust] leak you will get reversion". Really? Why is that?

Panther

The exhaust escapes thru the leaky gasket creating a vacuum.

Rage

The threads of both of my o2 sensor bungs one inch above the exhaust manifold flange on the 496HO exhaust risers do not make an air tight seal such that a water drop will occasionally wick out from the threads at idle. When I place my hand over the o2 sensor bungs I do not feel any exhaust flow at all when engine running.

Is that enough exhaust leak to cause reversion by itself?

Nordicflame

iTrader: (4)

Bill,
If your sensors are not sealing they will leak water even though this is not a clear case for reversion. This is a very common phenomina that occurs with CMI Etop joints as well. The water will find any path to the outside if it is there. I have seen this on numerous CMI setups and when removed for inspection there is no sign of water anywhere. Some have even welded this joint to eliminate this.
Use some high temp RTV on the threads and this should help from frying your sensors.
Dave

Rage

Dave,

HaMon are you sitting on some beach with a laptop and satelite feed reading OSO posts?

1.) "that occurs with CMI Etop joints" are these the joints where two of the exhaust tube sections are welded to make a continous tube and they missed a spot?

2.) "that occurs with CMI Etop joints" if the water is not from reversion then from what/where?

Actually I have not seen the sensor(which comes with a metal gasket) leak as yet. It is the bung plugs that leak the water by the threads on both risers. However I have been trying to protect the sensor by using the bungs until the engine is warm and in open water by running with the bung plugs to get there and then switching to the sensor just for test start. When I remove the bung plugs the water is puddled in the female threads. When I pop the risers there is only moisture visable above the flange except for the ceiling of the (long) front and rear exhaust manifold runners. The two short runners and everything else in the exhaust manifold is black and dry.

Any other thoughts besides sealing the threads of bungs and sensor?

Rage

If a previous post is correct and the following are the cam specs for.......
Merc HP525EFI 236 int,246 exh, 114 sep, .06++ lift
Merc HP500EFI 230 int,236 exh, 114 sep, lift int .598 exh .610

.....then for my cam : 230 int,236 exh, 114 sep, lift int .598 exh .610 to have reversion what could be the contributiong factors (in addition / other than an exhaust leak)?

Raylar

Rage:

The LSA is the difference in degrees between the centerlines of the lobes between the intake cam lobe and the exhaust cam lobe. This LSA when smaller generally creates more overlap or the period where the intake and exhaust valve are open at the same time depending on the valve event timing of the cam.
Generally on fuel injected engines this LSA is kept wider or larger to provide a lower manifold pressure (vacuum signal) at idle on a bigger cam to keep the MAP signal smoother to the ECM.
You will have to be careful with your motor at that duration and valve timing with a 114LSA. Reversion at idle and on decel could be an issue for your application. Who recommended your cam specs to you? On the specs you listed I believe you mean your intake closes at 44degrees after bottom dead center, not After top dead center as you listed it. This means by the numbers you listed that the intake and exhaust valves will be open at the same time for almost 100 degrees of overlap. That seems high so check your cam specs again. I am just not sure of your cam specs here and what the real situation may be on your motor.

Ray @ Raylar

Rage

The cam is a Crane #OEM0988 and the intake does close at 44 degrees ABDC.