Will more base timing help prevent reversion? Also what rpm is needed at an idle to reduce chances of reversion.

I have built 2 502's with pretty decent cams. They are the extreme marine comp cams. 238 248 on a 112 LSA. I knew the cam was kinda big going in but I am running dry risers that dump outside the boat at the end of the riser. Not in the exhaust but outside it. I am still getting reversion but only on the port motor.

I'm really curious why only one motor gets it. Motors are Identical. The cams were put in straight up (not degreed). The only hole I ever find water in is cylinder #7. I am running the log stlye manifold that exits in the back so #7 would be the cylinder to get it. But you would think #8 would get it as well.

Is there something else that may be causing this on the odd bank of the motor? All cylinders are firing I have run a compression check on the motor all cylinders are around 190. Manifold has been pressure tested.

Thanks Rob

More idle speed will help as will good flappers. I dont know about ignition timing, but I understand that cam timing is a factor.

190psi is high, your compression ratio must be up there 10.5-1???

I thought it was high too. Especially with the overlap of the cam. But CR is stock. about 9.2:1 Motor has stock replacement piston forged and stock heads pocket ported they were shaved about .002 to clean them up but that was it.

It's odd that you say flappers will help. I managed to avoid the reversion until I put the flappers on. I have taken them back off now and will test again tomorrow.

I really need to add some mufflers because its way too loud. I know as soon as I do the reversion will just get worse. I'm looking into the GGB Cyclones.

Could it be a crack on the inside of the manifold? Sounds just like what happened with my Gils.

Payton god thought. I did have a leaky manifold on that side at first. I have since replaced it with a new manifold and had that pressure tested so the manifold is good now. The riser has not been pressure tested though.

I can look down the end of the pipe after ideling and see the water heading up the exhaust. I'm 99% sure it's reversion.

"Less" ignition advance at idle can help reversion some. It helps in a couple of ways;
1) Less timing at idle means a larger throttle setting, lower manifold vacuum
2) Slightly higher egt's at idle helps vaporize water droplets

This is only a slight improvement. Cam choice, idle speed, and exhaust design are probably bigger factors.

I noticed you said log manifolds in your post. If they are the old type that have water passages between the base manifolds and the risers, you might have a leak at the gasket flange between the riser and the manifold. that would explain why only one engine has the problem possibly. I really don't like to see anyone today using the wet joint manifolds, they are an accident waiting to happen and newer manifolds are cheaper than new motors. Also its not apparent from your photo if there is any real drop in your exhaust circut after the riser, so I guess if its to straight or level, some water could re-enter on overlap, but I would expect to see that on all 4 manifolds. Good luck! I hope you find the source before the gremlins grab that motor!

Ray @ Raylar

Yes they are the manifolds with the wet joint. I have just replaced all 4 gaskets with some better gasket material because I had thought that was my problem. I don't think that one could be leaking but I will have to remove it and check.

As far as drop, on the trailer it may be kinda straight, but in the water the boat is very stern heavy which gives me a good drop.

I hope the above suggestions solve the problem. I once had water in a 502's #7 due to partial head gasket failure. The compression test didn't indicate a problem. I didn't perform a leak down. Good luck.

The Crane HI 6 M ignition box has a wire that can be grounded and introduce ignition retard. Start as normal, hit a switch or let a circuit activate to retard ignition, you would need to design some type of relay circuit to automate the retard. Be creative. You could use a switch activated by manifold vacuum to activate the retard.

Just a thought if you want to go that way.