2112

Can someone give me the magical cut off point at which the duration of the valves and their overlap (in degrees) at which reversion can be eliminated?

My engine builder and I are butting heads over this. His contention is that their is NO magical figure (ie 110 degrees of overlap vs. 114) and all cams have reversion, it is just a matter of how much. I do respect his years of experience but need others input here.

My stellings exhaust exits under a swim platform and I am sucking water back in when idling around the docks. No reversion running on hose on the trailer.

H2Xmark

one other item that can help is idle speed, the faster the idle the less water you will ingest, also a cam with a wide lobe seperation angle will work better[114degree's] now a cam ground on a 108 lobe seperation might make a little more power it will have more overlap, causing more water ingestion, duration of about 255degrees at .050 lift is starting to push a wet exhaust system a bit, good luck i'm sure someone else with more info than I have will help out soon
Mark R

Hydrocruiser

Interestingly enough with my stock 350 Magnums which have a 'moderate cam" in the oil samples I sent in a couple times after 25 hours the samples always came back negative on water content.

Sending in an oil sample is a pretty good idea. There are several places that do this; mine were done at Blackstone Labs.

Reversion has kept me from hot-rodding my engines. I don't think all engines have reversioin problems continually; though if the circumstances are right anything is possible.

CMS Racing

2112 give me some info on your package . so i can help you CMS Racing engines P4-5

2112

Thanks, I am resigned to making new tailpipes at this point.


Bore= 4.625"
Stroke= 4.5"
Compression 9.0:1
Flow intake 480 cfm at 28 inches
Flow exhaust 366 cfm at 28 inches
Intake valve 2.45"
exhaust Valve 2.02"

Cam specs
INTAKE EXHAUST
Duration @ .050 270 280
lobe separation 110 degrees
Seat duration @ .020 304 324
Gross lift .722 .722

Rocker ratio 1.73

Exhaust exitsunder the swim platform, there is a recess underneath near the transom, Pipes used to come out 6 inches but I had them shortened to only 1.5 inches past the transom. The boat sits very low in the water. the platform is right at water level. two pics to show how the exhaust is routed.

The pipes are not in the water but they stir things up when idling.

2112

Something compressed my outline

Cam specs
INTAKE Duration @ .050 270
Exhaust duration @ .050 280
Lobe separation 110 degrees
Gross Valve lift for both .722"
Seat duration @ .020 304 degrees for Intake 314 degrees exhaust

MESABALANCING

Be careful in thinking you have reversion until you check a couple of things such as the amount of drop you have in the system because ive seen instances were the boats were rigged from the factory with the exits real close to the water line and the water will actually come up the pipes during launching and you may get moisture in the engine that way Reguardless i believe the cams are big and the lobe sep. would benefit being slightly wider but check several things before you go to new pipes. The engines look great and Im sure your engine builder did a good job.Good luck Laz Mesa PS do you have water in the oil by any chance

2112

Yes, water in the oil is the problem.

I utilized the factory exhaust hole when having the custom exhaust made. I have flappers on them now.

I have also pressure tested the engine's cooling systems and oil cooler. the Engines will hold 25 lbs for about 20 minutes and then loose about 1 pound per hour for the next 12 hours.

PatriYacht

If you loosen the connection between the tailpipes and the header pipes water will pour out while the engines are running. With those cam specs, unless you run dry exhaust, I would guess reversion. I had mine welded closed except for two small holes to cool the tips and mufflers and dumped the rest overboard.

Comanche3Six

pressure test the exhaust itself.
Good luck.