Reversion
 

I'm helping a friend change cams in his 500HPs. He is having the heads cleaned up, a little mild porting etc. Would like to add a little more cam. Looking at something around a 236/242 duration.
How much duration & lift can I run with a 502 with Gill exhaust that have silent choice? The risers don't mix water until they are right at the diverter.

Do you know if he has the taller risers that Merc started using after they realized they had a reversion problem with the HP500 carb ?? If he has Silent Choice, the answer is probably no, in which case he's probably experiencing reversion already and just does not realize it.

Hopefully not a stupid question but....How do you know if you have reversion?

Thanks TomR for starting this thread (and for all of your much appreciated help!)..

Ric 232,
I do not have the taller risers. I have the earlier ones with Silent Choice.

Thanks!

I am running a mild 224, 232 cam with 114 degrees of sep. on that short Gil Magnum Choice setup. I dont have reversion with my limited overlap but like ric232 said, he probably already has reversion with the stock hp500 cam and doesnt know it. Higher idle rpm can help avoid it but it doenst help a bravo any shifting at the higher rpm's. The Gil turbulator plate helps too but only to a point. He really needs a longer riser exhaust or go dry pipes tp totally avoid the problem

Reversion can be seen by running a warm engine at idle for a while (lowest idle usually in gear) shutting it down and pulling a riser or manifold and looking for wetness in an exhaust passage. It also shows as pitted valve seats and worst case, broken valves.

My feeling is that we are probably on the brink of reversion now. If we add a cam with more duration we should stop using the silent choice, and should probably go to least dry risers.
I know that if we added tube headers that would increase the likelyhood of reversion, again unless you went to a dryer exhaust.
Ric232, I do believe that He has the taller risers.

If the risers look like this, be very very careful added any overlap.

You don't need dry exhaust. CMI's will do the trick.

Is the silent choice part of the reversion problem? Meaning is water more likely drawn in thru the prop.

hey ric232, does it matter which cmi's such as etops or sport tubes??? speaking of 232 baja's got a 2002 232 with 496ho has anyone put a whipple on one? very tight engine compartment(as far as in front of the crankshaft pulley). thanks

Yes and no. Silent Choice is part of the problem, but you will not draw water through the prop hub. The problem is that when you have Silent Choice, you usually have risers that dump water into the exhaust stream sooner, thus increasing the potential for reversion.

TomR, can you get a photo of the risers showing where the Silent Choice diverters hook up? Merc may have used a different setup on the HP motors.

No, both will work great, and the e-tops are much less expensive.

You need 2.75" in front of your crank pulley for a Whipple. Have you measured?

What prop are you running on your 232 and what is your best speed on GPS?

hey ric232, we added the whipple stage 2 computer upgrade, and crane gold roller rockers, also did some porting and clean up on intake manifold, with port matching of the heads. running a labbed 23p mirage plus from houston prop. at 5300rpm, our best gps was 73. got about 1.75" in front of pulley, but should be able to modify for more. heard from anyone running a whipple on a 496ho? likes or dislikes??

I'm running a '95 502 EFI Mag with aftermarket Gill, SS risers into Corsa silent choice. Thinking of putting big valved iron heads and a roller Cam in this season. What would be a good cam choice?

I could get a photo tonight. The risers are long, they meet the silent choice right at the transom. The silent choice is shaped like an "S" to feed back into the "Y" pipe.
I was thinking of adding overboard dumps and letting some of the water out before the end of the riser pipe. The end of the pipe only has four holes that are maybe 3/8 in diameter.