Checking for reversion and manifold riser Q's
 

I am going to be putting the rebuilt engine back in this weekend and have stepped up to an XM270H camshaft which several here have said they don't have reversion issues with, but I want to check to be sure...

SO - can I simply hook up the hose to the muffs and run the engine in the driveway to break it in (flat tappet - going to be running it 1800-2200 for 10-15 minutes) and then pull the manifold riser off when it cools down and check? OR do I have to do it immediately because the water might evaporate? Am I better off running it in the water under "real" conditions? (i.e. go out for a couple minute run, idle back to dock and pull one of the risers off to check)


If I do see reversion what can I do (short of swapping out the cam to something milder like the old XM262H which ran out of breath past 46-4800 or so) Does adding some riser spacers between the manifold and riser help? Does anyone have a "performance" riser that might help?

Make sure the bow is not pointing down hill. You shouldn't get any reversion at those rpms. Reversion generally happens at idle rpms.

Good point... bow will probably be uphill on the drive as it's slightly slanted (maybe 1-2*?). I guess I won't worry about checking when I break it in.

Should I put it in the water and then idle the engine around the dock area for several minutes then pull back in and check? Guessing that's about the best way so far...

Thats probably the best way. Right after idling for while, pull a riser and shine a light down the manifold an check for water. A 50-100rpm increase in idle rpm can also help alleviate reversion if its borderline.

I've always let the motor idle for 1-2 mins on the firing stand and then drain all water from the block and manifolds. idling on the engine stand and idling in the boat is the same thing. Then pull the riser and do your reversion check. I've done 3 motors this way with no problems later on. You could pull a riser later on but I have noticed that when you break the seal between the manifold and riser w/o draining you leak water into the manifold making you think you have reversion.

I had reversion with a 226/230 .537/.511 112+2 roller cam with my Imco/FastGlass short risers. I welded 16" extensions onto them to mix the water and exhaust further back and no further problems. This year I had reversion with
a 234/240 .580/.568 112+4 roller with those same risers. I had to cutoff and reweld 22" extensions to cure it. Risers extend into the tip making it a homemeade dry exhaust.

SO - I guess the only question I have left - will it be obvious (i.e. an obvious wet spot right under the riser) or will it be tiny tiny mist-like droplets that I am looking for?

I had very small puddles lying at the bottom of the manifold in the center runners. It will be noticeable if you have any. If you don't see anything then you don't have to worry. I know a few that had a few tiny droplets. They would rev their motors to 3K rpms before immediately shutting them down to blow out any water. They never had any problems.

Ryan has it right. I ran the 270 cam and never had reversion. The cam had a nice thump and really hauled. One thing I always did after idling to the dock or beach, before shutdown, rev up b-4 turning eng. off. Besides sounds good.
I have EMI exh. with the long risers. That could make the difference.

Sorry for my ignorance but I have not heard the term "reversion" before. What is it as not in the to distant future I would like to pull my 454's for rebuild and do some minor performance improvements, i.e. intake, carb, mild cam and exhaust along with a solid lower end. I don't want to have a failure due to not checking something.

The best thing you can do is have a cam custom-ground for your specific application. If the grinder knows every detail about your setup, subtle adjustments can be made without sacrificing performance while still keeping reversion at bay.

Best thing is, it doesn't cost any more than a good off the shelf cam.