Retarding cam - help reversion?
 

I ended up pulling my engine for some winter upgrades ( I can't leave anything alone) and in doing so it looks like I am getting some reversion like some on this site had noted I may have with my exhaust (Imco Thunder) and cam. I currently have it installed 2 degrees advanced as the cam card had suggested but I am not running 11:1 (actual around 10:1). I am also looking at increasing my upper RPM range to the 5700+ range. Currently the motor was all done at 5400. Would retarding the cam back to straight up or even 1 degree retarded help my reversion issue. This should help my upper RPM range but not sure how much it would as I have never done this. I am not against having another cam done but seeing if this might work. Attached is my cam card and some exhaust port pics.

the more overlap a camshaft has the greater the chance of reversion,imo 26 deg is the problem.i don,t think retarding the cam will cure the problem but it might help.

I believe I read on one of the posts someone mentioned 24 degrees as the most you want for overlap? I am contemplating on a cam and want to make sure I get everything right.

Is it just one exh port? I remember your build and if I remember right you dyno'd engine. Repost if u would. Meanwhile compare timing events with other MARINE friendly cams. You did a great job with boat. That almost looks like it could be condensation. Hard to tell from my ph driving.

In my opnion with no experience on this (shifting cam around trying to fend off reversion), I would think advancing that cam would be less like to revert.

Reason is overlap after TDC (when piston going down and exhaust valve still open) is when reversion happens...right ? So, retarding cam would put more overlap ATDC.

Again, my thoughts....speaking of which, I would think that cam, no matter where you have it installed, will revert with those exhausts.

It is in every exhaust port some worse than others. What I was hoping for with retarding the cam was to get more rpm out of the engine and hoping that would help the reversion. As discussed before with my exhaust fixing the reversion with this cam will be hard so I would rather buy a cam then some headers. I would like to be closer to 5700 rpm just for personal preference so I think this might be a good time for a new cam compatible with my exhaust.

Ok on a wet exhaust overlap should be kept under 6° according to crane cams.

I can't make out your duration so I can't give advice there.

one thing I can tell you is you are going to want to go with way less overlap a 114 lobe center and shoot for close to 6°overlap.
you will probibly need to reprop the boat by 2 inches or more so you spin it closer to 5000-5200.

They (Crane) say 6* overlap when measured at .050" .

Most measure overlap at .004" or ,006" . So, you'll need to run the #'s at .050" to compare..if you so desire.

Should have been 114 lobe seperation angle or lsa for short.

you are correct I should have explained it better.
Must be tired.