Lobe seperation
 

Newbie here.....
Can anyone explain to me the difference or affect running a cam with 110 deg lobe separation verses 112 deg sep?

Re: Lobe seperation
 

From what I've seen the 112 will idle a little better and carry the rpm a little further. The 110 has better bottom and mid range torque.

Re: Lobe seperation
 

110* would generally be more prone to reversion than a 112*.

My cam has 110* LSA. On my 3rd season with the engine (ZZ502) and no known reversion so far.

Not a mechanic here, but I would think if my cam had more/longer duration, the possibility of reversion would increase. My cam specs are similar to those of the HP500. Some HP500's seem to have a reversion issue, some don't. The right exhaust can help.

Like GPM said, the 110* LSA cam idles just a little rough. Mine produces a nice lope at idle...very cool.

BTW........Welcome :o) Lots of good info on this site. I'm sure more knowledgeable members will chime in.

Re: Lobe seperation
 

Thanks for the info gent's.
The reason I asked is I am in the process of rebuilding my 502's and my engine builder was surprised that my Crane roller cams where at 110 deg.When I bought my 31ss Sonic it came with two very strong 502's.The boat ran 80mph (gps) at 5150 rpm,turning labbed 3 blade 25 pitch props. All was well at a little over 200 hours when the starboard engine dropped an exhaust valve seat into the number 7 hole.
The engines already had all the top if the line internals and Crane Gold valve train.The heads are the GM iron Hi perf's with Manley Inconel valves. So we pulled both engines and decided to make them 509's while we were doing the freshen -up.We are also replacing all the exhaust seats with an alloy seat.I am running Gil maifolds with long tails.(wet) My cam's are still in perfect shape so I had not planned on replacing them and the lifters were sent back to Crane under the racer's exchange program.
Since the engines were not Dyno'd the first time I could only guess that they were around 525 hp ? When the build is complete they will be Dyno'd and if the HP is not at least 525 then I will be looking for different cam's.
I will get the current cam specs from the builder and post them for some feedback.
Thanks again and any comments or opinions are welcome.

Re: Lobe seperation
 

I just built a 540. I had Gil WetOffshore manifolds and pipes. The first run out with this set-up, I had real bad reversion. I ended up with CMI dry headers. Problem is now solved. Below is my cams specs...

intake exhaust
.578 lift .608 lift
238* @.050 .248* @ .050
114* lobe seperation
61* overlap @ .000 lift
15* overlap @ .050 lift
Cam is installed as recommended@ zero advance. I didn't have the idle set too low. It just sucked water back. Luckily I caught it right away and avoided any engine damage.

Re: Lobe seperation
 

Time for a cam upgrade. This is your ticket for a strong marine powerplant.
I would send OSO's Rmbuilder a private message or email and he can spec a cam that will be spot on for your application.

Re: Lobe seperation
 

Russ,
Now that I went to full dry, I will be upgrading the cam but not until the winter.

Re: Lobe seperation
 

Vinnie,
The response was not directed to you but to Madmax911.
I would like to know how and when you realized that you had a reversion problem.
Did you pull the exhaust to inspect for moisture or did some event direct you to do that?
Russ

Re: Lobe seperation
 

Update.
First dyno run was not impressive
Quick info......Peak HP 496 at 5100 rpm......Peak TRQ 565 at 4100 rpm.
Sorry forgot to bring home the cam specs on this cam.( 110* LSA )

Changed cams to the Crane 731 ( 112*LSA) and lost both HP and TRQ.
Thinking of bumping the compression from 8.75 to 9.0 ,but we are still going to play with cam timing first.
Also the AF ratio was 11.3 from 3500rpm through 5200rpm. Any opinion on whether this is tooo rich ?

Re: Lobe seperation
 

I was thinking the same.....thanks.
I would think that in the boat (wet exhaust ) it would fatten up even more.
I have seen posted run's with the AFR's as high as 14.4 !!!!!
Are these guy's re-jetting for the real world after the dyno run or are they counting on the exhaust and flame arrestors to richen them up to a safe AFR ?
Would like to leave the compression low enough to run 87 if I can.
What is the highest comp/ratio that can live on 87oc ?

Re: Lobe seperation
 

I talked with MM911 yesterday... they shaved the heads, and added a HP500 manifold and still only got 513hp @5200rpm and lower trq than they started with. Could it be the stock t-bolt ignition? This motor should be making more hp, I'd think...

Re: Lobe seperation
 

Russ,
Sorry I didnt answer you. Somehow I missed your post. Oh well, better late than never.
I found I had a reversion problem right away. I could not get the motor to idle in neutral or even idle in the no wake zones. After messing around with the carb settings I pulled the plugs. I saw small salt deposits on them. I pulled the risers off and there it was. The manifolds had a good amount of water in them. I first thought they may have cracked. I pulled them and pressure checked them. No leaks were found. So, I went for wet CMI's . While it was better, I still had a reversion problem. I found this out by luck.. When I put the headers on, I forgot to tighten one of the cool collar clamps. When I started the engine, water dripped from that joint. The next step was full dry CMI's. That solved all my reversion problems but created noise problems. I was getting pulled over by the noise police. It really was tooooo loud, even for me to take. A set of GGB extremes was the fix. They took the bite out of the noise while still keeping that sound that we all love. So far I have not been pulled over with the GGB's. No power loss at all. :D

Vinny

I know this is an old post.
Couple things to consider on lobe sep.
longer stroke engines are more forgiving to tighter lobe seperation because the piston hangs at top and bottom for longer period of time then travels faster once it gets past the tangent point far enough.
Also the hieght of your exhaust headers/risers. Keep them high then angled down towards transom so water cant get back in as easy

I know this is an old post.
Couple things to consider on lobe sep.
longer stroke engines are more forgiving to tighter lobe seperation because the piston hangs at top and bottom for longer period of time then travels faster once it gets past the tangent point far enough.
Also the hieght of your exhaust headers/risers. Keep them high then angled down towards transom so water cant get back in as easy

I disagree….stroke does not effect dwell time at tdc/bdc. Rod length does, though. A longer rod will dwell at tdc/bdc longer.

Most boater biotches prefer longer stroke and rods. 😂

yes rod length also effects it.

The 110 will definitely outrun a 114 as long as you don't have a reversion issue. Longer duration more reversion. Also shorter advance curve on distributor to allow more advance at idle. I'm about 18 degrees at idle. More duration , more advance
ad duration of int. and exh @ .050. Divide by 4 . Subtract lobe sep. Multi ply by 2. Use as a guide line
244+256=500
500÷4=125
125-114=11
11×2 =22
this is crane 651
Here is one I'm running
237/243 with 110
comes out to 20 overlap.
I need to prof read more