Cam and reversion comparison...
 

Just looking for some thoughts or opinions here…
Which of these two cams do you think would revert more water on a 564ci naturally aspirated motor?

Original Bulldog cam Hydraulic Flat Tappet 240/250 110 LSA .559/.578 -Timing at .004 has the intake opening at 43* and the exhaust closing at 42*. Timing at .050 has the intake opening at 15* and exhaust closing at 10*

The other cam is a newer Crane Hydraulic Roller 240/248 112 LSA .621/.632 –Timing at .004 has the intake opening at 40* and the exhaust closing at also 42*. Timing at .004 has the intake opening at 13* and exhaust closing at 7*

Thanks,
Dave

Re: Cam and reversion comparison...
 

The two cams look almost the same. The hyd. roller has slightly less duration but more lift. The hyd. roller has 2 deg. more lsa but I don't know if that will do much. On an engine that size with Gm or Merlin heads a good cam is the Crane 651. It's 244,256 @ .050 .630, .630 lift 114 lsa. It will idle at 800 rpm but it will revert a little. It needs thru transom tailpipes that inject the water at the tips.

Re: Cam and reversion comparison...
 

PatriYacht,
This is the cam I am running in my 502.It sounds like you have had experience with it.I am running Revolution marine manifolds and I am worried about reversion.Revolution says I should not have a problem with there manifolds and this cam.What is your thought?

Thanks Nordic95

Re: Cam and reversion comparison...
 

Don't know why but I thought you had 540's. I think both of those cams are right on the edge of what will revert with the Revolution manifolds. I'm sure that the 651 will revert with a 502. A better choice would be a manifold with through transom tailpipes that inject the water at the end. Gil and Stainless Marine make good ones. I have heard of people welding a piece of tubing to the inside of the exhaust to seperate the exhaust from the water for a longer distance with a manifold like the Revolution..

Re: Cam and reversion comparison...
 

Somewhere along the line, the math is wrong on those numbers.

IO=Intake opening
IC=Intake closing
EO=Exhaust opening
EC=Exhaust closing

A cam that is 240/250 @110LC would have the following events.

IO-10.....EC-15
IC-50.....EO-55

A cam that is 240/248 @112LC would have the following events.

IO-8......EC-12
IC-52.....EO-56


If you add the IO & EC together you get the overlap, the most critical part of the overlap cycle that prevents reversion is the EC number as the piston is on its way down and therefore creates the suction back pulse known as reversion(occuring at low engine speeds).

If you want to verify cam numbers, add the opening and closing events together, add 180, that is your duration. Take the duration, divide by 2 and subtract the opening event and you will end up with your theoretical lobe center phase angle.

Example, 240/248 @112LC advanced 4 degrees

IO=12.....EC=8
IC=48.....EO=60

The lobe separation is still 112, but the intake is now phased at 108 and the exhaust is phased at 116.

Re: Cam and reversion comparison...
 

The cam referenced HR-240/365-2S-12 IG (139681)
is on a 112* LSA with 5* advance
@.004"
................Opens..........Closes............. C/L...........Duration
Intake.....40.0 BTDC.....82.0 ABDC......107*..........302 °
Exhaust...88.0 BBDC.....42.0 ATDC......117*..........310 °
82* overlap

@.050"
................Opens...........Closes...........C/L.........Duration
Intake.....13.0 BTDC.....47.0 ABDC.....107*.........240 °
Exhaust...61.0 BBDC.......7.0 ATDC.....117*.........248 °

The Bulldog cam (13H000036) rates on a 110*LSA, 5* advance

@.0042"
................Opens..........Closes............. C/L...........Duration
Intake.....43.0 BTDC.....77.0 ABDC......105*..........300 °
Exhaust...88.0 BBDC.....42.0 ATDC......115*..........310 °
85* overlap

@.050"
................Opens...........Closes...........C/L.........Duration
Intake.....15.0 BTDC.....45.0 ABDC.....105*.........240 °
Exhaust...60.0 BBDC.....10.0 ATDC.....115*.........250 °

The 139681 is the MK IV Gen V flat nose core, however Crane does make the same cam (ground on a 114* LSA, 5* advanced) for the step nose Gen VI engine that is part #168771. Here is the valve events for that cam ground on a wider lobe sep

@.004"
................Opens..........Closes............. C/L...........Duration
Intake.....38.0 BTDC.....84.0 ABDC......109*..........302 °
Exhaust...90.0 BBDC.....40.0 ATDC......119*..........310 °
78* overlap

@.050"
................Opens...........Closes...........C/L.........Duration
Intake.....11.0 BTDC.....49.0 ABDC.....109*.........240 °
Exhaust...63.0 BBDC.......5.0 ATDC.....119*.........248 °
You can see how altering the centerlines moves the valve events. The only difference between the 13xxxx and the 16xxxx series cams from Crane is the core. They will grind any one of these configurations for you on the core of your choice if you feel you want the wide lobe sep to defer the possibility of reversion.
Bob

Re: Cam and reversion comparison...
 

Yes Bob,
I was not worried about when , but how much beings we all vary where we degree them at. The overlap is the number I'm interested in.
I'm actually pondering the 139681 (240/248) ground on 114 just for that reason. Reduces overlap to 78*.
Thanks,
Dave