Replacement camshaft for 502 EFI
03-16-2003, 12:23 PM
#1
Guest
Posts: n/a
Replacement camshaft for 502 EFI
Dennis,
I was talking with you before about a cam shaft.
I am rebuilding a 1995 502 MPI completly stock.
You told me what flat tappet cam I can use without redoing my ecm but I cant find the thread,,, can you give me the specs on the best cam to use again so I can give them to the builder.
Thanks!!
Obnoxious
My recommendation would be Comp Cams XE268H with 224/230 intake and exhaust duration and .515/.520 intake and exhaust lift with a 110 degree lobe separation angle. This will work without the need to change valve springs or go to adjustable rocker arms. The stock ECM will also work fine. This is NOT the marine cam.
Sincerely
Dennis Moore
I was talking with you before about a cam shaft.
I am rebuilding a 1995 502 MPI completly stock.
You told me what flat tappet cam I can use without redoing my ecm but I cant find the thread,,, can you give me the specs on the best cam to use again so I can give them to the builder.
Thanks!!
Obnoxious
My recommendation would be Comp Cams XE268H with 224/230 intake and exhaust duration and .515/.520 intake and exhaust lift with a 110 degree lobe separation angle. This will work without the need to change valve springs or go to adjustable rocker arms. The stock ECM will also work fine. This is NOT the marine cam.
Sincerely
Dennis Moore
03-16-2003, 02:57 PM
#2
Charter Member #1171
Charter Member
sorry about the inbox, I just emptied it,,, this is a touch bigger then the stock cam and the Comp marine cam correct?
Thanks again
Thanks again
__________________
I want to live in a world where a chicken can cross the road and not have its motives questioned.
I want to live in a world where a chicken can cross the road and not have its motives questioned.
03-17-2003, 07:52 PM
#3
Charter Member #1171
Charter Member
I had a couple people look at me wierd when I said im going to use a 110 degree lobe sep cam,,,, can you explain the difference between 110, 112,, 115 etc so i can explain it.
Dont get me wrong,,, Im using it,, just want to know how to explain it.
Dont get me wrong,,, Im using it,, just want to know how to explain it.
__________________
I want to live in a world where a chicken can cross the road and not have its motives questioned.
I want to live in a world where a chicken can cross the road and not have its motives questioned.
Last edited by obnoxus; 03-17-2003 at 07:55 PM.
03-19-2003, 08:37 AM
#4
Charter Member #1171
Charter Member
Also,,, will there be any reversion issue with this cam,, I am running Gil Manum choice headers with there silent choice.
__________________
I want to live in a world where a chicken can cross the road and not have its motives questioned.
I want to live in a world where a chicken can cross the road and not have its motives questioned.
03-19-2003, 03:00 PM
#5
Guest
Posts: n/a
Obnoxous- You have a Speed-Density EFI control system....the less INTAKE REVERSION you have, the better your system will work...wider lobe seperation angles reduce intake reversion...a 112 LSA would probably work with that amount of overlap, but I think you'll like the idle and tip-in better with the 114 LSA. Now would be a good time to upgade to a roller
Dennis' recommendation would be ideal for a carb.
Dennis' recommendation would be ideal for a carb.
03-20-2003, 08:23 AM
#6
Charter Member #1171
Charter Member
I would have to think he has used this cam before with out incident,, I was hoping he would respond to make me better understand it.
__________________
I want to live in a world where a chicken can cross the road and not have its motives questioned.
I want to live in a world where a chicken can cross the road and not have its motives questioned.
03-20-2003, 09:34 PM
#7
Guest
Posts: n/a
wider lobe separation angle
Obnoxus
The lobe separation angle is the amount of camshaft degrees that the intake lobe centerline is separated from the exhaust lobe centerline. A tighter angle will usually increase valve overlap decreasing manifold vacuum and a wider angle will decrease overlap and increase manifold vacuum. The computer makes calculations to air/fuel ratio changes based on the MAP sensor (it is a vacuum gauge).
The stock camshaft will have very slow opening and closing camshaft lobes. To arrive at sufficient valve open duration for an acceptable level of performance these slow moving lobes will start opening the valves very early and close the valves very late. This, despite the wide lobe sep angles of 115.5 degrees, creates a good deal of valve overlap.
With the very fast opening and closing lobes (of an aftermarket camshaft) the valve opening and closing points can be delayed considerably while still providing the same amount of open duration @ .050 valve lift and higher. A closer lobe angle (more horsepower and torque)can be used with an aftermarket camshaft while still maintaining the correct manifold vacuum and MAP signal.
Pretty tough subject to explain in a few words!
Sincerely
Dennis
The lobe separation angle is the amount of camshaft degrees that the intake lobe centerline is separated from the exhaust lobe centerline. A tighter angle will usually increase valve overlap decreasing manifold vacuum and a wider angle will decrease overlap and increase manifold vacuum. The computer makes calculations to air/fuel ratio changes based on the MAP sensor (it is a vacuum gauge).
The stock camshaft will have very slow opening and closing camshaft lobes. To arrive at sufficient valve open duration for an acceptable level of performance these slow moving lobes will start opening the valves very early and close the valves very late. This, despite the wide lobe sep angles of 115.5 degrees, creates a good deal of valve overlap.
With the very fast opening and closing lobes (of an aftermarket camshaft) the valve opening and closing points can be delayed considerably while still providing the same amount of open duration @ .050 valve lift and higher. A closer lobe angle (more horsepower and torque)can be used with an aftermarket camshaft while still maintaining the correct manifold vacuum and MAP signal.
Pretty tough subject to explain in a few words!
Sincerely
Dennis
03-20-2003, 09:53 PM
#8
Charter Member #1171
Charter Member
Just needed to prove why I would not have reversion,,,, Thanks !!!!!!!
__________________
I want to live in a world where a chicken can cross the road and not have its motives questioned.
I want to live in a world where a chicken can cross the road and not have its motives questioned.
03-21-2003, 07:11 AM
#9
Registered
Why does Mercruiser put in a camshaft with slow opening and closing camshaft lobes?
Dennis,
Why does Mercruiser put a camshaft in with slow opening and closing camshaft lobes? Does it make the engine more reliable? Is there some benefit to this? I'm just trying to understand why they would put in a camshaft that would cause reversion when they could avoid it.
Why does Mercruiser put a camshaft in with slow opening and closing camshaft lobes? Does it make the engine more reliable? Is there some benefit to this? I'm just trying to understand why they would put in a camshaft that would cause reversion when they could avoid it.
03-21-2003, 09:57 PM
#10
Guest
Posts: n/a
Yep
The highest wear point in an engine is between the lobe and flat based lifter. Friction and wear are increased when the lobe moves the lifter quicker to open the valve faster.
Closing the valve faster increases the wear between the valve and the valve seat, especially on the hot exhaust valve.
General Motors builds the marine engines with slow opening and closing lobes to cut down on warranty problems, especially for customers that neglect to change oil regularly.
A stock camshaft lobe may have the same amount of duration @ .050 valve lift as an aftermarket camshaft lobe, for example 224 degrees.
At valve opening and closing points, @ .006 inches of valve lift, the stock camshaft lobe will have 290 degrees of duration and the aftermarket camshaft will have a much shorter 270 degrees of duration. This will allow an aftermarket camshaft to make more vacuum or the same amount of vacuum with a tighter lobe sep angle.
A tighter sep angle increases horsepower.
Sincerely
Dennis Moore
Closing the valve faster increases the wear between the valve and the valve seat, especially on the hot exhaust valve.
General Motors builds the marine engines with slow opening and closing lobes to cut down on warranty problems, especially for customers that neglect to change oil regularly.
A stock camshaft lobe may have the same amount of duration @ .050 valve lift as an aftermarket camshaft lobe, for example 224 degrees.
At valve opening and closing points, @ .006 inches of valve lift, the stock camshaft lobe will have 290 degrees of duration and the aftermarket camshaft will have a much shorter 270 degrees of duration. This will allow an aftermarket camshaft to make more vacuum or the same amount of vacuum with a tighter lobe sep angle.
A tighter sep angle increases horsepower.
Sincerely
Dennis Moore
