Timing education
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Junior User
Joined: Feb 2006
Posts: 88
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From: Harrisburg area Pa.
Timing education
ok im replacing the cam and timing set in my 390 (if you have seen any of my past posts you know why....lol) Im pretty new to this so my question is... the lower timing gear i removed only had one groove in it so it could only go onto the crank one way.... The new set i ordered from comp cams has 3 grooves in it, -4, 0 and +4 degrees. Im not quite sure why this is or what the benefits of this is.
Can some one please try to explain this to me? Should i just go with the 0 (im assuming this is what the single groove on the original gear was) what is the purpose of the - and +4 degrees?
This is the cam set i bought(and no i didnt pay that much...lol)
http://www.compperformancegroupstore...&Category_Code=
Thanks,
Newby Tom
Can some one please try to explain this to me? Should i just go with the 0 (im assuming this is what the single groove on the original gear was) what is the purpose of the - and +4 degrees?
This is the cam set i bought(and no i didnt pay that much...lol)
http://www.compperformancegroupstore...&Category_Code=
Thanks,
Newby Tom
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Junior User
Joined: Feb 2006
Posts: 88
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From: Harrisburg area Pa.
Lol
Ok this has been here for quite some time now and there is no response can someone atleast suggest somewhere to post it?.. I know its a pretty general question but none the less i would at least like to be able to understand it a bit better
Senior User
Joined: Dec 2005
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I would just put the gear at 0 degree. From what I understand of degreeing a cam, is that by having it advanced, the engine will have more top end power. By retarding the cam timeing the engine will have power in a lower rpm.
I think this is right. It may be opposite. I would be safe and put it at 0.
I think this is right. It may be opposite. I would be safe and put it at 0.
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Post Fiend
Joined: Dec 2003
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From: "Islander"
Slinger your 180 degrees off on your reply, advance helps low end and increases dynamic compression, retard will raise the torque and hp rpm's.
Apology accepted Mr. Moderator JoWilker, Carl.....=o&o>.....
Apology accepted Mr. Moderator JoWilker, Carl.....=o&o>.....
Thread Starter
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Junior User
Joined: Feb 2006
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From: Harrisburg area Pa.
OK.....all I am building this truck for is something to get into scare the crap out of myself and then park till I fell the need again...or the next day whichever comes first..LOL.Its 2 wheel drive and will only be driven on the street. So if im going for maximum neck snapage your saying i should set it retarded? Just trying to be sure I got it right.. Its definatly not going to be a daily driver.
Post Fiend
Joined: Dec 2003
Posts: 6,658
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From: "Islander"
Again advancing cam lowers the torque rpm's at the cost of high rpm power. Retarded cam will reduce low rpm torque a little but increase power at high rpm's. You can't increase both unless you have variable valve timing like newer motors. It is moved (memory) 125 rpm's per/degree of change. I like to degree a cam and add +2 degrees only after degreeing all lobes as have found screwed up cams being off a few degrees between lobes to allow chain stretch over the miles.
On a stump pulling RV cam they already ground advance in, should you go too far advanced you will increase the dynamic cr and BMEP beyond pump gas and detonate. To correct by retarding timing makes for a dog of a motor.
....=o&o>.....
On a stump pulling RV cam they already ground advance in, should you go too far advanced you will increase the dynamic cr and BMEP beyond pump gas and detonate. To correct by retarding timing makes for a dog of a motor.
....=o&o>.....
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Advance it for a neck snapper. Retard is gonna make it a slug off the line but give you lots of top end speed. Which just isn't very useful except on the oval race track. ET is what counts on the drag strip, not max speed.
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Senior User
Joined: Dec 2005
Posts: 314
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From: North Carolina
Originally Posted by Beemer Nut
Again advancing cam lowers the torque rpm's at the cost of high rpm power. Retarded cam will reduce low rpm torque a little but increase power at high rpm's. You can't increase both unless you have variable valve timing like newer motors. It is moved (memory) 125 rpm's per/degree of change. I like to degree a cam and add +2 degrees only after degreeing all lobes as have found screwed up cams being off a few degrees between lobes to allow chain stretch over the miles.
On a stump pulling RV cam they already ground advance in, should you go too far advanced you will increase the dynamic cr and BMEP beyond pump gas and detonate. To correct by retarding timing makes for a dog of a motor.
....=o&o>.....
On a stump pulling RV cam they already ground advance in, should you go too far advanced you will increase the dynamic cr and BMEP beyond pump gas and detonate. To correct by retarding timing makes for a dog of a motor.
....=o&o>.....
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Post Fiend
Joined: Dec 2003
Posts: 6,658
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From: "Islander"
Cam off by 1 degree in which direction, advance or retarded?
Again I like to be advanced 2 degrees, later fine tune the carb and ignition advance curve. With 2 degrees that isn't much which allows for chain stretch over the miles. The only problem with advancing is you are prone to detonation specially if your compression is on the high side when you built the motor.
.....=o&o>.....
Again I like to be advanced 2 degrees, later fine tune the carb and ignition advance curve. With 2 degrees that isn't much which allows for chain stretch over the miles. The only problem with advancing is you are prone to detonation specially if your compression is on the high side when you built the motor.
.....=o&o>.....
Senior User
Joined: Dec 2005
Posts: 314
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From: North Carolina
Originally Posted by Beemer Nut
Cam off by 1 degree in which direction, advance or retarded?
Again I like to be advanced 2 degrees, later fine tune the carb and ignition advance curve. With 2 degrees that isn't much which allows for chain stretch over the miles. The only problem with advancing is you are prone to detonation specially if your compression is on the high side when you built the motor.
.....=o&o>.....
Again I like to be advanced 2 degrees, later fine tune the carb and ignition advance curve. With 2 degrees that isn't much which allows for chain stretch over the miles. The only problem with advancing is you are prone to detonation specially if your compression is on the high side when you built the motor.
.....=o&o>.....
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
Josh, your build sounds like a 410 that's .030" over with resurfaced stock heads to be approaching 11.1 cr vs stock 10.5 cr static. Even with aluminum heads your in the detonation zone beyond cruise with a empty truck. Even in 65 degree weather unless you have some big O cam to drop the dynamic compression back to 8.0 to 8.5 zone you'll have detonation problems and retarding ignition isn't the proper cure. Wait until you work the motor pulling a trailer or load up a long grade in 95 degrees weather. Don't get me wrong as i'm a 410 person that enjoys torque with fuel mileage, well on the bump side scale that is.
.....=o&o>.....
.....=o&o>.....
Hotshot
Joined: May 2003
Posts: 11,141
Likes: 25
From: south louisiana
I'd hesitate either advancing or retarding the cam based on hearsay. None of you know what the cam's optimum timing is ground for. It could be optimized to run at 0*, or advanced or retarded a few degrees. There's no way any of you could possibly make that recommendation sitting at your computer, hundreds of miles away. Go with what the engine builder recommended, he's the only one who's close to knowing. If you're not happy with it afterward, then either advance or retard it after running it awhile and see what happens then.
Senior User
Joined: Dec 2005
Posts: 314
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From: North Carolina
Originally Posted by Beemer Nut
Josh, your build sounds like a 410 that's .030" over with resurfaced stock heads to be approaching 11.1 cr vs stock 10.5 cr static.
.....=o&o>.....
.....=o&o>.....
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
That things going to be an animal with a veracious appetite.
When your running whats the idle rpm's and manifold vacuum readings?
Later when you have carbon buildup compressions going to be higher, this with
iron heads?
Yes i'm many miles away and plus 1 to 2 degrees allowing for chain, gear wear and stretch will be more than those 1 to 2 degrees added. Why start at zero or 1 degree retarded then add chain wear? This isn't like adding 5 or 6 degrees.
I bet you'll be back within factory spec by 10,000 miles.
.....=o&o>.....
When your running whats the idle rpm's and manifold vacuum readings?
Later when you have carbon buildup compressions going to be higher, this with
iron heads?
Yes i'm many miles away and plus 1 to 2 degrees allowing for chain, gear wear and stretch will be more than those 1 to 2 degrees added. Why start at zero or 1 degree retarded then add chain wear? This isn't like adding 5 or 6 degrees.
I bet you'll be back within factory spec by 10,000 miles.
.....=o&o>.....
Last edited by "Beemer Nut"; Oct 8, 2006 at 12:26 PM.
Senior User
Joined: Dec 2005
Posts: 314
Likes: 0
From: North Carolina
Originally Posted by Beemer Nut
That things going to be an animal with a veracious appetite.
When your running whats the idle rpm's and manifold vacuum readings?
Later when you have carbon buildup compressions going to be higher, this with
iron heads?
.....=o&o>.....
When your running whats the idle rpm's and manifold vacuum readings?
Later when you have carbon buildup compressions going to be higher, this with
iron heads?
.....=o&o>.....
