Camshaft retard

[emarine]

Does retarding a camshaft 4* have the same EXACT result as advancing 4 just oppisite ?

[bigjoe1]

In a simple answer---- NO

JOE SHERMAN RACING

[CamKing]

It depends on where you're starting from, and the application.
In some cases, yes.
In some cases, no.

[new engine builder]

I think many people are confused because a few of the cam makers grind 4* advance built in to compensate for timing chain stretch.

[CamKing]

cam makers grind 4* advance built in to compensate for timing chain stretch.

Chain stretch has noting to do with why we grind advance into the cam.
No chain in the world stretches 4 degrees.
That's an old wife's tale.
The advance is there to get the opening and closing numbers where they need to be.

[new engine builder]

cam makers grind 4* advance built in to compensate for timing chain stretch.

Chain stretch has noting to do with why we grind advance into the cam.
No chain in the world stretches 4 degrees.
That's an old wife's tale.
The advance is there to get the opening and closing numbers where they need to be.

I guess I learned something today.
But why 4 *??

[CamKing]

cam makers grind 4* advance built in to compensate for timing chain stretch.

Chain stretch has noting to do with why we grind advance into the cam.
No chain in the world stretches 4 degrees.
That's an old wife's tale.
The advance is there to get the opening and closing numbers where they need to be.

I guess I learned something today.
But why 4 *??

4 degrees is just a number that's used more then others.
I do a lot of cams with 2 degrees advance, and most of my turbo cams have no advance. Some circle track cams I make have 6 degrees advance.
There's no magic behind the 4 degree advance. It's just that it'll get you close to where you need to be in the majority of cases.

[1989TransAm]

From rumor control I have heard that over time the cam makes built in 4 degrees advanced because people tended to order cams larger than they should for their combination. The 4 degree advanced helped to mask the potential problem of too big of a cam.

[CamKing]

From rumor control I have heard that over time the cam makes built in 4 degrees advanced because people tended to order cams larger than they should for their combination. The 4 degree advanced helped to mask the potential problem of to big of a cam.

Too big of a port also requires more advance.
Rod Length also plays a role

[OldSStroker]

Assuming the advance was not done for lobe case depth purposes, I suppose you could have the cam ground straight up (0 advance/retard) if you had the valve events speced correctly.

It is interesting to look at the WOT phasing of the VVT 6.2L (L9H) cam. Lots of advance from idle rpm to around the torque peak and some retard after that to powerpeak and redline. Just about what you would expect.

[Strange Magic]

new engine builder wrote:
CamKing wrote:
new engine builder wrote:
cam makers grind 4* advance built in to compensate for timing chain stretch.

Chain stretch has noting to do with why we grind advance into the cam.
No chain in the world stretches 4 degrees.
That's an old wife's tale.
The advance is there to get the opening and closing numbers where they need to be.
I guess I learned something today.
But why 4 *??

4 degrees is just a number that's used more then others.

There is no exact answer. This has just been passed on down through time with no explaination or no factual findings. As far as i'm concerned, if you have to move an intake centerline more than 2 degrees off lobe sep for it to show it's best results, than the plotting of the camshaft events are incorrect.

[CamKing]

As far as i'm concerned, if you have to move an intake centerline more than 2 degrees off lobe sep for it to show it's best results, than the plotting of the camshaft events are incorrect.

That makes no sense.
LSA is nothing more then what you get when you add the intake centerline to the exhaust centerline and devide by 2.

With your way of thinking, an engine that needs an intake centerline of 102 should not have a LSA wider then 104. That's just not logical.

Bottom line, you calculate the intake centerline and the exhaust centerline, and whatever the LSA and advance end up, that's what's best.

Example:
I can be designing a cam for a long rod, short stroke, high compression, circle track engine with a good intake port, and a bad exhaust port.
My calculations show I need a 102 intake centerline, and a 112 exhaust centerline. That gives me a cam on a 107 LSA with a 5 degree advance.

[Lazy JW]

....
Example:
I can be designing a cam for a long rod, short stroke, high compression, circle track engine with a good intake port, and a bad exhaust port.
My calculations show I need a 102 intake centerline, and a 112 exhaust centerline. That gives me a cam on a 107 LSA with a 5 degree advance.

In other words, you first decide where the valve opening/closing events need to be and the LSA/advance numbers are an effect or "byproduct" of getting the valve events where you want them?
Joe

[emarine]

Wow thanks , this is great info , If a cam is cut on a 106 & installed on 106 , Moving it 4* retard < thats the easy way on my timing chain , bottom gear goes + or - 4 > I would close my intake from 56 to 60 ABDC , I should add some power in the high rpm range and loose some lower end ? I was told that after a 4* change it would be better to get a cam cut closer to your needs? Besides valve clearance is thier a dowm side to retarding a cam?

[CamKing]

Besides valve clearance is thier a dowm side to retarding a cam?

You just have to remember that on a single cam engine,when you're moving the intake opening and closing, you're moving the exhaust opening and closing too.

If you've got a cam on a 106 LSA, and the intake centerline is 106, then the exhaust centerline is 106 also.
If you retard it 4 degrees, now your intake centerline is 110, but your exhaust centerline is 102.
Sometimes the gain the engine would see from moving the intake is offset by the loss from moving the exhaust.