Why 4 degrees?

[Wesman07]

This may be an elementary question but I never got a straight answer on this. Why do cam makers recommend installing 4 degrees advanced?

[turbo camino]

When that's listed in the specs (like 110+4) it means that the cam has been ground with that advance already built-in. It doesn't mean that the builder/installer should advance it another 4 degrees from the straight up position. Installed straight up, the intake centerline would be at 106.

[Wesman07]

I think we are on the same page. Maybe my question should have been why install a 110lsa cam on a 106 intake lobe center.

[CamKing]

This is what confuses people.
The LSA is not a design parameter. It's a result of the opening and closing event parameters.
If I design a cam for a 106 Intake Center-line, and a 114 Exhaust center-line, it ends up to be a 110 LSA.
We use LSA for machining the cam, so that's the info we give the customer. We say it's a 110 LSA with a 106 ICL, or it's a 110+4.
Not all cams call for a 4 degree advance. In many cases on pushrod V8 engines, 4 degrees advance gets you in the ballpark of the correct opening and closing points, so that's what many cam companies put down, but that's just a starting place.
Even the term "4 degrees advanced" is misleading. If you worked on double overhead cams, and in testing, you found that the engine ran best with a 102 ICL, and a 112 ECL, you wouldn't say it's on a 107+5. In fact, you wouldn't even mention LSA or advance.

[Walter R. Malik]

About 4 degrees advance ground on a dual pattern camshaft will be closer to a "split overlap" position. Although, I see a lot of camshafts ground 6 degrees or 5 degrees or 2 degrees advanced or in strait-up lobe positions.
It is merely what that camshaft grinder prefers for a starting position for the particular grind.

[Dragsinger]

Only slightly off subject, in some situations, with big cams, the valve to piston clearance becomes a limit to cam position. It is always a balance between cutting deeper valve relief but wanting max compression. In my experience with auto trans drag race car, "generally" they are faster with the cam advanced. They move off the line and the first 300 feet or so best with that setting.

[1980RS]

In the old days when I used to run Comp cam stuff all the time, I would retard the cam timing 4° to get the cam closer to straight up when I would degree it in the engine. Did it work better? most of the time not on N/A engines but when running nitrous those cams retarded made way better top end power. It's always fun to move the cam around then testing to see if a few degrees here or there helps or not.

[Tom68]

Good to see we haven't had the old bench racers tale ''it's to allow for timing chain stretch''.

[digger]

Good to see we haven't had the old bench racers tale ''it's to allow for timing chain stretch''.

i thought it was because everyone chooses too much duration so needs +4 to make it work semi ok:lol:

[HQM383]

Thinking out loud could there be an element of lag moving air fuel and combustion mass? Engine might want valves open at and for a specific time/area but movement of mass is not instantaneous? Probably not applicable or equal for all events or every rpm point.

[Wesman07]

This is what confuses people.
The LSA is not a design parameter. It's a result of the opening and closing event parameters.
If I design a cam for a 106 Intake Center-line, and a 114 Exhaust center-line, it ends up to be a 110 LSA.
We use LSA for machining the cam, so that's the info we give the customer. We say it's a 110 LSA with a 106 ICL, or it's a 110+4.
Not all cams call for a 4 degree advance. In many cases on pushrod V8 engines, 4 degrees advance gets you in the ballpark of the correct opening and closing points, so that's what many cam companies put down, but that's just a starting place.
Even the term "4 degrees advanced" is misleading. If you worked on double overhead cams, and in testing, you found that the engine ran best with a 102 ICL, and a 112 ECL, you wouldn't say it's on a 107+5. In fact, you wouldn't even mention LSA or advance.

That makes sense. What makes you design a cam for a particular center line? Can you give me an example of a pushrod v8 cam that 4 degrees advanced would not be ideal?

[nevdos]

This is what confuses people.
The LSA is not a design parameter. It's a result of the opening and closing event parameters.

This 1,000000000000000000000000000000000000%

[Tom68]

That makes sense. What makes you design a cam for a particular center line? Can you give me an example of a pushrod v8 cam that 4 degrees advanced would not be ideal?

Not that I can answer for Camking.

Some boat motors.

Some cam restricted classes of racing.

Possibly exhaust manifold classes that need to rev.

When you’re on the dyno and find out the motor responds to another installed position.

When you have the wrong cam but changing position helps.

[ClassAct]

Good to see we haven't had the old bench racers tale ''it's to allow for timing chain stretch''.

I don’t care how tight a chain is, they retard with RPM. A belt does it too, but not as far as a chain.

Whether you account for that with your ICL is up to the builder. I chose not to run timing chains.

[Tom68]

I've seen it with a belt with a 750 lift roller but there was no need to prevent it.