Vintage Mustang Forums banner

1 - 10 of 10 Posts

·
Registered
Joined
·
866 Posts
Discussion Starter #1
Hi all,

I have a question to all the cam / engine experts. Can someone explain the effect of advancing or retarding a cam? The cam can be advanced or retarded using the timing chain. Some cams have already offset grounded into the cam from the manufacturer. E.g. the timing card of my Crowler 15212 says: 4 degrees of advance have been ground into this Camshaft. Timing card

I know what it means, but what are the effects on the engine, idle, vacuum, torque, horse power and so on. Did someone play around and can share the impact on the engine?

Thanks :)
 

·
Registered
Joined
·
949 Posts
Before you decide to adjust the keyway you should degree the cam. This is so you can verify the cam card is correct.

Generally speaking, advancing the cam is good for low end torque.
Retarding the cam is good for high rpm horsepower.

Before you decide, consider all the parts of your engine and how you intend to drive it.
If you want your engine to reach peak HP at 6500 rpm but weak valve springs allow the valves float at 5800, you’ll be very disappointed.
 

·
Registered
Joined
·
866 Posts
Discussion Starter #4
@2nd 66 and @MrFlash thanks for the feedback.

I am currently not planning to change anything. I just wanted to have a better understanding about the impact. Based on the table from Summit the the change of peak HP and peak torque is not dramatic (200 rpm for 4 deg).

Is it really necessary to degree each cam? Shouldn't be the quality control from a good company take care if this?
 

·
Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
Joined
·
20,669 Posts
Should, yes. But...
Some time ago I bought a timing set that was so far off I threw it away and bought a Cloyes set. Had I not checked the degreeing I would have surely wondered what was wrong with the car later. You don't have to buy a degree wheel. These days you can download one as a pdf, print it, and glue it to whatever kind of cardboard you have handy. So one tool you don't have to buy to get it done.
 

·
Registered
Joined
·
383 Posts
Advancing and retarding the cam changes when it makes its power. You talking about the most complicated part of the entire car. It depends on the type of racing you would be doing. Camshaft timing is pretty complicated. That's why its best to tell the cam grinder what type of racing you will doing. Do you want torque at the low end or do you want it at high end. If your running an engine at the Bonneville salt flats your not worried with a hard launch off the line. You want your engine making the most torque at high rpm so it has the torque to pull a high rearend gear ratio, producing the best top speed. It all depends on what rpm the engine will be used at. If you watch a Bonneville car leave the starting line it has to pushed by another car, not so much because it has some super high gear ratio as it is because its barely making any power at that low rpm. It doesn't have enough power to even get the car rolling The camshaft timing has been change to make the power at 7000-8000rpm.

This is the Wilson and Water #368 Roadster at Bonneville. 235 mph with 3.0L engine. Watch the tach, horsepower and speed. In order to beak this record. They do not need 700 hp off the line they need it at 8000 rpm. If they were drag racing they would want at a lower rpm because they only have a 1/4 mile to accelerate. Watch how long this engine has to accelerate between 7000 and 8000 rpm. They don't care about making power below 7000 rpm. This is a perfect example of how you would want change the timing of the camshaft to make power at high rpms.
The most important thing is to know how your engine will be driven. If you had this roadsters camshaft in your car any stock car could beat you off of the line. Because they are designed to have there torque created where a normal daily driver needs it.


Basic 4 stroke operation


Summit Cam Calculator


Checking the cam for accuracy.



Camshaft Timing. how to change it. I've used Cloyes Timng sets for years.

Cloyes Multi-Keyway High-Performance Crank Sprocket Adjustments

Types of timing chain sets.

How To Choose The Correct Timing Set For Your Application
 

·
Registered
Joined
·
760 Posts
One other point about advancing/retarding a cam is that it can also be used to counteract a specific valve set (either all intake valves OR all exhaust valves) from making mechanical contact with the pistons. This is often done when an aftermarket cam or a higher compression piston (taller piston or one that has smaller valve reliefs) is used in a performance engine.

It works because both the intake and exhaust valves are at there closest location to the piston near TDC (and always occurs within a few degrees of each other.) Actual valve lift has very little to do with valve contact and more to do with when the valve is opening or closing near TDC.
 

·
Registered
Joined
·
10,266 Posts
It's always a good idea to degree a cam. I learned this when a friend of mine installed a new cam in his '69 Chevelle years ago. He didn't degree it and later found out is was wasn't ground correctly. Although he installed it "Straight Up" as the instructions indicated, the result was significantly retarded valve timing. The car was a complete pig until it hit about 4,000 RPM. Then it took off like a scalded dog. Sounds like fun, but when he wasn't street racing, it really wasn't. I mean, how often does a daily driver get above 4,000 RPM?
 

·
Registered
Joined
·
7,017 Posts
With so many cam alternatives now including custom grinds, just seems like it would be better to get the grind the engine needs. Dialing up the cam (verifying the degreeing) so it matches the cam card spec's is a different situation. I have heard of dirt trackers monkeying with the cam timing though. It does let you slide the peak torque up or down some or it might be a patch fix for some extra valve clearance on one side or the other. Just my own 2 cents for free. It does pay to now exactly what you have. A lot of cams are ground with +4 degrees and some or zero.
 

·
Registered
Joined
·
866 Posts
Discussion Starter #10
Thanks for all the valuable information!
 
1 - 10 of 10 Posts
Top