Some thoughts on cams
Posted: Wed Mar 05, 2008 8:05 pm
Whilst I dont claim to be an expert on cam selection here are some thoughts on the damn things
Rule 1 Dont overcam with 1600 gearing 5500 rpm in fourth means 200kmh approx
A cam with more duration means that there is a time when the exhaust and intake is open at the same time with the exhaust open and flowing exhaust first this means that fresh petrol is also sucked out the exhaust .... Lousy mileage results
For racing cars this obviously doesnt matter much but...
It also seems that not all Billet cams are of such great quality and wears out quickly It takes fancy metalurgy and compatibility between lifter and cam to make it last. For the 1961 beetle vw went to a nice light 2 piece lifter and stuffed up so many engines that the 61 was known for years as a dud Opel did the same on the early kaddets
For mild aplications I favour the stock cam and lifters just reground to about 270 degrees
When people talk about hardening the cam I know here is a story coming. The black coating on cams is called Parkerizing.
This was a method invented during the second world war to stop US guns from rusting. it is essentialy dipping the metal in a boiling acid solution which etches the surface and this microscopic etching retains lubricant well. the way cams are hardened is by the rubbing action of the cam against the lifter. (think of you bending a piece of tin the more you bend it the harder it gets before breaking.
The next important part on cams is the angle the lobe makes with the length of the cam IE the highest point on the cam is not parralel to the length of the camshaft (Almost like a pinion) The lifter is ground at the same angle and resembles a mini crown wheel. The rough etched surface from the parkerizing acts like the gear teeth and this results in the lifter turning as the engine is running constantly lubricating the surfaces and promoting long life. stop the lifter from turning and the cam is eaten away within minutes. Obvously ths constant turning hardens each surface until both are strong enough.This proces continues until the surfaces are so hard that small flakes start falling off (after hundreds of thousands of miles) and a regrind is needed.
Now if you assemble that new engine with these super high pressure titanium gold platet 1000000 rpm valve springs you dont give that poor cam a chance to self harden and life is typically short.
Some of the best in the business actually start their high performance engines on soft valvesprings and gradually increase tension to just keep the vaves closing at the chosen Rpm.
Hope this clears a few issues
Armand
Rule 1 Dont overcam with 1600 gearing 5500 rpm in fourth means 200kmh approx
A cam with more duration means that there is a time when the exhaust and intake is open at the same time with the exhaust open and flowing exhaust first this means that fresh petrol is also sucked out the exhaust .... Lousy mileage results
For racing cars this obviously doesnt matter much but...
It also seems that not all Billet cams are of such great quality and wears out quickly It takes fancy metalurgy and compatibility between lifter and cam to make it last. For the 1961 beetle vw went to a nice light 2 piece lifter and stuffed up so many engines that the 61 was known for years as a dud Opel did the same on the early kaddets
For mild aplications I favour the stock cam and lifters just reground to about 270 degrees
When people talk about hardening the cam I know here is a story coming. The black coating on cams is called Parkerizing.
This was a method invented during the second world war to stop US guns from rusting. it is essentialy dipping the metal in a boiling acid solution which etches the surface and this microscopic etching retains lubricant well. the way cams are hardened is by the rubbing action of the cam against the lifter. (think of you bending a piece of tin the more you bend it the harder it gets before breaking.
The next important part on cams is the angle the lobe makes with the length of the cam IE the highest point on the cam is not parralel to the length of the camshaft (Almost like a pinion) The lifter is ground at the same angle and resembles a mini crown wheel. The rough etched surface from the parkerizing acts like the gear teeth and this results in the lifter turning as the engine is running constantly lubricating the surfaces and promoting long life. stop the lifter from turning and the cam is eaten away within minutes. Obvously ths constant turning hardens each surface until both are strong enough.This proces continues until the surfaces are so hard that small flakes start falling off (after hundreds of thousands of miles) and a regrind is needed.
Now if you assemble that new engine with these super high pressure titanium gold platet 1000000 rpm valve springs you dont give that poor cam a chance to self harden and life is typically short.
Some of the best in the business actually start their high performance engines on soft valvesprings and gradually increase tension to just keep the vaves closing at the chosen Rpm.
Hope this clears a few issues
Armand