Quarter Speed Cam

[righttirefire]

This subject was touched earlier, but why can't you make a cam that spins 1/4 the rotation of the crank. I'm aware the it would have two lobes. If you took a SB chevy cam, for example, ground one with half the angle of the origanl base circle and created two lobes, on opposing sides of tha base circle. Therefore the the cam is spinning half the speed of a normal cam, the duration would remain the same. I heard Buzz Schaller invented one, It was origanlly for Harley-Davidsons, and adopted into a Chevy Mickey Thopmson used in a indy car. Is it possible to ground one, if so why aren't they popular? It seems to me it would be more efficent, it would spin slower so higher rpms could be reached quicker, and there would be less friction which should directly effect horsepower and torque.

 

[patprimmer]

Most of the friction is at the cam/follower interface, which would not change. The small gains in spinning the cam in the cam bearings slower would be lost to the extra weight of the cam. It would cost considerably more to grind as there are twice as many lobes. The main advantage would be twice the area to resist wear as the lobes effectively do half the miles each, so life should double for the lobes, but the lifters will still wear.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[DesignOutsourcing]

I have no direct experience of these cams nor have I read anything authoritative about them. I was told by someone who works with racing engine development that the advantages of the quarter-speed cams were at very high rpms (like the 18,000+ of F1 engines) where the drag from air and oil are going up exponentially.

My concern/question just thinking about it now would be the very steep lobe ramps. Since the lobes will be half the original (in degrees), the ramps will be twice as steep. The valve train geometry would need to looked at as well. cheers, derek

 

[MikeHalloran]

Schaller quarter- speed cams for SBC were offered for sale at about the same time an article about them appeared in "Hot Rod". It was pure coincidence that editorial and advertising content would appear at the same time, of course. It was a long time ago.

As mentioned, the steep lobe ramps meant that it was basically impossible to grind them 'mild', as for street use.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[Speedfreaks101]

I have been intrigued by the Schaller 1/4 speed cam and have tried to find any info possible but there is not much to be had. I spoke with many cam grinders and even tried to find someone to grind one for me but no one seemed up tot he task.

The Schaller cams were ground with a reverse rotation since the cam gear ran directly against the crank gear. They came with a timing cover, distributor and the timing gears.The cam was billet roller and straddle-lobe roller lifters came with the kit. They were avalible for the 265, 283, 348 and 409 Chevys; 352 ('58-'61) Ford, 430 Linclon and "Competion Olds"

As I said I tried to find someone who would be interested in helping me with the cam and in the process I asked quite a few questions. When I spoke with Isky I was told that the cams had a problem with the cams breaking since the base circle had been cut down so significantly. Also there was a proble with not being able to produce enough lift in the short about of duration. What I mean is that when you reduce the speed by one half then you also have to reduce the effictive duration by the same amout in order to retain the original duration. I think that the the metal techknology of the time to would have played a role in the cams breaking along with the previous mentioned steep lobe angles.

Here is an opinon of mine. I thing if you could ever get a lobe that would equal the duraion and lift of a modern day race type solid roller cam that the action would be so violent that would very difficult if not impossible to control. There is also the issue of the cam gear running directly on the crank and the hormonics that would be transmitted to the valvetrain.


I don't know if this helps any but I figured it cold not hurt. BTW they cost 315.00 bucks and the patent # was 2,877,752


Later,
Bart

 

[MikeHalloran]

I think the problem for a cam grinder is that the transition between the lobes and the base circle has to be concave, unless you enlarge the base circle to a degree that's impossible in a production engine, and that makes the surface speed and the roller rotation speed go up, too.

Which in turn means that the actual grinding wheel in the cam grinding machine has to be a little bitty thing about the diameter of the roller, and it has to be spun at a bazillion rpm to cut. Whereas a normal cam grinding wheel is pretty large, and spins at a more practical speed.

By contrast, half- speed cam lobes are convex everywhere, so you could generate them with a grinding wheel of any size.



Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[ZoRG]

The F1 cams I have seen were all single lobes.