How much power can be found by running an asymmetrical lobe? I notice that Isky seems to using "old school" symmetrical lobes in many of thier small street cams. Can these compete with the newer lobe designs?

don't know if this relates ('cause I don't know much!) but the guy that did my head porting said that I didn't need a dual pattern cam (asymetrical?) and recommended an isky single pattern cam (symmetrical?) because of the way he ports the heads on the exhaust side.... does this sound reasonable?

Thanks for the input, but I should have clarified... I am talking about lobe shape, not a dual pattern cam. smile.gif

like I said, I don't know much.... smile.gif

No if im correct here symmetrical and assymetrical are not the same a single patern and dual pattern cams. I think it has to do with the opening and closing ramps. Where a symmetrical cam has the same opeing and closing ground into the ramp and asymmetrical maybe has a faster opeing and slower closing, or vice versa. Im not 100% sure and could be wrong maybe somone will chime in here.

Originally posted by Nickel333:
No if im correct here symmetrical and assymetrical are not the same a single patern and dual pattern cams. I think it has to do with the opening and closing ramps. Where a symmetrical cam has the same opeing and closing ground into the ramp and asymmetrical maybe has a faster opeing and slower closing, or vice versa. Im not 100% sure and could be wrong maybe somone will chime in here. Your correct.

thanks Nickel and Pat! now I know something I didn't before. graemlins/thumbsup.gif What's got me worried is what information was forced out of my brain to make room for this new stuff..... graemlins/clonk.gif

Originally posted by Purs:
thanks Nickel and Pat! now I know something I didn't before. graemlins/thumbsup.gif What's got me worried is what information was forced out of my brain to make room for this new stuff..... graemlins/clonk.gif Kind of like what happens to Kelly Bundy :D .

Originally posted by Nickel333:
No if im correct here symmetrical and assymetrical are not the same a single patern and dual pattern cams. I think it has to do with the opening and closing ramps. Where a symmetrical cam has the same opeing and closing ground into the ramp and asymmetrical maybe has a faster opeing and slower closing, or vice versa. Im not 100% sure and could be wrong maybe somone will chime in here. True, an assymetrical lobe is different on the opening and closing ramps. This can be done for many reasons. To help maintain control of the valvetain for better stability. To make use of a particular cylinderhead (ex.if the head has a particular sweet spot). Or to help promote better vacuum or low end torque......hope this helps :eek:

If I remember right, all of Harolds Ultradyne grinds were asymetrical. I think it works with large flat tappets to sit the valve down more gently on the seat.

As far as an asymetrical lobe being something new or better... it should be noted that Asymetrical lobes were first patended in the late 1920's.Like everything else there are different degrees ( pun intended ) to a given lobes asymetry .... some will be conservative with it and others will push the limit... IE just because any given lobes are asymetrical doesnt necessarly mean it's the same for all asymetrical lobes....same applies to symetrical lobes.... All depends on what the designer was trying to acomplish .

Symmetrical vs assymmetrical(or unsymmetrical) lobe designs......
I think the last symmetrical lobe designs I did were in 1976...... Many of them are still being sold today, and they work OK(not BEST, or I would still be designing them...).Assymmetric cam design merely means that the opening and closing sides are designed differently. You can open fast, shut slow, or you can open slow, shut fast.
I got my inspiration for unsymmetric cams from Racer Brown, who didn't do them,AFAIK. He wrote an article in the mid-60s about Toyota engines, in which he noted that cams that opened and shut the valve very fast made great power, but were brutal on parts. He also noted that cams that opened and shut the valve much slower were very stable in high RPM and didn't break parts, althought their low-end power was down.
I quickly identified shutting the valve hard and fast with breaking parts, and shutting the valve slower with less parts breakage and better high-RPM stability. Tying fast openings and slow closings seemed to me to be the best of both worlds, but it was at least 10 more years before I designed and made my 1st unsymmetrical cam lobe. This cam was the Comp Cams 324-4(I believe, I don't have a CC catalog available..), 324° at .020, 286° at .050, .4544 lobe lift---They still sell that lobe today. It turned 11,000 with ease back in 1977-1978.
My 1st unsymmetric hydraulic was the 268 High Energy cam, 268° at .006", 218° at .050", and .454" valve lift.
What I have said since 1977 is that by delaying the opening of the intake port, reversion(exhaust gas being pumped out by the rising piston on the exhaust stroke) is minimized, compared to a cam with an earlier opening. Because this reversion is minimized, when the piston starts down on the intake stroke, the lessened reversion cleans out of the intake port earlier, and starts airflow earlier. Would YOU let your opponent in a drag race have a .1th head start? What about a .25th?
Although I use very fat cams at high lift, this isn't actually a part of unsmmetrical cams. But because the properly-done unsymmetric cam has a higher port velocity, a fatter-duration cam in high lift area has MORE time to fill the cyclinder, and is filling it at a FASTER rate.
Shutting the valve gentler helps ensure aginst valve bounce, and the corresponding release of cylinder pressure back into the intake runner. It also helps parts life.....
I will try to answer more tomorrow/today. I have only Saturday and Sunday every week at home, The last 5 weeks have been spent in Bowling Green at Corporate HQS, learning how to fill out forms like a proper engineer.
There are also gains to be had with unsymmetric cams as exhaust lobes, and the two, intake and exhaust, work together very well.
I will see you all tomorrow....

UDHarold

Harold ,

Speaking of Racer Brown , there was an article in the book titled " Basic Engine Hotrodding #2 " circa
1975 or so.... They did a cam swap on a 327 useing RB's grind EH-4 ( .405 / 256 @.008 ) this was during the gas crunches and they were looking for economy...They did mention in the article that they were asymetrical lobes with the intake lobe being a slow opening type but the exhaust lobe was a fast opening / slow closeing type lobe... So the intake and exhaust were differet lobes but the same lift and durations. This was pretty late in his career and maybe was just an expiriment ? ... who knows ... Too bad we cant ask him !

There is also an article I read several years ago somewhere on the net about RB doing some Datsun cams with their odd OHC mechanism ... The OE Datsun cam lobes were visably asymetrical but due to the unuseual geometry the asymetrical lobe actually produced symetrical " Valve " motion.... So he decided to grind symetrical lobes useing the oddball geomerty to impart asymetrical " Valve" motion..... This back in the day when Datsun's 510 and 240Z were a force in the SCCA type stuff.

Intresting stuff.

I think my post asking about the Jag., May Fireball head got into the Toyota stuff that Harold mentioned that Racer Brown was into if not mistaken?? Maybe, maybe not???

http://www.chevelles.com/cgi-bin/forum/ultimatebb.cgi/topic/4/21543.html?

pdq67

Thanks, guys.....

With swinging-follower rocker geometry, whether you have symmetrical or unsymmetrical valve motion, the cam always has that odd look. Different engines, with different valve-train measurements, will look different even with the identical valve motion. The 2300 Pinto has a 44mm radius rocker arm, the 4.6L Ford has a 11.43mm radius rocker arm. No masters are interchangeable with swinging-follower cams.

UDHarold

Good stuff!

Are all of the modern grinds from the big companies asymmetrical?

Originally posted by novadude:
Good stuff!

Are all of the modern grinds from the big companies asymmetrical? The answer to that question is no they are not. Some like Reed or Bullet and others mention wether any given lobe is Symetrical or Asymetrical... Others dont divludge the info but will likely tell you if you ask.

Both style of lobes have been getting cars down the road since the beginning of cars (well almost). Harold is a big proponut of the Asymetrical lobes...In his old Ultra Dyne catalogs he mentions that is all he designs anymore , and he has his reasons as he has explained. Other cam companies offer both or just symetrical for what ever reasons they have...My last cam change I used a really old (mid 70's) symetrical lobe and am very pleased with the way it runs for my application. I have seen people run Harolds cams and they useully have a big grin on their face afterwards..... Both style lobes have thier place
and will be around for a long time to come.