Lift vs Duration
#1358975
12/25/12 07:17 PM
12/25/12 07:17 PM
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moparpollack
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Lil Herman
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Lil Herman
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Looked at a stocker cam and the class mandated a maximum lift but not duration. So stocker guys can you make decent power holding the valves open longer? 
56 Plaza 63 D100 step side 67 Coronet, 68 Roadrunner, 69 Super Bees, 69 Coronet 500 convertible, 70 Roadrunner Post, 79 D150 360, and a severe case of Mopar a,d,d
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Re: Lift vs Duration
[Re: moparpollack]
#1358977
12/25/12 07:49 PM
12/25/12 07:49 PM
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Yes, but just like most other modifications, bigger isn't always better. One has to balance the amount of duration with engine size, compression, car weight, gears, etc. The cam companies tend to have a pretty good idea what's required. But you just have to get one of their "Stocker Specialists". Racers can also experiment one way or the other on their own.
It's always amazed me how fast Stockers can run within the limited rules. Of course there are a lot of things you can do that help and there are racers who "push the envelope", but when you consider the limits on lift and carb size, car weight, etc., it's still surprising.
i.e: Elephuntman, a member here, has a '70 340-6 Challenger T/A that ran 10.30's! I believe there have been some high compression '71 340's that have been 10.40's! But it takes a lot of time, research, testing & money. I can't afford to be that fast, but I'm content where I'm at.
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Re: Lift vs Duration
[Re: Locomotion]
#1358978
12/25/12 08:23 PM
12/25/12 08:23 PM
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moparpollack
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Lil Herman
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Lil Herman
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My buddy's son runs a 305 camaro and the cam was very odd looking. The guy who designed the cam was a national record holder. Supposedly the cam centerline was at 100-102 degrees. He suggested bringing the cam in as fast as possible. If possible sink the valves in the head so they don't hit the pistons. Just another way to make racing interesting and expensive. 
56 Plaza 63 D100 step side 67 Coronet, 68 Roadrunner, 69 Super Bees, 69 Coronet 500 convertible, 70 Roadrunner Post, 79 D150 360, and a severe case of Mopar a,d,d
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Re: Lift vs Duration
[Re: moparpollack]
#1358979
12/25/12 08:31 PM
12/25/12 08:31 PM
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Quote:
If possible sink the valves in the head so they don't hit the pistons.
Gotta watch that too because sinking valves can hurt air flow. Late '70's 360's come in "big cam" and "little cam" versions. Yet, NHRA has rated them at the same HP. I've heard from a couple of racers that they do run about the same and some actually prefer the smaller lift cam version!
There are a few ways to change piston-to-valve clearance, including varying duration and advancing/retarding the cam. Depends what that particular engine likes.
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Re: Lift vs Duration
[Re: DrCharles]
#1358983
12/25/12 10:17 PM
12/25/12 10:17 PM
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Quote:
The advertised duration was 352/380 degrees! Square lobes...
All the factories not only under-rated their engines for an advantage, they also "fudged" on some specs. Those numbers are way more than an engine could run on, but it gave racers and cam grinders a wide margin to work within for cam specs.
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We bought two other cams to try in that motor on the dyno, the one that was in it was ground on a 107 LSA, I order the same cam ground on a 105 LSA and another sharp nose legal stocker cam from Lunati ground on a 106 LSA. I installed and dyno tsted all three cams in at straight up, 2,4,6 crankshaft degrees advanced and then 2 degrees retarded. The 105 LSA Isky installed at 4 degrees advanced made the most peak power and torque but the power range was very steap and fell off real quick. Lunati made 10 HP less peak power but it made peak power over a lot broader range before dropping off. The Lunati made 405 HP at 5000 RPM, 420 HP at 6000 RPM and 405 at 7000 RPM. The 105 Isky made 400 HP at 5700 RPM and 430 at 5900 RPM and fell off to 400 HP at 6100 RPM 
Lots of ways to make power, keeping it and applying it is the hard part 
