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The Dynamics of picking a camshaft #2710543
10/28/19 08:36 AM
10/28/19 08:36 AM
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Mt Morris Michigan
mopar dave Offline OP
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I thought I understood all the dynamics of a camshaft when I was a kid, But now 40 yrs later I still don't quite understand. Shorter durations, narrow lobe sep and advancing it help with lower rpm power. The further you open the valve to get as much air in the better. I would assume more lift affects the whole rpm band? So if you had a stock or tight convertor and picked a cam with a ton of duration it would be a pig on the bottom of the rpm scale. Here's the question, when picking a cam for an application with a 5100 stall and you want the best numbers on your time slip, shouldn't you just be picking the cam for your upper rpm scale? Mine would be 5100-6800. My foot is on the floor all the way down the track and my rpm is never below 5800rpm. What are the effects of the proper spec'd cam in the lower rpm band if my vert flashes to 5100?

Re: The Dynamics of picking a camshaft [Re: mopar dave] #2710563
10/28/19 10:13 AM
10/28/19 10:13 AM
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Val-haul-ass... eventually
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BradH Offline
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I've seen it stated from a couple of sources (Lingenfelter & McCandless, IIRC) that ET improvements generally result from power improvements targeted at the average RPM the engine sees during the full pass. That average is well below peak RPM, unless you're working with a something like a 5-speed stick car that is launched at 9000 RPM and shifted at 9500.

Take a 5000 - 7000 spread and factor in only 3 gears... that average RPM might be 6000 or even lower.

Re: The Dynamics of picking a camshaft [Re: mopar dave] #2710602
10/28/19 12:20 PM
10/28/19 12:20 PM
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I don't know where the torque peak should be for your car for the best ET. My guess would be that if the torque peak was somewhere around your stall speed and didn't fall off very fast after that then it would work great but I don't really know. It is a good question to ask but you would need to ask someone who knows. That is, someone who has a lot of dyno experience and a lot of track experience with a similar drivetrain to you. If it was me I'd probably spend some time on the phone with the torque converter guys and ask them what moves the car down the fastest. I think you want the torque peak lower in the range rather than higher but I don't know if it needs to be at the beginning of your RPM range or can be in the middle or where exactly it should be.

Re: The Dynamics of picking a camshaft [Re: AndyF] #2710622
10/28/19 01:43 PM
10/28/19 01:43 PM
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Mt Morris Michigan
mopar dave Offline OP
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Only benefit I see with the optimum cam below the vert flash point would be combo getting up on the power quicker and hitting the vert harder , possible creating a better 60 foot.

Re: The Dynamics of picking a camshaft [Re: mopar dave] #2710742
10/28/19 07:19 PM
10/28/19 07:19 PM
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So Near, Yet So Far
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Car weight & gearing are a factor, street or strip, which is why converter guys always ask about them.
I've made the mistake once of too much duration (MP 284/.484) for a 3600-lb street 383 with a stock converter & 3.23s; kinda soggy under 3000 RPM, but ran hard above that.
For a drag car, I've always heard the stall should be a couple hundred RPM above the torque peak, so the car always pulls @ max torque/HP.
And that certainly works with my foot-brake drag car with a 6000 stall Lupo converter. (Low-10s 368" Duster)
Cams around .500 - .560 lift with durations @ .050 of 214 - 240s respectively (110 CL) has always made for a strong street car with good manners, even with 3.23s, stock converter or 4-speed, on my stuff.
(Smaller #s being 406" SB, larger #s being 438" RBs, car weights 3400-3600)
In the simplest terms, a converter is kinda like a lever.

Re: The Dynamics of picking a camshaft [Re: mopar dave] #2710753
10/28/19 07:50 PM
10/28/19 07:50 PM
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Melbourne , Australia
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Originally Posted by mopar dave
I thought I understood all the dynamics of a camshaft when I was a kid, But now 40 yrs later I still don't quite understand. Shorter durations, narrow lobe sep and advancing it help with lower rpm power. The further you open the valve to get as much air in the better. I would assume more lift affects the whole rpm band? So if you had a stock or tight convertor and picked a cam with a ton of duration it would be a pig on the bottom of the rpm scale. Here's the question, when picking a cam for an application with a 5100 stall and you want the best numbers on your time slip, shouldn't you just be picking the cam for your upper rpm scale? Mine would be 5100-6800. My foot is on the floor all the way down the track and my rpm is never below 5800rpm. What are the effects of the proper spec'd cam in the lower rpm band if my vert flashes to 5100?


How the engines performs across the RPM band would be a by product of the valve timing events, rather than the valve lift itself I would think, but I am not at all an expert.


Alan Jones
Re: The Dynamics of picking a camshaft [Re: LA360] #2710772
10/28/19 08:55 PM
10/28/19 08:55 PM
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Mt Morris Michigan
mopar dave Offline OP
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I know the cam needs to perform from the launch and thru the traps ideally, but seems like some get hung up on what's going on under the vert flash speed when the engine spends most of it's time working above vert flash speed. Maybe that's why some get away with huge durations cams that some say won't work, but do. Just looking for opinions that's all.

Re: The Dynamics of picking a camshaft [Re: mopar dave] #2710786
10/28/19 09:30 PM
10/28/19 09:30 PM
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Bend,OR USA
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Not all theory on Hi Po parts and combination are dead on whistling grin
My old pump gas six pack stroker motor was one of those shruggy It made max torque at 4500 to 4600 RPM and max HP at 5500 to 5600 RPM on several different engine dyno, that stupid motor like to be shifted above 7000 RPM at the track for the best ET and MPH shock shruggy
As the professor said, we don't race dyno, do we shruggy Same thing on race theories work
Test, test and test some more to learn how to go faster up

Last edited by Cab_Burge; 10/28/19 09:30 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: The Dynamics of picking a camshaft [Re: Cab_Burge] #2710882
10/29/19 10:16 AM
10/29/19 10:16 AM
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Frostbitefalls MN (Rocky&Bullw...
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There is a reason stock and super stock guys usually have a number of converters. To try and best match the highest average hp they can make. I would pick the cam based on the max rpm the heads will use, then have the converter adjusted to match. That would be the fastest way down the track. A lot of guys shoot for a narrow window, tighter than what I run which is 6,000 to 7350 rpm on the data logger. The higher you can stall the converter and still have some efficiency the better. Even though a loser converter loses some efficiency if it is still producing a better average hp through the gears the car will be faster.


8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
Re: The Dynamics of picking a camshaft [Re: gregsdart] #2710901
10/29/19 11:15 AM
10/29/19 11:15 AM
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Val-haul-ass... eventually
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BradH Offline
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OK, we're back to "It depends..."

Re: The Dynamics of picking a camshaft [Re: BradH] #2710904
10/29/19 11:24 AM
10/29/19 11:24 AM
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So. Burlington, Vt.
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Originally Posted by BradH
OK, we're back to "It depends..."


It’s always “it depends” smoke


68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123
Dealer for Comp Cams/Indy Heads
Re: The Dynamics of picking a camshaft [Re: fast68plymouth] #2710909
10/29/19 11:48 AM
10/29/19 11:48 AM
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north of coder
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and the older one gets, the more "depends" one needs. biggrin
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