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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Joined: Jan 2003
Posts: 20,645 So Near, Yet So Far
topside
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 20,645
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.
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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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Joined: Jan 2003
Posts: 6,130 Melbourne , Australia
LA360
master
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master
Joined: Jan 2003
Posts: 6,130
Melbourne , Australia
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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? 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
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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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Joined: Aug 2003
Posts: 43,007 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,007
Bend,OR USA
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Not all theory on Hi Po parts and combination are dead on My old pump gas six pack stroker motor was one of those 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 As the professor said, we don't race dyno, do we Same thing on race theories Test, test and test some more to learn how to go faster
Last edited by Cab_Burge; 10/28/19 09:30 PM.
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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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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Joined: Jan 2003
Posts: 9,963 Frostbitefalls MN (Rocky&Bullw...
gregsdart
master
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master
Joined: Jan 2003
Posts: 9,963
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
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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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Joined: Jan 2003
Posts: 14,479 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,479
So. Burlington, Vt.
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OK, we're back to "It depends..." It’s always “it depends”
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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