Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483030
04/15/18 12:57 PM
04/15/18 12:57 PM
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Joined: Mar 2011
Posts: 3,076 Michigan
A727Tflite
master
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master
Joined: Mar 2011
Posts: 3,076
Michigan
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At least in the mid 70's when I ran my stocker - going through tech in 1975 at Englishtown - they checked lift, duration and overlap.
NHRA Tech used a degree wheel on the damper and tape around the damper to mark the opening and closing events.
Yes they were called cheater cams back then - why I don't know because they checked all the specs. Today they only care about lift.
I'm guessing the lobe had a fast acceleration ramp so at any point between the base circle and toe you had more valve opening but never exceeding max lift - so you were cheating compared to the standard cam rate.
Maybe you can clarify what you are actually trying to achieve - are you limited to some specification and if so why? There are a bunch of cams to choose from - why are you trying determine the trade offs - not being critical - just wondering why.
Last edited by Transman; 04/15/18 01:02 PM.
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483034
04/15/18 01:00 PM
04/15/18 01:00 PM
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crabman173
Unregistered
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crabman173
Unregistered
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In my experience in the real world as you said stockish engines on the street lift unimportant--duration is the way to get it done on hyd cam street engines--as a first step--it simply works-- and is the governor when aiming to make more HP on a street stock type engine ( in addition to more compression up to pump gas limit) Lift on stock heads is chasing the last area to look IMO Lift tends to benefit more at higher RPMs that a street engine usually never sees The ones section of Hi lift cams in the Comp book are aimed at engines with everything else dead on and to take last bit of advantage with really nice heads -- or at least let you THINK that is what is happening--it is all marketing--a street pump gas engine does not need all the latest theory and tricks -- Decent heads with sharp valve job--all the compression you can run with cam and fuel choice--correct intake a sharp carb and most importantly a correctly curved distributor is all you can do on a street engine --then you get the 511 CI big blocks that have it all done right and you can't stick it to the slick public pavement and a 340 Duster with a 4.10 gear smokes you so......... Keep it simple folks--keep that loot in your jeans not under the hood
Cheater cams with that flat nose for lift rule--is the only way they can do it in that crazy class of a few folks--Those cams beat the S%#* out of the valve train and are just stupid to use unless you run in one of those classes In the end...drag racing has some very evolved stupid rules that street guys should never even look at
The world famous .509 cam was made so it was the max lift you could squeeze in on a STOCK 440--just add valve springs and go--NO topping of stock guides --changing seals etc so...they did consider it important to get all they could but really less lift and that same duration would get you 97% of what they were after I bet
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483037
04/15/18 01:02 PM
04/15/18 01:02 PM
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Joined: Jan 2005
Posts: 4,243 Charlotte, North Carolina
sgcuda
master
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master
Joined: Jan 2005
Posts: 4,243
Charlotte, North Carolina
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I think the cheater cams went the other way. I had an old Cam Dynamics hydraulic cheater cam that was .470 lift but was advertised at 352/360 duration. I think they might have only checked duration above a certain lift, so low lift letting extra air/fuel in was flying under the radar.
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483040
04/15/18 01:05 PM
04/15/18 01:05 PM
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Joined: Jan 2003
Posts: 14,499 So. Burlington, Vt.
fast68plymouth
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 14,499
So. Burlington, Vt.
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When my friend first started running his gto in Stock, and it was kind of a dog, we were trying some cams. After about the 5th cam, and not really seeing any noticeable improvements we decided to put the old street/strip solid lifter cam in the motor to see how it responded. We wanted to know if there was something significant to be gained with the right cam, or if we were just chasing our tails. The car picked up like .35 ET and 3-4mph with the "real" cam in it. So, after seeing that, we continued on with our search for the right legal stocker cam.
I guess what I'm saying is, 99% of the time it's going to be pretty easy to beat some lift rule type cam by using a cam that does a better job of providing more area under the curve. And it will probably be more reliable at the same time.
68 Satellite, 383 with stock 906’s, 3550lbs, 11.18@123 Dealer for Comp Cams/Indy Heads
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483045
04/15/18 01:13 PM
04/15/18 01:13 PM
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Joined: Jan 2003
Posts: 20,179 Park Forest, IL
slantzilla
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 20,179
Park Forest, IL
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I had an older Cam Dynamics 'Stocker" cam for my 350 Buick. It would check legal for lift and duration in the '80s. Instead of looking egg shaped the lobes were almost rectangular. The idea was it opened the valve to full lift very quickly, held it at max lift longer, then slammed it shut. They were murder on valvesprings.
"Everybody funny, now you funny too."
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483154
04/15/18 04:57 PM
04/15/18 04:57 PM
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Joined: Jan 2003
Posts: 15,439 Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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... take a stock 1971 340 cam spec 462/473 with a twist of 320-330* of duration. How do I calculate how much more lift can I substitute and lower the duration and achieve the same results. You can't. Google "David Vizard cam duration vs lift" and see what you can find. Although not a direct comparison like you're looking for, he does have at least one example showing how a lower-lift/longer duration cam performs vs a high-lift/shorter duration cam with both making about the same peak HP.
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483195
04/15/18 06:11 PM
04/15/18 06:11 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
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master
Joined: Oct 2007
Posts: 4,206
New York
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There is no direct (linear) cross-over, and it's highly cylinder head-specific. The cylinder pressure curves of "high lift short duration" vs. "low lift long duration" will look completely different even with the same torque and power peak numbers. A hemi or steep inclined stem axis (SBC 23°) unmasks the intake valve toward the cylinder centerline immediately. A shallow wedge (B/RB & Buick 15°, Olds 6°, Cadillac 11°) doesn't and needs lift to clear the wall.
Depending on whom you read, one of 2 events is primary: 1. most authors: intake closing point ABDC, which has no relation to lift 2. Vizard (and Harold Brookshire?): intake opening point BTDC, which has no relation to lift
Boffin Emeritus
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483197
04/15/18 06:14 PM
04/15/18 06:14 PM
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Joined: Oct 2007
Posts: 4,206 New York
polyspheric
master
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master
Joined: Oct 2007
Posts: 4,206
New York
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longer durations within a given lift contributes to steeper ramps That's a design feature, not an engineering requirement. The ramp must be faster when the valve has less time to open.
Boffin Emeritus
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Re: LIFT/DURATION PARODY
[Re: 451Mopar]
#2483495
04/16/18 10:00 AM
04/16/18 10:00 AM
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Joined: Jan 2003
Posts: 10,000 Frostbitefalls MN (Rocky&Bullw...
gregsdart
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 10,000
Frostbitefalls MN (Rocky&Bullw...
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are any of those profiles designed to toss the valve open, and close it smoothly? I have heard that a valvetrain (pushrods?) can be "tuned" to loft the valve over the nose of the cam lobe far enough to be very much worth the trouble. I would asume that would be brutally hard on valvetrain parts!
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky
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Re: LIFT/DURATION PARODY
[Re: polyspheric]
#2483605
04/16/18 02:16 PM
04/16/18 02:16 PM
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Joined: Jan 2003
Posts: 5,894 Florida
Locomotion
master
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master
Joined: Jan 2003
Posts: 5,894
Florida
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longer durations within a given lift contributes to steeper ramps That's a design feature, not an engineering requirement. The ramp must be faster when the valve has less time to open. Not sure if we're saying the same thing. I'm open to gaining a better perspective. But basically, unless I'm misunderstanding something, the longer the duration at a set lift, the less room there is left for the ramp, so it has to be more aggressive/steeper. That's where the exaggerated term "square lobes" come from. It doesn't look like one has a choice.
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Re: LIFT/DURATION PARODY
[Re: A/MP]
#2483615
04/16/18 02:39 PM
04/16/18 02:39 PM
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Joined: Jun 2005
Posts: 6,257 gulfport, ms, west mi
rowin4
master
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master
Joined: Jun 2005
Posts: 6,257
gulfport, ms, west mi
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Anybody that was around class racing back in the 60-70's can recall the sound of the 'STOCK' cam, the only thing stock about them was the specs. Square lobes as Locomotion stated. Similar to running a flat tappet lifter on a roller cam, roller lifters weren't around at that time. Maybe that's where the roller idea came from.
it's ok to butt heads, just don't do it with a butthead
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Re: LIFT/DURATION PARODY
[Re: rowin4]
#2483623
04/16/18 02:57 PM
04/16/18 02:57 PM
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Joined: Aug 2003
Posts: 43,190 Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,190
Bend,OR USA
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I use to race a 1968 street hemi in NHRA stock back in the early 1970s, the first "cheater cam was a Clay Smith conventional lobe type solid lifter cam. The last legal 340 motor I built had a Isky round nose, AKA as a "square" nose cam that would check legal in the motor with the proper rocker arms on it I tested three different cams in that customers motors, the best performing cams was a Lunati with standard designed lobes, pyramid or pointy nose lobe cam. Both Iskys where square nose cams, one ground on a 107 LSA and the other one was on a 105 LSA where real peaky on the engine dyno, they made 10 HP more than the Lunati did but the Isky cams wouldn't make 400 HP until above 5500 RPM and would nose over real bad after 5900 RPM and be below 400 HP at 6100 RPM. The Lunati would make 400 HP at 5000 RPM peaking at 6000 RPM with 420 HP and make 400 HP at 7000 RPM That was back in the early 1990s I think I ran 160 lbs on the seats and around 350 + lbs. opened. The Isky cams in that motor liked to be shifted at or lower than 6400 RPM, the Lunati liked to be shifted at or above 7000 RPM, it picked that car up around 2 MPH in the 1/4 mile also
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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