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Author
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Topic: Help me understand rockers and push rods.
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Fastymz
Moderator Posts: 18703
From: Reno Nv USA MEM#1240
Registered: Apr 2001
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posted 11-29-2002 08:36 PM
   
Sorry more dumb questions.1.5 1.6 1.7 ratio rockers how do they get a greater ratio out of them.
Why and when would you use them.
Push rods why would you use a longer one. I understand how all the parts work together. Alex you helped with my questions,But I had more so I thought I'd post them in case any one else.Was in need of more knowledge like me.  SCOOP ------------------
oddly obsessed with big scoops on little Mustangs 2.26 60'S
14.9 @ 90.86MPH 65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede. https://mustangsandmore.com/ubb/Fastymz.html
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SteveLaRiviere
Administrator Posts: 43151
From: Saco, Maine
Registered: May 99
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posted 11-29-2002 08:51 PM
When you look at the fulcrum {pivot} of a rocker arm, you see they aren't centered. The side that has the pushrod is shorter than the side that contacts the valve stem. So with a 1.5:1 ratio rocker, so the distance pushrod goes up, the valve stem goes down 1.5. If your cam lobe's lift is .300", the valve will open .450" {.300" x 1.5 = .450"} Using rockers with great ratios will in effect give you a greater lift at the valve with the same cam lobe. It will also give you slightly longer duration since the time the valve will be off it's seat will be longer. You change the length of the pushrod in order to keep your rocker arm geometry correct. You want to center the tip of the rocker arm over the center of the valve stem for as much of it's travel as possible. That prevents side loading of the valve guides and premature wear and friction among other things. ------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150 Be sure to remember our sponsors, Mustangs Plus, NPD, and Osborn Reproductions.
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Moneymaker
Administrator Posts: 25883
From: Lyons, IL, USA
Registered: May 99
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posted 11-29-2002 08:53 PM
The rocker arm ratio is determined by the position of the rocker arm fulcrum or stud mounting point. Simply put, the closer the push rod is to the stud, the greater the ratio. This allows the rocker to push the valve open further using more geometry. The rocker will push the valve open (down) 1.5, 1.5, 1.7 etc times the amount of gross camshaft lift.The duration is also increased. There are many situations where you would want a higher ratio rocker arm. The most common is to increase cam performance without having actually replace the cam. Others are to create more power on extreme race applications where lobe designs are already so radical that you can't physically get a much larger cam to work. This is very common in Superstock racing. I have different ratio rockers on MM on the intake and the exhaust.
You would need to change push rod lengths to correct rocker arm geometry. Many times afterhead machining or cam/roller rocker changes the rocker is no longer centered on the valve stem tip. To achive this you may need a shorter or most times longer push rod.
There is also some horsepower available with longer push rods when using hydraulic roller cams but that is a science in itself and a closely guarded secret among NHRA'/IHRA stock eliminator and NMRA pure stree racers.
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Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
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Moneymaker
Administrator Posts: 25883
From: Lyons, IL, USA
Registered: May 99
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posted 11-29-2002 08:54 PM
OK so it takes me longer to type on Beth's laptop.  ------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
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SteveLaRiviere
Administrator Posts: 43151
From: Saco, Maine
Registered: May 99
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posted 11-29-2002 09:03 PM
Slow poke. ------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150 Be sure to remember our sponsors, Mustangs Plus, NPD, and Osborn Reproductions.
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Fastymz
Moderator Posts: 18703
From: Reno Nv USA MEM#1240
Registered: Apr 2001
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posted 11-29-2002 09:12 PM
Thanks guys I read that a couple of times, it helped alot. 
I do feel dumb asking simple questions like that on an open forum,but I also need to learn some were.So why not learn from the best.  SCOOP ------------------
oddly obsessed with big scoops on little Mustangs 2.26 60'S
14.9 @ 90.86MPH 65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede. https://mustangsandmore.com/ubb/Fastymz.html
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Fastymz
Moderator Posts: 18703
From: Reno Nv USA MEM#1240
Registered: Apr 2001
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posted 11-29-2002 09:21 PM
Setting up the motor,and turning it.Is that the only way to know for sure what lenght push rods will work with what cam and rockers.SCOOP
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Moneymaker
Administrator Posts: 25883
From: Lyons, IL, USA
Registered: May 99
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posted 11-29-2002 10:08 PM
G.A.S. with one of your 'stangs sometime Steve and see just how slow I really am. Ron, I have said it before and I'll say it again, there are never any stupid questions on M&M. You do have to have the engine assembled with the heads on and cam in to assertain correct rocker arm geometry. ------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
IP: Logged |
Bloose
Gearhead Posts: 621
From: Milwaukee, WI
Registered: Dec 2001
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posted 11-30-2002 01:30 AM
Guys,One thing about rocker ratio's. I don't know how it is possible for duration to change with rocker arms. The total duration of the cam cannot change and the duration at .050 lift I believe is measured at the cam lobe not the valve, do I have that correct (that's what it said on my cam card). Regardless, no matter the rocker ratio closed is closed. The valve will not open until the lifter meets the ramp of the cam lobe. It will then be fully closed when it reaches the bottom of the ramp, but the ramp never changes, therefor the total duration doesn't either. So the valve is not really open any longer no matter the rocker arm ratio. What the longer arms would do is cause the valve to open and close at a faster rate, and I think that would cause the cam to act like it had a longer duration, much like having a longer duration at .050 but the same total duration on two different cams. Does this make sense to anyone but me? The real question is whether the duration at .050 is at the tappet or at the valve. If it is at the tappet then the duration at .050 cannot change either, but longer rocker would give the effect of more duration, though it would actually not change. If it is at the valve then the duration at .050 would change, but total would not. From reading my cam card it looks like the duration at .050 is at the tappet but it is not 100% clear. Anyone reading me? B-loose
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68F100
Gearhead Posts: 2377
From: Fort Madison, Iowa USA - United We Stand
Registered: Oct 99
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posted 11-30-2002 05:30 AM
Hey SCOOP, you aren't the only one learning when you post these "dumb" questions. I just don't think to ask them before you do. Got a buddy in AZ who has a 65 Chivvy pickemup with a big block that I want to be able to stomp when I'm done with mine, so I read and learn all I can here.
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Mario428
Journeyman Posts: 76
From: Charlottetown, PEI, Canada
Registered: Nov 2001
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posted 11-30-2002 06:29 AM
Yes .050 duration numbers are measured at the cam lobe. Effectively that method takes the rocker ratio out of the picture and the lobe can be checked in any engine regardless of rocker ratio.
Duration from valve .050 open to .050 from closed does increase with increased rocker ratio though. A 1.6 rocker needs .031 of cam lift to open valve .050, 1.7 rocker only needs .029. Valve is at .050 lift ealier increasing duration.
The 1.76 ratio on FE's makes their camshafts look like completly different lobes with big valve lift numbers.
IP: Logged |
SteveLaRiviere
Administrator Posts: 43151
From: Saco, Maine
Registered: May 99
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posted 11-30-2002 11:34 AM
quote:
Originally posted by Moneymaker:
G.A.S. with one of your 'stangs sometime Steve and see just how slow I really am.
No thanks, I know better than to bring a knife to a gun fight... ------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150 Be sure to remember our sponsors, Mustangs Plus, NPD, and Osborn Reproductions.
IP: Logged |
Moneymaker
Administrator Posts: 25883
From: Lyons, IL, USA
Registered: May 99
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posted 11-30-2002 11:42 AM
When it comes to a keyboard partner, you da man though! ------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/IHRA/SRA member and licensed Superstock driver
MCA member# 53321
NHRA and IHRA SS/LA National Record Holder '00, '01, & '02
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28
Professional Manwhore
The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
IP: Logged |
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