Rocker Arms - Page 4

Dgal · 05-07-2010, 09:40 AM

I reserve the right to be wrong, but I believe the Nascar teams have experimented with larger ratio rocker arms in order to reduce the amount of spring pressure on a given lift/duration. Less spring pressure should equate to less parasitic hp loss within the valve train.

Greg Reimer 7376 · 05-07-2010, 10:00 AM

On another thread, I remarked about a 283 racer who went through about 100 stamped OEM rockers to get the 16 that he used. That was back in the day when OEM was all that was allowable, and the best arms were the ones with the little triangle on top of the tip above the valve stem tip.I don't know ,however, if he was attempting to achieve accurate lift, or whether he was striving for as accurate a ratio as possible.With all the latitude that various length pushrods can produce,there is an almost infinite degree of possibilities. Yes, it's interesting what an open forum can produce.Thanks to Travis for the expose' on how rocker arm ratios are calculated.

Dwight Southerland · 05-07-2010, 03:58 PM

The higher ratio rocker arm will increase any action ground into the camshaft profile by a mathematical amount. One of the limitations of how radical a camshaft profile can be ground is the lifter diameter. So, when the camshaft has been designed to maximum acceptible rate of lift change dictated by the lifter diameter, then there is no more that can be done to make the valve open any more at a given lobe lift. The higher rocker arm ratio allows a little bit more lift at a given lobe lift, hence "more area under the curve". Also, you can grind a faster ramp into a camshaft profile if the lobe lift is less, also providing for more area under the curve.

See what Alan said above. If I could draw pictures here, it would be easier to see.

Alan Roehrich · 05-07-2010, 06:52 PM

Quote:

Originally Posted by Dwight Southerland

If I could draw pictures here, it would be easier to see.

Ain't that the cryin' truth.

Greg Reimer 7376 · 05-07-2010, 09:15 PM

Quote:

Originally Posted by Jack McCarthy

elgin rocker arms, then ship to jim bailey he will harden and polish them... shazaam nice pieces and very reasonable pricing

captain jack

Elgin part number for the 7/16 rocker arms is R-1840.The rocker arm ball isn't included and the part number for the rocker arm ball is RM-1000. Don't try and use a big block ball. It won't fit down in the arm. 7/16" screw in studs and poly locks are everyplace . I've had to do other things on other engines to make stuff right such as using different length push rods on some valves. Good luck on your project.I'm in the middle of this on a 327 I'm doing for my Chevelle. Short block's done, I'm assembling and sorting out the heads and the valve train,now its time to measure lobe lift and compare it to total lift. One more thing to do.

Jeff Lee · 05-07-2010, 11:05 PM

Well at least the lowly AMC came with 1.6 rockers and .903" lifters...

Adger Smith · 05-08-2010, 12:39 AM

Some of the latest Spintron "best results" have been with reduced ratio rockers and cam lobes that are larger diameter and shaped quite a bit different than what was once thought good. Less deflection, less spring pressure, less failure, sometimes more power!

05-07-2010, 09:40 AM	#31
Dgal Member Join Date: Dec 2009 Posts: 169 Likes: 0 Liked 0 Times in 0 Posts	Re: Rocker Arms I reserve the right to be wrong, but I believe the Nascar teams have experimented with larger ratio rocker arms in order to reduce the amount of spring pressure on a given lift/duration. Less spring pressure should equate to less parasitic hp loss within the valve train.

05-07-2010, 10:00 AM	#32
Greg Reimer 7376 VIP Member Join Date: Nov 2008 Location: Glendora,Calif. Posts: 1,137 Likes: 172 Liked 719 Times in 220 Posts	Re: Rocker Arms On another thread, I remarked about a 283 racer who went through about 100 stamped OEM rockers to get the 16 that he used. That was back in the day when OEM was all that was allowable, and the best arms were the ones with the little triangle on top of the tip above the valve stem tip.I don't know ,however, if he was attempting to achieve accurate lift, or whether he was striving for as accurate a ratio as possible.With all the latitude that various length pushrods can produce,there is an almost infinite degree of possibilities. Yes, it's interesting what an open forum can produce.Thanks to Travis for the expose' on how rocker arm ratios are calculated.

05-07-2010, 03:58 PM	#33
Dwight Southerland VIP Member Join Date: Dec 2001 Location: Arkansas - In the middle of everything. Posts: 2,001 Likes: 64 Liked 780 Times in 194 Posts	Re: Rocker Arms The higher ratio rocker arm will increase any action ground into the camshaft profile by a mathematical amount. One of the limitations of how radical a camshaft profile can be ground is the lifter diameter. So, when the camshaft has been designed to maximum acceptible rate of lift change dictated by the lifter diameter, then there is no more that can be done to make the valve open any more at a given lobe lift. The higher rocker arm ratio allows a little bit more lift at a given lobe lift, hence "more area under the curve". Also, you can grind a faster ramp into a camshaft profile if the lobe lift is less, also providing for more area under the curve. See what Alan said above. If I could draw pictures here, it would be easier to see.

05-07-2010, 11:05 PM	#36
Jeff Lee VIP Member Join Date: Jul 2007 Location: Anthem, Arizona Posts: 2,766 Likes: 0 Liked 3 Times in 3 Posts	Re: Rocker Arms Well at least the lowly AMC came with 1.6 rockers and .903" lifters... __________________ Jeff Lee 7494 D/S '70 AMX

05-08-2010, 12:39 AM	#37
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: Rocker Arms Some of the latest Spintron "best results" have been with reduced ratio rockers and cam lobes that are larger diameter and shaped quite a bit different than what was once thought good. Less deflection, less spring pressure, less failure, sometimes more power! __________________ Adger Smith (Former SS)