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| School me on rocker arm ratios https://slantsix.org/forum/viewtopic.php?t=27091 |
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| Author: | Jopapa [ Sat Feb 09, 2008 1:46 pm ] |
| Post subject: | School me on rocker arm ratios |
Basically, I have no idea what the ins and outs are of using different rocker arm ratios. From my understanding, the stock arms are a 5.7 ratio and the in-process group buy for the T&D roller rockers is for a 1.6 ratio rocker arm set (is this right?). So what's to be gained (or lost) from using different from stock ratio rocker arms? |
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| Author: | AndyZ [ Sat Feb 09, 2008 4:12 pm ] |
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Stock rocker ratio on a slant is 1.5 The reason people use a 1.6 ratio is to open the valve more and have the slope of the lift increased throughout the cam lift. It doesn't always get you better performance though. |
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| Author: | SlantSixDan [ Sat Feb 09, 2008 5:04 pm ] |
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Stock ratio is nominally 1.5, but factory tolerances being as sloppy as they were, the actual ratio varies. I was pretty sure Doc had some specific comments on the ratios he's measured in stock rocker arms, but I can't find the post. |
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| Author: | dakight [ Sat Feb 09, 2008 5:33 pm ] |
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Someone set up a jig and measured the ratios using a dial indicator. I don't think it was Doc but I remember the post. |
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| Author: | Bren67Cuda904 [ Sat Feb 09, 2008 5:48 pm ] |
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I beleive it was argentina-slantsixer |
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| Author: | sandy in BC [ Sat Feb 09, 2008 7:12 pm ] |
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Sam Powell |
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| Author: | Jopapa [ Sun Feb 10, 2008 3:55 am ] |
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Quote: Stock rocker ratio on a slant is 1.5 The reason people use a 1.6 ratio is to open the valve more and have the slope of the lift increased throughout the cam lift. It doesn't always get you better performance though.
Wow, that's alot simpler than I thought it would be. I wonder where the heck I got the 5.7 number from...
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| Author: | dakight [ Sun Feb 10, 2008 4:04 am ] |
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You probably read the thread about Heckshemi's experimental head. He recently posted a question about the oil pump gear where he says something about 5.7 rockers. What he's talking about is the rocker arm from a 5.7 L "Hemi" engine from which his head is derived. |
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| Author: | engnbldr [ Mon Feb 11, 2008 12:40 pm ] |
| Post subject: | Re: School me on rocker arm ratios |
[quote="Jopapa"]Basically, I have no idea what the ins and outs are of using different rocker arm ratios. From my understanding, the stock arms are a 5.7 ratio and the in-process group buy for the T&D roller rockers is for a 1.6 ratio rocker arm set (is this right?). So what's to be gained (or lost) from using different from stock ratio rocker arms?[/quote] >>>*We have used longer ratio rocker arms for years. It is common to use them with Smallblock Chevrolet, especially stroker engines as the cam lobe can hit the crank on those. So to get more total lift, we would reduce the cam base circle and increase the rocker arm ratio. There are other ways to do that of course but the fast way to add more cam is to use the arms. It is a fairly easy and cheap way to find out if an engine design wants more camshaft lift. A typical example is basic math. A common cam lobe that has .280" lobe lift is .280" X 1.5= .420" gross valve lift. .280" X 1.6=.448" total valve lift. The valve also opens more quickly through the cycle.......*EB |
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