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I was wandering what the differance is in using 1.52 and 1.6 roller rocker arms. Will using the 1.6 rockers result in any extra power or cause more valvetrain wear? Also will the 1.6 rockers change idle charictoristics at all?
Which ratio would result in the most power for a 40 over 350 with a .470 lift 270 duration cam?
This has been discussed a number of times on several threads so that a search might lead to some of those old postings, although maybe since the search engine likes more than three symbols you won't catch the "1.6" postings but still "rockers" or "rocker ratios" should lead to other facts. Anyway, as far as I know (this is of interest to me as well) you just multiply the cam lift by (1.6/1.5) to get the higher lift using 1.6 ratio rockers. However the duration will also be lengthened by a small amount at the 0.050" lift degree value. I don't know of any easy way to figure the new value for the lift at 0.050" with the 1.6 ratio rockers. Note there is an old thread with a comment by Dr. Bowtie warning that for high lift cams the 1.6 rockers may cause the pushrods to rub on the holes in the heads, but maybe not for lower lift cams. I am just about to check this on my 882 heads which have D-shaped holes for the pushrods and I will just rotate the engine by hand slowly and look for contact between the pushrods and the edge of the holes in the heads. Another related situation is that although the stock stamped metal rockers are supposed to be 1.5 ratios, some articles I have read say that the actual ratio of these stamped rockers is really only about 1.42 and even then they are not all the same so I am setting up with 1.5 roller-tipped rockers on the intakes and 1.6 roller-tips on the exhaust under the assumption that aftermarket 1.5 rockers may actually be slightly higher lift than the stock lifters. Some dyno runs show that short duration cams in a SBC 350 really can use 1.6 ratio rockers on the exhaust valves but with the price of gas as it is now I am going to use 1.5 ratios on the intakes. Note that 1.6 on the intakes might lead to more power and torque but that a greater amount of lift on a short duration cam could lead to detonation if the C.R. is too high. The Comp Cams Extreme Energy cams use some very high lift on short duration intake timings but pay attention to the C.R. to avoid detonation unless you have a tight quench volume above the piston at TDC, since higher C.R. usually have a longer duration and some overlap with the exhaust opening to reduce the extreme pressures, but probably below C.R. of 9.5:1 this is no problem. Take a look at some of the dyno runs on the CompCam site. Again the stock lifters actually RUB hard on the end of the valve stem and this leads to a lot of heat so the roller-tips are supposed to lead to lower oil temps which in turn leads to (maybe) cooler running overall?
Don Shillady
Retired Scientist/teen rodder
Never have done any dyno pulls to confirm it, but a number of years ago we ran 1.6 rockers on the exhaust and seemed to pick up the mid-range power a bit (3,500 to 6500). Didn't seem to hurt the low end, might have lost just a touch on the top. Absolutely no data to back this up, just seat of the pants feel on a circle burner.