Rocker Arm Ratio

Greg Reimer 7376 · 08-08-2012, 10:28 AM

I remember talking with a very successful builder of 283's years ago who mentioned going through a bucket of about 100 stock rockers before he found 16 that were right. OEM stamped parts can be all over the place as to their actual ratios.It is very possible to assemble a stocker motor with a set of them and have one or more over as well. If they check lift at the retainer, then lobe lift and even though net lift at the valve is OK, it can be and often is that the OEM rocker arm is over enough to render the combination illegal. On a SBC, rocker arm ratio is 1.5 to 1. That is a finite spec. Check the lobe lift at the lifter, multiply by 1.5, there is your maximum allowable valve lift. If lobe lift checks, rocker arm ratio is good, but valve lift is a little shy, try different length pushrods to see if it brings things up where they belong.That can be your variable to make this whole thing work. Remember, check EVERYTHING, leave nothing to chance, because they will if you don't, and nobody wants to be sent home early over something as simple to avoid as this.We had a very fun involved discussion on push rod length determination here in the last off season if you care to locate and review it.

08-08-2012, 10:28 AM	#26
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 Arm Ratio I remember talking with a very successful builder of 283's years ago who mentioned going through a bucket of about 100 stock rockers before he found 16 that were right. OEM stamped parts can be all over the place as to their actual ratios.It is very possible to assemble a stocker motor with a set of them and have one or more over as well. If they check lift at the retainer, then lobe lift and even though net lift at the valve is OK, it can be and often is that the OEM rocker arm is over enough to render the combination illegal. On a SBC, rocker arm ratio is 1.5 to 1. That is a finite spec. Check the lobe lift at the lifter, multiply by 1.5, there is your maximum allowable valve lift. If lobe lift checks, rocker arm ratio is good, but valve lift is a little shy, try different length pushrods to see if it brings things up where they belong.That can be your variable to make this whole thing work. Remember, check EVERYTHING, leave nothing to chance, because they will if you don't, and nobody wants to be sent home early over something as simple to avoid as this.We had a very fun involved discussion on push rod length determination here in the last off season if you care to locate and review it.