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Converting 302 to roller rockers, what is involved?
I had the valvecovers off of my 302 the other day while I was painting them. I noticed that the lift on the cam must be in the milimeter range, because I really couldn't tell much difference between the open valves and the closed valves.
I figured a fairly cheap way to get a little more out of the engine might be to increase the rocker ratio, but I don't know what the "gotchas" might be.
The engine is a '74 302 that would seem to be stone stock. It was rebuilt many years ago so technically I guess it's a 306. I can't imagine that the springs would be original, but they're probably not really a performance spring either. The rocker studs appear to be pressed in.
I guess my question is, what is the stock rocker ratio (1.6 for ford small blocks?) and what ratio can you go to on a stocker before you start running into valve spring and piston clearance issues? Also, do you need to replace the rocker studs, etc?
I can ramble off the necessary parts on a chevy LT1 in my sleep, but this is obviously a slightly different beast. Thanks!
Stock ratio on the SBF is 1.6:1 and there are 1.7 and some 1.72 ratio rockers available. If your existing heads use rail style rockers(the tip has skirts to keep them on the valve stem) you either need to replace with this type or add guideplates... which is a bit more involved because of the push in studs of course. This usually means a trip to the machine shop and if that's the case simply substituting a newer head or a set that have already been reworked is the beter way to go. All late model SBF heads(from about 1978 on) use pedistal mount rockers which don't need guideplates and are therefore easier to add rockers too, but in most cases the combustion chambers are larger than the early heads so you could lose some performance. That's not a certainty though it depends what heads you have right now, the casting number would tel the story and that can be found on the head gasket side near one of the intake ports.
Hmm... That's exactly what I was afraid of. In GM world we just call them self aligning rockers. I did not see any on Summit that looked like they would fit my head and be self aligning. Guideplates normally wouldn't be a big deal except for the push in studs as you mentioned. Looks like the truck is just gonna have to stay stock for a while.
Ah, I see them now. Comp makes them in 1.7 but they are only roller tip. My previous search ruled them out because I had specified full roller. They do make a full roller 1.6, they would be mostly pointless. The majority of the HP gain from rockers comes from the higher ratio, not decreased friction. If I get really bored I might try the 1.7 roller tips one day. Better yet I may just hold off and get some good heads.
Well, I've dyno proven 14 RWHP by swapping rockers before. And I've also dyno proven 32 HP by swapping heads, and that was on an engine with a cam / fuel injection system that could take advantage of the swap.
50 HP for heads might be a tad optimistic unless you're planning on putting in a new cam, intake, and headers. Then again, I'm sure the heads I was starting with weren't nearly as bad as what these are, so who knows.
SBF heads are pretty bad... way more restrictive than any stock SBC casting for example, so heads alone can produce dramatic power increases on these motors if the induction, cam, and exhaust needed to support them are already in place.
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