Thread: Rocker Arms/ Valve Lift question: will it clear?

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So, i had a set of 289 heads built for my truck. They are 1965 289 heads with oversized valves put in. The machine shop said that they would be fine with a mild cam but not anything over .550 lift (i think thats what he said).

Anyway, will they clear with my stock 302 cam and roller rockers with a 1.7 lift ratio instead of the factory 1.6? The reason i am asking is due to the fact i already own a pair of 1.7 ratio rocker arms.

Thanks for any info!


ben

what is the lift at your cam??? Find this number, multiply it by 1.7 and it will tell you your valve lift.... As for using the 1.7 ratio rockers vs. the stock ones, I played with them on a small block Ford years ago..... Got the best results (dyno) using the 1.7's on the exhaust and stock ratio on the intakes....

i cant find the stock lift for my cam.. google is not helping me...

its an 87 302 ..

General rule of thumb that I follow with a SBF with flattop pistons - that is no eyebrows milled in the top or compression ratio lowering cup is .500. Beyond .500, it's best to check clearances between valve head and piston, JIC.

Depending on which heads you have, probably 52-55cc, aren't you possibly running into an excessive compression ratio situation with 289 heads on a 302??

Depending on too many variables here. Dig through the kid's toybox and score some modelling clay. Clay the piston and drop the head on with a used head gasket or a double thickness of coke carton to get aprx .041" and rotate the engine through a couple of revolutions. Make sure the head bolts are only indexing the heads and not tight. If you feel resistance, stop and back up. In any case, pull the head and cut the clay through the valve impressions and whip out your verynear calipers for a reading. If you are in the neighborhood of .100" exhaust and .080" intake, that is where you want to be. Stay on the plus side since your lifters are going to pump up a tad bit and add a shade more lift.

Don't get all logical and assume that you check this at TDC because that does not take into account how you indexed your cam.