1.65 or 1.7 ratio rocker arms

[Eluding]

My plans call for a cylinder head upgrade in the near future. I believe I'll need more valve lift to make the most of the heads' increased airflow. However, I would like to keep the stock cam and just increase rocker ratio. The stock cam has .357 intake lift and .390 exhaust lift. With 1.6 rockers the lift would be .380 intake and .416 exhaust lift. With 1.65 rockers the lift would be .392 intake and .429 exhaust. With 1.7 rockers the valve lift would be .404 intake and .442 exhaust. Crane makes these rocker ratios and I would need guidplates and hardened pushrods, I have both items already from a leftover small-block Chevy project.
Crane tech also told me the effective duration would increase 2 degrees with the 1.6s and 4 degrees with the 1.7s. Crane recommended against the 1.7s because they are not emmissions-legal. However, he could not give me any other negatives on their use.
What does every here think? Anyone ever try this? What were your results? I'm sticking with the stock cam to minimize duration increases and the tuning problems that come with it.

 

[myclone]

1.7s increase the load on the valve train tremendously. Just make sure the rocker studs and push rods are up to the task. Puts the push rod closer to the stud so make sure the push rod hole/slot will clear at max lift.

If you have 1.7s left over from a SBC project then you prolly have all your bases covered with parts and all. Other than those issues I say have at it and let us know how it works out.

 

[Eluding]

Thanks Myclone. I did know that the pushrod holes in the heads would be elongated. What do you think about the 1.65s? Would there be substantially less valve train stress? Harland Sharp makes a 1.65 that is substantially cheaper than the Crane 1.7s.

 

[myclone]

Kinda depends IMO.

If the heads are off and your preparing them for screw in studs/guide plates/etc then Id open up the slot to work with 1.7s BUT... Id prolly start with the 1.65s. Id try em out and if I felt more lift would help all Id hafta do is yank the 1.65s and install the 1.7s. Cheaper that way too should you decide not to step up to 1.7s later.

If the heads are on and the eng is still in the truck Id stick with 1.65s as the best you'll be able to do is pin the stock rocker studs and open up the push rod slot a little. A bunch of grinding on the slots for 1.7s would just worry me due to the amount of debri it creates. No matter how careful you are some always ends up in the eng some how. The less that does the better IMO.

Short version of above: :wink:

Prepare heads for 1.7s but start with 1.65s if they are off the truck.

If they are on the truck stick with 1.65s

HTH

 

[Pittman]

Im running .500 intake and .510 exhaust. qouted in specs using 1.5 rockers. I have 1.6 rockers..

How much stress do you think this is putting on the valvetrain??

 

[myclone]

Im running .500 intake and .510 exhaust. qouted in specs using 1.5 rockers. I have 1.6 rockers..

How much stress do you think this is putting on the valvetrain??

IMO it depends on what valve springs your using and what RPM your turning.

Higher RPMs or heavy valve train require higher spring rates which puts more stress on the parts as would a higher lift cam. IMO a ~.500" lift cam in our low RPM (relatively speaking) engines doesnt require huge valve springs. Start spinning the eng up to 6k and your gonna need some decent springs. IMO if you stay below that RPM range then most cam companies (comp cams is one) offer drop in springs that dont require machining to the heads and wont collapse the hyd lifter.