Increasing rocker ratio

[wilson1970]

Thoughts on increasing rocker ratio from 1.5 to 1.6? Should I do 1.6 intake 1.5 exhaust? Cam is a Comp Cams XE .520 .540 .236/242@.050 110lsa. 355 SBC 0 deck 10.3 compression, Sportsman 11 cylinder heads, rpm air gap, 750 D/P . This is a street engine 3200 converter with 3.73 gear. Thanks

[dwilliams]

You'll get a lot of opinions, but the before and after timeslips are the final answer.

[psychomotors]

You'll get a lot of opinions, but the before and after timeslips are the final answer.

I "assume" it's NA but yeah, I agree with dwilliams. Are you currently running 1.5's or is this something you are currently building. Just curious.

[Walter R. Malik]

I usually buy rocker arms in sets with half of each ratio, simply because I can swap them between intake and exhaust to find out which works best with THAT combination.

[wilson1970]

Currently have 1.5 Harland Sharp. This is a engine refresh with cam and intake change to more street friendly setup.

[andyf]

Sometimes more ratio helps, sometimes it doesn't, sometimes it hurts. If you want a more technical answer then you need to put the engine on a dyno and test it. There is a complex relationship between the rocker arm ratio, the cam profile, the cylinder head flow and the engine demand. The relationship is too complex to understand mathematically so you just have to test it. Once you have a lot of experience with a set of cylinder heads you can get good at guessing which rocker arms might work with which lobe profile but it is still guessing. If it wasn't guessing then there wouldn't be hundreds of engineers sitting in front of dyno cells all day long testing combinations.

[psychomotors]

Jmho, but you wont know till you install the cam "as is" then experiment from there. I'm not really the one that should be commenting , due to the fact that the next engine I assemble, I'm planning on doing the same thing,lol. Because I was playing around with a program and it said there would be a small increase.

[groberts101]

Thoughts on increasing rocker ratio from 1.5 to 1.6? Should I do 1.6 intake 1.5 exhaust? Cam is a Comp Cams XE .520 .540 .236/242@.050 110lsa. 355 SBC 0 deck 10.3 compression, Sportsman 11 cylinder heads, rpm air gap, 750 D/P . This is a street engine 3200 converter with 3.73 gear. Thanks

Sounds like the same cam I ran in my 383 with 1.8 ratio on both sides. Similar street strip combo as well but I ran 11.6:1 and a Brodix single plane. Picked up past peak compared to running 1.8 intake and 1.7 on the exhaust.. but YMMV.

Just be aware that if spings are marginally good to begin with you'll likely need about 5-10% more pressure to help control the faster valve action.

[F-BIRD'88]

)On a SBC like yours) When if the cam is a mild-ish duration choice (like yours) then adding the 1.6 ratio rockers to the intake side of a SBC always helps. It opens the flow gate wider (higher intake valve lift)/within the same time (intake open close duration).
If you are buying rockers for this now I would buy a split 1.6/1.5 set.

The sportsman II heads like the valve lift. If you port them correctly you can make a lot of power with them too.

[wilson1970]

Thank you F Bird. Another question is the cam is .520/.540 lift. By going to a 1.6 on the intake that would raise lift to .555 would that throw off how the camshaft was designed to do as far as exhaust lift being greater?

[GARY C]

Thoughts on increasing rocker ratio from 1.5 to 1.6? Should I do 1.6 intake 1.5 exhaust? Cam is a Comp Cams XE .520 .540 .236/242@.050 110lsa. 355 SBC 0 deck 10.3 compression, Sportsman 11 cylinder heads, rpm air gap, 750 D/P . This is a street engine 3200 converter with 3.73 gear. Thanks

In general most test show increasing intake rocker to be better, exhaust rarely shows a gain from higher lift.

[groberts101]

Thoughts on increasing rocker ratio from 1.5 to 1.6? Should I do 1.6 intake 1.5 exhaust? Cam is a Comp Cams XE .520 .540 .236/242@.050 110lsa. 355 SBC 0 deck 10.3 compression, Sportsman 11 cylinder heads, rpm air gap, 750 D/P . This is a street engine 3200 converter with 3.73 gear. Thanks

In general most test show increasing intake rocker to be better, exhaust rarely shows a gain from higher lift.

While that's typically true.. you also gain area along with overlap if the exhaust suits it. And this is not necessarily a small cam for a 355 and those heads aren't really the strongest on the exhaust side either.

[CGT]

Most likey your bigger gains will come from increasing the ratio on the intake, provided you maintain valvetrain control. But I've had a couple instances recently where increasing ratio on the exhaust also helped power a bit, even from lower in the dyno pull. Both times Ive seen this have been on "smaller" type hydraulic rollers, like the one you mentioned running.

[groberts101]

Most likey your bigger gains will come from increasing the ratio on the intake, provided you maintain valvetrain control. But I've had a couple instances recently where increasing ratio on the exhaust also helped power a bit, even from lower in the dyno pull. Both times Ive seen this have been on "smaller" type hydraulic rollers, like the one you mentioned running.

Study the as-cast exhaust port on this head. Assuming the rest of the exhaust system is up to par?.. I have cash that says this one picks up with higher rocker ratio too. Figuratively speaking of course.

[wilson1970]

Exhaust system is 1 3/4 Hooker Super Comp headers into dual 3" Flowmaster.