Increasing rocker ratio

[statsystems]

The OP should search some threads on here (or maybe Hoffman can do it...seems he has all the good threads saved somewhere) and read what AndyF found when he flogged rocker ratios. He didn't really find anything but a bunch of work for his effort.

I know "back in the day" on my nitrous stuff I ran more ratio on the exhaust. Of course that was before there were many nitrous grinds available because I ain't no spring chicken.

[CGT]

The OP should search some threads on here (or maybe Hoffman can do it...seems he has all the good threads saved somewhere) and read what AndyF found when he flogged rocker ratios. He didn't really find anything but a bunch of work for his effort.

I know "back in the day" on my nitrous stuff I ran more ratio on the exhaust. Of course that was before there were many nitrous grinds available because I ain't no spring chicken.

The rocker ratio changes are like spacer plate changes, not very transferrable to another engine, or engine family. I've tested ratio, where its done absolutely nothing on the dyno. But I didn't and wouldn't stop testing it on future stuff because of that.

[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.

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.

Thats why I said "in general"... Exhaust usually benefits from duration, not lift... In general! Without being on the dyno to test it, it is only an assumption, in some cases adding more intake rocker would require retarding the cam to compensate for the faster ratio but again you will only see this on the dyno as any gain will be a very few hp.

[GARY C]

The OP should search some threads on here (or maybe Hoffman can do it...seems he has all the good threads saved somewhere) and read what AndyF found when he flogged rocker ratios. He didn't really find anything but a bunch of work for his effort.

I know "back in the day" on my nitrous stuff I ran more ratio on the exhaust. Of course that was before there were many nitrous grinds available because I ain't no spring chicken.

In theory nitrous would be reverse to NA in regards ex to int needs.

[BigBlocksOnTop2]

Do away with the flow masters and use magnaflow or pypes raceflow mufflers. Both are straight through design and don't have the flow restriction or drone as the flow master ''chamber'' muffs do. Try spacers under the carb especially with the dual plane intake.... both sides of the intake see all four barrels. Stagger the jetting too. You will find better results going this path over higher rocker ratio.

[F-BIRD'88]

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?

No, on a sbc it is a +++.
The ex reacts to duration/ valve timing changes.
The sbc intake especialy with those heads likes the lift increase. The intake valve (heavy) does move faster up and down within the same duration. So be sure the spring is up to the job.

[MadBill]

The perhaps cynical explanation for the higher exhaust lift on many catalog split-duration cams is that the lobes all come from the same family for both IN & EX. so the longer EX duration automatically comes with more lift.

[F-BIRD'88]

The perhaps cynical explanation for the higher exhaust lift on many catalog split-duration cams is that the lobes all come from the same family for both IN & EX. so the longer EX duration automatically comes with more lift.

true..