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By scott5560 - 13 Years Ago
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Has anyone tried running different ratio rockers on the IN & EX? It can be done just what are the effects? Wondering have enough to put 1.54's on EX or IN. Will one set-up be better for torque?
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By GREENBIRD56 - 13 Years Ago
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I would vote for using the higher ratio on the intakes. (1) easier to drop total backpressure (piping and muffler choice) than to increase intake flow (2) exhaust flow is "pressurized" by nature
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By glrbird - 13 Years Ago
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We used higher ratios on the intake when we wanted more lift and duration on a race car. Make sure your valves are not to close to the pistons.
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By NoShortcuts - 13 Years Ago
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Running 1:43 to 1 rockerarms on one set of valves and 1:54 to 1 rockerarms on the other set of valves is a way to change not only effective valve lift, but also valve opening and closing time (valve open duration).
You also end up with the equivalent of a dual pattern camshaft in that the valve open duration and lift for the intake valve (measured at the valve) is not the same as the valve open duration and lift for the exhaust valve (measured at the valve).
IF you had a camshaft that seemed like it was a little too much or too little for your engine application, changing rockerarm ratio is a means to slightly adjust total lift at the valve and valve open duration measured at the valve.
Within limits, you can slightly adjust valve lash setting larger or smaller to adjust ultimate lift at the valve and valve open duration event measured at the valve.
From what I've read, Les Ritchey was a master at tuning engines for optimum performance employing techniques such as what you've brought up to make vehicles he worked on perform better than others comparably equipped at the drag strip. I'm going back to the early '60s and the heyday of y-blocks with this reference. Rest his soul... he was an out-of-the-box thinking Ford man akin to Karol Miller!
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By slumlord444 - 13 Years Ago
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We all normaly go with higher lift rockes to get more performanc but following this logic you could tame down a cam that was too radical buy using lower lift rockers.
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By scott5560 - 13 Years Ago
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I am wanting torque. I built this combo as a streeter. 292+0.040, mild cam, 8.9ish:1 comp, headers with 2.5" pipes to 2.5"flowmaster copies and still holley 2 barrel. Running 1.43 rockers now but have 8 good 1.54's. Wondering if them on intake will add or deminish low end torque. Maybe EX who knows just wondering.
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By charliemccraney - 13 Years Ago
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When I switch from stock 1.54 to 1.6, I couldn't feel any difference. I'm sure something would show up on the dyno or maybe when racing but for the street I doubt you'll notice anything.
Since you have them and it will cost only time, experiment, see what happens.
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By pegleg - 13 Years Ago
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the bast way to improve low end power would be to try advancing the initial timing. You'll probably have to limit the total advance. You aren't trying to run with the old "loadamatic' distributor are you?
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By Talkwrench - 13 Years Ago
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Cut your exhaust pipe size down. Also wondering if a 390 or 465 Holley might be better as the primaries maybe smaller than your 2 bbl ??
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By NoShortcuts - 13 Years Ago
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After mulling what you've said, Scott, I'm thinking that you're looking for better low end 'pull' off-idle and/or better throttle response.
- Gary and Slumlord are right... higher valve lift is generally associated with increased performance
- Charlie's right though, too... you'll never feel the change going from 1:43 ratio rockers to 1:54s
With 298 cubic inches, almost 9:1 compression, non-restricted exhaust... you shouldn't be having a problem with off-idle performance or throttle response unless the camshaft is something with excessive overlap for street use. Your engine should be making plenty of torque and horsepower.
- Frank is likely asking the right question. What distributor are you using? Does it have a centrifugal advance mechanism? A distributor ignition advance issue will KILL engine performance.
- Talk Wrench is also asking a good question. What Holley 2 barrel carburetor are you using?
Other thoughts...
- what kind of vacuum gauge reading are you getting at idle speed?
- what gearing do you have in the rear end?
Looking forward to your responses so that we can resolve the problem. Little stuff can create big problems... Murphy's Law
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By Grizzly - 13 Years Ago
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Scott, I will probably spend the rest of my life fathoming the technicalities of cams and engines. (I know nothing, probably never will) Generally a cam that has more duration for exhaust, than intake, favors acceleration. Cams with close to semetrical timing favor constant speed. I have seen some cams that are designed for torque that have high lift. As previously stated by playing with rocker ratio you are altering the caracaristics of your cam. Torque likes port velocity and low end volumetric efficiency. If you have not hogged out your ports the added requirements of a slightly larger engine and a better cam should help port velocity. A small 4 barrel carb and work with ignition will help also. I cannot help but feel that the experience of the cam grinder and the knowledge of your engine builder is being overlooked. By using a rocker with less ratio could restrict the valve that it is being used on. why let more air in if it cannot escape. In saying that nothing ventured nothing gained. there are plenty on the list that have found a mixed set of rockers and not known the difference. Personally I'd be looking for another set of 1.54's even if it's a full set of 16. Checking to get the best of the lot and using those. Research the outcome you want, knowledge is a potent weapon. cheers Warren
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By DryLakesRacer - 13 Years Ago
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I don't know if this info will help but we ran 1.65 rockers on our 1/2 mile dirt Super Stock and when we changed to 1.5 on the exhaust the driver accelerated off the corners better and dropped lap time by .2........Good Luck
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By scott5560 - 13 Years Ago
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Thanks for the responses. There is an interesting article in the latest "Hot Rod" magazine. Its about this sort of question and L/D (lift/valve diameter) ratio. Some interesting reading. I picked it up while on vacation last week at the cottage. And was like wow imagine.
Scott
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By scott5560 - 13 Years Ago
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Well my cam is regrind by Oregon #819 which is 219/219 @ 0.050", 264/264.5 adv, 0.437/0.437" @ 110. So I if they use the standard 1.5 rocker ratio for there calculations would be 0.291" base cam lift. By the numbers in the hotrod article L/D ratio on exhaust is 0.28% (good) but low on intake 0.23 with 1.43 rockers. But with 1.54 on intake makes it 0.25% and closer to there recommendations. And gain roughly 0.030" lift with it. So thats what I did 1.54's on IN and changed out mufflers to some Flowtech Raptors (turbo style). Well the exhuast note at idle is sweet. Off idle response is better and so is the low down torque it seems ie. Ability to dig into its torque to pull away and climb hills with no extra push to the pedal. So far seems to be good move.
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