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Old 02-24-2010, 12:53 AM   #1 (permalink)
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1.725:1 ratio rocker arms????

Has anybody used a rocker arm that has a differant ratio than stock? Thinking about trying this. Anybody with real world experiance use these before? How do you use the math to get total valve lift? So if I was using a .510 cam, what would the lift be with these differant lift ratio's. Thanks
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Old 02-24-2010, 06:16 AM   #2 (permalink)
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The .510 divided by the stock ratio, 1.62, equals .3148 . Multiply THAT number by the new ratio rocker. So that would be: 1.72 x .3148 = .541 lift.
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Old 02-24-2010, 06:41 AM   #3 (permalink)
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Here's a good thread on higher ratio rockers

http://harleytechtalk.org/htt/index....c,15107.0.html
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Old 02-24-2010, 07:39 AM   #4 (permalink)
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They can work great, good, not at all, or worse than stock ones. Depends on many things, like head flow as a major factor and cam profile as another...

For a .510 might give a slight bump in power as it makes the whole cam a bit more agressive not just the top lift of it.
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Old 02-24-2010, 11:46 AM   #5 (permalink)
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You are better off buying a cam that does what you need, than trying to modify it. ratio rockers that mount the same as stock ones have a different geometry and should have some work done to the valve stems. HD engines(other than flat head and sportster have bad valve geometry in the first place, why try to make it worse?
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Old 02-24-2010, 12:19 PM   #6 (permalink)
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I used to use a higher ratio set on the intakes of hot rod Chevy's, and leave the exhaust stock, due to the exhaust flow characteristics or "over" flowing the port. It gave a few more ponies on the top end, sorta like advancing/retarding a cam a couple degrees, to fine tune your bottom end or top end. Maybe a lower lift cam with mild timing would benefit the most, like if you decided to flow the heads after a bolt in camset was put in. But the more radical cams would probably not show as much gain. IMHO.
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Old 02-24-2010, 06:09 PM   #7 (permalink)
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Good flowing heads are where is starts.
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Old 02-25-2010, 07:17 AM   #8 (permalink)
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let's hear some opinions on what's better, 1.725 on just the intakes or intake and exhaust with the increased rocker ratio?
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Old 02-25-2010, 07:57 PM   #9 (permalink)
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I think you'd have to try it out on the dyno and see.
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Old 02-25-2010, 08:40 PM   #10 (permalink)
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Quote:
Originally Posted by C-Cat View Post
let's hear some opinions on what's better, 1.725 on just the intakes or intake and exhaust with the increased rocker ratio?
This depends on what the intake to exhaust flow ratio is and how you want this ratio to taper off at higher rpm. Lots to consider.
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Old 02-26-2010, 09:59 AM   #11 (permalink)
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thanks for all the replys

I think I will run just straight roller rockers in my build. too much math to deal with lol lol lol. If I can decide on a cam soon. lol
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Old 02-26-2010, 05:50 PM   #12 (permalink)
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Quote:
Originally Posted by C-Cat View Post
let's hear some opinions on what's better, 1.725 on just the intakes or intake and exhaust with the increased rocker ratio?
First there is no standard answer to this.As with any engine combo its just that a combonation of parts that work together or against each other.
Some heads flow more air at differant lifts.Some cams have the valve at optimum flow point for longer than others.A higher raitio can help tune this in.At same time it could hurt byt having to much lift for best flow.If you look at flow charts you will usually notice that after certain point the heads gain very little flow.After this point extra lift isn't very benifical.Higher raitios will have small effect on duration too.
Its matter of tring both and swapping around to find what works best for your combonation.While you can gain its usually not enough to justify the trouble and cost,unless you have to have every pony you can get.In racecar or bike it might be worth it.For street bike I really doubt you will notice it.
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Old 02-26-2010, 07:23 PM   #13 (permalink)
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i already have 2 s&s 1.725's that i ran last year on the intakes and have all 4 of the se stock ratio roller rockers if i go that route. was going to try 1.725's on the exhaust too, but don't want to spend the money on rockers and dyno time. more than likely will try it with the se rr's and the try the s&s 1.725's on the intakes and take it from there. if i see a big gain (4hp is reasonable anything under 3 isn't) then i might spend the cash and try the 1.725's for the exhaust side. cams are s&s 640's on a 124 dyna.
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