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Old 01-13-2010, 09:02 AM   #1 (permalink)
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Changing Rocker Arm Ratio

I'm running Andrew's 54's with stock 1.6 ratio rocker arms. If I went to 1.725 ratio, I would think the cam timing stays the same, but what effects would I see from the amplified lift? Would it move the power to a higher rpm range, or increase it in the same areas where it's strong right now?

Doing a little backwards math, to me, it looked like my .555 lift cam would be like .598 lift. Or am I way off base?

I saw S.E. 1.725 stock style rocker arms for $175. Is that pushing towards needing rollers? Would it be any bang for the buck? That's an easy swap if it was worth it performance wise. I'm happy with my motor, but wouldn't mind getting the adjustable pushrods out and it would be an excellent 2 for 1 opportunity.
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Old 01-13-2010, 09:45 AM   #2 (permalink)
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claydbal is reading this now saying WTF is this?
you gonna chance it, or reclay the motor? dang redneck got tinkeritis? what happen, jr. outrun you again?
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Old 01-13-2010, 10:10 AM   #3 (permalink)
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the stock ratio is 1.625:1. Therefore the change to a 1.725 ratio yields 0.589" peak lift for your cam. The increase in ratio not only increases lift but also accelerates the valve off the seat that little bit more also. With a change like this, you need to be sure that as the piston(s) are in and around TDC that the new valve positions have proper clearances to your pistons. That cam's TDC lift numbers would change from 0.165" / 0.158" to 0.175" / 0.168". And, keep in mind it's not just TDC to be concerned about as just after TDC, the intake valve chases the piston down the hole as it is just beginning to re-accelerate.

Regarding the need for rollers at this point is debateable. If you go non-roller, wear can become an issue. You're right in the gray area. Good rollers are nice but increase the cost alot, so some folks choose the accelerated wear option.

Any benefit derived from doing this ratio change would be dependent on what the rest of your components are capable of with it and what the actual state of tune is before and after.
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Old 01-13-2010, 12:06 PM   #4 (permalink)
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HDMD88 is reading this now saying WTF is this? HDMD88 is reading this now saying WTF is this?
Quote:
Originally Posted by Totenkopf View Post
the stock ratio is 1.625:1. Therefore the change to a 1.725 ratio yields 0.589" peak lift for your cam. The increase in ratio not only increases lift but also accelerates the valve off the seat that little bit more also. With a change like this, you need to be sure that as the piston(s) are in and around TDC that the new valve positions have proper clearances to your pistons. That cam's TDC lift numbers would change from 0.165" / 0.158" to 0.175" / 0.168". And, keep in mind it's not just TDC to be concerned about as just after TDC, the intake valve chases the piston down the hole as it is just beginning to re-accelerate.

Regarding the need for rollers at this point is debateable. If you go non-roller, wear can become an issue. You're right in the gray area. Good rollers are nice but increase the cost alot, so some folks choose the accelerated wear option.

Any benefit derived from doing this ratio change would be dependent on what the rest of your components are capable of with it and what the actual state of tune is before and after.
100% right on....there is soooo much more to setting these rockers up than what you guys think. They also through off your valve to rocker geometry and that could be an issue you should give thought to also.
Good job Tote
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Old 01-13-2010, 12:19 PM   #5 (permalink)
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Depending on the set up the extra lift on the exhaust side can lead to over scavaging and drive heat into the engine. It will be interesting as tuners test these on different head/cam combo's. We have used 1.725's on the intakes and gained with some S&S cams and gained by using 1.725's on the exhaust side only with some HQ cams.
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Old 01-13-2010, 01:39 PM   #6 (permalink)
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Those heads are a little bit of a sleeper. They have very open chambers and are unshrouded by that feature. They flow well. The downside is a lack of squish area, but they still work pretty well. The 54 is an interesting cam and I wished Andrews would have released it as a high lift 37 but that would really compete with themselves I guess. But at .590 lift and with a 38 (advanced 4 and the exhaust still at good opening and closing points) intake close with those heads and ~10/1 compression you might be surprised how well they do. You can set up the rockers (with the supports) with checking springs installed and a dial indicator (or a Trock) and watch the sweep and determine what needs to be done to optimize geometry or at least verify that it is close.
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Old 01-13-2010, 02:26 PM   #7 (permalink)
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claydbal is reading this now saying WTF is this?
nw-guy, is the 4* built in or did you use a gear?
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Old 01-13-2010, 02:41 PM   #8 (permalink)
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Thank all of you for the input. It sounds like I should have explored this while it was apart, if I wanted to go this route. I had a feeling there was implications beyond simply pulling a cover & changing a rocker arm. I'm gonna leave well enough alone!

No, Dennis. Junior is down by 36 ponies and disturbed by it. He's saving his pennies. This morning... out of the blue, he vowed to beat my dyno numbers. Dang kids. I don't know where he gets it from...
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Old 01-13-2010, 07:06 PM   #9 (permalink)
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Quote:
Originally Posted by claydbal View Post
nw-guy, is the 4* built in or did you use a gear?
I only spoke hypothetically
I have advanced them but 1st choice is to get the right cam straight up
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Old 01-13-2010, 08:35 PM   #10 (permalink)
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My motor is torn down and an option is put it back together with the SE 1.725 rockers. I've run the cam ( wood 6 ) through big boyz cam selector, and I like the lift, but I'm concerned about TDC lift and how steep the ramps are... The valve would be seeing even steeper ramps than it does now - the TDC lift of the little 6 cam and SE 1.725 rockers is right up there with the 9f. Has anyone run this combo?

I like the fact that expensive rollers aren't needed (with a lower-lift cam like the Wood 6) - my rockers have over 50,000 on them and they look flawless
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Last edited by splitting_lanes; 01-14-2010 at 10:18 AM. Reason: clarification...
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Old 01-13-2010, 08:39 PM   #11 (permalink)
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claydbal is reading this now saying WTF is this?
thanks don.
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Old 01-13-2010, 09:11 PM   #12 (permalink)
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I am running the 54's with the SE rockers. Power moved to the right. The cams made so much low end I hardly missed it and liked the linear pull to redline. Mike
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Old 01-14-2010, 09:45 AM   #13 (permalink)
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"I like the fact that expensive rollers aren't needed - my rockers have over 50,000 on them and they look flawless"
the wear to be concerned about is not specificly to the rocker itself. more worries to the valve guides and stems. once you get to a certain point, the rocker imposes a side load to the stem. correct geometry prevents that to a certain degree, but for me, piece of mind is important. i'd think the non roller 1.7 would be ideal for smaller cams keeping the total valve lift under .600?
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Old 01-14-2010, 10:46 AM   #14 (permalink)
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It all depends on how reliable you want your heads to be.
All my motors run rollers period..
I never want to deal with worn out valve guides or hung valves.
Rollers are reliable and give back free HP, reduced guide wear.
Just depends on where your head "excuse the pun" is at.
My 80 inch has 120k miles on her and only 20k without rollers.
She puts out 104 hp and has had zero problems in the head department.
My 127 has rollers and is a tire eating bitch.
She has no head problems.
To me, it's cheap insurance.
Be sure to throw in a set of aluminum pushrods too.
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