Anyone ever go faster with less lift?
#3015684
02/15/22 03:09 PM
02/15/22 03:09 PM
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Joined: Jan 2007
Posts: 8,042 Mt Morris Michigan
mopar dave
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Anyone ever go faster after switching from 1.6 intake rockers to 1.5? I’m thinking velocity increase with less lift. Which is better, velocity or volume on intake flow?
Last edited by mopar dave; 02/15/22 03:11 PM.
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Re: Anyone ever go faster with less lift?
[Re: mopar dave]
#3015696
02/15/22 04:00 PM
02/15/22 04:00 PM
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HotRodDave
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Anyone ever go faster after switching from 1.6 intake rockers to 1.5? I’m thinking velocity increase with less lift. Which is better, velocity or volume on intake flow? Waht andy said, and I would add that you need to make sure you are still controlling the valve, if you add lift with a higher rocker ratio and lose control of the valve you will probably lose power. If your talking SB I would always run the highest rocker ratio I can find to bring the pushrod up straighter (I know it's not much but it don't hurt) then match my cam to those rockers to get the valve action I want.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Anyone ever go faster with less lift?
[Re: mopar dave]
#3015733
02/15/22 06:15 PM
02/15/22 06:15 PM
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LA360
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Personally I feel that you will see more of a change with changes to the valve timing events, rather than just lift itself. Using rocker arm ratio as an example, is the increase or decrease in lift making the power? Or is it the change of valve timing events and valve velocity showing the increase/decrease in power?
Billy Godbold has talked about a multiplication factor he uses for calculating valve lift.
He works on 0.45 - 0.48 of the intake valve. As an example 2.25" intake valve x 0.45 = 1.0125" of valve lift. On a Super Stock or Pro Stock style engine it sounds about right. You're probably not going to apply that factor to some of the engines we build.
The only way you'll know is test it
Alan Jones
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Re: Anyone ever go faster with less lift?
[Re: AndyF]
#3015758
02/15/22 07:21 PM
02/15/22 07:21 PM
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Clanton
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There are various formulas to get you in the ball park but you have to understand the assumptions used to create the formula before you know if you should use it or not. PipeMax will tell you how much lift you need for a certain combination to avoid choke. I always run the engines thru PipeMax before ordering parts. It is just a quick and easy way to double check my assumptions. There is a lot of info on this page I just came across. cylinderhead flow tech book
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Re: Anyone ever go faster with less lift?
[Re: mopar dave]
#3015809
02/15/22 09:26 PM
02/15/22 09:26 PM
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Diplomat360
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Read something awhile back, I think it was Joe Mondelo. You want no more lift than 15% of your bore diameter... ...and that theory was based on what? So here is what I'm thinking: 1) assuming that a wedge head is used, and therefore for a particular valve diameter size increasing the lift brings the valve closer to the cylinder wall, therefore shrouding the valve 2) but #1 above is certainly going to be impacted by the valve angle in the head (which is why I said "wedge" b/c a hemi chamber would certainly not follow these rules quite as readily I'm thinking) Not saying this theory has no merit to it, but I'd like to understand what criteria it is based on.
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Re: Anyone ever go faster with less lift?
[Re: Diplomat360]
#3015821
02/15/22 09:51 PM
02/15/22 09:51 PM
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mopar dave
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Anything more than 15% of the bore diameter in valve lift and turbulence is created off the back of the valve, which kills the velocity. With a 1.65 rocker I’m over 15%, plus I have a [censored] designed head. Thought it might be a win win for me. Plus I might gain a bit of p/v clearance too. So a win win win actually.
Last edited by mopar dave; 02/15/22 09:57 PM.
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Re: Anyone ever go faster with less lift?
[Re: mopar dave]
#3015923
02/16/22 09:54 AM
02/16/22 09:54 AM
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Brad_Haak
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I've never reduced rocker ratio and gone faster, but I've added rocker ratio without seeing any gains.
2021 Challenger 6.4L Scat Pack 1320 100% stock: 1.680, 11.894 at 113.75 (DA 175 ft) weight reduction, wheels, tires, Hellcat air box: 1.661, 11.686 at 115.97 (DA 710 ft)
1973 Challenger 452 ci street/strip [2008] pump gas, DOT radials: 1.454, 10.523 at 126.44 (DA 514 ft)
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Re: Anyone ever go faster with less lift?
[Re: mopar dave]
#3015948
02/16/22 12:07 PM
02/16/22 12:07 PM
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polyspheric
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[Have a nice day
Last edited by polyspheric; 02/17/22 10:23 AM.
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Re: Anyone ever go faster with less lift?
[Re: mopar dave]
#3015985
02/16/22 01:22 PM
02/16/22 01:22 PM
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AndyF
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Your right, I was thinking that wrong. The writer wrote that more than 15% of bore in lift created turbulence, killing velocity. I don’t know his theory. That doesn't make any sense so I'd avoid following that theory. Race engines almost always have valve lift that is greater than 15% of the bore size. A 4.50 inch bore would be restricted to 0.680 lift which isn't enough for a big race engine. A big bracket engine will use lift somewhere in the 0.750 to 0.850 while a pro built engine will be up to an inch of lift.
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