Rocker ratio ?

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Rocker ratio ?

Post  1951 ford on August 22nd 2013, 9:09 pm

Hey guys just wondering if i have the right ratio. Im running those comp cams magnum 1.72 should i be running the 1.73
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Re: Rocker ratio ?

Post  bbf-falcon on August 22nd 2013, 9:12 pm

They will be fine.

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Re: Rocker ratio ?

Post  c.evans on August 22nd 2013, 9:24 pm

X 2 what Rick said.

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Re: Rocker ratio ?

Post  GT300TD on August 23rd 2013, 10:34 am

How much lift would he lose, and how much lift would you lose with a 1.70 compared to a 1.73 on say a .500 lift cam?


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Re: Rocker ratio ?

Post  kjett on August 23rd 2013, 11:24 am

GT300TD wrote:  How much lift would he lose, and how much lift would you lose with a 1.70 compared to a 1.73 on say a .500 lift cam?

If the cam is made to be used with a 1.73 ratio rocker, the math is easy. Take .500 and divide by 1.73, then multiply by 1.70 which would give you around .491 lift. There is more to it than just the noted ratio stamped on the rockers, i.e. BBC 1.73 rockers are noticibly different from BBF 1.73 rockers. I learned that the hard way when I bought a set of rockers that were supposed to be for a bbf 1.73's, turns out they were bbc 1.73. Swapped to a new set for for a BBF, and my geometry was all fixed. Lesson learned!
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Re: Rocker ratio ?

Post  GT300TD on August 23rd 2013, 6:23 pm

kjett wrote:
GT300TD wrote:  How much lift would he lose, and how much lift would you lose with a 1.70 compared to a 1.73 on say a .500 lift cam?

If the cam is made to be used with a 1.73 ratio rocker, the math is easy. Take .500 and divide by 1.73, then multiply by 1.70 which would give you around .491 lift. There is more to it than just the noted ratio stamped on the rockers, i.e. BBC 1.73 rockers are noticibly different from BBF 1.73 rockers. I learned that the hard way when I bought a set of rockers that were supposed to be for a bbf 1.73's, turns out they were bbc 1.73. Swapped to a new set for for a BBF, and my geometry was all fixed. Lesson learned!
Thanks Smile 

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Re: Rocker ratio ?

Post  quick 52 on August 23rd 2013, 9:25 pm

a lot of guys have used BBC rockers and got by with them including myself... don't think there is most HP to gain changing them if they are working leave them...

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Re: Rocker ratio ?

Post  GT300TD on September 23rd 2014, 11:46 am

kjett wrote:
GT300TD wrote:  How much lift would he lose, and how much lift would you lose with a 1.70 compared to a 1.73 on say a .500 lift cam?

If the cam is made to be used with a 1.73 ratio rocker, the math is easy. Take .500 and divide by 1.73, then multiply by 1.70 which would give you around .491 lift. There is more to it than just the noted ratio stamped on the rockers, i.e. BBC 1.73 rockers are noticibly different from BBF 1.73 rockers. I learned that the hard way when I bought a set of rockers that were supposed to be for a bbf 1.73's, turns out they were bbc 1.73. Swapped to a new set for for a BBF, and my geometry was all fixed. Lesson learned!

Would that work in reverse? A buddy has a sbc w/.750 lift cam, he normally uses 1.60 rocker arms but switched to 1.65 and bent a 1/2" pushrod and broke a Jesel roller rocker arm. .750 divided by 1.60 times 1.65 equals .7734375 according to my calculator. So he would have .773 lift instead of .750, correct? It cost him a semi-final win at the US Nationals.

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Re: Rocker ratio ?

Post  kjett on September 23rd 2014, 12:33 pm

Pretty much. The question is did he check all of the piston to valve clearances with the 1.65 rockers to begin with or did he just swap and hope?
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Re: Rocker ratio ?

Post  GT300TD on September 23rd 2014, 3:37 pm

These guys (two brothers) are serious drag racers, they have a few "Wallys". Jeff, the driver has cut a couple perfect lights and cut an .004 and an .002 light Saturday. He dialed in at 9.99 and went 9.99 both passes that he ran. Had the second race won but slowed down to keep from breaking out and got beat. His engine builder suggested he use these. The rocker arms had a few runs on them already, leading them to believe it was the rocker arm. I asked if he knew how to figure the difference in lift when the rocker arm ratio was changed and he said they didn't have the 'formula'. I remembered this thread and thought it would work in reverse but wanted to make sure before I told him about it. Of course I told him that I got it off the BIG BLOCK FORD forum lol! . These guys are good friends of mine, have known each other for more than 40 years. They're Chevy guys but respect Fords, in fact John who I used to run around with just bought a 2013 Lincoln and also has a '90 or '91 T-Bird Super Coupe that he bought new. It just felt good to know something about performance cars that they didn't  Shocked  cheers .

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Re: Rocker ratio ?

Post  bosshoss on September 24th 2014, 1:42 am

I know plenty of great drivers that cant change their own spark plugs... You dont have to be a mechanic to drive a race car.

dkp
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