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 Post subject: Gains from 1.8 rockers?
PostPosted: Sat Mar 10, 2018 12:32 pm 
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Joined: Tue Oct 30, 2012 4:50 am
Posts: 49
Has anyone tested 1.72 vs 1.8 rockers to see how much HP there is to be gained if any?


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PostPosted: Sat Mar 10, 2018 2:43 pm 
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Joined: Mon Oct 29, 2012 9:05 am
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Depends on the engine. On a .500" lift camshaft, it only gives you .020" more lift. You'd probably gain more lift than that from optimizing your current rocker arm geometry. I doubt you'd see any gains whatsoever unless it was a really polished combination.

I run 1.8 rockers quite a bit, but they are on ported heads with high lift cams.

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PostPosted: Sat Mar 10, 2018 7:59 pm 
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Joined: Wed Oct 31, 2012 4:57 am
Posts: 158
Gday
Just something i noticed the other day in the process of doing p-v clearance and setting up my coil bind height was i had a lot more lift than what i should have.
I have t and d shafts , one piece stand 1.75 ratio,
Pushrod geometry done, measured lobe lift agreed with the cam dr report,
Rockers worked out etween 1.78 - 1.79 ratio.
Cheers


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PostPosted: Mon Mar 12, 2018 12:50 pm 
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Joined: Wed Oct 31, 2012 11:24 am
Posts: 280
I have T&Ds also and noticed the ratio is a bit "over" 1.75 when the geometry is correct.

To answer the original question, IF the change to a 1.8 picks up performance, it means the cam duration and lift "could" be increased. I have also done the switch and slowed down , so I backed up to a 1.6 and picked up , indicating I had "too much" cam.


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PostPosted: Tue Mar 13, 2018 6:43 pm 
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Joined: Mon Oct 29, 2012 1:52 pm
Posts: 467
Another thing you have to remember when you change rocker ratios is to always change your lash setting to go along with the change if you want to keep the seat to seat duration the same. When the ratio goes up so does the lash requirement. Take your existing lash divide by the current rocker ratio and then multiply by the new ratio. This can sometimes make a big difference.


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PostPosted: Mon Apr 23, 2018 7:55 am 
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Joined: Mon Nov 05, 2012 3:54 pm
Posts: 33
This topic has me thinking!

My Crane hydro-roller cammed 351W has the standard 1.6 rocker ratio, .542I lift, .563E lift, 220 duration I, 228 duration E, both at .050. I know if I switched to 1.7 rockers, "I" goes to .576, "E" goes to .598 but what does my new duration become?

Don't know how to calculate same. I guess more importantly, will my hp gains be enough to make the switch or would they be minimal?

blykins wrote:
Depends on the engine. On a .500" lift camshaft, it only gives you .020" more lift. You'd probably gain more lift than that from optimizing your current rocker arm geometry. I doubt you'd see any gains whatsoever unless it was a really polished combination.

I run 1.8 rockers quite a bit, but they are on ported heads with high lift cams.


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PostPosted: Mon Apr 23, 2018 12:40 pm 
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Joined: Mon Oct 29, 2012 1:52 pm
Posts: 467
machoneman wrote:
This topic has me thinking!

My Crane hydro-roller cammed 351W has the standard 1.6 rocker ratio, .542I lift, .563E lift, 220 duration I, 228 duration E, both at .050. I know if I switched to 1.7 rockers, "I" goes to .576, "E" goes to .598 but what does my new duration become?

Don't know how to calculate same. I guess more importantly, will my hp gains be enough to make the switch or would they be minimal?

blykins wrote:
Depends on the engine. On a .500" lift camshaft, it only gives you .020" more lift. You'd probably gain more lift than that from optimizing your current rocker arm geometry. I doubt you'd see any gains whatsoever unless it was a really polished combination.

I run 1.8 rockers quite a bit, but they are on ported heads with high lift cams.


Your duration figures won't change at the cam obviously but they will change at the valve with a higher ratio rocker, not a lot but some. You could check this easy enough using a degree wheel or by plotting the cam profile and figuring the change in duration at X lift.

I wouldn't expect to gain anything from an increase in rocker ratio but it is possible I'd say about 30% of the time from what I've seen. Most of the time it runs about the same and sometimes its a loser but you never know until you give it a try.


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PostPosted: Mon Apr 23, 2018 1:03 pm 
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Joined: Mon Nov 05, 2012 3:54 pm
Posts: 33
Thanks Dave!

DaveMcLain wrote:
machoneman wrote:
This topic has me thinking!

My Crane hydro-roller cammed 351W has the standard 1.6 rocker ratio, .542I lift, .563E lift, 220 duration I, 228 duration E, both at .050. I know if I switched to 1.7 rockers, "I" goes to .576, "E" goes to .598 but what does my new duration become?

Don't know how to calculate same. I guess more importantly, will my hp gains be enough to make the switch or would they be minimal?

blykins wrote:
Depends on the engine. On a .500" lift camshaft, it only gives you .020" more lift. You'd probably gain more lift than that from optimizing your current rocker arm geometry. I doubt you'd see any gains whatsoever unless it was a really polished combination.

I run 1.8 rockers quite a bit, but they are on ported heads with high lift cams.


Your duration figures won't change at the cam obviously but they will change at the valve with a higher ratio rocker, not a lot but some. You could check this easy enough using a degree wheel or by plotting the cam profile and figuring the change in duration at X lift.

I wouldn't expect to gain anything from an increase in rocker ratio but it is possible I'd say about 30% of the time from what I've seen. Most of the time it runs about the same and sometimes its a loser but you never know until you give it a try.


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