Roller rockers
That is really strange that crane claims 20hp and you lost 40hp
Valve timing may be off, to much preload could easily do it, not enough and you will quickly know it. BTW, what is the weight difference? The hp claimed is gained from less inertia and lower friction.
Geometry is not variable. Everything is fixed operating in an arc. The quick lift ratio comes from the pushrod seat being lower on the rocker so it basically contacts the rocker lower on its operating arc... Less lever advantage, more movement at the start.
Valve timing may be off, to much preload could easily do it, not enough and you will quickly know it. BTW, what is the weight difference? The hp claimed is gained from less inertia and lower friction.Geometry is not variable. Everything is fixed operating in an arc. The quick lift ratio comes from the pushrod seat being lower on the rocker so it basically contacts the rocker lower on its operating arc... Less lever advantage, more movement at the start.
Preload was adjusted correctly when I installed them. On a side note, it takes a long time to install these things correctly. The only thing I can think of that may have caused this kind of power loss is the quick-lift geometry of the rockers along with the aggressive lobes on the cam could have hurt my dynamic compression ratio. I was stunned when I took it to the dyno as well. My tuner has even said that he has not seen any aftermarket rockers make more power than the stock pieces and in most cases actually lose power. Also, I am not using stock springs, I have Patriot dual springs installed. Valve timing did not change when I put these in, the cam and timing chain were not touched during the install. Anyway, I pulled them back out last night and re-installed the stock rockers. Anyone want to buy the Crane rockers? Disappointing to say the very least. And about the weight, these are a LOT heavier than the stock rockers, I am sure that played a part in it as well. Other than that, the Crane rockers are at least very well constructed, they still looked like new when I pulled them out. No stress fractures or anything of that nature. I will likely be off to the dyno again this coming week to see if I reclaimed that power I lost. 
Preload was adjusted correctly when I installed them. On a side note, it takes a long time to install these things correctly. The only thing I can think of that may have caused this kind of power loss is the quick-lift geometry of the rockers along with the aggressive lobes on the cam could have hurt my dynamic compression ratio. I was stunned when I took it to the dyno as well. My tuner has even said that he has not seen any aftermarket rockers make more power than the stock pieces and in most cases actually lose power. Also, I am not using stock springs, I have Patriot dual springs installed. Valve timing did not change when I put these in, the cam and timing chain were not touched during the install. Anyway, I pulled them back out last night and re-installed the stock rockers. Anyone want to buy the Crane rockers? Disappointing to say the very least. And about the weight, these are a LOT heavier than the stock rockers, I am sure that played a part in it as well. Other than that, the Crane rockers are at least very well constructed, they still looked like new when I pulled them out. No stress fractures or anything of that nature. I will likely be off to the dyno again this coming week to see if I reclaimed that power I lost.
That is really strange that crane claims 20hp and you lost 40hp Valve timing may be off, to much preload could easily do it, not enough and you will quickly know it. BTW, what is the weight difference? The hp claimed is gained from less inertia and lower friction.
Geometry is not variable. Everything is fixed operating in an arc. The quick lift ratio comes from the pushrod seat being lower on the rocker so it basically contacts the rocker lower on its operating arc... Less lever advantage, more movement at the start.
Valve timing may be off, to much preload could easily do it, not enough and you will quickly know it. BTW, what is the weight difference? The hp claimed is gained from less inertia and lower friction.Geometry is not variable. Everything is fixed operating in an arc. The quick lift ratio comes from the pushrod seat being lower on the rocker so it basically contacts the rocker lower on its operating arc... Less lever advantage, more movement at the start.
It's actually supposed to be a "worst case scenario" for setting up rocker geometry. The last place you want peak ratio (i.e peak acceleration) is as the valve slams into the seat.
To be honest with you, it was more of a joke. One of the mounting studs for the Crane rockers was damaged getting them back out of the motor. The rockers, pushrods, pushrod guide plates, adjusters, and stud installation pieces are all in like new condition. I would sell all of that for $250, but I am not sure of the availability of the studs themselves seperate from the kit.
To be honest with you, it was more of a joke. One of the mounting studs for the Crane rockers was damaged getting them back out of the motor. The rockers, pushrods, pushrod guide plates, adjusters, and stud installation pieces are all in like new condition. I would sell all of that for $250, but I am not sure of the availability of the studs themselves seperate from the kit.
To be honest with you, it was more of a joke. One of the mounting studs for the Crane rockers was damaged getting them back out of the motor. The rockers, pushrods, pushrod guide plates, adjusters, and stud installation pieces are all in like new condition. I would sell all of that for $250, but I am not sure of the availability of the studs themselves seperate from the kit.
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TECH Fanatic
Joined: Jun 2002
Posts: 1,979
Likes: 3
From: Upstate NY
Actually, the rocker ratio isn't constant. It changes throughout the arc of travel. It peaks when the rocker is 90* to the valve centerline, thereafter it's decreased. Thats how the "quick lift" works. 1.7:1 "quick lift" rockers are more like a 1.8:1, except that the rocker geometry is set where it's about 1.7:1 at max lift but 1.8:1 when the valve opens/closes.
It's actually supposed to be a "worst case scenario" for setting up rocker geometry. The last place you want peak ratio (i.e peak acceleration) is as the valve slams into the seat.
It's actually supposed to be a "worst case scenario" for setting up rocker geometry. The last place you want peak ratio (i.e peak acceleration) is as the valve slams into the seat.
Valve seat bounce is your enemy.
An interesting subject is "mid lift" rocker geometry. Google is your friend.
Jon