1.7 rockers on SBC? - Nova Tech
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  #1  
Old Apr 1st, 08, 10:50 AM
patman patman is offline
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Default 1.7 rockers on SBC?

I have a set of 1.5 scorpion roller rockers waiting to go into my engine. I am going to run a solid roller cam, and it has .564/.570 lift with the 1.5 ratio.

The other day I was mulling the idea of putting 1.6 rockers on...that would bring the net lift up to .602/.608, and gives me a few extra HP on the simulator.

While I was checking prices, and I discovered that I can get 1.7 ratio too. I ran *that* up on the simulator, and it was good for an extra 20 HP over the 1.5's at peak HP. The mind boggles. That would put the lift at .639/.646 which sounds crazy big to me.

Obviously I'd need to check P->V clearance, but since I have dished pistons, I think I could get away with it. I had a bunch of clearance with the 1.5 ones (something like .250 at the closest spot)

So...other than the obvious P->V clearance issues...is there any reason to *not* run 1.7 rockers on a SBC? (I'm thinking of picking up a set to try on a dyno...)
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  #2  
Old Apr 1st, 08, 11:16 AM
rj67bu rj67bu is offline
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Default Re: 1.7 rockers on SBC?

im wondering if spring rate comes into play on this? will they bind, can they handle the lift also you will have to reshim? i'm just adding to your questions i guess but for instance, my heads were good for a 700 lift my cam has a 676 intake lift with a 1.5 rocker valve adjusted at .016 this would have been alright except i bought 1.52 rockers this put my lift at 718 with the same valve setting so i exceeded my spring rate and had to get differant springs. so will your springs handle the lift?
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Old Apr 1st, 08, 12:35 PM
patman patman is offline
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Default Re: 1.7 rockers on SBC?

Actual coil bind is .735 measured relative to correct installed height, spec'ed coil bind is at .655. I'd have to check the retainer-to-seal clearance, but I think I'm OK there too.

Spring pressure is 420 at .600 lift, so I would be increasing the pressure there some, that would stress things more...

The other thing that occurred to me is the pushrod length might need to change
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Old Apr 1st, 08, 05:39 PM
Big Dave Big Dave is online now
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Cool Re: 1.7 rockers on SBC?

If your push rod length is correct now it will not need to change. You will have to worry about push rod contact with the roller rocker and roller rocker hitting the spring's outer diameter at some point. As you have noted coil bind is the same and is related to total lift as is the retainer to valve stem oil seal.

Where radical accelerations rates are at issue is in spring life and control of harmonics. You will need high quality tool steel springs and titanium retainers with hollow stem valves to lighten the load the (force equals 1/2 the mass times velocity squared) at higher RPM levels. IF you have no interest in pushing the envelope by racing then I would recommend a set of 1.6 ratio rockers for the intakes only and let it go at that.
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Old Apr 1st, 08, 09:23 PM
patman patman is offline
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Default Re: 1.7 rockers on SBC?

Quote:
Originally Posted by Big Dave View Post
IF you have no interest in pushing the envelope by racing then I would recommend a set of 1.6 ratio rockers for the intakes only and let it go at that.
Big Dave
I think that's what the final answer is going to be...it was fun dreaming though!
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Old Apr 7th, 08, 09:07 AM
Wally Wally is offline
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Default Re: 1.7 rockers on SBC?

Quote:
Originally Posted by patman View Post
Actual coil bind is .735 measured relative to correct installed height, spec'ed coil bind is at .655. I'd have to check the retainer-to-seal clearance, but I think I'm OK there too.

Spring pressure is 420 at .600 lift, so I would be increasing the pressure there some, that would stress things more...

The other thing that occurred to me is the pushrod length might need to change
You also need to check the push rod contact on the head itself. As you increase ratio the push rod changes the angle it contacts the rocker and on stock heads requires you open the push rod hole to allow it to clear, this is true for 1.6 rokers, I can't imagine the problem you might encounter with 1.7 rockers.
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