Need more lift
Need more lift I put new stock LS3 rocker arms on my almost 2 year old and 20K mile SBE LS3 build. Also added BTR Platinum valve springs with titanium retainers. I think I probably need to change the valve springs and probably rocker arms too. Currently, it has a 226/234 115+4 Cam Motion custom with .620 lift on both sides. Build here TxSpeed heads and mild cam build - CorvetteForum - Chevrolet Corvette Forum Discussion
I'm considering adding 1.8 ratio rockers of some sort. That will bring valve lift to .656. I have a couple of questions:
The heads are milled .010 and installed with .040 Cometic MLS head gaskets. Am I OK PTV wise?
Is this worth doing? I think it's time to change the valve springs and don't have a whole lot of confidence in the stock rocker arms either. Hopefully I'll get a little bump in power. Anyone hazard to guess what that power bump might be...
If I did this, what would your valve spring of choice be? The BTR"s I have now are rated to .660. Valve lift with proposed 1.8 ratio rockers is .656. I'm somewhat allergic to Comp Cams and Tx Speed valve springs as I've had failures with both and little to no factory support from either.
Help appreciated.
I'm considering adding 1.8 ratio rockers of some sort. That will bring valve lift to .656. I have a couple of questions:
The heads are milled .010 and installed with .040 Cometic MLS head gaskets. Am I OK PTV wise?
Is this worth doing? I think it's time to change the valve springs and don't have a whole lot of confidence in the stock rocker arms either. Hopefully I'll get a little bump in power. Anyone hazard to guess what that power bump might be...
If I did this, what would your valve spring of choice be? The BTR"s I have now are rated to .660. Valve lift with proposed 1.8 ratio rockers is .656. I'm somewhat allergic to Comp Cams and Tx Speed valve springs as I've had failures with both and little to no factory support from either.
Help appreciated.
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From: Carnation, WA
I have a 227/232 114+1 in my SBE LS3, running 1.8 rockers for .650"/.646" lift, and the measured clearances were .060" intake and .080" exhaust using a Cometic .040" gasket. I'm running Mamo 220 heads that were milled to get me a 62.5 cc chamber.
Your intake valve is opening (.050") a degree and a half before mine does, 2 BTDC rather than .5 BTDC. ... so that will steal a little clearance.
Given the clearances I measured, I let the engine warm up before I beat on it. I haven't had any issues.
What I'm getting at here is, I think it may be very close. I think the big unknown is what the difference in our heads does to the clearance. If it was me, I'd put some test springs in it and measure the clearance with a dial indicator on the end of the valve. I think you are close enough to having an issue that a measurement is the only way to really know. You could even measure with the rockers you've got in it now, and then adjust for the additional lift (and reduced clearance) that the 1.8 rockers would give.
Your intake valve is opening (.050") a degree and a half before mine does, 2 BTDC rather than .5 BTDC. ... so that will steal a little clearance.
Given the clearances I measured, I let the engine warm up before I beat on it. I haven't had any issues.
What I'm getting at here is, I think it may be very close. I think the big unknown is what the difference in our heads does to the clearance. If it was me, I'd put some test springs in it and measure the clearance with a dial indicator on the end of the valve. I think you are close enough to having an issue that a measurement is the only way to really know. You could even measure with the rockers you've got in it now, and then adjust for the additional lift (and reduced clearance) that the 1.8 rockers would give.
Last edited by grubinski; Nov 21, 2020 at 02:27 PM.
With 1.8 rockers you may need a valve cover spacers. But PTV clearance is pretty much a non-issue. Anyway, PTV issues is WAY MORE related to cam duration specs than to cam lift or heads mill...
I ran Comp Cams Ultra Pro-Magnums with Texas Speed ported heads and Lingenfelter cam LS3 for a while...... 229*/242*, 114* + 0*, .668"/.668' lift and .040" Cometic head gaskets....no PTV issues at all.
KW
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Joined: May 2008
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From: Carnation, WA
And I guess I'd wonder what does "no PTV issues" mean? I haven't had any either, but I'm running .060" on the intake side for clearance. Did you measure yours?
Shoot. I'm trying to get away without measuring. Was looking for a consensus of opinion here. Not saying either is right or wrong. Anyone care to take a shot at my other questions? Hell, if it's more trouble than it's worth, I may just plant grass...or do something else constructive.
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Joined: May 2008
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From: Carnation, WA
I am running Manley Nextek springs in mine, I'm at .650" lift on the intakes. Not sure if I'm using the .660" or .700" lift springs ... maybe .700" to give an allowance to shim the springs for installed seat load, but not sure, I didn't do the valvetrain setup.
YT rockers because it's a Mamo spec'd top end. I had to use thicker valve cover gaskets to clear the rockers.
YT rockers because it's a Mamo spec'd top end. I had to use thicker valve cover gaskets to clear the rockers.
