[Z06] Well...heads are coming off....
02-10-2012, 02:52 PM
#141
Melting Slicks
To adjust for rocker geometry, and let's be specific....rocker to valve tip geometry on the LS7 head, is to change rocker pivot height. There is no way to do this with this particular head without machine work. Some will suggest shimming the rocker, but that is not a good idea as the pedestals are cupped, not flat. I would not consider shims a good alternative. Therefor, the most logical, and also most reliable option would be a rail system conversion. With a rail set up, you can use shims to correct geometry. But....(always a but when moving away from OEM) with a rail system you have other issues to contend with. The first and most prominent is cost. The next is nose weight. All rail systems will have increased nose weight. Jessel has a couple options that are the lightest, but still add about 8 grams. The next is Crower, then you have T/D and Yellow Terra 'mini rails'. If you do go with a rail set up, you need to make sure it has adjusters for pre-load / lash if you are running light weight short travel or solid lifters.
Keep in mind that 6 grams at 7000 rpm will introduce significant valve train instability, and expect to loose upwards of 500 peak rpm before float if no other weight reduction and spring changes are made. This holds true for valve weight too.... There is no free lunch when screwing around with a carefully engineered valve train design that operates above 6000 rpm.
There are a few ped mount rocker options, as previously mentioned, but be careful. I do not know of ANY that do not nose over without careful spring selection. I do not like any of the ped mount options for this head, but that's just my personal preference.
The OE rocker is an extremely good piece. The trunnion could stand a bit of work. There are options for upgrading the trunnion. CHE, Comp and H/S all offer upgrades. Pick your poison.
The shop that is working my heads recommends the OE rocker for up to .800" lift. This is a white label shop that does not typically deal with the end user and primarily works heads for the racing community (hundreds of LS7 heads). He talked me OUT of running a rail system for my engine (I had intended to go with a Crower system), and he does not recommend ANY other ped mount rocker other than OEM. He sees the same heads he works after each race season and he has not seen any guide issues with heads that have correct stem and seat eccentricity with lifts in excess of .700 running OE rockers. He does not advertise, and shut down his web sight years ago as they were generating too much business. His business is via word of mouth anymore, which is why I do not mention his name. He'd be pissed if I drug him into this drama, and I do not want to **** him off as I want him to continue working my projects...
I was initially concerned about the OE rocker with lifts over .620, but have since put those concerns to bed. I mocked up a rocker and ran several wipe tests and find it has a good sweep up to .700. Above that and I'd be a bit concerned, but I'm fussy.
Moral of the story: don't believe what someone says just because you read it on a forum.... Pick up the phone and call someone who actually works on this stuff day in / day out. Many of my paradigms based on my experience with other engines were shattered after I stared really digging into this particular engine. It has been an interesting adventure, so say the least......
Keep in mind that 6 grams at 7000 rpm will introduce significant valve train instability, and expect to loose upwards of 500 peak rpm before float if no other weight reduction and spring changes are made. This holds true for valve weight too.... There is no free lunch when screwing around with a carefully engineered valve train design that operates above 6000 rpm.
There are a few ped mount rocker options, as previously mentioned, but be careful. I do not know of ANY that do not nose over without careful spring selection. I do not like any of the ped mount options for this head, but that's just my personal preference.
The OE rocker is an extremely good piece. The trunnion could stand a bit of work. There are options for upgrading the trunnion. CHE, Comp and H/S all offer upgrades. Pick your poison.
The shop that is working my heads recommends the OE rocker for up to .800" lift. This is a white label shop that does not typically deal with the end user and primarily works heads for the racing community (hundreds of LS7 heads). He talked me OUT of running a rail system for my engine (I had intended to go with a Crower system), and he does not recommend ANY other ped mount rocker other than OEM. He sees the same heads he works after each race season and he has not seen any guide issues with heads that have correct stem and seat eccentricity with lifts in excess of .700 running OE rockers. He does not advertise, and shut down his web sight years ago as they were generating too much business. His business is via word of mouth anymore, which is why I do not mention his name. He'd be pissed if I drug him into this drama, and I do not want to **** him off as I want him to continue working my projects...
I was initially concerned about the OE rocker with lifts over .620, but have since put those concerns to bed. I mocked up a rocker and ran several wipe tests and find it has a good sweep up to .700. Above that and I'd be a bit concerned, but I'm fussy.
Moral of the story: don't believe what someone says just because you read it on a forum.... Pick up the phone and call someone who actually works on this stuff day in / day out. Many of my paradigms based on my experience with other engines were shattered after I stared really digging into this particular engine. It has been an interesting adventure, so say the least......
Cheers, Paul.
02-10-2012, 03:44 PM
#142
I don't disagree with any of what you've said but, I am curious about where you got your over the tip weight figures...particularly the plus 8 grams being the least amount of increase? Certainly this is in conflict with the measurements I've taken. Might also want to consider that a significantly shorter pushrod (which may be necessary) can weigh 5-8 grams less.
Cheers, Paul.
Cheers, Paul.
Reducing lobe side weight helps, but don't you think the nose side would have a more pronounced effect as the spring has to overcome mass moment of inertia, no? Not arguing, just thinking out loud.
02-10-2012, 09:01 PM
#144
Racer
True story...I appreciate these guys discussing this stuff in depth. Dont know what all of it means in the grand scheme of things but their input has saved me from a few bad decisions
02-13-2012, 08:45 AM
#146
Melting Slicks
I'd rather not say, but it wasn't me. I wish I had access to all of them to verify for myself, but that's a lot of coin sitting around that I don't have. What did you measure, and what rocker? I'm curious as this was a factor that weighed into my decision. I will circle back to my source and ask for clarification.
Reducing lobe side weight helps, but don't you think the nose side would have a more pronounced effect as the spring has to overcome mass moment of inertia, no? Not arguing, just thinking out loud.
Reducing lobe side weight helps, but don't you think the nose side would have a more pronounced effect as the spring has to overcome mass moment of inertia, no? Not arguing, just thinking out loud.
Agreed that lobe side weight wouldn't seem to be as important, but most people don't even realise that changes too. The other point is, a roller tip will create less resistance than the stock tip, so how much 'weight' do you think that sort of resistance can cause at 7000 rpm??? Don't get me wrong here, I'm not trying to say there's something wrong with the stock rocker, but it can be improved upon, now whether that improvement is necessary is a completely other question.
Michael, PM me if you want some exact numbers.
Cheers, Paul.
02-13-2012, 10:58 AM
#147
Thanks Paul, will do.
I can go on with discussing lobe side weight, but will save that for another day, another thread. In short, my personal opinion is to use a railroad tie for a pushrod if it improves stability, and to hell with the weight as I do not think it matters as much as conventional wisdom would have one believe.
I am in complete agreement with you on the valve weight, as is my head guy. The lightest solid SS valve is 20 grams heavier than the OE ex vlv. That slaughters revs at 7K. Any idiot with a calculator can figure that out...... But if doing that gives folks a piece of mind, then more power to them. I hope to here back today what my hollow stem options are. Most of the blanks come from Argentina, and apparently, there's some unrest in that part of the world that has hindered supply, so there is a six week min lead time on a custom piece. I may have to move to a 5/16" stem if I want to move away from OEM. And I'm inclined to stay OE at this point....
I can go on with discussing lobe side weight, but will save that for another day, another thread. In short, my personal opinion is to use a railroad tie for a pushrod if it improves stability, and to hell with the weight as I do not think it matters as much as conventional wisdom would have one believe.
I am in complete agreement with you on the valve weight, as is my head guy. The lightest solid SS valve is 20 grams heavier than the OE ex vlv. That slaughters revs at 7K. Any idiot with a calculator can figure that out...... But if doing that gives folks a piece of mind, then more power to them. I hope to here back today what my hollow stem options are. Most of the blanks come from Argentina, and apparently, there's some unrest in that part of the world that has hindered supply, so there is a six week min lead time on a custom piece. I may have to move to a 5/16" stem if I want to move away from OEM. And I'm inclined to stay OE at this point....
02-13-2012, 01:31 PM
#150
Pro
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02-13-2012, 06:35 PM
#151
Le Mans Master
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The HS rocker is superior in strength and design to the factory counterpart. It's an upgrade all around but only necessary in high rpm or high lift cams. Imop it is better than the YT rockers.
If the weight of rocker over the valve is a worry to you, that can be offset by going with lighter retainers, and or valves.
If the weight of rocker over the valve is a worry to you, that can be offset by going with lighter retainers, and or valves.
02-13-2012, 10:12 PM
#152
Melting Slicks
Thread Starter
Update: The heads are all bolted back down as is the blower and all the rest. All I am waiting on is the dealer to provide me with a pass side head coolant plug. We should be able to get her fired up.asap.
02-14-2012, 01:08 AM
#154
02-14-2012, 05:38 AM
#155
Burning Brakes
Thanks Paul, will do.
I can go on with discussing lobe side weight, but will save that for another day, another thread. In short, my personal opinion is to use a railroad tie for a pushrod if it improves stability, and to hell with the weight as I do not think it matters as much as conventional wisdom would have one believe.
I am in complete agreement with you on the valve weight, as is my head guy. The lightest solid SS valve is 20 grams heavier than the OE ex vlv. That slaughters revs at 7K. Any idiot with a calculator can figure that out...... But if doing that gives folks a piece of mind, then more power to them. I hope to here back today what my hollow stem options are. Most of the blanks come from Argentina, and apparently, there's some unrest in that part of the world that has hindered supply, so there is a six week min lead time on a custom piece. I may have to move to a 5/16" stem if I want to move away from OEM. And I'm inclined to stay OE at this point....
I can go on with discussing lobe side weight, but will save that for another day, another thread. In short, my personal opinion is to use a railroad tie for a pushrod if it improves stability, and to hell with the weight as I do not think it matters as much as conventional wisdom would have one believe.
I am in complete agreement with you on the valve weight, as is my head guy. The lightest solid SS valve is 20 grams heavier than the OE ex vlv. That slaughters revs at 7K. Any idiot with a calculator can figure that out...... But if doing that gives folks a piece of mind, then more power to them. I hope to here back today what my hollow stem options are. Most of the blanks come from Argentina, and apparently, there's some unrest in that part of the world that has hindered supply, so there is a six week min lead time on a custom piece. I may have to move to a 5/16" stem if I want to move away from OEM. And I'm inclined to stay OE at this point....
However, Katech also indicated that a higher load valve spring would most often be the solution to this, and the discussion goes on to further things to consider with new valve springs.
Here is the article:
http://www.gmhightechperformance.com...e/viewall.html
The article implies they were going to do a follow up with different springs and cam lobes, but I can't find it if it was published.
Last edited by Rock36; 02-14-2012 at 06:00 AM.
02-14-2012, 10:46 AM
#156
I don't understand what your point is? The article also stated that the valve train was stable up to 7600rpm with oe components. You MUST add spring with a heavier valve if you want to maintain the same peak rpm capabilities, but adding spring does not guarantee anything but increased force the lifter must deal with. In many cases, a solid lifter would be required to keep the same red line. Messing with engineered OE valve trains has a trickle down effect.
02-14-2012, 02:01 PM
#157
Awesome ! This has been an excellent thread. Thanks so much for allowing all of us share in your engine work.
Any chance of a Vid when it's running? I would love to see/hear this sucker run.
02-14-2012, 05:02 PM
#158
Safety Car
I don't understand what your point is? The article also stated that the valve train was stable up to 7600rpm with oe components. You MUST add spring with a heavier valve if you want to maintain the same peak rpm capabilities, but adding spring does not guarantee anything but increased force the lifter must deal with. In many cases, a solid lifter would be required to keep the same red line. Messing with engineered OE valve trains has a trickle down effect.
"According to several valvetrain experts, even with high valvespring loads it is nearly impossible to force all the oil out of a well-designed hydraulic roller lifter at speed. It is accepted that spring pressure will force some oil out of the lifter, affecting preload somewhat, but total lifter collapse due to high spring pressures is unlikely, unless the lifters suffer from wide internal clearances. Nevertheless, it's an accepted fact that hydraulic-roller engines do not deliver the same rpm potential as their mechanical cousins. Illustrating that point, Car Craft performed a test to compare three cams: a flat-tappet hydraulic, a hydraulic roller, and a mechanical roller cam ("Three-Way Cam Lobe Shootout," Oct. '07, pg 28). The results were surprising because the hydraulic roller cam practically duplicated the mechanical roller cam's power from 3,000 rpm to 6,000. Only from 6,200 to 6,600 did the mechanical-roller version forge ahead, besting the hydraulic by 17 hp A majority of this power advantage could have been attributed to the mechanical cam's higher spring pressures, because the mechanical roller enjoyed 575 pounds over the nose versus the juice cam's mere 400 pounds. A good additional test would have been to increase the spring pressure on the hydraulic, something we didn't try at that time."
Read more: http://www.carcraft.com/techarticles...#ixzz1mOcu0LML
Interesting read...1/2 of you don't need solid lifters in your LS7...hell I don't think I even need them on my BBC either, but, that's what I got in now so might as well stick to it. That article wasn't out 10 years ago so I went solid on my BBC...knowing now what I didn't know then, not so sure I would use solid unless for a very specific application.
enjoy the read! good stuff!!
Last edited by mirage2991; 02-14-2012 at 05:08 PM.
02-15-2012, 11:36 AM
#159
I have always used hydraulic lifters in my builds whenever possible. Some builds however demand solid due to spring pressure.
Short travel hydraulic lifters work well, but be advised that they require adjustable rockers to properly set pre-load.
This is my favorite IC book that I reference all the time.......... http://www.amazon.com/Internal-Combu...=2QH5SJW2ML0FJ
This one is also a good read....... http://www.amazon.com/Internal-Combu...=2QH5SJW2ML0FJ
Short travel hydraulic lifters work well, but be advised that they require adjustable rockers to properly set pre-load.
This is my favorite IC book that I reference all the time.......... http://www.amazon.com/Internal-Combu...=2QH5SJW2ML0FJ
This one is also a good read....... http://www.amazon.com/Internal-Combu...=2QH5SJW2ML0FJ
02-16-2012, 12:43 AM
#160
Melting Slicks
Thread Starter
Update: The Z is back safe in the garage. Everything went fine on the drive home. The new Hinson trans mounts...combined with the already installed HMS motor mounts felt pretty good too. The new DRM shocks rode well and lifted the car maybe 1/4"....hrrrm..wonder why? Maybe my stock shocks were sagging or giving out??
Tomo morning I am going to change the oil and try to clean up under the hood a little bit more. My new Gatorback belt was squeaking just slightly...I think because there was coolant on the pulleys from the head swap.
Question?? Should I retorque the ARP head BOLTS after a few heat cycles or leave them alone? They were installed with the supplied ARP Ultratorque and fastened to spec. Thanks all!
Tomo morning I am going to change the oil and try to clean up under the hood a little bit more. My new Gatorback belt was squeaking just slightly...I think because there was coolant on the pulleys from the head swap.
Question?? Should I retorque the ARP head BOLTS after a few heat cycles or leave them alone? They were installed with the supplied ARP Ultratorque and fastened to spec. Thanks all!
