Spinmonster

The 1.8's on an XER lobe as per Charlie at comp and Brian at crane, are still less agressive than the LSK lobes with stock rockers. If you have enough spring then you can do it. Brian actually was the one who helped with the set-up and he posted publically on it.

I didnt dyno the car yet but if I do I will send you a copy of the results. Good hearing from you Tony, take care.

vettenuts

iTrader: (4)

The beehive design spring is what you have in the car now, and will require the least amount of parts/work to install. PSI (or ISKY Tool Room) makes a good beehive spring as well, but not sure on what retainer to use with it. This is the spring that Dart uses on their heads. I was running the Crane 832's, and they setup without shims at about 1.77 or so, and with the 0.030 shim will be even lower.

bigdsz

iTrader: (1)

Why don't you just go with a bigger cam and stay with the stock rockers with upgraded springs, then valve float won't potentially be an issue. Tony Mamo's thoughts sum up the situation well.

jmproductions

Because the cam is pretty close to as big as I want to go, but I definitely need new pushrods and springs to spin faster with no problems. The 1.8's just make good sense in my situation and are a lot less labor obviously.

Dbl.0.Five

Has anyone tried the adjustable split shaft rockers from Curtisbilt?

jmproductions

That's the first time I've heard that name, but I'll admit that I'm fairly new to modding LSx engines.

bigdsz

iTrader: (1)

Harland Sharpe has rockers for less than $400.

~JOSHUA

iTrader: (92)

Harland Sharpe has heavy crap for under $400.

When I was changing from one cam to a larger one luckily I noticed that one rocker body at the roller tip bearing was about to fail. Very heavy rockers over the nose too which gives the springs more work to do. Trash can garnish.

I caught that rocker just in time. I wish I had pics.

Joe Vinci

iTrader: (3)

With a ratio of over 1.7, Tony is talking about our 1.7 quick lift rockers. They are the only 1.7s I know of that produce over a 1.7 ratio. We have taken a dial indicator and found that with the stock rockers the valve comes off the seat at a ratio of 1.54 and does not reach a ratio of 1.69 until .480". Whereas with our 1.7 rocker geometry, the valve come off the seat at 1.79 ratio and by .250-.350" net valve lift the ratio decreases to a ratio of 1.72. This ratio is maintained through the rest of the lift profile until the valve is within .250-.350" from going back on the seat. It is then returned to the seat at a ratio of 1.79. The 1.8 rockers follow the same principle at a 1.89 to 1.82 and back to 1.89. Benefits of this geometry include more flow into the cylinder earlier in the cycle, quicker closing of the valve to trap cylinder pressure before combustion, more effective duration at .200” net valve lift while maintaining a relatively short seat-to-seat timing, and less valve spring seat pressure required because of the mechanical advantage of the higher seat ratio.
What is happening at the valve is more important than what is happening at the lobe. 1.54 (1.69 at.480" up only) vs 1.72 or 1.82. That is a no brainer for me. Maybe this will help shed some light on why we use the lobe lift and rocker ratios we do. This is enough info at this hour to chew on. I am tired (truth is the wife has some work to do on the computer). Tomorrow I will try to address valve float and higher rocker ratios. Joe

Spinmonster

.625 lift from the cam is likely to have just as much valve float if not more that a .592 xer lobe that has a net lift of .625. The concept of the rocker ratio not having as much spring pressure requirments have been discussed before. The LS7 uses 1.8 rockers now and there is a spring that allows that thing to rev to 7500 so why there are hard and fast rules being spread makes no sense to me. I'd like to know what springs were used that resulted in valve float for people that had it.

I am aware of the weight of the total rockers assemblies being 140 grams for the stock 1.7's and 152 grams for the 1.8 cranes but that is the total unit weight and may not reflect what the true reciprocating weight is for each which is the only thing that matters. It would require disassembling one of each to find this value but perhaps Vinci can shed some light on the topic. If the reciprocating weight for the crane 1.8's is greater than it will contribute to valve float.

My car is not showing any sign of valve float up to 6800 rpm. My springs again are crane 832's with an installed height of 1.74 inches. Someone incorrectly stated it was 123 seat pressure with a .030 shim but the hardened seats are set at a 1.77 height so I beleive it is closer to 128-130 pounds seat pressure at 1.74 inches.

vettenuts

iTrader: (4)

I have not done the measurement, but it is the rotational mass moment of inertia that is the key property, not the overall weight. The weight on the Cranes is likely higher overall likely because they have a better roller bearing setup than the stock rocker even though the rotational mass moment of inertia is supposed to be lower therefore they should be less susceptible to float. I believe the Cranes use a barrel shaped bearing rather than a straight needle bearing, but Joe can answer that better than I can.

I have used the 1.8's and the 1.7's (now on the car) and did have an issue with the 1.8's early on. On my recent dyno testing, the 1.7's were run out to 6,700 RPM with a gorgeous flat curve. Bottom line is the valve train needs to be up to task. I will likely re-install the 1.8's when I do my first spring maintenance in 10K miles.

I spent a lot of time over the winter looking into valve train geometry, valve float and other valve train related issues and when I set up my new heads I also set up a spreadsheet and figured out installed heights, shim requirements, etc. and then took my time and set up the heads and managed to get each valve spring within plus or minus 0.003" of each other for installed height. In the end it paid off.

The other thing I think you will find is that these rockers are very quiet as well. I contemplated returning to the stock rockers while setting up my new heads, but as I set up the stock rocker and the Crane in the new heads on the work bench measuring wipe patterns, I just couldn't bring myself to re-install the stock rockers because the Cranes were such a high quality component.

I personally think the Crane rockers get a bad rap, and not from the guys using them but from those who simply spout "you will have valve float" that either haven't ever used them but are repeating something they read or have not set them up correctly.

Spinmonster

Actually I tried 3 times by posting and was unable to find anyone that even tried them on a XER cam let alone had a bad experience.

Dbl.0.Five

The Curtisbilt rockers are shaft mounted so the the static weight is held up by the shaft so your only dealing with rotational weight.

smask04C5

iTrader: (1)

you'll be fine with 1.8's.

vettenuts

iTrader: (4)

If you decide to go with the doubles, and haven't yet bought them, I would go with the newer Crane 833's and set them up without any shims.

vettenuts

iTrader: (4)

Found it, this is the cam he is running with the 1.8 Crane rockers:

Comp XR281HR (228/230 Dura.) (.606/.608 I/E lift) 112 degree LSA

jmproductions

Interesting... do you know what springs he is running?

Spinmonster

Who is?

vettenuts

iTrader: (4)

His handle is "zo6vetteman2003". Last time I spoke with him, he was running the Comp 918's. However, I know he just did a lot of stuff to his car so I am not sure what springs he is currently running. He smoked his clutch on the dyno the same day I was there getting my tune from Slowhawk.

zo6vetteman2003

iTrader: (1)

Like Vettenuts said, the Crane (833) or Comp 918 spring would be my choice from past experience for your application to alleviate any valvefloat issue and have the ability to run to 6800rpm without any fuss. The 921's in combination with these rockers will cause valvefloat above 6000rpm. Slowhawk at DEZ Racing, Vettenuts and I stumbled across this issue and found that the 918's worked without valvefloat. The .510" of lift, plus the rockers (.035" additional lift) = .545" inches of lift which is well within the lift spec. of the 918's, and be almost identical lift to the LS6 ZO6. The stock LS6 springs would be an option only to 6600rpm equaling the approximate lift of the stock LS6 cam. You have your choice between the three, 833, 918, or stock LS6. I emailed VHP regarding the article in CHP magazine on their red silverado build and said a 918 valvespring swap from the 921's would cure their valvefloat issue above 6000rpm, lift under .600" ofcourse. If they read it I don't know. So VHP is correct in what they are telling you. I'm also running Crane Gold Race 1.8 ratio roller rockers in mine, but have seen valvefloat above 6000rpm with Comp 921's with the Gold Race rockers. Vettenuts was one that had this issue and Crane has come out with their own spring that will work without valvefloat (833's) and he is running them now on his Vette.