I have a cam with the same lift. I put a set of Comps Pro Mag roller rockers w/ 1.75:1 ratio. I had to get a 1" valve cover spacer, but the rockers got me up to ~ .588" in. and .590" ex. Everything worked out great for me. One note: There is a guy that lives down the road from me that went 8.11 in the 1/4 mile with stock rockers in an '02 T/A, so I don't know if you realy need to spend the $$ on after market rockers. I didn't find that info out untill after I had already baught mine.

 

You better tell the guys at Chevrolet that! Looks to me like they must have made a gross mistake with the LS7. At least according to you and the other experts on this site!!!LMAO

 

Read carefully Tahoe, Adrenaline said FAST RAMPS (LOBES). I seriously doubt the LS7 has radical lobes, so they slapped 1.8's on them to wake it up a bit, while still being able to pass emissions.

 

It's ok Predator...Tahoe is probably a 20 yr. old magazine mechanic that
doesn't know the difference.

The LS7 camshaft was designed with 1.8 ratio rockers in mind. Therefore,
the ramp rates are within reason.

People like yourself that take a stock motor and begin to modify the internals
have no idea what they're up against. If you were to stick say...a T-Rex
cam into the LS7 without changing the rocker arms, you would probably end
up with broken parts in no time at all.

Here's a link to a site that warns the use of high ratio rockers:

http://www.thunderracing.com/catalog...2&sid=88#P2466

About 3/4 down the page you will see, "Due to the fast ramp rate of this camshaft, the use of 1.8 rockers is not recommended."

Correct me if I'm wrong, but I believe the LS7 uses a large base circle diameter
than LS1/LS6?

So you can't even compare the two ramp rates.

Thank you Tahoe. Have a nice day.

 

I'm so glad there are people out there like the two of you. I have only personally built over 800 of the over 3000 engines that ran out of my shop. Your attitudes exemplify the "follow the leader" mentality that makes up the "rest of the pack". My engines won a lot of races and championships because people like you believe what other people say instead of finding out what really works. Keep it up, I like having guys like you behind me!!

 

Oh that's cool!

PM me, or post your phone number, real name and shop name. I'll give you a shout Monday morning.

We can talk about valve train tech and ramp rates. We can also talk about
why camshaft MFG's warn about high ratio rockers on fast ramps.

 

The point of this discussion is that if you want more lift and/or duration buy a bigger cam for less than $400, than a rocker arm kit that probably costs twice as much. Where is the logic?

 

You built 800 lsx motors, so that is about a 100 a year since they came out in 97 which leads me to believe an average of about one every 4 days (no holidays taken).
Man that is a shitload of modified LSx's for a state that has the highest population over 60 per square mile.

 

Speaking of "reading carefully," where does he say all or any of them were LSX motors?

 

Add to the cost of the cam the cost of its installation and the price of the rockers then becomes less. Anyone that knows one end of a wrench from the other can change a set of rocker arms in an hour or less. The same can't be said for a cam swap. There's the logic you missed.

 

It's interesting though that the vast majority of the mainstream shops seem to suggest that the OEM rockers are more than ample to well into the 500++ RWHP range. Is not the additional inertia also a consideration with most after market rockers?

 

Yes, this can be a factor, but the Cranes I am using are very lightweight for being full roller rockers and are noticeably lighter than the Comp versions.

I don't think there's any question about the OEM rockers being "ample" or not, but the fact is you will make more power with higher ratio roller rockers. I can't argue with the results as I picked up 10 rwhp and 8 rwtq going from the SLP 1.85 rockers (identical to the stockers except for their ratio) to the Crane 1.80 rockers even though I lost ~.010" of max valve lift in the process.

Also, fwiw, the last few 500+ rwhp motors I've seen built this year all had one brand or another full roller rocker arms installed, albeit stock ratio versions.

 

(meant for BigDsz and Tahoe)

Every engine builder is going to have their own method for making power.

Let's look at this from an endurance and practicality stand point.

There is a valve, rocker and spring sitting static on the base circle of the cam
with no less than 100 lbs. seat pressure.

We have a pencil thin pushrod trying to transfer motion from a dead stop to
more than half an inch lift HUNDREDS of times per second at peak RPM.

Now we're going to throw on a higher ratio rocker which mutliplies the rate
by 0.1, or 0.2. Maybe even swap cams with fast acting lobes.

The pushrods and rocker studs are going to take more of a beating. I can
see those rods bending more than a guitar string in rock-n-roll solo at 6500+
RPM.

On top of that, spring open pressures are going to be through the roof to
keep the lifter on the lobe, and valve from floating. The energy used to turn
the valve train is going to increase.

On a race motor that is stuffed with robust valve train parts, yeah it would
probably work...but for how long?

I wouldn't sell that system to a daily driver who wants to run the track for
the odd weekend. Just my humble opinion.

 

Again, this is why Crane does it correctly and offers their roller rockers (stock and higher ratio versions) in a kit which includes new studs, guide plates, and heavy-duty pushrods.

As to the Crane rockers themselves, this is what Mark Campbell, VP of Research and Development for Crane, had to say about them.

At Crane R&D, we constantly evaluate our competitor’s lobes, rockers, valve springs, etc. I'm sure they constantly check ours as well. We test lobes with various combinations of rocker arm types, rocker ratios, valve springs, installed seat pressures, various spring rates, etc. We do it all day, every day because that is our passion. In addition, we work with many outside specialists such as Vinci High Performance in Orlando. With all that said, I can state with 99.99% certainty that our "Quick-Lift" rocker arms will only enhance the performance of any LS1-family cam you have. They will not, in any way, lead to damage of other components. Our "Quick-Lift" geometry is based on the location of the pushrod seat with respect to the valve tip and the center of rocker rotation. A 1.7 (advertised) rocker starts the valve off the seat at a ratio of 1.79 and due to the motion of the pushrod seat the rocker ratio changes to 1.72 by .250-.300 net valve lift (depending on profile design). At approx. .250 valve closing, the ratio returns from 1.72 to 1.79 by the time it reaches the valve seat. This designed rocker body geometry provides an additional 4-6*of duration in the .200"-.300" net valve lift area. This means the valve is getting open faster and closing later on any lobe. This provides more effective duration with the same seat-to-seat timing. What we are trying to do here is get as close as possible to the opening and closing rates available to OHC engine designs. If you are not convinced that we have done our homework on these rockers, install a degree wheel on the engine and plot lift per degree of rotation with our rockers vs. our competitor’s rockers. In addition, put some machinist blue on the tip of your valve stem and adjust your rockers and turn the engine through a couple of revolutions. Remove a rocker and check the nose wheel sweep area in the bluing on the tip of the valve. Then do the same thing with a Crane "Quick-Lift" rocker. You will find that the nose wheel sweep on our rockers is considerably less than any of our competitors. This reduces valve stem side-loading and valve guide wear (friction). It also results in slightly more valve lift. Again, the use of Crane "Quick-Lift" roller rockers (part # 144750-16, 1.7 advertised ratio; 144759-16, 1.8 advertised ratio) will only enhance valve action of any lobe with which they are used!

 

I know they weren't. I was being sarcastic.
There is nothing that says that you can't put higher rockers on high lift cams. But you will run into problems sooner or later with radical ramps.

 

Guys I've got the OEM rockers and you wouldn't believe what I've been through, with very close P/V contact and potential coil bind. I had to get .025+ titanium retainers specially made by Terry at Racetech, Great guy.Had to have my pistons notched because I only had .055 P/V instead of minimum of .080. There are a lot of guys running around that have no idea how near their valves are to the tops of their pistons. All I know is I'm glad I'm done with my valve train for a while.

 

Amen to that!

I was glad to get mine finally squared away too.