53wanab and Gary’s04 have both talked recently about higher ratio rocker arms for our SSRs. After doing some preliminary research, I’m encouraged enough to both look further and to comment that valvetrain mods (NOT just rocker arms alone) might be a particularly good idea for owners of 03 and 04 SSRs (NOT 05s).
Let’s first clarify what we are talking about. Most people think only about the rockers arms, but in fact we should be looking at the entire valvetrain, for reasons that are explained below. Starting at the camshaft and working upward towards the valves:
The purpose of the camshaft is to regulate when, how high, and for how long the valves are opened to admit or expel air. Our ¾ SSR’s LM4 “truck oriented” engine has VERY mild cam timing specs, compared to the “performance” Chevy engines in Corvettes and Camaros. Below, I list our SSr specs and then the performance engine specs in brackets for comparison). In general, more is better for all numbers:
Exhaust valve lift (after rocker arm multiplication): 0.466 inch (0.479 to 0.551)
Intake valve lift: 0.457 inch (0.467 to 0.555)
Duration for exhaust/intake: 190/191 (207 to 218 / 196 to 204)
Lobe separation angle: 114 (116 to 119.5)
Valve timing: 112 / 116 (113 to 117 / 115 to 122)
This means that our cams open the valves to a lower height than most, and keep them open for less time. Both of these attributes work against making maximum power. The reason GM did this is because trucks (not SSRs) are tuned for low and mid range torque versus high end horsepower. We would ideally like MORE lift and MORE duration, but changing cams has 2 downsides:
1. It is not easy given the underhood packaging in an SSR
2. Cams with more duration have lumpier idles that also kill emissions performance
Ideally, we’d like to “get more area under the lift curve” without changing cams, and rocker arms with higher ratios will do that for us (see rocker arms below).
These connect the cam to the pushrods, and include a hydraulic reservoir system that provides the required reliable clearance in the valvetrain as the parts change temperature. The lifters in the SSR have one good feature: they ride on the camshaft using roller bearings instead of a friction surface. That is why GM refers to this as a “roller drivetrain”. (However, most people (including me) at first think that means that the rocker arms also have roller bearings where they ride the tops of the valve stems. That is NOT true)
These are the physical connection between the lifters and the valve rocker arms. They need to be STIFF. If they deflect at high rpm, our valves don’t follow the intended opening and closing profile, and power suffers. Our stock rods are good, but better ones are available, and if you want to spin past 6000 rpm, a good idea.
These are the “levers” being pushed UP by the pushrods. They rotate about a fulcrum and push DOWN on the tops of the valve stems. The ratio of the two levers here establishes how HIGH the valves are lifted in comparison to how high the cam profile is at a specific point. Our SSRs are advertised as having a ratio of 1.7 This means that for each 0.001 inch that the cam profile lifts a lifter, the valve will be lifted 1.7 times that much, or 0.0017 inch. In actual fact, the geometry of the rocker arm changes as it rotates, so that we actually only get about 1.54 multiplication for most of the cycle, and PEAK at 1.7 very briefly. The obvious question is why not increase the ratio for more lift? On the higher performance engines, you don’t need to. The 1.7 ratio on those engines (GM likes 1.7 currently) lifts the valves high enough to make good power and not enough to hit the pistons, because the cam profile is higher than ours! But, on our low lift LM4s, this IS a good question. Rocker arms up to 1.8 nominal ratio are available, and some of those have variable geometry that actually delivers up to 1.89 ratio when it is safe to do so (NOT when the valve is at peak lift and near the piston head!).
Remember up above we said that we would ideally like more “area under the lift curve”. Well, it turns out that PROPERLY designed higher ratio rocker arms WILL give us more area under the curve, because they lift the valves higher everywhere in the lift cycle. The other good thing is that they do NOT increase duration, so idle and idle emissions do not suffer.
There is more. Remember above I said that only the lifters on our LM4s have roller bearings? Aftermarket rocker arms are available that have one or BOTH of the following features:
1. Rollers at the tips where they ride on the valve stems
2. Roller bearings at the fulcrum where they rotate in response to pushrod actuation
Getting one, or better, BOTH, of these features is a big plus on reducing friction at high rpm, because friction is lost power AND more generated heat (wonder why the tips of factory rockers look discolored?)
The cam causes the valves to LIFT, but does nothing to bring them BACK down! The valve springs bring them back down. The valve springs in our LM4s are fine at “truck” rpms, and will even work fine up to 6500 rpm or so before they “lose control” of the valves. That loss of control is referred to as “valve float” and it has two really bad results:
1. You lose power (because the valves aren’t where they are supposed to be!)
2. Over time, and sometimes immediately, valve float weakens the valve springs so that they no longer work even to rpm they formerly worked fine at.
Stronger springs would be a really good idea if you want to spin past 6000 rpm, and since that is the easiest and least costly way to make more power, you will some day be shopping for stronger and better springs.
Retainers are the small devices that keep the highly compressed valve spring from flying off the valve stem. They seem low tech but are NOT. The lighter you can make them, the faster you can spin your engine before you get that destructive valve float. At 6000 to 6500 rpm, the inertia loads of even small parts are so high as to create tremendous loads for the valve srpings. Hence, the current fascination with lightweight titanium retainers. They are a good idea!
These are the tiny parts that “keep” the retainers in place on the valve stems. Again, less weight is VERY helpful. Again, titanium is a really good idea.
These not only hold the valves in place, but they also provide the bearing surface for the valve springs to ride on. If you spin the engine faster, you need more valve spring pressure to avoid valve float, and that extra spring pressure bears on the valve seat which bears onto soft ALUMINUM in an aluminum head (like on our SSRs). Therefore, if you increase valve spring pressure, you want beefier valve seats that are not distorted by the extra pressure. If they distort, they threaten not only the aluminum bearing surface under them, but also the valve stem.
These are what seals the valve stem so that oil does not leak down into the combustion chamber. The only reason I mention them is that on current GM engines, the valve seats and the valve seals are combined into ONE part. So, if you want stronger valve seats, you need to buy the SEPARATE valve SEALS used in previous GM engines.
If you change to stiffer pushrods, you MAY need pushrod guides that help keep the stronger pushrods aligned so that they don’t improperly WEAR other adjacent softer parts on the rocker arm.
One other thing. Valvetrain noise is very bad. Not because it interferes with your stereo system, but because it can falsely set off the knock detectors on your engine, which are unfortunately located VERY close to the valvetrain. If your valvetrain makes enough noise to set off the knock detectors, your protective PCM will assume you are suffering detonation and will aggressively retard your engine’s timing, thus KILLING your power output. Stronger springs and roller bearings tend to make more noise than stock parts. You need to make sure you buy high quality parts that have specifically targeted noise reduction in order to avoid this false triggering of knock detectors.
So, there’s your complete valvetrain.
To review what we might want to do:
1. Increase the area under the valve lift curve by changing to higher ratio rocker arms
2. Spin the engine faster (easiest way to make more power)
3. Increase the spring pressure to avoid valve float at higher rpm
4. Protect the valvetrain against the higher spring pressure
5. Lighten EVERYTHING that reciprocates at high rpm
6. Stiffen the pushrods
7. Add roller bearings wherever we can to replace frictional surfaces
It turns out that you can buy a variety of valvetrain kits from companies like Crane and SLP. You want as many of the following features as your budget can stand:
1. Variable ratio rocker arms that hit high ratios (like up to 1.89 or so) at SAFE points in the lift cycle as these can maximize the area under the lift curve
2. Roller bearings at the tips of the rocker arms
3. Roller bearings at the fulcrums of the rocker arms
4. Titanium keepers
5. Titanium retainers
6. Valve springs that are as LIGHT as possible but HIGH enough in pressure to prevent valve float reliably at even 6500 rpm, but not so high as to unduly stress the entire valvetrain
7. Sturdy valve seats to protect the aluminum heads without distorting
8. Possibly separate valve seals if you do need stronger valve SEATS
9. Stiffer pushrods
10. MAYBE pushrod guides
11. QUIET high quality parts that won’t falsely set off the knock detectors
Oh, one more thing. A COMPLETE kit (encompassing all or most of the 11 features listed above) will cost about $700 to $800 just for the parts.
Then, you also need two more “tools” that you need to buy or borrow:
1. A valve spring compressor that works by bolting onto the head for each valve position, and allowing you to SAFELY compress each spring using a wrench, until the keeper and retainer can both be removed
2. An air tool that threads into the sparkplug hole, that keeps the cylinder pressurized while you have the valve spring and retainer off, so that the valve does not fall into your engine!
Why go through all this complexity and expense?
On most “performance” engines, doing all the above will get you only a few horsepower – maybe 5 or so. However, on our “truck” engines, with their extremely mild timing, this combination of mods is likely to get you much more than that.
In fact, while I have not yet fully analyzed the Crane 1.8 rocker arm article in the August edition of “Chevy High Performance” that 53Wanab quoted in one of my threads, and I already DO know it has a couple of flaws, I am nevertheless persuaded that it MAY be very close to reality for our SSRs. That particular article shows dyno results that exceed 20 hp gains at many points in the rpm band – especially at the higher rpms, and they stopped their dyno runs at only 6000 rpm, presumably because their spoilsport Silverado PCM shut down the festivities there.
A good mechanic could probably do this job in 4 hours or so, maybe up to 8 hours if he is dedicated to getting the BEST (and QUIETEST) settings for the hydraulic lifters (requires waiting for bleeddown for 30 minutes or so several times in an iterative manner). That still makes this a good “bang for the buck” mod, because regardless of what the aftermarket peddlers try to imply, there are no magical “20 to 30 hp” gains for under $1500. (As I’ve said before, selling high performance work is similar to selling crack cocaine to an unquestioning market. . . )
I am at least convinced enough to do more research myself.
And, I will analyze that Chevy High Performance article in a future posting.
Finally, notice that I said "not 05 SSRs". This is because those engines ALREADY have their valve lift pretty much maxxed out (to SAFE limits). If you put in higher ratio rockers, you might hit the valves! So, you guys with 05s are again shut out of this one I'm afraid. Then again, you already HAVE 90 more hp than the 03s and 04s do.