Understanding LS Valvetrain Upgrades
Anyone who has ever built or modified their own engine knows that the innards of their cylinder head can literally make or break the engine. The valvetrain inside a factory-stock LS is actually pretty good, all things considered. However, we all know anyone who owns an LS usually gets a severe case of the mod bug and feels the need for more power, and we want to make sure you get the most bang for your buck when you upgrade your LS valvetrain.
Make sure all of your components match – if there is a weak link in your valvetrain eventually you’re going to have a very bad day. – Ryan Pritcher, COMP Cams
Old school small block Chevy guys can swap out stock rocker arms for a set with more leverage and can pick up some reasonably decent power just by that upgrade alone. But, just like many other areas of the Gen III and IV LS family, because the new engines are so good from the factory, there isn’t a lot of power to be gained from the traditional valvetrain upgrades that paid big dividends with earlier Chevy V8′s. That doesn’t mean there isn’t anything left on the table, though – it just means you have to be smart about it, and know where to look.
Consulting the Experts
Here at Power Automedia, we literally have the numbers of just about anyone you could imagine in the automotive industry. That’s not to brag – far from it! We know that there are plenty of people out there who are smarter than us on any given topic, and we’d much rather have you get the information straight from them. For this article, we had the chance to talk to a few valvetrain experts from Crane Cams, COMP Cams and Lunati. Allow us to introduce our panel of experts, who will be leading us to enlightenment:
- Ryan Pritcher, COMP Cams
- Jerry Clay, Crane Cams
- Shane Pochon, Lunati
How Does the LS Stack Up to the SBC?
The reason the [LS] camshaft is larger is because the larger the diameter of the camshaft, the stiffer it will be and the more stable it will be. – Jerry Clay, Crane Cams
Since the beginning of the LS’s time, there’s been the argument between new school LS guys and the old school Small Block Chevy guys – which is better? We asked our experts to get their professional opinion …
Jerry Clay of Crane Cams stepped up to the table first. “When comparing LS rockers to SBC rockers at a stock level, the LS version are stud mounted to the cylinder head. The stockers have also been increased from a 1.5 to a 1.7 ratio – even to a 1.8 on the LS7.” While that means more lift for any given cam lobe profile, it also means that more power isn’t as easy as a rocker swap. “The rockers can then use a tad bit longer lever. However, the LS rockers cannot be adjusted, like in on a SBC rocker, nor do they have moving parts inside and are very plain to the trained eye.”
Another difference in the LS valvetrain is that they come stock with a fairly large diameter camshaft. “The reason the camshaft is larger is because the larger the diameter of the camshaft, the stiffer it will be and the more stable it will be,” Clay explains. The GenI and GenII Chevy small blocks came with comparatively small journal camshafts. The GenI’s cam was 1.868″ in diameter, and the LS cam is roughly about 0.300″ larger at 2.165″.
A lot of the extreme things that guys used to have to do with old motors to gain an advantage really aren’t even necessary on the new LS engines. – Shane Pochon, Lunati
Shane Pochon of Lunati adds, “Compared to the older small block 350′s and LT1′s, the LS1 has better springs and rockers, and the cams have a lot bigger bearing journal that allows you to run a bigger barrel, which helps make it a LOT more stable. However, you can find a downfall, with the LS engines already having a 1.7 rocker ratio. There are heads that are out there that like a lot of lift so it’s becoming more commonplace to swap in cams with a .550 or .600 lift.”
Many of the old-school hot rodder tricks that were developed for the SBC are baked right in to the LS design from the factory. “A lot of the extreme things that guys used to have to do with old motors to gain an advantage really aren’t even necessary on the new LS engines,” Pochon continues. “It’s got the cool firing order that guys building an SBC will pay extra to have incorporated into their engine. Putting in higher ratio rocker arms used to be a big thing, but now the stock LS comes with 1.7′s.”
Making or Breaking the LS Valvetrain
Like every other engine in the world, the LS has its strengths and weaknesses. We asked our panel of experts about their take on what the weak links of the LS valvetrain are, for both street and race use. While for the most part, it’s pretty good as designed, there are some clear areas that need attention.
“Anything you can do to make the valvetrain stiffer is a good thing, obviously, because no one wants a weak link within their cylinder head,” says Jerry Clay. “You want to do anything you can to raise what is called the “natural frequency” of the valvetrain. This goes for every kind of valvetrain – whether it be in your daily driver or on a NASCAR racer.”
Clay continues, “The valvetrain can reach a point where it is moving so far that the cam lobe and the valve spring do not harmonize. When this occurs, the valvetrain becomes so unstable that the lobe is no longer controlling the valve because the spring is in a harmonic all its own. This takes us back to the point made that anything you can do to increase the natural frequency and stiffen up the valvetrain is a very good thing.”
“Spring technology has advanced so much in the recent years. In an attempt to reduce weight in the valve train, technology led us to a spring that is large in diameter at the base and tapers to a smaller diameter,” adds Clay. “With that smaller diameter, we can also use a smaller retainer – further reducing weight. You’ve probably also noticed that on beehive springs, the wires aren’t perfectly round, but more of an oval shape, which helps increase the spring’s natural frequency. As with any hydraulic roller system, there is no lash in the system and you are actually pre-loading the plunger of the lifter. GM spent a great deal of time and money developing the LS’s valvetrain system and the result is a very, very stable system.”
It All Starts With The Bumpstick
One traditional mod, an upgraded camshaft, is particularly effective in LS engines. In turn, when upgrading cams, it’s a must to upgrade the factory valvetrain. Per Clay, “Lift is going to be a huge limiting factor on the stockers. It’s important to upgrade springs to make sure you have the correct seat and open pressures for the lobe on the new cam.”
- New springs should always accompany a cam swap
- Don’t assume you have the right pushrod length – use a “check” pushrod, even with hydraulic lifters
- Make sure your cam grinder knows the truth about your intended use, not what you’d like to brag about doing
Anytime you stray from the factory set up, even with a very mild mannered cam, it’s going to require more seat and open pressure. Even though the LS6 and LS2 stock springs can handle a little bit more lift, they will still be on the weak side as far as seat and open pressures go. It’s a false economy to do a cam swap without dealing with these potential failure points at the same time.
“Generally, the stock valvetrain components are designed to take a lot, within their limits – that being stock rev points. GM created lots of ‘safety’ features to ensure protection from over-rev damage and any other damage done from exceeding the factory limits,” says Clay.
Of course, deciding on stronger valvetrain components will depend on a lot of things, taking your camshaft profile into consideration. Some advice when considering solid lifter cams and aggressive hydraulic cams: “Once you get into these types of cams, this is when we really have to start talking about a whole host of other factors that need to be upgraded as well: higher compression ratios, exhaust systems, aftermarket heads, better intake manifolds, larger throttle bodies, and almost always, some kind of tuning,” states Clay.
Clay can’t stress nearly enough the importance of tuning. “Regardless of the choices you’ve made on components, and even if they’re matched very well, the guy with the laptop can literally make or break you. Often times guys are just looking for that big number on the dyno, and they may find ways to get it, but only to find later that their drivability has suffered tremendously because of it.” He concludes, “It’s one thing to put something on the dyno and tune for a peak horsepower number and it’s a completely different thing to get that peak horsepower number but still have a completely drivable vehicle.”
Frequently, people don’t question their build in relation to their cam profile – and you should. What kind of ports do your cylinder heads have? Are you running rectangular or cathedral? “They like different things. Most LS engines, in particular, like split pattern cams with a larger duration on the exhaust side,” says Clay.
“As an example, a stage 1 type car with stock LS1 cylinder heads would like about an 8 degree split between the intake and exhaust durations. When we get into the LS3/L92, and especially LS7 heads, you’ll tend to see camshafts with 20 degrees or more of extra exhaust duration. This is because the intake ports on these heads work so well that you will really have to increase the exhaust duration to get the spent exhaust gasses out of the way,” Clay explains.
With the vast majority of LS engines running EFI, the rules about lobe separation angle are somewhat different. “It’s not uncommon to see cams in a catalog with 118 degrees. That tends to be because the wider we make the lobe separation, the less overlap we will have, which is the time when both the intake and exhaust valves are open. And with less overlap, the easier these cars are to tune with a computer. You may see a lot of race type cams with 110 LSA’s, but I can assure you that a lot less tuning has gone into making that car run right. The average guy doesn’t have the time to spend getting a car like that to run good on the street,” says Clay.
Ryan Pritcher from COMP Cams had a whole lot of input on camshaft selection as well. “Stockish cathedral port heads usually like lifts in the .580 to .600 range, but the L92 style rectangular port heads like to be just a little over .600 to about .625. You really have to look at what kind of cylinder head you are using, especially if you have a factory casting. Compare that to a good stock-style head for the GenI small block like the Vortech heads; they were capped off around .525 even with beehive valve springs. The LS heads are a 15 degree head, and they really like to move some air and breathe a lot,” he explains.
“When I’m setting someone up with a new cam package, I want them to know it’s best if you do new valve springs and pushrods at the same time,” Pritcher adds. “If the lift is under .600 then we can do a beehive spring and it will be a drop-in that can use the factory locks and retainers. If the lift cracks over the .600 mark, they really need to get set up with a dual valve-spring kit with some full-steel retainers. LS guys really seem to understand that valve springs are just a necessity when doing a cam swap and they know that if they don’t, it can get really messy.”
Of course, one thing that hasn’t changed over the years is the mistaken idea that since a little is good, a lot must be better. We all know someone who is guilty of this. And LS guys are as bad as anyone about getting hung up on their dyno numbers and being only interested in reaching that giant peak number at the rear tires. It’s just too easy to get fixated on what the dyno sheet reads and how it compares with other cars that they’ve seen on the internet or YouTube. When you do that, it is easy to forget about the drivability and how the engine is going to act in at lower RPM where it will spend 90% or more of its life.
“If you’re mostly cruising around town and hit the drag strip two or three times a year, 226/228 228/230 112 LSA is plenty rowdy enough to give you the camshaft sound you’re looking for and still be plenty streetable,” says Pritcher.
We sometimes have to read between the lines when a customer says they want one thing, but how they plan to use the car doesn’t match up. – Ryan Pritcher
Of course, the value of their advice is directly proportional to the amount of information about your build and goals that you provide. “We are going to ask what kind of motor you are running and how many cubic inches it is,” Pritcher explains. “Then we will need to know what the compression ratio is, what kind of cylinder heads you have, if the heads have had any work done to them and if you have any flow numbers on the cylinder heads. We will need to know about what kind of intake manifold you are running, along with what kind of fuel system and what kind of gas you intend to run. Then we will move right along to the powertrain; what kind of transmission. Is it an auto or manual? What kind of torque converter? What is the gear ratio on the car? We will also want to know how tall the rear tires are since that plays into the overall rear gear ratio. We’ll even want to know how much the car weighs with the driver in it, since I’ve never seen a car going down the road or drag strip without a driver!”
“And finally, we’ll want to know what is the car going to be used for,” he adds. “Is it a daily driver? Is it a weekend toy to drive down to the cruise-in? Is it a dedicated race car? We will need to determine where the car needs to perform the best. We sometimes have to read between the lines when a customer says they want one thing, but how they plan to use the car doesn’t match up. Selecting a cam can be just as much about the driver as it is the car.”
How, exactly, do all these factors play into the cam decision? “You’ve got to look at the gear ratio and see where it’s going to put the cruise RPM, how much it weighs and getting it off the line to really get it moving. In a heavier street car, you’ll want to step down just a bit on your camshaft selection to try to get more low-end torque to help get it moving. But if it’s a full blown race car, you don’t need to worry about that as much since you’ll likely be launching at 4,500 off the transbrake or really slipping the clutch so you don’t have to be as worried about how it does down low,” says Pritcher.
Living at the Redline
If you’ve got a dedicated race car, chances are that you’re building an engine from scratch. You’re likely going to crank some heavy compression into it and if you do that, then you really can’t run pump gas. “In that case, you’ll cam the car accordingly for the powerband to come in somewhere around 4,500 and turn it all the way up to 7,000 or more,” says Pritcher. “This just isn’t going to be the type of combo that you are going to want to drive on the street because it’s going to be WAY too temperamental. It will buck and surge, you’ll have have to slip the clutch a lot to get it moving even from a stop light. If you’re running an auto with a high stall converter, just the amount of heat produced on the street could be devastating to some components. And on top of all that, your engine is going to feel really lazy in the low RPM range.”
We’ve noticed all tech guys think alike when it comes to truly knowing your car’s intended use and how they feel about dyno numbers versus street drivability. Pritcher isn’t alone in his views on street versus full race applications. Lunati’s Pochon adds, “We see people too often who build a race engine for their car, but then all they end up doing is idling it around on the street and it hardly exceeds 3,000 RPM. With a race spec valvetrain, the valves are opening and closing just as aggressively whether it’s at 1,000 RPM or 6,000 RPM. If it’s intended use is quarter mile passes, cruising it down to the local car show may only be 10 miles away but in an engine like that, it’s equivalent to 40 quarter mile passes. Everyone thinks that they need a race lobe so that they can make the big numbers on the dyno. And that’s not necessarily true, because often times you won’t make that much more power by setting an engine up for all-out race duty. It comes down to the question of ‘Is it really worth it?’”
We cannot stress it enough – be honest about what you want to use the car for! Do you want to street drive it? Mostly public roads with a little bit of drag strip? Full-on drag car? All of those have different requirements, and the aftermarket can handle just about any request from you, as long as you know what you want the car’s application to be.
“So often, guys are only concerned with creating a big peak horsepower number so they can beat out what all their buddies’ cars can do, and then end up with a car that can barely make it down the street,” Pochon continues. “That’s the guy that will get that cool peak power number, but a few months down the road, he’ll be the guy that will break a spring or have a lifter go out, and then he’ll be disappointed because he has to rebuild his engine. Whereas his friend who made 40 horsepower less is still driving his car every day. At the track, 40 horsepower less will barely get you 1/10 of a second. So the guy with 40 horsepower less is a 10th slower at the track but he can still drive his car anytime he wants and doesn’t have the durability concerns that his full out race buddy does.”
With Great Lift Comes Great Responsibility…
It’s always a good idea to play it safe and upgrade important valvetrain components when doing a cam swap. Not only is it easy to do, but it’s also affordable and very much worth every hard earned penny spent. While the stock components are durable and trustworthy with a stock cam, once you increase the lift, duration, or both, supporting mods are a necessity.
Per Pritcher, “Anytime you need a cam like that, you’ll also need the spring package to match it. The stock LS valvetrain is pretty light for what it is.” For those looking for a few extra revs, there are also components to help span the divide between street and full race. “We have some new short travel roller lifters that are kind of a bridge-gap between a hydraulic lifter and a solid lifter that will allow you to get some more RPM out of the engine,” Pritcher explains. “They take about 4-7 thousandths of preload and they will have limited plunger travel. These don’t take a lot of preload to work properly and you really only want to get the plunger moved off of the locating clip. Lifters work best when the plunger is up near the top of it’s travel, but you have to have the right valving inside to allow them to do that. They are also able to handle some more spring pressure. If you’re looking at building a full race application, you would at least need a set of rollers like the short travels or you would want to step up to a solid lifter and springs to match. Then you will “feel” the springs on the street. That kind of spring package should be looked at as an expensive ‘consumable.’”
Pochon from Lunati had the same views on the essentials of what needs to be included in a camshaft swap in the LS. “New pushrods and valve springs are the bare minimum for the swap. I encourage people to go ahead and upgrade the pushrods at the same time as your cam because the stock pushrods aren’t very rigid and they have a lot of flex in them.”
Diamonds are Forever, But Springs Aren’t
Stock valvesprings will live for a very long time in a factory-spec engine, which is amazing considering how many cycles they go through in the car’s lifetime. But asking more from the valvetrain means matching up springs that can handle the extra stress. “I wish more people with LS engines would keep an eye on their valve springs,” Pritcher admits. “Even in a street motor, guys tend to overlook valvesprings even though they do tend to wear out. Sometimes they fatigue enough to the point of failure. Valvesprings DO need to be changed out periodically, especially with the aggressive ramp rates on today’s cams. Even on an LS1 with a mild cam package and a set of beehives that’s daily driven, I would suggest looking at changing the valve springs in about two years’ time. Ultimately, they aren’t that expensive and you can change them in just a few hours. They are just a cheap piece of mind.”
Pritcher thinks that rocker arms are the coolest upgrade within the LS valvetrain. “The stock rocker is very stiff and a very lightweight design straight from the factory, but it still definitely leaves some room for improvement. We offer a titanium upgrade kit that replaces the bearings in the stock rockers with a caged needle bearing. The average guy can do it at home with a bench vice in about an hour and a half.”
Finally, Pritcher wishes that more people would pay more attention to their pushrod length – especially in the LS. “So often, when people do a cam swap in an LS engine, they will overlook making sure they are using the proper pushrod length and will in turn use the ‘go-to’ length that most folks typically throw in – a 7.4-inch pushrod. That will usually get you by but it doesn’t exactly get the lifter pre-load where it needs to be. Pushrod length is something you ALWAYS need to check because of different base circles used on various aftermarket cams. The typical hydraulic roller lifter likes to see anywhere from 0.03 to 0.06 worth of preload, so you’ve got a 0.03 window there to play with. We like to see you get your preload right in the middle of that range, right around 0.045.”
Since LS engines don’t have adjustable rockers, the pushrods are what determine the amount of preload. Most aftermarket cams have a smaller base circle, which in turn, means that you will need a little bit longer pushrod. In a situation like that, if you don’t get longer pushrods you won’t have enough preload and you will get some valvetrain noise.
“One of the biggest misconceptions about LS engines is that you can determine what length pushrods you need based solely on what components you have. The truth is that the only way to find out what length pushrod you need is to measure it for yourself because of all the variables that can come into play; the deck on the block, the deck on the heads, and whether or not a valve job has been done will all affect pushrod length,” says Pochon of Lunati. “I recommend getting your cam, springs and getting everything all set up, then using a pushrod length checker tool and get your length right the first time. You want to be looking for about 20 to 40 thousandths of preload on a hydraulic roller set up. On the pushrod length checker there will be hash marks that will tell you what the preload is.”
Pochon sums up the goal of any valvetrain upgrade, saying, “The biggest thing we try to focus on with the valvetrain in the LS engines is just do everything you can to keep it stable. Use a good pushrod, match your valve spring pressure to the needs of your cam, and combine it with a good, stable rocker arm. Go in as aggressive as you can on the lobe design and match it with your rocker arm ratio.” Pritcher adds, “Make sure all of your components match – if there is a weak link in your valvetrain eventually you’re going to have a very bad day.”