Less Shock, More Awe Pt. 3: LST Lobes For Big And Small-Block Chevy

This is a great time to be an engine tech geek. A few months ago we introduced a dyno test of one camshaft that is part of a new line of camshafts that COMP Cams’ Director of Valvetrain Development calls the Low Shock Technology (LST). You can check out the introductory story here. This new lineup of lobes was developed for the larger cam journal diameters of the GM LS and Chrysler Gen III Hemi families of engines.

We’ve covered the details on how cool these new LST lobes are at offering both a power gain along with increased durability — but the expanded news here is that COMP now offers similar lobes that can work with the smaller journal diameters of other engine families including the small- and big-block Chevys. There are a ton of details to cover so let’s get started.

In an earlier story on a 404ci stroker LS engine at Westech Performance, we tested an LST cam versus an earlier Extreme Energy version revealed an increase of 16 horsepower.

We first learned about the benefits of the LST-style lobes when we performed the aforementioned test at Westech using a 404ci LS engine. If you want all the killer details you can check them out here, but the highlights are that we started with a 281LRR-lobed hydraulic roller camshaft that is considered an excellent street performance cam. The specs on the cam were 231/247 degrees at 0.050-inch duration with a lift of 0.617 inch/0.624 inch and a 113-degree lobe separation angle.

This is the graph from that Westech test. The engine lost a small amount of torque below 4,000 rpm (below where this graph starts), but as you can see the LST improved the power curve at every point above 4,000 rpm with as much as 16 horsepower.

After establishing baseline power, we swapped this cam for a new COMP LST version with specs that were nearly identical. The new cam checked in with 231/244 degrees at .050 with 0.614 inch/0.606-inch lift with a 115.5 degree LSA. The only other change was to add COMP’s recommended dual valve springs. Any experienced performance engine builder would expect very little power difference between these two cams based on their specs. Despite appearances, the LST lobe design delivered a 16-horsepower improvement over the previous cam with a power increase at every data point above 4,000 rpm. Frankly, we were more than a little surprised.

Mechanics of More Power

Now let’s get into exactly what drove this new line of cam development along with how these new lobes are able to improve power. It all comes down to managing the valvetrain while adding improvements to both power and durability. Stick with us as this is a deep dive into how engines make power.

Let’s start with how a lobe design tweak can increase power. EngineLabs readers may recall a project that involved Godbold and EFI University’s Ben Strader called Project Spinal Tap. That 11,000 rpm effort pointed to some interesting approaches to lobe design that Godbold used to create the LST family.

LST Lobe Families

Hydraulic Roller

MGZ, MGH, MBZ, LPM, LSD, XLD & LSO

Endurance Solid Rollers

LGW, LGA, LIH, LHW, LXW, LDW, LKD, LXE

Drag Race Solid Rollers

LMS, LMX, MMO, MMX, OLM, MBW, MST, MJN, MJW, MJO, MDW, MNP, MFP, MTW, MSL, LXC, MSM

What Godbold learned was that controlling the valvespring demanded a gentler initial opening ramp. The old, accepted way of doing things was to smack the valve open as quickly as possible. That approach was to look for a lobe with shorter duration numbers at 0.020-inch lobe lift and bigger duration numbers at 0.200-inch lobe lift. These numbers identified a cam that initially accelerated the valve open very quickly.

While this approach made power, it was also abusive to valvesprings. For drag racers, they might get 10-20 passes on a spring before it lost enough load that replacement was required. Godbold’s idea was to slow the initial opening side down and not hit the valvespring as hard. That would minimize what was often seen as a huge dynamic wave that would travel through the spring during the valve opening and closing event. With this new design, the spring could now use more of its natural load to control the inertial forces of the valve at high RPM instead of sharing that load to control the massive wave surges traveling through the spring itself.

Most current version cams that accelerate hard right off the seat enhance lift with the piston near TDC where airflow is just getting started with the intake valve just beginning to rise off the seat. LST lobes delay this with no cost to power and instead enhance lift on the closing side where the cylinder head can offer much more substantial gains in cylinder filling.

To make up for this slower initial ramp, Godbold then enhanced the acceleration in the middle of the curve with special attention paid to the closing side. As Godbold explains, there is very little airflow occurring at the initial intake valve opening because the piston has just moved past TDC. However, on the intake closing side (as the piston is moving upward) there is the potential to move additional airflow into the cylinder using the inertial ram effect of the high-velocity air moving past the intake valve, despite the fact that the piston is moving upward.

If additional lift is generated on this closing side, the cylinder will eventually trap more air after the intake valve closes. This will make more power. This is exactly what the LST cam lobe design accomplishes, while at the same time, offering improved valve control that also may not require as much valvespring load. The resulting lighter spring loads reduce strain on the valvetrain, which in turn, means everything will last longer.

This is a graph of the exhaust lobe (left side) and intake lobe (right side) comparing the red outline LST family intake lobe to an older design. The closing side of the intake lobe offers additional valve lift in the area where the piston is rising but can still do a better job of cylinder filling. This is where the small increase in power originates. Even with the greater lift, the intake closing (IC) is the same for both lobes.

Applying Science to Other Cam Families

This is what we saw with the LST cam test on that 404ci LS engine and what prompted us to look into similar lobe designs that might be available for engines beyond the Gen III/IV engine family. While our examples will concentrate on the small- and big-block Chevy, the same approach can be taken with virtually any engine that can accept the accompanying LST-style lobe families.

We’ve also included a list of journal diameters for popular engines. There are certain specific requirements you need to know that are necessary to ensure the cam will work in your engine. We won’t get into those details here, but they are outlined in COMP’s Master Lobe Catalog. If you have questions, the best place to get answers would be to call COMP’s Tech Line, directly.

Cam Journal Diameters

SB Chevy BB Chevy 50mm SB Ford BB Ford LS / 55mm 60mm
1.868 1.968 1.968 2.02 1.561 2.165 2.362

There are some basic recommendations that Godbold has come up with that may help you with lobe selection, across any engine family. Because the LST lobe offers a gentler opening acceleration, LST lobes employ slightly longer advertised duration numbers even if the duration-at-0.050 numbers are the same as the previous cam. The real benefit, as mentioned, is the additional lift generated on the closing side of the lobe.

Given this, Godbold suggests that if you would like to try an LST family lobe, that you can choose a lobe with perhaps 1 to 2 degrees more advertised duration. Plus, what we’ve discovered is several lobe families offer significantly more lift for the same duration at the 0.050-inch tappet lift numbers.

Using a small-block Chevy as an example, we have a 383ci small-block that uses Comp’s Xtreme Energy roller with the specs listed in the small-block Cam Specs chart. To replace the existing cam, Godbold suggested the MGZ family for the intake side and ESX for the exhaust side. Each family of lobes offers multiple durations at 0.050. We chose a lobe with a slightly longer advertised duration of 296 while the duration at 0.050 number was only one degree longer with 237 degrees versus 236 for the Xtreme Energy cam.

SBC Example Camshaft Specs

Existing Hydraulic  Roller Cam  357ci SBC

Xtreme Energy XR288HR

Adv.              Dur.              Lift                LSA    Adv.   Lobe

Dur.              0.050            (inches)                             Lift

I – 288           236               0.520            110     4      0.347

Ex – 294        242               0.540

 

383 – LST Custom Cam – MGZ intake and ESX exhaust lobes

33396S Intake Lobe / 33701S Exhaust Lobe     33396S / 33701S HR112 4

Adv.              Dur.              Lift                LSA    Adv.   Lobe

Dur.              0.050            (inches)                             Lift

Int. – 296       238               0.585            112     4      0.390

Exh. – 308     249               0.585                                 0.390

MGZ Lobe Family

This is a selection of several different MGZ lobes that are part of the Low Shock Technology family of intake lobes. This particular section features a lobe lift of 0.373-inch.

Lobe Number Duration at 0.006 Duration at 0.050 Duration  0.0200 Lobe Lift Theoretical Valve Lift at Rocker Ratio
1.7 1.77 1.8
23302 296 238 158 0.373 .634 .660 .671
23304 300 242 162 0.373 .634 .660 .671
23306 304 246 166 0.373 .634 .660 .671
23308 308 250 169 0.373 .634 .660 .671
23310 312 254 173 0.373 .634 .660 .671
23312 316 258 177 0.373 .634 .660 .671

The maximum valve lift for the newer MGZ cam is also greater by 0.065-inch on the intake side which is a substantial increase. This will affect piston-to-valve (P-to-V) clearance so it would be best to check P-to-V on the original cam before making this change. In street engines, P-to-V can often be as much as 0.200-inch or more, so a big increase in lift may not pose a problem but you must check this. We won’t detail how to check that here but you can reference that story here.

The combination of those benefits from the LST cam improved power on our LS engine by more than 16 horsepower and our LS engine test did not increase valve lift. If the heads on your engine can accommodate the additional airflow, this could easily be worth 20 horsepower — or more — on a good, large displacement small-block.

These new LST families of lobes generally make it easier on the valve springs but there may be instances where the lobe may require a spring change. Or, if the new cam adds significant lift, make sure the spring can handle the additional lift without retainer-to-seal problems or creating coil bind.

One advantage to the low-shock lobes is that they also respond very positively to adding rocker ratio. Our existing small-block is using the 1.5:1 rocker ratio and a shift to a 1.6:1 ratio would improve the valve lift across the entire lift curve. This likely will not be necessary with the additional valve lift generated by the new MGZ lobe but if your engine can accept the additional lift, this could push the maximum valve lift to 0.624-inch! That is big-block Chevy territory.

Going Bigger Than Big

Speaking of big blocks, let’s address the Rat motor using a 496ci stroker with a mechanical roller cam as an example. In the Comp catalog, this engine’s cam is listed as a circle track cam with the specs listed in Chart 5. This is a big cam with 261 degrees at 0.050 using a COMP RX intake and RZ exhaust lobes.

Godbold suggested the LGW / LGX mechanical roller low-shock lobes as an upgrade. Looking through the specs of those two lobe families, we found an intake lobe that was very close in 0.050-inch duration numbers. This added 1 degree to the advertised duration and had actually slightly less intake valve lift, which was already very tight on piston-to-valve clearance. However, with the additional area under the curve on closing, this promised a slight power increase.

This 496 spent some time on the dyno at Westech making 707 hp at 6400 with the Comp oval track mechanical roller camshaft. With a conversion to a suitable LST-style lobe, we think a 25-horsepower improvement is very likely. Plus, the valve springs would last longer.

Big-Block Chevy Mechanical Roller Cam Specs

294RX-8       PN 11-851-9

Adv.              Dur.              Lift                LSA              Lash

Dur.              0.050            (inches)                             (inches)

I – 294           261               0.734            108               0.020

Ex- 303         270               0.737                                 0.022

This cam uses an RX Intake Lobe and RZ Exhaust Lobe

LST lobes – LGW intake and LGX exhaust custom cam recommendation

Adv.              Dur.              Lift                LSA              Lash             Lobe

Dur.              0.050            (inch)                                 (inches)

Int. 295         264               0.717            111               0.014”*          23327

Ex-303          272               0714                                  0.016”*          23375

This particular big-block sports 10.5:1 static compression with a relatively tight 0.045-inch piston-to-head clearance, and with the initial roller cam, we measured barely 0.050-inch of intake-valve-to-piston clearance. With a more aggressive closing side low-shock lobe, this could easily push our piston-to-valve clearance way too tight. For this reason, Godbold recommends adding lobe separation angle to the cam with an additional two to three degrees. The original cam offered a 108-degree LSA while this new low-shock cam would probably best be spec’d with a 110- to 111-degree LSA.

By widening the lobe separation angle, this will automatically retard the intake lobe centerline and increase the piston-to-valve clearance. Because this is difficult to estimate, any new lobe selection here might be best enhanced with a discussion with a COMP tech representative in order to make sure the cam will work in the engine. This is worth emphasizing since too aggressive of a lobe selection could result in piston-to-valve interference which would then require machining the valve reliefs and a loss of compression.

Increasing lift on the closing side also will move the valve closer to the piston at its nearest point, roughly 10 degrees After Top Dead Center (ATDC). It’s best to know what your piston-to-valve clearance is before altering the cam timing. With our big block, our intake piston-to-valve was very close so this becomes critical to ensure any cam change does not reduce the clearance.

But again, the advantages of this move are significant with the potential increase in cylinder pressure. This particular 496 had already been dyno tested with the original cam at 707 hp. The original LST test on the 404ci LS engine increased power by 16 horsepower or nearly four percent. A four-percent gain would mean as much as a 25 horsepower bump with our 496. That would put this big block over 730 peak horsepower, which would be outstanding.

Another advantage in favor of the low-shock family of lobes is that not only is there a horsepower gain, but often valvespring life will also see a major improvement. This is based on the reduction in stresses imparted into the valve spring thanks to the softer initial acceleration of the valvetrain. Godbold has seen this on Comp’s Spintron, where, after extensive testing, the springs exhibit only a slight loss in pressure, which means the springs are happier and will last longer.

Degreeing the cam means checking for the placement of the intake centerline. This is critical information to help ensure that should you have to change cam position, there is a reference point to establish which way to go. Retarding the cam, for example, will increase intake valve-to-piston clearance while advancing the cam decreases piston-to-valve clearance.

A final thought from Godbold emphasized that dyno tests do not tell the whole story. Early reports from road race and street applications are that the LST cam family also contributes to improved throttle response, as well. The bottom line is that this new Low-Shock Technology approach offers the double-barrel advantage of not only more power but at the same time improving valvetrain durability, and it’s not just for the LS and Gen-III Hemi families of engines. This truly is the Golden Age of Horsepower, especially when you know where the good parts are stashed!

Article Sources

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
Read My Articles

Hardcore Chevys in your Inbox.

Build your own custom newsletter with the content you love from Chevy Hardcore, directly to your inbox, absolutely FREE!

Free WordPress Themes
Chevy Hardcore NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

We'll send you the most interesting Chevy Hardcore articles, news, car features, and videos every week.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

Chevy Hardcore NEWSLETTER - SIGN UP FREE!

We will safeguard your e-mail and only send content you request.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...



Hot Rods & Muscle Cars

Drag Racing

Engine Tech

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

Thank you for your subscription.

Subscribe to more FREE Online Magazines!

We think you might like...

  • Hot Rods & Muscle Cars
  • Drag Racing
  • Engine Tech

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

Thank you for your subscription.

Thank you for your subscription.

Chevy Hardcore - The #1 Performance Bowtie Online Magazine

Thank you for your subscription.

Thank you for your subscription.

Loading