GM's L92 and LS2 V8 engines
Having recently glanced under the skin of Mopar's pushrod Hemi V8, it seems proper to do the same with GM's overhead-valve (OHV) small-block engines. We'll take a look at the LS2 6.0L and L92 6.2L engines, both of which are relative newcomers to the line-up and are considered to be part of the GenIV family (the better-known LS1 comes from the GenIII series).
This brings us to the first point - if there's anything that GM did seriously wrong with these engines, it's the lack of a proper brand name. "Hemi" rolls off the tongue for any of the varied characters in Chrysler's ad campaigns, where as GM's 3-character SPID designations come naturally only for hardened fans of the General. Sure, there's the Vortec name that's been weakly marketed in the truck lineup for about 15 years now, but does the average person comprehend that the 5.3L V8 under the hood of his Tahoe is related to the LS7 in the Corvette Z06? Even so, GM's modern take on the small-block V8 is one of the most widely-used engines in the United States.
I think that GM does a great job on its cutaway displays, but I really wish they wouldn't paint every damn part in the same shade of silver - it makes it a bit tough to describe things. Regardless, we'll do our best.
Let's start off with one of the newest additions to the GM V8 family - the L92 engine that will find its way under the hood of the 2007 Cadillac Escalade.
I really wish I could roll this engine up to the others that we've examined in this series for the purpose of showing just how compact of a package that GM has created. There are a fair number of OHC V6 engines out there that are larger than the GenIII/GenIV engines, and the variety of vehicles that make use of these pushrod V8s are testament to their compactness.
On the valve covers are the coil packs. Where as most modern engines use a coil-on-plug (COP) design that completely eliminates high-tension spark plug wires, the plug location of a wedge head doesn't allow such a setup. If this display had plug wires installed, you'd see them running down just ahead - to the left - of each exhaust manifold primary tube.
Speaking of the exhaust manifold, this is definitely a decent piece of engineering. A true 4-1 long-tube design would likely improve peak power and broaden the powerband a bit, but this is a vast improvement over older, log-style manifolds.
We've spent a lot of time talking about intake manifolds during these engine posts, and for good reason - port fuel injection has allowed the development of some pretty radical intake geometry, and as such, intake manifolds may have overtaken cylinder heads as the most critical contributor to an engine's powerband.
Like we've seen on most other engines that are designed for something just short of all-out top-end performance, here we find the barrel-shaped long-runner manifold. There's plenty of plenum volume, and a not-outrageously-large runner cross-section. In other words, this is exactly what we'd expect to see on an engine designed to have a broad powerband that's biased somewhat towards the lower end.
While the L92 makes use of GM's Displacement on Demand (DoD) technology, it's not something that lends itself well to static display. We can see the lifters in the valley, but not much else - you'll just have to go on faith that it's really in there. The toothed gear at the rear of the crank, ahead of the last crank journal, is the reluctor for the crank position sensor (a piece of technology that keeps on showing up in these cutaways), and we can also see the spark plug at the lower left of the photo. Note it's aimed directly at the center of the chamber, despite the fact that it's coming in from the side (unlike the Hemi, which points its pair of plugs straight down into the chamber).
If there's port geometry, I'm going to comment on it. Compare this intake port to that of the Hemi, and it would seem obvious that the Hemi's straighter shot into the cylinder would offer better performance. Ah, but that's not the case. GM has developed wedge head port geometry to an art form, and has the intake charge turning corners and sliding over the back of the intake valve as if it had a straight shot into the cylinder. Despite having dramatically different port geometry, the GM and Chrysler approaches basically yield similar (and excellent) results.
Think of the L92 head as a slightly smaller version of the LS7 part (the smaller bore of the 6.2L requires the use of smaller valves), and that gives some insight into what kind of performance can be expected. Only three or four years ago, this level of output gave Corvette fans reason to drool, and now it's being dropped into an SUV. I'm not sure if that qualifies as progress, but it's at least something to ponder.
It should be noted that there's a price to pay for the GenIII/IV's head flow, and that's a head bolt. These engines provide four bolts around each cylinder, while the original small-block and the LT1 GenII derivative have five bolts around each cylinder. Unfortunately, that fifth bolt got in the way of the intake runner, and so something had to go. This isn't a problem until the engine is modified well beyond reason.
Note that the "skirt" of the block drops down well below the centerline of the crankshaft, and supports the main bearing caps via crossbolts. This is a very solid bottom end. That beefy oilpan adds a bit of extra structure as well.
To the lower left of this shot, we see the valvetrain - note the beehive springs and the use of cast-aluminum rockers that ride on needle bearings and actuate the valves with a roller tip. Ten years ago, those would have been considered exotic features. At the middle of the right edge lies the electronically-actuated throttle body.
There's the actuator for the variable valve timing (VVT). While installing the VVT system on a single-cam OHV engine doesn't offer up any adjustability of intake/exhaust overlap timing, it should be noted that simply advancing or retarding the overall valve timing can have significant effects on an engine's powerband, as hot-rodders have known for decades. Typically speaking, advancing the cam timing offers more low-end power, while upper-end performance benefits from retarding camshaft timing. I'm sure that GM employs this system in other ways as well, such as to improve cold-start emissions.
And now we move on to the 6.0L LS2. This is an interesting engine, for despite the many differences between it and the L92, they both generate peak torque at the same RPM, with the LS2 having a horsepower peak about 300 RPM higher in the rev range. Ah, but there's way more than just peak numbers, and what these single points on the graph don't tell us is what happens before and after the peaks on the graph, or what happens at part throttle. Unfortunately, GM has yet to provide dyno plots for the L92, so we'll have to revisit this issue at a later date.
Note the different intake used on the LS2 - it's lower, with shorter runners. That helps not only with packaging this engine under the ultra-low hood of the Corvette, but it also aids in moving the powerband slightly higher in the rev range.
The intake port geometry on the LS2 is derived from that of the LS6, which means that it was basically the benchmark for pushrod V8 airflow until the LS7 came along. A whole lot of additional peak HP awaits those brave enough to perform a camshaft swap, but at the price of reduced low-end power and drivability.
Here's the same beefy lower end. Note that there's just a simple gear hanging off the camshaft - no VVT is employed on this engine.
To no one's surprise, this looks a lot like the rear of the L92. The LS2 does not make use of DoD, however; it's definitely not needed in the light and tall-geared Corvette, but the CTS-V and GTO would likely benefit from the cylinder deactivation scheme.
So there we go. Which is better, you ask - the Hemi, or the GenIV? Let's put it this way - I'd be glad to have either powerplant under the hood. Both of these engines produce an impressive combination of power, compact packaging, and fuel economy; they just take slightly different paths.
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Reader Comments (Page 1 of 2)
Justin 11:38AM (2/21/2006)
Thanks for the excellent write up with the close up pics. I have admired GMs small block V8 ever since the LS1 came on the scene. I'm not a big fan of pushrod technology buy GM has been able to push it far and beyond OHC. These engines are smaller and lighters than all of the Europeans 4 and 5 litre V8s and V10s. For example the 500hp LS7 is almost 100lb lighter than BMWs 5.0 litre DOHC V10. Yet it produces the same 500hp and 90lb/ft more than the V10 at lower RPM. Also the lower lower reciprocating mass and fewer moving parts of the pushrod engine generally delivers better fuel economy than the competitive DOHC V8s.
BMW 90 degree V10
500hp at 7750rpm
383lbft at 6100rpm
4999cc
8250 rpm max
40 valves
Bore x Stroke (mm) 92 x 75.2
12.0:1 CR
528lb dry weigth
LS7 90 degree V8
505hp at 6300rpm
470lb/ft at 4800rpm
7000cc
7000 rpm max
16 valves
Bore x Stroke (mm) 104.8 x 101.6
11.0:1 CR
458lb dry weight
Anybody that would write off these pushrod engines as old tech just doesn't know what they are talking about. Too bad GM can't transfer some of this powertrain advantage to the rest of the car.
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Bob Miller 11:46AM (2/21/2006)
I've always loved the small block V8s from GM. My 1998 Camaro Z28 (sold it a few years back, I wish I hadn't) with the LS1 was perhaps the best car I've owned to date. (of course my standard issue GM gripe was the awful interior, which I didn't care about at 24 but I would definitely care about these days, luckily GM is working on this issue). That car got over 30 mpg on a road trip one time between Houston and Denver. I was completely amazed. On the highway that car consistently performed in the 25 to 28 mpg range, with high teens to about 20 or so in the city, which is still great considering the all out push back in your seat, never miss a beat performance from the engine and drivetrain. The sound of the motor under full throttle was just short of completely amazing too. Not that I would drive like that on public roads, right?
This new Camaro that may or may not come out of GM can't come soon enough. These V8s are one of the few shiny bright spots for GM - and these engines can't just be relegated for the GMT-900s and an expensive Caddy and Corvette. Let's get a few slick looking Buick and Pontiac sedans (think 300C/Dodge Charger) and perhaps a real, rear drive Impala (think a modern, slicker version of mid 60s Impala Sedan, Coupe and Convertible) to get these engines into as well as the SUVs and trucks.
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TheAwesome 11:46AM (2/21/2006)
I have to say that I'm impressed with the write-up! Thanks.
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Shyam 12:19PM (2/21/2006)
the small block v8 gm has is quite amazing (coming from a diehard porsche and bmw lover)...its just so frustrating why they can't design even a semi decent interior. Nothing about the vette's interior oozes class. If they could match the wonderful LS7 with an audi level interior, both in design and materials...and it trickled down the line of cars, then GM wouldn't be in its predicament. I'd be willing to pay an extra 15 grand on top of the vette or ls7 price if it had a decent interior design.
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Shyam 12:28PM (2/21/2006)
I meant Z06 instead of LS7.
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MikeW 1:05PM (2/21/2006)
What is with this crossplane V8 junk? L R L L R L R R just hurts my ears.
How about a review of modern V6s?
Personally the M5's V10 is dissapointing, I was hoping for an even firing 72 degree V10 with 550hp & 400 ft-lbs
German engines are built to different standards than american engines, just look at the oil that the M3 uses 7.5 quarts 5w-50 or 10w-60, corvette (regular, wet sump) 5 quarts of 5w-30 + filter ,corvette Z06-dry sump, 7.5 quarts of 5w-30 + filter. Look at the gearing, the M5 can do 202 mph (in 7th gear), corvette 7.0 198 mph (in 5th gear)
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Christian J 1:15PM (2/21/2006)
Pushrod engines are not as good as OHC engines. Sorry, its just the way it goes. There are one or two clear advantages, which is why OHV is still around, but the greater share of advantages (and not just performance) belongs to the DOHC/SOHC motors. This is why they are used in all the top performance cars, excepting most North American ones. Try comparing the LS2 to the Ford AJ-V8 in the Aston Martin Vantage, just to get you started. 6.0L/400hp vs. 4.2L/380hp.
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Eric Bryant 1:31PM (2/21/2006)
"What is with this crossplane V8 junk? L R L L R L R R just hurts my ears."
Your ears, maybe; to many others, that sound is music.
"How about a review of modern V6s?"
We're working on it.
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gallogeorge 2:52PM (7/29/2009)
I thought Chevy was still 1-8-4-3-6-5-7-2 which
comes out a little different than the R & L that you
have cited. Have not seen the firing order numer-
ation from which you derive your information....
I finally got annoyed with the stupid block numbering
of Ford and transcribed it back into GM speak and,
lo and behold it had the equivalent of 1-8-4-3-6-5-7-2
on one 302 and I think 1-8-4-2-6-5-7-3 on the HO.
There is only one other cross plane scheme that
seems to have been used but I cannot pull up my
notes and type at the same time.
George Gallo
Christian J 1:46PM (2/21/2006)
""So there we go. Which is better, you ask - the Hemi, or the GenIV?""
Oh and to answer your question: neither. Take the MOD 5.4L DOHC or the AJ-V8 DOHC. Otherwise give me a flatplane Cosworth V8.
-C
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Spear 2:34PM (2/21/2006)
i'd melt that shit down and make 2 more blocks for my STi....
american shit....
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olderty 2:45PM (2/21/2006)
Brittany Spear = dumbass
I'd melt down your STi and make 3 new LS2 V8's....
foreign crap....
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david l 2:59PM (2/21/2006)
#7 and #9...Ah isn't ignorance grand? Both of you make uniformed/snide remarks with no evidence to support your suppositions. Why don't you go bark somewhere else little doggies or come back with some specific evidence on why 'DOHC always beats OHV' or 'My STI kicks an OHV's ass' before you open your mouths? Try again.
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Hemidakota 2:59PM (2/21/2006)
Thanks for the write up guys and the closeup pics of the Hemi, 5.4 Ford, LS1, and the LS2.
Keep up the good work.
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Spear 3:06PM (2/21/2006)
I'd melt down your STi and make 3 new LS2 V8's....
At least my car can turn.
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md 4:10PM (2/21/2006)
"7. Pushrod engines are not as good as OHC engines. Sorry, its just the way it goes. There are one or two clear advantages, which is why OHV is still around, but the greater share of advantages (and not just performance) belongs to the DOHC/SOHC motors. This is why they are used in all the top performance cars, excepting most North American ones. Try comparing the LS2 to the Ford AJ-V8 in the Aston Martin Vantage, just to get you started. 6.0L/400hp vs. 4.2L/380hp"
Things are not so black and white. Just because one style is more common in high performance cars does not automatically make it better, and these engines here are proof of that. Another example is Porsche. They have stuck with rear-mounting the engines for a long time. Very few others do that, but Porsche does a great job of utilizing the design. You can't make a comparison purly on peak numbers, that is just stupid. Look at a dyno sheet. OHV engines make better low end torque, often times weigh less, and are less complex which lends to their better fuel economy and durability. OHC engines make better horsepower at the high end, which is an advantage in high performance applications, but again it can be worked around if the designers choose to. Both designs can be made to work equally well. Fords motors used in their trucks make great low end torque, but they are OHC.
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jm 4:13PM (2/21/2006)
Eric, how about adding in some numbers by the part in the pics when mentioning a certain part. Sometimes it takes some searching to find what you are talking about, other than that, great review.
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Justin 4:39PM (2/21/2006)
Try comparing the LS2 to the Ford AJ-V8 in the Aston Martin Vantage, just to get you started. 6.0L/400hp vs. 4.2L/380hp"
The LS2 is still a smaller package, lighter, gets better fuel economy and cheaper than the AJ-V8 or whatever you want to call it. Sorry, its just the way it goes.
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Justin 4:53PM (2/21/2006)
The non supercharged 300hp AJ-V8 weighs 440lb without the added weight of the supercharger and inter cooler. The 400hp 6.0 litre LS2 weighs a mere 450lb with all accessories. Supercharger not required. What are you smoking md?
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branbiel 4:59PM (2/21/2006)
Finally some respect for the GM gen IV's. These are amazing engines and thats why the aftermarket is there for them. No other company has that.
These engines are directly competing with OHC engines and even beating them in many of the catagories. Less complex engine and a less expensive engine. GM does what they do with the pushrods because its tried in true in these big vehicles and the people that use them trust them.
Before you bash these engines realize that they aren't going into a honda. Yes some smaller displacement engines make amazing power, on par with the larger displacement ones. But its all about power under the curve. Some of these go into some SUV's while others go into sports cars. Truly versatile when they are engineered like this.
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