Pontiac, Michigan — Chevrolet has unveiled the Gen 5 Small Block V8 that will power the 2014 C7 Corvette. Here’s the first in-depth look.
It’s amazing on one hand, but on the other hand, it’s no surprise at all. The latest Chevy V8, the 6.2L LT1 destined for the C7 Corvette that will be unveiled to the world on January 13, has pushrods and but one camshaft. In the block.
Of course, we know why General Motors, and the Corvette engineering team in particular, are still crazy about pushrod V8s after all these years, even while DOHC four-valve designs rule the rest of the biz. Here are the attributes as GM lists them: compact, lightweight, powerful, efficient, durable.
For example: at 465 lbs complete, the new Gen 5 V8 is nearly 50 lbs. lighter than most comparable DOHC V8s. And at only 25.3 inches tall, it’s 4 inches shorter than oh, say, a BMW 4.4L V8 of similar output. In terms of power density that’s impressive, and makes for a sweet package indeed in a front-engine sports car like the Corvette: light and powerful with a dramatically low hood.
So starting with the LT1 version that will be standard equipment in the C7 Corvette, the Gen 5 replaces all current General Motors V8s. The Small Block is dead. Long live the Small Block.
But in 2012, how can a lowly two-valve, pushrod V8 possibly hope to compete with the latest four-valve, twin-cam V8s in overall output and efficiency? According to GM, through the careful implementation of four key “next-gen” technologies:
+ Direct fuel injection
+ Active Fuel Management, aka displacement-on-demand, using four and eight cylinder modes
+ Continuously variable valve timing
+ A radically new combustion design with ultra-efficient 11.5:1 compression ratio
So let’s dig in and take a closer look at the Gen 5 LT1, starting with the block:
The Gen 5 cylinder case is 319-T7 aluminum with cast in-place iron liners. The liners are induction heated during casting to draw in more aluminum around the liner walls. None of the iron liner shows on the finished aluminum cylinder deck. Bore is 103.25 mm (4.060 inches).
The six-bolt main caps are nodular iron while each cylinder gets a dedicated oil sprayer baked into the block design from the start. Bore spacing (4.40 inches, naturally) and other key dimensions, including cam and deck height, head bolt pattern, and so on are identical to previous Gen III and Gen IV engines. However, only a few minor parts such as starter bolts and valve keepers are actually carried over to the Gen 5.
The LT1’s crankshaft is a 1538MV twisted steel forging with induction hardened journals. Rod and main bearings are polymer-coated bi-metal (so long, lead) with a narrower oil groove than previous designs. Stroke is 92 mm (3.62 in.). Note the 58x tone wheel outboard of the rear counterweight to support the coil-on-plug ignition and GM E92 engine controller.
The Gen 5 LT1 cylinder head, shown here with an LS3 head for comparison, is a major departure. Note that the intake and exhaust valve locations have been swapped—to provide room for the direct injector and a more centrally located spark plug.
Above is a view of the deck side of the LT1 cylinder head. Valves are splayed 2.5 degrees and an additional 2 mm of installed spring height has been built in.
Here’s a closeup of the compact combustion chamber illustrating the injector and spark plug locations. The intake valve is 54 mm (2.13 in.) while the exhaust is 40.4 mm (1.59 in.) and sodium-filled.
The head fastener layout is a carryover from the Gen III/Gen IV, but the screws have been upgraded from 11 mm to 12 mm in diameter and the length has been increased to accommodate more generous coolant jackets.
The LT1 cam phaser can swing 62 degrees, 10 more than previous GM pushrod V8s, and the dual-equal variable timing program is, for the first time, able to use the entire range in optimizing pumping efficiency. The lobe design is based on the previous LS3 stick but optimized for the variable timing and displacement systems, with 0.551-inch (14mm) intake / 0.524-inch (13.3mm) exhaust net valve lift and 200-degrees intake / 207-degrees exhaust (at 0.050-inch) duration. Lobe separation angle is 116.5 degrees. Just ahead of the rear cam bearing journal is the “tri-lobe” lobe station that drives the direct injection fuel pump.
Here are the LOMA (Lifter Oil Management Assembly) valley cover and valvetrain pieces that enable the Active Fuel Management system. Upon demand, the hydraulic roller lifters on cylinders 1,7,6 and 4 release, deactivating those cylinders. So essentially , the engine is a V8 under high/normal demand and a four banger under low load for maximum fuel economy. Firing order is 18726543 in eight-cylinder mode and 8253 in four-cylinder mode.
Above is the direct injection manifold assembly with its camshaft-driven mechanical fuel pump that operates at nearly 2200 PSI. Each 22 cc/second injector employs six carefully angled orifices and fires once per engine cycle, twice on cold start.
In order to manage the harsh noise that direct injection is noted for (caused by the extreme pressure hammering) the injector manifold is mounted in isolation, and the injectors are free to float vertically in the cylinder head bores.
The flow-tuned “runner-in-a-box” intake manifold assembly employs plastic composite construction and mates to an 87 mm fly-by-wire throttle body.
Here’s the key piece in the Gen 5 LT1 program, which engineers call “the most beautiful part of the C7 Corvette that people will never see”—the piston. The intricate crown profile, optimized for direct injection, required untold hours in testing and analytics, but it allows an impressive 11.5:1 compression ratio, one of the features that allows this pushrod V8 to compete with DOHC four-valve engines on the world automotive stage. Rods are 6.125-in. powder forgings; the ring pack is an adaptation of the three-piece LS3 kit.
Dyno validation is still in progress, but so far the LT1 develops more than 450 hp at 6000 rpm and over 450 lb-ft of torque at 4400 rpm. Fuel cutoff redline is 6600 rpm. Brake specific fuel consumption is 330 g/kW-h in normal mode and 270 g/kW-h with AFM enabled—impressive. Stay tuned.
Gen 5 Small Block LT1 Specifications
Engine type: 90-degree V-8 with overhead valves; continuous VVT
Displacement: 6.2L (376 cubic inches)
Bore x Stroke (in / mm): 4.06 x 3.62 / 103.25 x 92
Cylinder block: cast aluminum with nodular main caps
Main bearing fasteners: six, including two cross-bolts per cap
Crankshaft: forged steel
Connecting rods: powder metal, 6.125 inches in length
Pistons: eutectic aluminum alloy
Compression ratio: 11.5:1
Cylinder heads: 319-T7 cast aluminum with 59.02cc combustion chambers
Valve angles (degrees): 12.5 intake, 12 exhaust
Intake valves: 2.13 inches (54mm) hollow
Exhaust valves: 1.59 inches (40.4mm) hollow sodium
Camshaft: Hydraulic-type with tri-lobe for fuel-pump drive
Camshaft lift: 0.551-inch (14mm) intake / 0.524-inch (13.3mm) exhaust
Camshaft duration: 200-degrees intake / 207-degrees exhaust (at 0.050-inch)
Lobe separation angle: 116.5 degrees
Fuel delivery: direct injection
Intake manifold: “runners in a box” design; composite construction
Throttle: 87mm electronically controlled throttle body
Ignition: 58X with individual coil-on-plug and iridium-tip spark plugs
Horsepower / kW: 450 / 335 (estimated)
Torque – lb.-ft. / Nm: 450 / 610 (estimated)
Max. engine speed 6,600 rpm (fuel cutoff)
It looks like an aluminium small block with a fancy electronic fuel injection/ timing. Good for old skool but where are the small displacement, hign revving, double overhead cams and four valves per cylinders to compete in a global 21 century? Must have something to do with development funds after the bailout.
The article spells out the GM philosophy behind the engine.
Sadly, the engineers at GM are the last to appreciate the benefits of a 2-valve OHV V8 engine architecture. It’s cheap, compact, lightweight, and gives decent fuel consumption with cylinder deactivation, in a N/A engine. However, a smaller displacement, highly boosted DOHC V6 with VVT and GDI would likely give the same power, would be smaller, weigh a bit less and give better fuel economy. Of course the V6 would also cost more and provide inferior throttle response.
The people that don’t appreciate what GM has achieved with this engine are euro-snobs that drive BMW’s.
I disagree an equivalent V6 turbo DOHC would be lighter and smaller when you include all it’s associated plumbing and required intercooler (items that many forget to include in the equation).
I think it’s fantastic to see supposed ‘old tech’ come along with the Gen 5, a credit to GM’s engineers in a time when the rest believe that 92 valves and 43 camshafts are needed to move forward.
GM engineers obviously understand that at the end of the day it’s what happens inside the engine that counts, not the peripherals around it.
Looking forward to at least 10 more years of old 2 valve pushrods kicking behinds!
euro-pukes blow a lot of smoke,most don,t understand the meaning of the speces on this engine.to those of you that don,t understand there are 100 poines left on the table.
Automotive technology is truly a grand stage. Wether GM has it right or wrong is for the market, emmisions compliance, legislative compliance, consumer acceptance along with a long service life with minimul/low cost in maintennace charges and good overall gas mileage.
GM does not always get it right (GM Starfire Four Cylinder – Google that rubbish!) but their current engines are extremely competitive. Ecotec V6 (now gone) V6 Alloytec along with the LS series.
Let alone the all time favourite Small Block Generation One V8 engine. The revolution was introduced in 1955 and 90,000,000 odd of the buggers were made.
We can all argue manufacturers offerings with what is best or worse. Sure Japanese Lexus offerings are great. But when you want to tow a 2.5 tonne boat behind a medium family station wagon (1.75 tonne car), do theuy have an offering. Gets back to choice. If I want to do F1 racing I don’t do it in an Australian V8 Supercar, mind the V8 Supercar does same trACK TIMES (OR SO….)
AS i HAVE indicated, A BM troubleyou will be a fabntastic car,but haven owned and driven many many 250,000 mile HOLDENS AND cHEVROLET’S That have never had the heads off or any other wexpensive driveline repairs, compare terribly to company cars like Mazda’s, Toyota’s, Nissans and Hyundai’s that need serious expensive work at barely 100, 00o KM. Mind we are also talking suspension as well. Bare in mind GM and Ford are also responsible for lemons/expensive mistakes as well.
Its horses for courses. Personally, I like GM tedchnology. At least I can pull it apart, make it go better and give really good life at the 450 HP level out of a 5.7 litre engine as well as get great gas mileage. Same goes for my 3.0 L Evinrude two stroke outbourd. Sure I can make great horse power, but only for so long.
5 minutues at take off power in a heavily loaded Boeing B377 Stratocruiser is different to a quick squirt around the track in a Subaru WRX turbo fuzzy dice ricer hell missile.
Just remember, the market will dictate retail terms and manufacturers will comply. PS do a head change on a Bugati Veyron. I’d do my head in and do a head change quicker on a GM car…
But then I wouldn’t need to. Europe has some great technology, then theres Fiats, Alfa Romeo, Morris Marina’s, British Leyland, Citeroen, Mercedes, Renault BMW, Skoda, Lada, Seat, VW, Lamborghini, Ferrari, Bently and Land Rovers…
Now A Toyota Land Cruiser vs a Land Rover is another subject…. Remember the 2.6L Side valve over head valve Series Three…
I do, my hands are still scarred….
My two cents worth…
Imagine how low (and lightweight) this would be if it were a flathead engine.
I hate to say it Jon, but there are now 2 new flat head aircraft engines being made. The same company makes both in Belgium. One is a 4 cylinder and the other a 6. They are very new and yet, somewhat exciting!!!
As for the Chevy, they list 4 points that make the LT1 so great. Only the combustion shape is unique. The direct injected, active fuel managment/variable displacement, continuously variable valve timing, and high compression are common to almost all of the V8 DOHC engines.
Weight and size are more critical. The history of the manufacturers and the state of the market. The LT1 is lighter and smaller than the DOHCs. GM puts most of the LT1’s in trucks and large cars that are mid priced, as they have with previous pushrod engines. GM barely has a tradition of OHC. All the other manufacturers have a long tradition of OHC coming as they are from a market of smaller cars where OHC/DOHC rules. Many of the newer cars with DOHC are more expensive than the GM cars, especially the europeans.
I am still hoping for a large capacity 60 degree ohv V6 to continue the tradition of the LT1 in a slightly smaller size… The cam should be as high as possible to reduce push rod length.