The Best Keeps Getting Better
October 24th, 2012
by: Alex Villani
Well, it has been quite a ride waiting for the fifth generation small block, but the day has finally come to see the next iteration of Chevrolet historic performance power plant. It seems like only yesterday that people were dreaming up 5.5 liters of overhead cam engines or twin-turbo V6 power plants to replace the historic Small Block, but it seemed that we were right all along. Be damned with CAFÉ requirements and welcome the all-new fifth generation Small Block Chevy engine, one of the most advanced engines ever to be assembled. There is a whole bunch of really great info that Chevy and GM's Powertrain guys threw out there and now it is time to dig through all of it and find the really good stuff as well as go over some of the highlights of the new engine.
First, let's go over the basics of the new engine. 99.9% of the Gen V engine is all new, with only the starter bolts, the wrist pins for the pistons and the valve spring keepers being the only parts carried over from the fourth generation. The engine that they unveiled today was the engine that will power the base model seventh generation Corvette, and its name will be LT1. As of right now, they have the engine rated at 450 horsepower and 450 foot-pounds of torque while matching the current Corvette’s highway rating of 26 miles per gallon, but that is far from official.
Many of you might remember the very potent LT1 from the 90s, but the very first LT1 dates back to the peak of the muscle car era. The 1970 LT1 debuted in the Corvette, pumping out 370 gross horsepower in a time when big block cars were putting out 350-400. The LT1 showcased the most powerful Small Block ever created, and it was not until the late 90s was it eclipsed by the LT1 and LS1.
The LT1 was designed and built to meet the requirements that Tudge Juechter, Chief Engineer for Corvette, demanded from the Small Block team to hit. Power, efficiency, power, compactness, power, and power is what the man wanted, so the Powertrain team had to make sure it could hit every single demand from the Corvette guys. Making sure that the engine remained compact to keep hood profiles low meant keeping with the tried and true push-rod design. The demand for power locked in the displacement from LS3, giving the team a bunch of cubes to make power from. Efficiency was the next big issue and solving that would come from several different technologies, namely direct injection, active fuel management, and constant variable valve timing.
Starting with the block, the bore spacing remains the same, but larger head bolts help improve clamping force and a new block casting technique is used to set the iron cylinder liners into the aluminum block. Where the current model has the iron liners pressed into the block, allowing the top to protrude ever so slightly from the top of the deck, the new design superheats the liner and allows the aluminum to form around it, leaving a clean and flush surface to mount the heads to. This also solves the issue that GM was running into of not totally surrounding the iron sleeves with engine material. Now that the engine is cast around the iron sleeves, this helps strengthen the engine and allow it to take more abuse, as well as pressure.
We asked the Powertrain guys if they explored the implementation of plasma coating the aluminum walls like what Nissan, Ford, and Porsche has done. They had done research into doing so, but none of the high-tech coatings could match the iron bore’s toughness, and since GM does not have to worry about additional mass or physical dimension problems found with overhead cam engines, they stuck with the iron sleeve design.
To further built a bullet-proof foundation, GM went with six-bolt nodular iron main and rod bearing caps, a forged crankshaft, and forged powder medal connecting rods. For this naturally aspirated application, the pistons are still hypernetic castings to save on weight. To aid with lubrication, an updated oiling system, complete with variable displacement oil pump, will be able to get oil to the vital parts that need it the most.
There are also little oil squirters that spray the backside of each piston to help keep them cool and quell detonation. The whole system can be upgraded with an optional dry-sump oiling system for those of you who will be buying C7 to take to the track. Talking with the engineers and product guys, they said that the dry-sump system will be an option for the standard Corvette, so no need to buy an upgraded performance package. The dry-sump upgrade also means a new oil pump to feed the whole system as well and yes, you will be able to have dry-sump and AFM together.
It all sounds too easy, right? Just throw some direct injection stuff in there and let it fly, right? Well, there is way more to making sure that the engine is not some botched science project, and putting together a well designed and engineered engine. It was here that the Powertrain guys and gals had their work cut out for them. They went through countless hours of computer model testing, going through hundreds of combustion chamber combinations and cylinder head configurations to make it all work. The cylinder head alone has seen the largest change over the last generation.
The all-new cylinder head design has as many dramatic changes when compared to the current small block as the third generation small block was changed from the original. First, the intake and exhaust valves have all been swapped around and are splayed slightly to make room for the direct injector nozzle. This change not only helps improve the revised active fuel management system, it helps improve air flow into the chamber. The new intake runner design allows for a radically different intake design that what we are used to seeing with the last two small blocks.
This all new intake was designed to help the flow of air into the chamber, designed using data pulled from the Corvette racing team as well as computer model testing. The new intake manifold design places long runners inside a plenum box, allowing each individual cylinder to pull air from the plenum when the valves open. This helps supply the air flow to the rear two cylinders, which has always been a problem for small block engines in the past. This "runners in a box" design, as Powertrain is calling it, is also flatter which lowers the total height of the engine, therefor lowering the cowl height. This new intake does not have to deal with having a few fuel injectors being plugged into it as the direct injection system moves them under the intake.
Yes boys and girls, direct injection has finally made it to the big V-8! Many naysayers out there said it could not be done, but sure enough, GM found a way. The direct injection system is fed by a mechanical fuel pump that sits under the intake as well, towards the back of the engine and is driven by a triangle-shaped cam lobe on the back of the camshaft. This fuel pump can vary fuel pressure as the engine demands it, helping to deliver you power when you need it and back off the pressure when you do not. The injectors themselves are not pezo injectors like what can be found on other direct injected powerplants, as the cost of the system was too high and did not offer any benefit over the system that they ended up using. And thanks to direct injection and the combustion chamber changes, you can run on regular gas instead of premium with only a minor drop in performance.
The exhaust gasses will be shuttled quickly through a set of cast exhaust manifolds that implement the use of longer runners to help separate the gasses and improve flow. A lot of work went into designing the manifolds so that it could aid in evacuating the exhaust gasses as well as still fit between the rails of the tiny sports car.
The LT1 will receive a constant variable valve timing system, allowing an additional ten degrees of timing change over the current system, but there is more to it than that. See, due to the current engine's combustion chamber design, they could never take full advantage of the VVT system, but thanks to the countless hours of engineering and testing, this new engine will be able to take full advantage of the additional cam timing. What does that mean? All that delicious power will be spread out over a much wider power band, and what a powerband it will be.
To the layperson, it might seem that all that GM did was add direct injection to an LS3, and all they were able to pull out of it was a few more ponies, but if you read through all the technical stuff that GM has, you will quickly see it is much, much more than that. In fact, the combustion chamber design is so innovative that the SAE is currently writing a paper about it to help explain it to everyone else. I could go into the cam profile changes and torque curves and chat till the wee hours of the morning about the fluid modeling that the powertrain guys did to optimize the fuel and air mixture, and how they created the piston design to help the quench area, but in the end what you really want to know are the basic facts.
While the 450 power ratings are not official, we expect to see a nice bump when the final numbers come out. Our prediction is around the 470 mark matched with a flat 465 foot-pounds of torque. We will be seeing an all new era of performance, just as the previous Small Blocks before it. GM is touting that the LT1, as well as the rest of the family, is one of the most advanced engines ever to be designed, and by looking over the pages of tech specs, I am willing to agree with them. The big question is to see how long it will take the aftermarket to pick up on the new small block.
Do not expect to see any engine swap plans right out of the gate as it will take some time for the engine to earn its stripes, just like the current engine had to. GM understands that the engine could have huge potential for the aftermarket, which is why right after we got to see it in person, the LT1 was being hauled off and headed west to Las Vegas for the upcoming SEMA show. That should speak volumes about how GM feels internally about the engine hitting those who love to tinker. Expect to see Corvette make its debut with the LT1 under the hood on January 13th and ripping up the streets sometime in the third quarter.
The LT1 on GM's Tilt Dyno. Because Racecar