Justin@GMHTP

iTrader: (1)

Looking at the Gen 5 LT1 V-8 as a complete package, the specifications are impressive. With 6.2-liters of displacement, 11.5:1 compression, direct injection, continuously variable valve timing, active fuel management, variable displacement wet or dry-sump oil control, an advanced combustion system, and an estimated 450hp, the Gen 5 LT1 doesn't just set the bar, it becomes it. This is, without a doubt, the most advanced small-block engine platform that GM has ever designed and we believe the changes, both evolutionary and revolutionary, will continue to keep GM poised atop the sports car market well into the foreseeable future. However, the new engine design hasn't come without its fair share of criticism. Fans of single and dual overhead camshafts, along with the three- and four-valve-per-cylinder contingent, have already slammed GM's choice to retain an "archaic" cam-in-block, two valve pushrod design. And they may have a point, although the merits of the traditional small-block are hard to argue, if it wasn't for the massive amount of R&D that GM has poured into the Gen 5 design. No technology was spared, and none used for the sake of making headlines, in the new Gen 5 LT1. Each piece was selected, tested, refined, and tuned for maximum power in a lightweight, durable, robust, and efficient engine package. What the Gen 5 represents is a class leading 450/450 engine with all of the refinement you would expect from a world class design. And it'll reportedly propel the 2014 Corvette to 60mph from a dead stop in under 4-seconds, which will excite even the most cynical of techno-nerds. So, what's inside the new LT1 small-block? Let's dig in and find out.

Old Parts:



Let's start our technical discussion with the parts that GM carried over from the Gen 4 engine design. Yep, that's all of them... A couple of bolts, the wrist pins, a retainer or two, and the LS3 locks. That's it. Literally everything else in the Gen 5 LT1 engine is brand new and was designed specifically for the new Gen 5 engine platform. This clean sheet approach wasn't about making things difficult for the aftermarket, it was about creating the most technologically advanced pushrod small-block V-8 ever produced and, in turn, one of the best sports cars in the world.

Direct Injection:



The heart of the Gen 5 LT1 engine is the direct injection system. Unlike a traditional port fuel injection system (PFI), which introduces fuel into the air intake charge prior to the intake valve, direct injection works, as one could imply, by introducing fuel directly into the combustion chamber at exactly the right time. By precisely controlling the timing and pattern of the injected fuel, GM engineers were able to maximize "every drop of fuel" used within the combustion process, and this system is the primary contributor to the Gen 5's increased efficiency and power output. And, due to direct injection's unique cylinder cooling capabilities, GM engineers were able to increase compression to 11.5:1, while "recommending" but not "requiring" 93-octane fuel. The heart of the system lies underneath the composite intake manifold and places the injectors underneath the intake ports, suspended in the cylinder heads by the rail to isolate the injector pulses (and thus, noise). This unique "burying" of the system underneath the intake manifold allowed GM engineers to create a compact design, but equally important, a quiet system, which won't have the same noise and vibration issues of other similar systems. The injectors, which feature 6 holes each and specially designed injector spray and droplet patterns, have a flow rate of 125.7 lbs/hr at 1,450 psi, and can be fed up to 2,175 psi from the 1.48 cc/rev geometric displacement fuel pump. The pump is mechanical (fed by an electric in-tank unit) and is driven off the rear of the tri-lobe camshaft. Upgradability will remain the number one question from aftermarket enthusiasts.

Cylinder Heads and Valvetrain:



Over 6-million hours of computational analysis went into the design of the new "advanced combustion system" found on the Gen 5 engine and one look at the cylinder heads proves it. Cast from 319-T7 aluminum, the Gen 5 LT1 cylinder heads feature large straight rectangular ports that incorporate a slight twist for the most efficient air tumble and maximum "mixture motion," compact combustion chambers, raised intake ports, and a centralized spark plug design. The 59cc chambers were designed specifically for the Direct Injection system (along with the AFM and CVVT camshaft) and feature reversed intake and exhaust valve locations, compared to the Gen 3/4, which significantly straightens the incoming air path into the combustion chamber. Large 2.130-inch (down from the LS3's massive 2.160-inch units) nitrided hollow intake valves paired with 1.59-inch hollow sodium-filled exhaust valves are present, actuated by stiffer 8.7mm pushrods and individually mounted 1.8:1 ratio non-offset common rocker arms. Along with the new intake and exhaust valve locations, the valvetrain has been further optimized with 12.5 and 12-degree valve angles (intake/exhaust, compared to 15-degrees found on the Gen 3/4), which have been splayed 2.5-degrees for increased airflow and reduced valve shrouding. The more centralized spark plug location promotes optimal ignition events by moving the flame closer to the center of the combustion chamber, which engineers cited as being "an essential enabler of the direct injection system's efficiency."

Camshaft:



The Gen 5 LT1 camshaft features 200/207 degrees of duration at .050-inches, .551/.524-inches of lift, and a 116.5-degree lobe separation angle. These specs are quite similar to those found on the LS3 (204/211-degrees of duration, .551/.522-inch lift, 117 LSA) although the design has been optimized for the splayed valves, 1.8-ratio rockers, and the AFM system, and reversed for the new intake and exhaust valve locations. Unlike previous generations, the base LT1 will come standard with continuously variable valve timing (CVVT) and the ECM works with an oil-driven camshaft phaser to command up to 62 crank degrees of camshaft phasing. The rear of the Gen 5 camshaft is radically different from previous generations, with a tri-lobe designed lobe that drives the engine-mounted high-pressure direct injection pump. A new rear cam bearing was designed to work with the addition of the tri-lobe, although the overall position of the camshaft relative to the crank remains the same. Active Fuel Management is also new to the Gen 5 and special AFM lifters are present on cylinders 1, 4, 6, and 7. Both electronically and hydraulically controlled, the AFM system shuts down 4 of the 8 cylinders under "low load" conditions, which saves gasoline and increases the effective MPG rating of the LT1. Surprisingly, and somewhat counter intuitively, the large 6.2-liters of displacement is helpful here, with the engine running on 3.1-liters in AFM mode, enabling it to power the Corvette effortlessly under many light load conditions. If the engine was smaller, say 5.5-liters as many had hypothesized, AFM would run at 2.25-liters, which likely would have been difficult to maintain in many driving situations.

Read much, much more: http://www.gmhightechperformance.com...#ixzz2Aoe7eAxS

-TheBandit-

iTrader: (1)

While I realize it is a clean sheet design, do we have any word on interchangeability with the gen III/IV? For example, differences in overall length, bell housing pattern, rod length & bores, any bolt patterns that may be similar, etc?

01_SuperSlow

iTrader: (7)

No interchangeability as far as I can tell. And it looks like cam swaps will be a lot more work now too.

dr_whigham

iTrader: (49)

There's a small part of me that wonders if those heads would bolt to a gen III/IV block. I'm well aware of the work that would have to be involved with the injectors and whatnot, but the dimensions themselves...

It's interesting to say the least.

bww3588

iTrader: (49)

direct injection uses a much higher fuel and injector pressure. This is the same technology that has been used on diesels for 30+ years, and I can assure you, the cylinder pressures in a diesel making 60+lbs of boost, and 16:1 compression (think duramax) will far exceed the pressures you will see in this lt1.

Also, keep in mind this setup is very similar to the direct injected 3.6 that is in 2010+ camaros and other models. Which have already seen serious boost and power on the stock injection system.

Exidous

iTrader: (11)

I have but one question. Will it fit in my Rx-7 with the T-56 I already have? :-)

Edit: Of course they just HAD to change the bell housing....one bolt different it seems.

TrentSS

Justin - Not that it's important to me but I am curious what GM is or will claim for gas mileage as compared to the standard 430 horse LS3...

Justin@GMHTP

iTrader: (1)

Trent - It will get better mileage than the LS3, that is for sure. GM is currently saying "26" but that seems very low considering all of the new technology here (DI, AFM, CVVT, efficiency, etc...) I would hope we're in the 28 range when it is all said and done.

Bandit - From what we have seen it looks like the heads would physically bolt on to a Gen 4 block. The bore spacing, cam/crank height, etc. are all the same and the bolt pattern also looks similar. The issues would be numerous. Remember, the intake/exhaust valves have been reversed, the DI system would need to be removed/plugged, the camshaft is different with a new tri-lobe rear which requires a different rear cam bearing, and the intake is different thanks to the raised intake runners.

If you could overcome all of that (of which the camshaft would be the most difficult IMO), you still have to deal with the radical piston/chamber design, which have been built specifically to take advantage of the DI system... I think it would be neat to see it done (or try it) but I can't ever really see how the benefit would outweigh the cost.

1bad - Rail pressure can be as high as 2,175psi and, as bww pointed out, is a similar system to those found on both diesel trucks, and the current V6 LFX engine. Boost shouldn't be an issue, I believe the major hurdle will be fuel control (pump upgrades? larger injectors?) for the initial couple of years.

J-Rod

Justin, I want to thank you for getting in here and sharing this information. I think many folks are anxiously waiting on this engine.

I think there are certainly concerns from the performance community around DI since it is something "new" to many folks. But as you pointed out, its been in the HO Ecotec and the V6 LFX already.

I think the biggest concerns I have heard so far has been around a concern that GM may lock the PCM. That has been one of the things that has driven GenIII/GenIV innovation. If you look at the aftermarket, once the software was avaliable to properly tune the PCM, the aftermarket really exploded.

I understand why Mfg's want to keep end users out of the PCM, but it certainly does limit innovation and improvements in the aftermarket. My hope is that GM does not stifle innovation in this new platform.

From a purely engineering standpoint its a pretty incredilble piece of engineering.

SSCamaro99_3

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The GM slide said "More than 26 mpg". What constitutes "more than" remains to be seen.

-TheBandit-

iTrader: (1)

Thanks for the reply. I was thinking along the lines of crankshafts, rods and pistons to understand if it might be possible to carry over a lot of the aftermarket stuff to the new engine without having to reinvent and re tool. As an example, aftermarket rods that were developed for the LS1 carried over to future incarnations, so we benefit from the wide range of applications.

With regards to the heads, I noticed they moved the locating dowels from the lower bolt holes to the upper bolt holes and eliminated all but the outside 2 small upper bolts.

I could see people throwing carburetors on these things (much to my chagrin) or fitting them with port injection and running Gen III/IV control systems, though I don't know how well the combustion system (chamber & piston design) would work with that since as you mentioned it is optimized for DI.

With regard to the cam, are you mostly concerned about the torsional flex of the cam when driving the HP pump? Or bending? I have a few ideas on how to get around that.

trumperZ06

Justin,

will the AFM system be deleted from the manual transmission... dry slump engines ?

If so... can we expect an increase in horsepower?

Also, will the open exhaust system (first seen on the C6-Z06) be available?

Horsepower increase

02sleeperz28

iTrader: (26)

Very interesting stuff.

Wnts2Go10O

iTrader: (12)

id bet that the heads will "interchange" just... you wont have the smaller bolts by the intake with the LT heads.

the BIGGEST issue with using an LT1 top end on an LSx is the mech fuel pump. how on earth would one go about retrofitting the injection system? (i REALLY want the LT1 top end)

a "reverse" ground cam wouldnt be hard. neither would using the older LS series computers (i dont think). retrofitting VVT would be pretty cool though.

i would also bet a big mod will be removing the piston oil squirters (i would look to GM for removing the squirters on later iterations that arent boosted).

Wnts2Go10O

iTrader: (12)

the mech fuel could possibly use a cam drive or belt drive pump... if theres one out there that can do ~2100 psi of fuel pressure.

Justin@GMHTP

iTrader: (1)

Having never tired it (obviously) I would think that the existing Gen 3/4 LSX crankshafts and connecting rods would swap over, although you would need to have a set of "DI specific" pistons built by your piston manufacturer of choice...

I do agree with you that we will probably see port fuel injection additions (keeping the DI and adding additional fuel with the other injectors), and even a carb swap or two, but I think the real interesting tech will come from people willing to really dig deep and push the limits of the DI. I think there will be more head room in DI than we expect but eventually it will become an issue. For example, we recently installed a IPF Supercharger system on a LFX V-6 2012 Camaro (DI and VVT) and picked up 129rwhp (285 to 414) and 100 lb-ft of torque (238 to 338) with 6 pounds of boost. No fuel changes made at all (except in the tune of course)... That's a 45-percent increase in power on the stock pump/lines/injectors, which is substantial.

J-Rod

JL WS-6 point out the cam issue in another thread. The issue lies in putting something at the rear of the engine that loads the cam. So, you end up with cam twist. If that pump puts a significant ammount of load on the rear of the engine, at higher rpm (7000), you could see issues with twist, cam timing, etc... You run into the issue today which is why you see Gen I SBC's move up to BBC cam journals, and BBC move up to 60MM cam journals. The Gen I SBC has an extremely small base circle, and for high RPM, or high lift you have to open the cam bore to get a bigger cam core.

My buddies 353" SBC has just over .800 lift (ex B/SM motor) at the valve and requries a bigger core for the lobes to obtain that lift, and also to keep the cam from twisting at 7800+.

So, the concern around the GenV is if you add a lot of load to the pump, to supply the fuel needed when you go for more power, what are the "unintended conequences" to the rest of the system.

dmaxvaz

iTrader: (1)

No issues, its high psi injection. Its been done on turbo ecotecs for years. Turbodiesels operate in the same manner, but at higher injection pressures.

-TheBandit-

iTrader: (1)

I couldn't find the thread you referred to, but I see your point on cam twist. I think one way to help with this would be to smooth out the fuel pumping by using more lobes that are smaller. That would at least prevent the peak twisting torque and pulsing. It would also push harmonics to higher frequencies which could help. If additional fuel is required, you could use a combination of more lobes with the same lift or smaller lift depending on what you need, but this is all subject to twisting the cam as you mentioned and whatever the fuel pump needs (don't know the mechanics of it). Solid core cams (non-VVT) may twist less.

Is there room in the block to bore out for larger cam bearings (and therefore a larger base circle cam)?

-TheBandit-

iTrader: (1)

High boost levels in diesel engines are also used for driving EGR. At least that was one of the key reasons for high boost when I was working at Garrett eight years ago.