we really do have a state of the art engine

George

Original poster
Member
Dec 8, 2011
57
View attachment 19056

More than 1 hp per cubic inch. Mention that phrase to Chevrolet enthusiasts and you'll probably hear about early Z/28 engines, fuel-injected 327s, and a few big-blocks. But Chevrolet has a completely new engine that not only delivers that kind of power, but also does it with fuel-efficient performance and unmatched smoothness. The engine is called the Vortec 4200 I6 and was initially created for General Motors midsize sport utility vehicles. Chevrolet engineers created a 24-valve, dual overhead cam, all-aluminum straight-six that produces 270 hp from 256 cubic inches, with 90 percent of its torque coming in from 1,600 to 5,600 rpm.

Variable-Valve Exhaust Timing

One of the most interesting aspects of the Vortec 4200 I6 is what's called variable-valve exhaust timing. This feature adjusts the exhaust camshaft timing within a range of 25 degrees as engine operating conditions change. To do that, an onboard computer first collects several points of data including throttle position, engine load, and vehicle speed. From there, a control valve adds or removes oil from a cavity and piston chamber at the front of the camshaft. Thus, advancing or retarding the exhaust camshaft not only enhances the torque curve, but also improves idle quality and reduces emissions. With the ability to change timing, a more aggressive camshaft profile can also be used.

Mass Reduction

To increase casting accuracy and minimize engine weight, the aluminum block and cylinder head of the Vortec 4200 I6 are made using a lost foam process. This casting technology provides both improved control of the manufacturing process and allows direct-mounted accessories that reduce vibration and weight. With the exception of the power-steering pump bracket, all engine accessories bolt directly to the engine.

Coil-on-Plug Ignition

The 4200 I6 ignition system employs an electronic spark-control system that uses no moving parts and does not necessitate timing adjustments. This coil-on-plug system delivers a high-energy spark for a cleaner and more consistent combustion. This contributes to increased engine efficiency, improved fuel economy, and better performance, and eliminates the use of spark-plug wires. The ignition system also utilizes a crank and camshaft-position sensor for accurate engine-condition monitoring and added reliability. If one sensor fails, the engine can continue to operate, but the computer will activate the check engine light to alert the driver of a component failure.

Advanced Powertrain Control

The Vortec 4200 uses an engine-mounted electronic Powertrain Control Module that records hundreds of measurements per second and makes immediate adjustments of air, fuel, spark control, and valve timing to provide optimal engine operation.

Electronic Throttle Control

To eliminate the mechanical link between the accelerator pedal and throttle, the Vortec 4200 uses an electronic throttle control (ETC). The ETC sends a series of signals from an accelerator-pedal module using a sensor that relays acceleration-intent data to the powertrain control module (PCM). The PCM then signals an electric motor to position the throttle to match the drivers intent.

Compression

The Vortec 4200 has a 10:1 compression ratio that helps it achieve impressive power levels. The engine produces 90 percent of its torque from 1,600 to 5,600 rpm running on unleaded fuel. This is due in part to good combustion-chamber design and the cylinder heads ability to efficiently transfer heat.
 

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Juicy K

Member
Feb 14, 2012
433
Indianapolis, Indiana
I just know I love the smoothness of the 4200, the fact its a Mass Produced American Twin Cam engine, Seems like we are the only ones still producing push rod engines. For an American engine of this displacement it makes decent power. I remember driving my moms 4.3L 95' Blazer and it was a pig compared to the lovely I6, and it got worse gas mileage.

The first thing back in High School that turned me on to the new Trailblazer was this engine. First time I drove one was back in 2007, I liked them more, until the Test Drive of our Bravada... Then I was in love.


I just wish production would have continued for this engine. In my opinion its one of GM's great engines. I know I could get more power out of the V8, but this engine is so damn great. It really does not bother me that there was not a V8 option for the Bravada. Maybe an SS equivalent with an LS2 would have been cool. But I am fully content with my I6.:cool:
 

Wyle

Member
Dec 4, 2011
200
nice artwork.
 

MedicatedMike

Member
Feb 24, 2012
101
lol, I had sooooo many blazers, trucks, and even a van wit the 4.3. Loved everyone. Those engines were nearly indestrucable and always heard they were the 350 block without the last 2 cylinders, and a 350 was indestrucable, at least for me.

Anyways, neat post, especially the artwork! Thanks for sharing George! :thumbsup:
 

400Magnum

Member
Dec 23, 2011
49
Well, just to give myself a little pat on the back, I'd like to just comment that I was the designer for the intake manifold. I spent over a year of my life mostly focused on just that one part, and of course all the associated pieces, the cover, the insulating liner, etc. The guy on one side of me did the oil pan, the guy on the other side of me did the exhaust manifold, the guy behind me did the throttle body. We were a tight knit little group back in the day, which seems like it's been ages ago.

The engineers had even bigger plans for this engine, but the bean counters canned a lot of stuff just because of costs.
 

Juicy K

Member
Feb 14, 2012
433
Indianapolis, Indiana
400Magnum said:
Well, just to give myself a little pat on the back, I'd like to just comment that I was the designer for the intake manifold. I spent over a year of my life mostly focused on just that one part, and of course all the associated pieces, the cover, the insulating liner, etc. The guy on one side of me did the oil pan, the guy on the other side of me did the exhaust manifold, the guy behind me did the throttle body. We were a tight knit little group back in the day, which seems like it's been ages ago.

The engineers had even bigger plans for this engine, but the bean counters canned a lot of stuff just because of costs.

Myself and other im sure are curious as to what the bigger plans were. :undecided:
 

ScarabEpic22

Member
Nov 20, 2011
728
Well actually producing a twin turbo version would have been SICK and probably one of the things that got axed. I like the shaving of cylinders to get the I4 and I5 for the GMT355s too.

I keep dreaming about a TT I6 with a forged bottom end and drop the CR to like 9-9.5:1. Think 10-14psi of boost minimum with a late head + cam set would be good for at least 400rwhp. Probably 450ish though. :eek:
 

400Magnum

Member
Dec 23, 2011
49
There was a lot of plans that we designers weren't even told about. One thing that the engineer mentioned to me was the possibility of a turbo, and they had initially wanted to be able to do a larger displacement version, thinking that it'd be the base model engine in the full size trucks. But, typically, all we ever really heard from the engineer was "#$%& budget won't let us do anything fun!"
 
Jan 2, 2012
72
Someone is rolling around with the TT I6 concept out there. I think this was talked about before on the "forum who will not be named." What we need to do is track down this TB if it's still around and copy the s**t outta the setup. There's enough ppl out there who have been working with the I6's and tuning where someone could def come up with some kinda kit for it.
 

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limequat

Member
Dec 8, 2011
519
I'd like the inside scoop on a couple things. Dunno if you heard people talk, but...

1) Is it true that engine speed is limited to 6200 RPM due to crank harmonics?
2) Why are the cam drive gears so friggin huge?
3) How much boost can the plastic intake manifold take?
4) Do you still have access to the 3d models of any of this?
 

limequat

Member
Dec 8, 2011
519
xx_gearhead_xx said:
Someone is rolling around with the TT I6 concept out there. I think this was talked about before on the "forum who will not be named." What we need to do is track down this TB if it's still around and copy the s**t outta the setup. There's enough ppl out there who have been working with the I6's and tuning where someone could def come up with some kinda kit for it.

I'm on it :wink:

Actually, if you have a 2006+, you can buy everything electrical you need to run a turbo on lime-swap.com: reflash, injectors, injector harness. Just need to weld up some pipes at that point. Even 2002-2005 could run the 2006 PCM, but you'd have to splice in the right connectors.

I'm planning on developing an up-pipe that will the stock exhaust manifold to an easily obtainable junkyard turbo. Stay tuned!
 

limequat

Member
Dec 8, 2011
519
400Magnum said:
There was a lot of plans that we designers weren't even told about. One thing that the engineer mentioned to me was the possibility of a turbo, and they had initially wanted to be able to do a larger displacement version, thinking that it'd be the base model engine in the full size trucks. But, typically, all we ever really heard from the engineer was "#$%& budget won't let us do anything fun!"

I had speculated that much. The 4.2's bore is pretty narrow compared to its stroke. The 4 and 5 cylinders got the bigger bore in 2007. They probably got the big pistons that were slated for what would have been the 4.4l I6 to launch in the 2007 full size pickups. The good news is that anybody can create this engine using 3700 Colorado liners and pistons.
I suspect that you could go even further. A square I6 would be 102mm B & S. Exactly 5 liters. Pure speculation, but the idea of a modern 5 liter straight 6 makes me weak in the knees.
 
Jan 2, 2012
72
Now your talking! I imagine with a setup like that with the bigger pistons alone you could get into 330+hp range easily. Much less with a fi setup, then you could start surpassing many of the newer V6's. This engine has soo much potential that hasn't even been uncovered yet. I'm glad there are such dedicated mechanics and engineers out there to keep things like this going.
 

Jkust

Member
Dec 4, 2011
945
I never quite got the why the I6 was developed for this truck. The V8 does everything at least as good and the mileage is nearly identical albeit more money to have bought when new. Maybe not as smooth obviously given the V set up on the v8 but other than that why spend the money to develop it? I've gotta think GM spent a bundle on it. I get that time moves on and technology does too but all that work for one platform to receive it in its 6 cylinder format. Were they just ahead of their time or developing for the sake of developing something to replace the 4.3. By the way the 4.3 is still sold in brand new boats since it has huge torque across the spectrum when marinized.
 

limequat

Member
Dec 8, 2011
519
Jkust said:
I never quite got the why the I6 was developed for this truck. The V8 does everything at least as good and the mileage is nearly identical albeit more money to have bought when new. Maybe not as smooth obviously given the V set up on the v8 but other than that why spend the money to develop it? I've gotta think GM spent a bundle on it. I get that time moves on and technology does too but all that work for one platform to receive it in its 6 cylinder format. Were they just ahead of their time or developing for the sake of developing something to replace the 4.3. By the way the 4.3 is still sold in brand new boats since it has huge torque across the spectrum when marinized.

Keep in mind, when this engine was developed, the Gen 3 v8 wasn't available in trucks. The 360 team was given a clean sheet and they decided that the straight six was the best compromise for power, manufacturability, and cost. Compard to the v8, 2 less rods, pistons, 1 less head, 1 less exhaust manifold. The I design allowed them to mount the PCM on the engine for reduced harness complexity. I have to believe that the I6 is cheaper than a V8.

Why not the 4.3? Because it's an uncompetitive turd (I own one, I can say it). Sure its fine for a boat or a cargo van, but GM was trying to make a splash in what was then the fastest growing market: midsize SUVs.
 

Jkust

Member
Dec 4, 2011
945
limequat said:
Keep in mind, when this engine was developed, the Gen 3 v8 wasn't available in trucks. The 360 team was given a clean sheet and they decided that the straight six was the best compromise for power, manufacturability, and cost. Compard to the v8, 2 less rods, pistons, 1 less head, 1 less exhaust manifold. The I design allowed them to mount the PCM on the engine for reduced harness complexity. I have to believe that the I6 is cheaper than a V8.

Why not the 4.3? Because it's an uncompetitive turd (I own one, I can say it). Sure its fine for a boat or a cargo van, but GM was trying to make a splash in what was then the fastest growing market: midsize SUVs.

When was the v8 available in the EXT version...was it model year 2002 or 2003? The SWB Rainier got it in 2004's sold in calendar year 2003. I get the alure of newer technology and the need for a 6 cylinder as an offering and that the 4.3 was old school and lacking HP but would presume you opt for a 6 cylinder for substantially better mileage combined with that better technology in exchange for a little less power if naturally aspirated. I realize a v8 works less and so an I6 would have to lean on its technology to attain that substantially better mileage that it doesn't achieve. I'd have thought the V8 would be substaitnally less money if GM never spent money developing the I6 in the first place. Had GM put the 4.2 in a bunch of other vehicles where it was say the most powerful option, I could understand but to me the engines are close enough that they cannibalize eachother and would have had to charge more for a v8 that you could buy on every street corner so to speak (I realize our platform's 5.3 is slightly different than other truck's 5.3's) . If the platform never received the v8 option, and you never experienced how much better the v8 can tow heavy things, I'd understand a bit better. Sort of look at this great new engine we have developed and please ignore the 'better at everything but mileage' engine behind the curtain.
 

400Magnum

Member
Dec 23, 2011
49
limequat said:
I'd like the inside scoop on a couple things. Dunno if you heard people talk, but...

1) Is it true that engine speed is limited to 6200 RPM due to crank harmonics?
2) Why are the cam drive gears so friggin huge?
3) How much boost can the plastic intake manifold take?
4) Do you still have access to the 3d models of any of this?

1. I don't know why the engine speed is limited, because they had a few of these engines running on the dyno's downstairs and a few of them were literally screaming 24/hrs a day for days on end, it was like listening to jet engines at times. Others were run thru a lot of cycles simulating "normal" driving. In short, I don't know the answer to your question. I'd like to say that the production engines can rev higher safely, but I can't because I also know that the engines they had on the dyno's were special prototypes, which sometimes had special internal parts with the intention of pushing other parts harder than they would see in normal use just to make sure that the warranty issues would be as minimal as possible.
2. Sorry, can't answer this one either.
3. At the time, I think they did a burst test well into double digits, but I can't remember a specific number. It's been almost 14 years ago since I worked at GM.
4. Sadly, no, I don't have access to the models anymore. All the guys that I used to know and work with have been scattered into other groups and a lot of them have been "relieved of their duties" so I don't know anyone on the inside anymore that could even acquire the models for me.

Jkust said:
I never quite got the why the I6 was developed for this truck. The V8 does everything at least as good and the mileage is nearly identical albeit more money to have bought when new. Maybe not as smooth obviously given the V set up on the v8 but other than that why spend the money to develop it? I've gotta think GM spent a bundle on it. I get that time moves on and technology does too but all that work for one platform to receive it in its 6 cylinder format. Were they just ahead of their time or developing for the sake of developing something to replace the 4.3. By the way the 4.3 is still sold in brand new boats since it has huge torque across the spectrum when marinized.

Actually, the straight six is naturally balanced (theoretically) than the V8, so they don't have to spend as much effort/time/money/expertise to get the actual engine balance of the I6 as smooth as the V8. Yes, they spent a bundle on it, but like I mentioned, at the time I think they were expecting it to eventually make it into more platforms, so they wanted to "get it right" as much as possible up front, rather than release it for one platform and realize that it wasn't going to be suitable for the next application and require a massive redesign, which would cost more in the long run. So, yes, they were trying to think ahead, but even back then the signs of the economy taking a downturn were beginning to show up and future plans were axed almost as fast as they were thought of.

limequat said:
Keep in mind, when this engine was developed, the Gen 3 v8 wasn't available in trucks. The 360 team was given a clean sheet and they decided that the straight six was the best compromise for power, manufacturability, and cost. Compard to the v8, 2 less rods, pistons, 1 less head, 1 less exhaust manifold. The I design allowed them to mount the PCM on the engine for reduced harness complexity. I have to believe that the I6 is cheaper than a V8.

You are exactly right, it was all a matter of getting the most power and efficiency for the manufacturing dollar. One head for the I6 is cheaper to manufacture than two heads for a V8. Keep in mind that there is more to a part than just the one that you bolt onto the car. For instance, one head is cheaper to cast and machine and inventory (one less casting part number, one less machined part number, one less assembly part number) than for a V8. And, it's easier to machine the block for one intake/exhaust manifold and have everything seal better just because they're flat surfaces. Plus, inline vertical engines have a consistently good track record for durability and low wear. So, for a given displacement, the inline engine will always be cheaper to manufacture and maintain than a V8 all things being equal.
 

Menthol

Member
Dec 8, 2011
177
400Magnum said:
Well, just to give myself a little pat on the back, I'd like to just comment that I was the designer for the intake manifold. I spent over a year of my life mostly focused on just that one part, and of course all the associated pieces, the cover, the insulating liner, etc. The guy on one side of me did the oil pan, the guy on the other side of me did the exhaust manifold, the guy behind me did the throttle body. We were a tight knit little group back in the day, which seems like it's been ages ago.

The engineers had even bigger plans for this engine, but the bean counters canned a lot of stuff just because of costs.

Who was the guy that designed where to put that bottom bolt on the alternator.....let me at him :biggrin:
 
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