have we all heard that GM is moving to a 2.5L 4 cyl to replace the 2.4?

if this is true will that be it's only "improvement"?

will it maybe be a SOHC with independent vvt?

will it get some other better tech?

make it HCCI future ready?

any ideas?

will it just be made to hit 200HP?

have we all heard that GM is moving to a 2.5L 4 cyl to replace the 2.4?

if this is true will that be it's only "improvement"?

will it maybe be a SOHC with independent vvt?

will it get some other better tech?

make it HCCI future ready?

any ideas?

will it just be made to hit 200HP?

No Info yet. But, if it's me, I'll do the following:-

• Chain Driven16-valves Overhead Concentric Cam (aka SOHC with independent VVT)
  
• 2-stage cam switching (Atkinson cycle at idle/low-loads, Otto Cycle at medium-high loads)
  
• Idle Stop-Restart Control using precision cam position sensor and stopping at TDC
  
• Homogeneous Charge Direct Injection
  
• 11.3:1 Compression (NA); 9.8:1 (Turbo)
  
• Garrett GT2252 Turbocharger @ 10.3 psi
  
• Dual Balance Shafts
  
• Ionic Knock detection (using spark plugs instead of acoustic sensors)
  

Naturally Aspirated Version Performance Targets

Oil Type: 0W-20 Mobil 1 Advanced Fuel Economy or 5W-20 DEXOS 1

Fuel Grade Target: 87 Octane Unleaded Gasoline Required

Output Target: 213 hp @ 6500 rpm

Torque Target: 193 lb-ft @ 4500 rpm

Rev Limit: 6600 rpm

Turbocharged Version Performance Targets

Oil Type: 0W-30 Mobil 1 Supersyn or 5W-30 DEXOS 1

Fuel Grade Target: 91 Octane Unleaded Gasoline Recommended

Output Target: 270 hp @ 6000 rpm

Torque Target: 240 lb-ft @ 1800~5800 rpm

Rev Limit: 6600 rpm

a 2.5l update with 200hp would be entirely appropriate.

No Info yet. But, if it's me, I'll do the following:-

• Chain Driven16-valves Overhead Concentric Cam (aka SOHC with independent VVT)
• 2-stage cam switching (Atkinson cycle at idle/low-loads, Otto Cycle at medium-high loads)
• Idle Stop-Restart Control using precision cam position sensor and stopping at TDC
• Homogeneous Charge Direct Injection
• 11.3:1 Compression (NA); 9.8:1 (Turbo)
• Garrett GT2252 Turbocharger @ 10.3 psi
• Dual Balance Shafts
• Ionic Knock detection (using spark plugs instead of acoustic sensors)

Naturally Aspirated Version Performance Targets

Oil Type: 0W-20 Mobil 1 Advanced Fuel Economy or 5W-20 DEXOS 1

Fuel Grade Target: 87 Octane Unleaded Gasoline Required

Output Target: 213 hp @ 6500 rpm

Torque Target: 193 lb-ft @ 4500 rpm

Rev Limit: 6600 rpm

Turbocharged Version Performance Targets

Oil Type: 0W-30 Mobil 1 Supersyn or 5W-30 DEXOS 1

Fuel Grade Target: 91 Octane Unleaded Gasoline Recommended

Output Target: 270 hp @ 6000 rpm

Torque Target: 240 lb-ft @ 1800~5800 rpm

Rev Limit: 6600 rpm

What fuel economy numbers would you be looking at Malibu (3,500) lbs, and Cruze (3,200) lbs?

What fuel economy numbers would you be looking at Malibu (3,500) lbs, and Cruze (3,200) lbs?

No miracles due or expected here... Probably around 22/35 on the NA engine -- which is about 3 mpg (city) / 5 mpg (hwy) better than current DOHC DI-VVT 2.4 in the Regal (which is about the same weight). Most of it due to the Atkinson cycle operation at low loads and steady state cruising. This is also about 1 mpg worse than the Honda Accord in the city, but 2 mpg better on the freeway -- which makes sense given that the Accord is 300 lbs lighter.

Expect to lose 1~2mpg on the turbo engine from the reduced compression and "shorty" intake.

That's lower performance than the Sonata Turbo

That's lower performance than the Sonata Turbo

I see you got the obligatory Sonata reference in there, that is now required for every new car thread...

That's lower performance than the Sonata Turbo

Different mission, different philosophy. The idea here is not to get the most power, but to have the broadest torque plateau, greatest linearity, highest efficiency, lightest weight and smallest engine package. To that end, boost is low, Intercoolers are small, compression is on the high side, the bore spacings are tight and cylinder walls are thin. The engine is destined mostly for FWD vehicles of modest mass. This means that a modest torque output is not necessarily a negative. Basically, you can think of the powerplant as a replacement for the 3.0 liter V6 -- same power, better economy, slightly more torque and greater linearity.

For high output turbocharged designs, I'll prefer the 2.0 liter displacement using the same block. The smaller combustion chambers are better for knock resistance. The thicker walls are better for strength. Power wise you can easily top 300bhp which is enough.

i like what you're thinking Dwight.

But if it can't out accelerate the Sonata Turbo, no one will buy it. Additionally, the Sonata Turbo's torque plateau starts at 1750rpm on 87 octane, so how much broader of a torque plateau are we talking?

That's lower performance than the Sonata Turbo

Well even Chuck Norris is lower performance than the Sonata Turbo

But if it can't out accelerate the Sonata Turbo, no one will buy it. Additionally, the Sonata Turbo's torque plateau starts at 1750rpm on 87 octane, so how much broader of a torque plateau are we talking?

It's not just the rpm at which maximum torque is reached, is how soon the plateau is reach after the driver applies throttle. It always takes longer to go from vacuum to 10 psi than it does to get to 18 psi at any rpm. The combination of higher static compression (9.8:1 vs 9.0:1) and lower boost makes for a more linear, more "NA like", engine.

We can easily make this a 312 hp engine with 280 lb-ft (limited by the torque capacity of the 6T70 transmission) by cranking up the boost to about 17.6 psi and swapping in a GT2560 turbo. But, it won't be as linear and as transparent as a low boost engine, and it will lose an mpg or two. Running 280 lb-ft through the front wheels also raises issues with torque steer and handling detriments. Again, because the 2.5T is destined as a family sedan V6 replacement, performance isn't exactly the most important thing here. Overall driving experience, practicality and economy trumps outright performance.

Um why 2.5? I mean GM has the 2.0L turbo that can make 290 hp with the GM performance parts module. Im sure if we subtract the turbo they can get it to hit 200 hp. I think GM has hit a time in history where they don't need more displacement to get more power.

Besides the 2.5 will be known forever as the iron duke.

For example look at these ratings from 78 I think we can do much better.

151 c.i. is = to 2.5L by the way...

without a turbo, generally the larger displacement, the lower rpm that torque becomes available.

Um why 2.5? I mean GM has the 2.0L turbo that can make 290 hp with the GM performance parts module. Im sure if we subtract the turbo they can get it to hit 200 hp. I think GM has hit a time in history where they don't need more displacement to get more power.

Besides the 2.5 will be known forever as the iron duke.

i know its possible for the 2.0 to have 200 horsepower, but realistically if they don't do two hundred with the 2.4 i doubt they will do it with a 2.0, and im beting this 2.5 will make about 215 hp or so

i know its possible for the 2.0 to have 200 horsepower, but realistically if they don't do two hundred with the 2.4 i doubt they will do it with a 2.0, and im beting this 2.5 will make about 215 hp or so

It's more than the fact that they won't do it or can't do it. It's also that most drivers won't appreciate a 100hp/liter NA engine very much. In general, the amount of of torque you are going to get out of a liter maxes out at 75~78 lb-ft per liter even with direct injection and lofty compression. There is not a lot you can do about that. It means that you'll have to rev it into the stratosphere to get power to 100 hp/liter. You'll need to be making 140 lb-ft, at 7500 rpm to generate 200hp. To do that, you'll probably have to hit your 150~156 lb-ft peak no earlier than 1500~2000 rpm before that. 200hp @ 7500 rpm + 156 lb-ft @ 6000 rpm... might be nice in a sporty car, but will also be a rather frustrating engine for average family sedan. Not to mention, the current breed of GM 6-speed automatics have a maximum shift speed of 7000 rpm, meaning you need a new family of high rpm compatible transmissions.

Making 170hp on 2.0 liters or 200 hp on 2.5 liters allow you to have a more palatable power delivery. Probably something like 170hp @ 6600 rpm + 150 lb-ft @ 5000 rpm & 200hp @ 6400 rpm + 187 lb-ft @ 4800 rpm respectively. It'll also be compatible with the 6L45, 6T40 and 6T70 transmissions.

Edited November 13, 201015 yr by dwightlooi

You make some very good points...

I guess I think It is wasteful to make a new engine instead of improving what they already have like the 2.2 2.4 2.0 and the 1.8 im sure that 1.8 has some hidden ponies as well.

The 2.5 is probably just a 2.4 with a slightly longer stroke and improved valve timing.

The 2.5 is probably just a 2.4 with a slightly longer stroke and improved valve timing.

The current 2.4 has an 88mm bore x 98mm stroke. It also has a 96mm bore center.

What this means is that there is basically no room for the engine to be bored out any further. Stroking out the already pretty long stroke will also make the stroke overly long.

Maybe just rounding up then, to make the next version sound new.

The current 2.4 has an 88mm bore x 98mm stroke. It also has a 96mm bore center.

What this means is that there is basically no room for the engine to be bored out any further. Stroking out the already pretty long stroke will also make the stroke overly long.

How much is the minimum bore increase + minimum stroke increase that would accomodate a 0.1 liter increase in displacement, and do you think it's doable?

we need to look ahead to the 2013/2014 time frame..

200hp and 200tq should not be unreasonable, and by that, i also mean with a somewhat flat torque curve......

How much is the minimum bore increase + minimum stroke increase that would accomodate a 0.1 liter increase in displacement, and do you think it's doable?

2mm bore increase or 5mm stroke increase or some partial combination thereof.

2mm bore increase is practically out of the question. The 96mm bore center means that the cylinder walls will be a mere 6mm thick. That's really thin, even the current 8mm is considered thin -- too thin for any significant amount of forced induction.

103 mm stroke is OK, but with an 88 mm bore it'll also make for a very long stroke engine. hp/liter will be poor, energy recovery might be better but if that is what you are trying to achieve an Atkinson cycle cam is probably the better way to go.

It's more than the fact that they won't do it or can't do it. It's also that most drivers won't appreciate a 100hp/liter NA engine very much. In general, the amount of of torque you are going to get out of a liter maxes out at 75~78 lb-ft per liter even with direct injection and lofty compression. There is not a lot you can do about that. It means that you'll have to rev it into the stratosphere to get power to 100 hp/liter. You'll need to be making 140 lb-ft, at 7500 rpm to generate 200hp. To do that, you'll probably have to hit your 150~156 lb-ft peak no earlier than 1500~2000 rpm before that. 200hp @ 7500 rpm + 156 lb-ft @ 6000 rpm... might be nice in a sporty car, but will also be a rather frustrating engine for average family sedan. Not to mention, the current breed of GM 6-speed automatics have a maximum shift speed of 7000 rpm, meaning you need a new family of high rpm compatible transmissions.

Making 170hp on 2.0 liters or 200 hp on 2.5 liters allow you to have a more palatable power delivery. Probably something like 170hp @ 6600 rpm + 150 lb-ft @ 5000 rpm & 200hp @ 6400 rpm + 187 lb-ft @ 4800 rpm respectively. It'll also be compatible with the 6L45, 6T40 and 6T70 transmissions.

well, that was what i was getting at, if they have the power band too high in the 2.4 for it to be a nice drive, it would be that much higher in a 2.0, and you would have to wind it to ninety-million rpm to get any power out of it

Edited November 21, 201015 yr by CanadianBacon94

A few things...

(1) First of all, I fail to see why getting from 2.4 to 2.5 liters is that important that GM needs to bend over backwards to do it. The power/torque difference between a 2.4 and 2.5 mill is negligible.

(2) If they REALLY want to do it without a completely new block (different bore centers) they can probably bore the engine out from 88 to 89mm (7mm wall thickness; same as LS7) and lengthen the stroke from 98 to 100 mm. This will yield a displacement of 2.488 liters.

(3) If it's me, I'll actually drop the displacement from 2.4 to 2.1 liters. The resulting engine -- in NA and turbo trims -- can then be used to replace the 1.8, 2.0, 2.2, 2.3 and 2.4 liter power plants. I'll use the following dimensions:-

• Bore Center: 98 mm (+2mm)
  
• Bore x Stroke: 89 mm x 85.6 mm (Same bore size as 3.0 DI V6; same stroke as 3.6 DI V6)
  
• Displacement: 2130 cc (Good median displacement for replacing 1.8 through 2.4 engines)
  
• Compression Ratio (NA): 11.7:1 (Same lofty compression ratio as 3.0 DI V6 using 87 octane)
  
• Compression Ratio (Turbo): 9.7:1 (0.5 points higher than LNF 2.0T)
  

(4) The idea here is that the pistons, valves, valve springs, lifters, seats and guides are the same ones as those used in the 3.0 DI V6. The connecting rods are shared with the 3.6 V6. This offers a great degree of logistical commonality. Using the same piston and combustion chamber geometry as the V6 also means that we can achieve a very predictable output from the engine with minimal R&D. This will be pretty decent at between 84 and 90 bhp per liter on 87 octane naturally aspirated -- more than enough to be competitive. Add a turbo and you will be pushing 300bhp easily.

• NA Power: ~185 bhp @ 6800 rpm
  
• NA Torque: ~170 lb-ft @ 4800 rpm
  
• Turbo Power*: ~320 bhp @ 6000 rpm
  
• Turbo Torque*: ~280 lb-ft @ 2600 rpm
  

* Premium 91 Octane Recommended (not required)

Edited November 21, 201015 yr by dwightlooi

If only GM did something like that. Although 320 is optimistic out of a 2.1 T and try to keep some reliability. High boost isn't the best thing for engines.

Dwight, since you bring the 2.1 L displacement - what if we reduce the 4.3L Atlas I6 into three cylinder model and apply DI, VVT with another optional turbo engine?

Dwight, since you bring the 2.1 L displacement - what if we reduce the 4.3L Atlas I6 into three cylinder model and apply DI, VVT with another optional turbo engine?

It'll do well efficiency wise -- because you'll have 12 valves instead of 16, 3-cylinders instead of four. But, it'll be somewhat lacking in refinement. A 3-potter is 1st order unbalanced. You can cancel most of that out with a balancer. The key word here is most, a because two rotating shafts (the crank and the balancer) cannot match and cancel a non sinusoidal reciprocating mass shift 100%. 3-potters are tolerable unbalanced up to 1.0~1.3 liters. A balancer may make a 1.3~1.8 liter somewhat palatable. I am not so sure about a 2.1 liter-- especially one based off the Vortec 4200 which has a pretty long 103mm stroke.

But really though... if we want to shoot for minimum parasitic efficiency losses, I'll go SOHC or Concentric Cam before I build a very big 3-pot. It's a lower hanging fruit. I'll also make a 1.5 or 1.8 3-potter based off the HF V6 rather than a 2.1 liter based on the I6.

Edited November 23, 201015 yr by dwightlooi