[SpeedIsLife]

Large displacement+high revving+N/A=Emissions Hell

It was a challenge for Ford to get the 5.2 Voodoo to pass emissions at 5.2L and 526 HP...I doubt an even larger engine could do it..but I could be wrong.

[DGthe3]

Originally Posted by SpeedIsLife

Large displacement+high revving+N/A=Emissions Hell

It was a challenge for Ford to get the 5.2 Voodoo to pass emissions at 5.2L and 526 HP...I doubt an even larger engine could do it..but I could be wrong.

But a large displacement engine doesn't need to rev as high as a small engine to make the same kind of power. It also doesn't need to go as aggressive with things like cam profile to make that power.

[SpeedIsLife]

Originally Posted by DGthe3

But a large displacement engine doesn't need to rev as high as a small engine to make the same kind of power. It also doesn't need to go as aggressive with things like cam profile to make that power.

The kind of motor some of the folks were talking about is a high revving motor, IE probably 7,000+.

It just seems like they're not taking production reality and regulation into account, especially since these motors will have to meet future emissions goals, not just current.

[whiteboyblues2001]

Originally Posted by SpeedIsLife

Large displacement+high revving+N/A=Emissions Hell

It was a challenge for Ford to get the 5.2 Voodoo to pass emissions at 5.2L and 526 HP...I doubt an even larger engine could do it..but I could be wrong.

Can you provide an explanation of why large displacement and high revving has a negative effect on emissions, and how FI doesn't have the same issues? Or at least a reference I can read. I have never found any information on this subject.

[HumanWiki]

Originally Posted by whiteboyblues2001

Can you provide an explanation of why large displacement and high revving has a negative effect on emissions, and how FI doesn't have the same issues? Or at least a reference I can read. I have never found any information on this subject.

http://www.driverside.com/auto-libra...el_economy-317

http://www.caranddriver.com/features...ration-feature


There's stuff related to volumetric efficiency and that an NA motor has to pull air in from ambient at whatever the pressure and density is. While an FI motor is force-fed. You can make a smaller motor have the power of a larger one, because your VE goes over 1 (or 100%) and you're no longer relying on just suction on the intake stroke + some other stuff that goes on and listed in the link above and get some of the better fuel of the smaller NA motor. There's trade off in there, but you'll notice more and more places going to smaller motors with turbos since you'll get the power, plus you're re-using wasted heat energy to provide some of your power that would otherwise be robbed from the crank to turn a belt/gear for a supercharger.

[USP45]

In my perfect world both the Grand Sport and the Z/28 would have a naturally aspirated engine in the 550hp range... Personally I think that the GS would be better than it already is (not that is a slouch now) and the Z/28 would be nicely positioned in between the 1LE and the ZL1 with such an arrangement. Maybe stick with the 6.2 liter displacement, but increase rpm's to somewhere in the 7500 range. Not that GM cares about my 2 cents!

[whiteboyblues2001]

Originally Posted by HumanWiki

http://www.driverside.com/auto-libra...el_economy-317

http://www.caranddriver.com/features...ration-feature


There's stuff related to volumetric efficiency and that an NA motor has to pull air in from ambient at whatever the pressure and density is. While an FI motor is force-fed. You can make a smaller motor have the power of a larger one, because your VE goes over 1 (or 100%) and you're no longer relying on just suction on the intake stroke + some other stuff that goes on and listed in the link above and get some of the better fuel of the smaller NA motor. There's trade off in there, but you'll notice more and more places going to smaller motors with turbos since you'll get the power, plus you're re-using wasted heat energy to provide some of your power that would otherwise be robbed from the crank to turn a belt/gear for a supercharger.

Thanks, but your explanation and articles are about Fuel Efficiency, I was asking about emissions.

But since we are on the subject, volumetric efficiencies don't add up to better fuel efficiency in the real world. For example, the first article mentioned "Newer turbocharged engines are much more efficient than those from previous generations. That means a smaller displacement engine can generate more power and use less fuel than one without a turbo."

That statement is not true.

Yes, a smaller displacement turbo engine can produce more power than a N/A motor OF THE SAME DISPLACEMENT, but not of one that is of larger displacement necessarily. The LT1 produces more power than any of these 2.0L Turbos on the market. But it will be less fuel efficient.

Instead of holding displacement constant, look at engines that produce the same power (approximately). For example, the M4 and ATS-V produce similar power numbers than the Camaro, and they have similar performance numbers, but the Camaro has significantly better fuel efficiency: M4 = 425HP with 17/24 MPGs, ATS-V (auto) = 464HP and 16/24 MPGs, Camaro (auto) = 455HP with 17/28.

I know there are many other factors including aero, rolling resistance, gearing, etc., but my point is valid. In order to produce X amount of power, you are going to have to burn Y amount of air/fuel mixture in Z amount of time NO MATTER HOW you got it into the cylinder (FI, N/A, or High Revs). In fact the biggest difference factor for the ATS-V vs. Camaro is the ATS-V has shorter final gearing. Change that, and the performance gap and efficiency gap will both get closer.

The big difference back in the day was two fold. 1. You need a minimum amount of air/fuel just to keep the engine running and producing a minimal amount of torque (I'm talking about cruising down the highway), and that was directly proportional to the displacement. Larger displacement meant larger amount of minimum air/fuel, and worse highway MPG's. But with direct injection, you can go into "ultra lean mode" and use significantly less air/fuel to produce minimal torque for cruising down the highway. Add cylinder deactivation, and you can get competitive highway MPG's for a large displacement engine. 2. In order to reduce turbo lag, many engines have gone with multiple turbos, larger turbos with a waste gate, extra plumbing for an intercooler, etc. These things work as designed, and help reduce turbo lag, but they do it by putting more air/fuel mixture in the cylinder. Plus that just adds back weight that was saved by going lower displacement. Not saving MPG's now though...

So, yes, in the old days a smaller displacement engine with a turbo was more Fuel Efficient, but not so much anymore.

Most car manufacturers are going with smaller displacement turbos to help consumers who live where there is a displacement tax. Not for fuel efficiency.

[HumanWiki]

So, with all of that knowledge already, it wasn't a possible step in thought that the word emissions in this case was used with regard to the EPA ratings on a vehicle to help with the overall fleet mileage ratings and not a literal meaning of the gasses being expelled post catalyst? It's quite possible it was a literal meaning of the exhaust gas composition, I don't know since I didn't write the comment. I was only answering with links as requested to what I'd read and interpreted as meaning.

[whiteboyblues2001]

Originally Posted by HumanWiki

So, with all of that knowledge already, it wasn't a possible step in thought that the word emissions in this case was used with regard to the EPA ratings on a vehicle to help with the overall fleet mileage ratings and not a literal meaning of the gasses being expelled post catalyst? It's quite possible it was a literal meaning of the exhaust gas composition, I don't know since I didn't write the comment. I was only answering with links as requested to what I'd read and interpreted as meaning.

The original comment was:

"Large displacement+high revving+N/A=Emissions Hell"

I assumed that emission meant exactly that, because if you have a specific HP goal, going FI or N/A will have a negligible effect on efficiency.

Also, the fuel efficiency regulations in the US are CAFE which is an average. They won't sell enough Z/28's or Z06's to worry about that, and even if it doesn't meet the standard, you just have to pay a gas guzzler tax. In the end, you can still produce the car.

Emissions is another story, it is not an average across many vehicles, and there is no extra tax for too much emissions. Too much emissions = no such car.

But how emissions are effected by FI vs. N/A, I don't know. GM stated that they were working on an N/A engine for the Z06, but it couldn't meet their emissions goals, so they went with FI. I tried to look into that statement, and haven't found any material to explain that phenomenon.

I personally suspect that GM was going with a 7.0L engine with DI and VVT, but couldn't meet HP requirements NOT emission requirements. They used the emissions excuse because implies that it wasn't their engineering that was at fault or their decision, but strict government regulations. (remember, blame is better to give than receive). If they said they wanted more HP, so they went with FI, many buyers would say, "so produce it N/A with less HP, we don't care if it's 550HP instead of 650HP, we want N/A for the track". But that is pretty wild speculation on my part.

In the mean time, I would like to find a technical (but not too technical) explanation of how FI is more emissions friendly than N/A.

[Bhobbs]

GM said it couldn't meet emissions regulations, or their durability standards or power goals.

They wanted to keep VVT, AFM and DI, so they probably had a hard time keeping the AFM lifters in one piece, while spinning the engine hard enough to make the power. At least, that's my guess.

F/I isn't always more efficient than n/a. F/i can be more efficient if you are using a smaller engine and not making boost. Without the boost, the engine will take in less air and burn less fuel. The issue is you are not making the same power. F/i does well in mileage testing because they don't stay in boost, so it uses less fuel. In real world, people are used to the power, so they keep the boost up and use more fuel than advertised.

[whiteboyblues2001]

Originally Posted by Bhobbs

GM said it couldn't meet emissions regulations, or their durability standards or power goals.

They wanted to keep VVT, AFM and DI, so they probably had a hard time keeping the AFM lifters in one piece, while spinning the engine hard enough to make the power. At least, that's my guess.

Thanks for the info! That explains much.

In your opinion, how high is the rpm requirement if we assume a 7.0L with VVT, DI, and we wanted to make 550HP?

[whiteboyblues2001]

Originally Posted by Bhobbs

F/I isn't always more efficient than n/a. F/i can be more efficient if you are using a smaller engine and not making boost. Without the boost, the engine will take in less air and burn less fuel. The issue is you are not making the same power. F/i does well in mileage testing because they don't stay in boost, so it uses less fuel. In real world, people are used to the power, so they keep the boost up and use more fuel than advertised.

Agreed, and on top of the fact that turbos have inflated EPA numbers compared to real world, those EPA numbers are still worse than similar HP N/A motors in many cases.

[Bhobbs]

Originally Posted by whiteboyblues2001

Thanks for the info! That explains much.

In your opinion, how high is the rpm requirement if we assume a 7.0L with VVT, DI, and we wanted to make 550HP?

GM engines generally don't make peak power at peak RPM. The LS7 made peak power at around 6500 rpm, but still spun north of 7k. With the addition of DI, I don't think they would have to spin it much faster than 6500 rpm to make their goal. If they can't make a 7 liter work, they might have to spin higher, for a 6.2 or some other displacement.

[fradaj]

Originally Posted by whiteboyblues2001

Agreed, and on top of the fact that turbos have inflated EPA numbers compared to real world, those EPA numbers are still worse than similar HP N/A motors in many cases.

One of the advantages of the turbo is torque at low RPM. Some of the new turbo motors have almost their maximum torque right above idle and it stays flat almost to redline.