Just chiming in,


The points expressed in this thread are certainly indicative of very intelligent and technically orientated-individuals.


M&M has a valid point about the throttle response on N/A cars being better, I would have to agree that it is better despite evidence to the contrary.

On the move, the gearing of a car and its engine displacement/configuration will also have a great, contributory effect on the perceived throttle response. M&M's M3 has undoubtedly a set of very high gear ratios that spin the engine much more viciously than in the comparable AMG 5-speeder or 7G Tronic. This, in addition to the very,very linear torque curve of a good N/A engine, one that is low in displacement with piston sizes designed for high revving results in much better throttle response. The flywheel, piston material and weight also contribute to better throttle response.

The AMG supercharger is not permanently connected, it is load dependent. At low engine speeds and on light throttle, the supercharger is disconnected. However, upon the subjection of high loads and always above 2500rpms, the supercharger is connected "instantaneously" via an electro-magnetic clutch. One indication of the slightly, apparently unlinear throttle response of FI cars can be attributed to the torque curve. You will see that the AMG 55K's torque curve is very much like an ordinary, 5.0L Mercedes V8 one, just much, much more of it. This is also indicative of the benefits of supercharging over turbocharging. With the supercharger attached to the flywheel, torque is dependent entirely upon throttle response. With turbocharged cars it is the same, however, it is the exhaust gases after combustion that decide the torque, which inevitably causes some delay if the turbo's are huge and the engine is small (see the typical 911 Turbo delay).
With longer gearing and perhaps obviously, the use of a large displacement engine, which causes the pistons to have to travel further, throttle response can be delayed by such variables.

In conclusion, I would add that the displacement, piston weight, engine configuration, are (inter alia) variables that affect the throttle response. FWIW, I am very much a fan of large-displacement, N/A engines and I hypothesise cars which will receive the 6.3 V8 in unmolested form, will be very good to drive.

 

You have the right idea but possibly not quite the right implimentation. For example, a larger displacement engine does not always mean the pistons travel farther. An increase of the bore alone will increase displacement. Also, are you implying that the increase in stroke (pistons traveling farther as you say) will casue throttle lag? Your comments are not clear. However, increasing the stroke will increase piston speed at any RPM and create more suction. More suction means higher vacuum at idle and improved throttle response in the low RPM range.

Naturally aspirated engines do have very linear torque curves, especially small, high revving ones becasue they are not making much torque at low RPM. Consider the nearly verticle path the curve takes. Usually, you will see a very small bubble in the curve around the point of peak V.E. which is a very small RPM band at peak torque. Add a SC (without the clutch engagement issue) and the bottom of the torque curve is lifted closer to horizontal and the torque bubble around V.E. peak becomes most of the RPM band. In identical cars, which one of these engines do you think will have better throttle response?

 

The FI case will allow air to enter more quickly because it's under higher pressure. It's a matter of fluid dynamics.


So, the evidence states that FI has better throttle response than NA, but you agree that it doesn't? WTF???


In general, the engine that has the highest intake charge velocity at a given RPM will have the best throttle response. If you take two identical engines and put a S/C on one of them, the engine with the S/C will have the best throttle response since the higher pressure in the intake tract will cause a higher velocity of the intake charge.

WRT turbos: If you install a properly-sized turbo that has variable vanes (a technology that has been around for over a decade) on an engine, it can have better throttle response than a NA engine because it will spool up faster at lower RPMs, and then at higher RPMs, when the vanes move, it will generate higher air flow. The best of both worlds.

To summarize, no given engine type has a throttle response advantage over another. It's all dependent on how the engine is designed. As I stated earlier, the engine with the highest intake charge velocity at a given RPM will have the better throttle response at that RPM.

 

Grumpy Quote: If you take two identical engines and put a S/C on one of them, the engine with the S/C will have the best throttle response since the higher pressure in the intake tract will cause a higher velocity of the intake charge.

I appreciate your input, Thanks Grumpy

 

Grumpy, I believe in an ideal world you may well be correct. However, the air doesn't just enter in vias the sohrtest route as it does in an NA car. A turbo car has to send the air, via boost pipes, to the intercooler to get cooled,& then come back & then enter.

Sure the pressure is higher so it may travel faster. But its got a much longer distance to travel. I'mnot very familiar with the AMG s/c engines, but I have learned that the intercoolers sits very close to the engine. But even so, it still has to travel that short distance to get cooled& then back. Even if it's 1 foot & back, the air isn't going to enter as instantaneously as in an NA engine.

Then there's the fact that NA engines generaly have higher static CR"s that their force-fed counterparts.

 

It seems no one is going to agree about anything here ...

M&M ... I understand what you mean that the air has to travel that bit further etc ... but it does not happen in a binary fashion .. i.e. it does not go from there being no air and suddenly there is intake charge air ... the boost is there pretty much all the time (assuming the charger is on) - its the addition of fuel that gets the wagon going ... so ito TR I cannot see it being slower than N/A. If the charger is not enagged there may well some lag as I experienced in a C32.

What gets confusing is the E55 motor has so much instant power, the lag - if present - is not noticed at all.

I am convinced it comes down to the specific engine design / application...

Rgds Steve.

 

You definitely right there. SOme FI engines may well have better TR than some NA engine. But once again, I'm not talking about lag. Even on boost in an RS6, you canlift off in the peak of the torque. Then re-apply throttle. It still take a fraction of a second to respond, even on boost. Try the same in an M3, especially in Sport mode, you can feel what I'm talking about.

My argument has always been a high CR, well tuned NA engine with ITB's.

 

MaM... your ongoing argument frankly has been to continue offering your magazine inspired versions... followed by you continuing to ignore the facts.

PRESSURE is the key variable in the N/A versus S/C argument and if you really are like you say, here to learn, then simply consider the math and science of two identical engines, the S/C version will have improved throttle response due to more PRESSURE>

Please reread Grumpy's input as he sums up very well what we are really trying to share with you.

 

Perhaps everyone needs to take a step back and define throtle response. I define it as follows:

How quickly after I mash the gas pedal do RPMS start increasing.

That being said, it has to do with a whole lot more than pressure and fuel. It is about weight of the flywheel, as well as other components. I have found significantly better throttle response in my beemers than in my E55. I make this judgment based on when I am in manual mode, I have selected the lowest gear I can be in , and I mash the gas, I don’t get the same instant response as my Z4. The Z4 in the same scenario has 0, zip nada lag. The E55 as a slight (very) hesitation that I would probably never have noticed if not for my M3 and Z4.

 

Don't forget the SL models all come with adaptive accelerator. Instantaneous throttle response goes out of the window if you drive "normally" everday and only mash it occassionally.

 

You guys need to take the engine out of the car to make an accurate comparison. The arument is SC vs. NA. Toss in a lighter car with a lighter and more efficeint drivetrain, steeper gearing and a manual transmission and your comparison is completely invalid. I keep hearing M3 this and Z4 that so obviously, you don't understand proper scientific testing methods as well as internal combustion engine building.

 

DRCrowder I agree with you 100%. If you drive a good SC car in isolation you will probably think "WTF are these idiots on about? My TR is fantastic."

You seriously won't feel what I'm talking about & think I'm an idiot (probably a bit late for that ). But you have often driven both back to back. That's where you feel it. I drove a C32 & C55 almost back-to-back (probably an hour between). That's when I felt it. The C32's response was great & in isolation I wouldn't have noticed anything.

But compare to the 55, the 32 felt a bit flat & dull. And I'm willing to bet the components like flywheels, etc are very similar in both cars.

We can solve this puzzle very easily. There must be owners on here that have upgraded from the 32 to the 55. They would be the best people to ask as most components on the cars are the same.

 

Is that really feasible and worth discussing?

 

I assume you question is directed to E55AMG99?

 

Such a shame you can't have honest debate without being condescending. Perhaps if you were open minded and read, then you would notice that I defined throttle response in a pragmatic sense to qualify my statement. I feel you have tried to take this argument more academic since that is now the only ground you have to stand on. I couldn’t care any less about the academic argument; I care about how fast the RPMS go up after I mash the gas.

As far as your academic debate on SC vs. NA. Well I think in that sense it is convenient to forget that the drag on the engine due to the SC which most likely is the culprit for its lack of responsiveness in comparison with a NA car. If you truly want the academic answer, perhaps you should ask one of our forum members who as added a SC to their NA car but didn’t add any lightweight components in the upgrade.

I would implore you to try and be more respectful when you disagree. Should you really feel you have a sounder grasp on science, be it physical, medical, computer, or mechanical. I would welcome a friendly debate via PM as I am more than confident in my knowledge in these areas.

 

Just tired of the ignorance. I have built or modified over 30 engines for the street and at least 25% had SC. Most were big inch, high compression and high torque motors that had excellent TR but none compare to anything with a SC. Currently, I am running a Whipple on my '04 GMC Denali and I'm working with Magnacharger to get the first one for an '06 Denali. So, I know a thing or TWELVE on this subject! Even the motor in my '32 Ford coupe (500+ cubic inches and has over 600 pounds of torque) can't beat my Denali in terms of response and it's 1500 pounds heavier!

The SC does add drag but that is already accounted for in the HP number on the dyno. The added drag does recude throttle response but like the HP number, it is shadowed by the huge increase in HP and TR the SC adds. Within the working range of the engine it costs much less HP and TR to run the SC compared to what it is adding to the engine in both areas.

 

I'll buy that, while I have done extensive engine work in the past, it has all been to 305's and 360's in Jeeps. I really only have my exp to draw from here and it is not exp with cars that are necessarily comparable.

My only question based is that based on your last paragraph, you are inferring that hp and trq play a part in TR, is that correct?

PS don’t be tried of ignorance, people can learn. Be tired of stupidity.

 

LOL You are right WRT ignorance vs. stupidity. I need to remember that.


Torque plays a huge role in TR. Remember that volumetric efficiency VE in a NA motor is nowhere near 100% anywhere on RPM band except at peak torque. In some cases, a superior motor can exceed 100% VE but again only near peak torque. TR is best at or around peak torque where VE is highest. Motors that have broad and flat torque curves are generally more responsive than those that have more vertical, ascending torque curves. The reason is that the engine is usally closer to its VE peak over more RPM.

Does this make sense?

 

makes a ton of sense and explains my E55 lag. I am driving the car like a NA car, downshifing to 5000+ RPMS and I'm outside max trq, therefore am not geeting max VE and best possible TR. Correct?

 

We are not talking about the engine being reponsive, but the throttle. A lighter drivetrain has less mass to rotate & will respond quicker to throttle inputs. In general the torque of an SC car means it needs a beefier drivetrain & hence the throttle it s lazier to respond. Note the engine may well respond immediately, after the throttle has opened. I think that's where the confusion lies. You are confusing engine response with throttle response.

The only way fo you to realise this to drive a car that is universally acknowledged to have fantastic TR.

 

?

 

Now I get it!

 

I'm now thinking that MaM should apply for a service advisor position at a dealership and they bring him off the bench ONLY when they can't solve a car's problem.
His job will be to explain to a frustrated customer what is wrong and what they are doing about it.

 

Your logic is seriously flawed. The length of the tubing is irrelevant to the speed of the air entering the combustion chamber. Pressure differential between the cylinder and intake tract will determine how quickly the air enters.You could circle the globe a few times with the tubing before you connect it to the throttle body, it still wouldn't matter. As long as the pressure is maintained, the air flow will be higher. The only way this would not work is if the tubing was too small to support the needed volume of air.

In the case of the E55, there is no tubing. The S/C is connected directly to the IC. The IC empties immediately to the throttle body, which splits off to both intake manifolds. You could bolt the throttle body directly to the head on a NA engine, it still would not flow more quickly than an engine that has higher pressure in the intake tract. You can't get around the laws of physics.

Again, flawed logic. The compression ratio is just an indicator of how much the A/F mixture will be compressed prior to ignition. Cylinder pressure is the true measure of throttle response, not compression ratio. If you take a high CR engine and throw in a long duration camshaft with a lot of overlap, cylinder pressure will be bled off at lower RPMs due to the overlap and the engine will have poorer throttle response than the same engine with a lower CR and a cam with less overlap.

 

Ok Grumpy but what about thus. The air might be ready to flow, but the throttle plate has got to open first right? I think that we have have found the answer right there. The car that gets the throttle plate open the soonest after pressing the throttle pedal will have the bext response.

Obviously a car with individual throttle bodies will respond quicker, with almost a hair-trigger like TR. Some cars have a sport button which different programs for how quickly the throttle bodies open. RS4 is one of them as well.

But I feel a car with a lighter drivetrain, has less mass to rotate & will spring open the throttle quicker than a car with a beefier drivetrain. Does that make sense now?