"If the horsepower has a sharp peak, then the torque must also have a sharp peak. You multiply the torque curve by RPM to get horsepower. So if the HP has a peak then torque has a peak in exactly the same RPM range. "

I don't even know where to start on this one......let's just say this is incorrect.

"I don't see any scenario -- except for formula cars with extremely high redline -- where you would prefer 10 ft-lb over 20 HP."

Or maybe with street cars with little torque and an extremely high redline......like a Honda S2000.


'04 G35X Graphite/graphite, NAV, wood, premium

"May you lead an interesting life..." -- Old Gypsy Curse

 

I would take the 20 hp over the 10 ft-lb any day.

 

<blockquote><font class="small">In reply to:</font><hr>


"If the horsepower has a sharp peak, then the torque must also have a sharp peak. You multiply the torque curve by RPM to get horsepower. So if the HP has a peak then torque has a peak in exactly the same RPM range. "

I don't even know where to start on this one......let's just say this is incorrect.



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HP is proportional to the product of torque and RPM. Are you refuting the laws of physics? I guess you are even smarter than I thought.

 

If Neffster doesn't mind me reproducing the Dyno sheet he posted, please observe:

Please show me where the torque peak and HP peak are the same.


'04 G35X Graphite/graphite, NAV, wood, premium

"May you lead an interesting life..." -- Old Gypsy Curse

http://370358-370165-Daniel_Wes_Rich...0smoothing.jpg

 

<blockquote><font class="small">In reply to:</font><hr>


If Neffster doesn't mind me reproducing the Dyno sheet he posted, please observe:

Please show me where the torque peak and HP peak are the same.


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For some reason, the picture you tried to attach is not visible.

Nobody said the peaks are in the same place -- I said that if the HP curve is "sharply peaked" then the torque curve must be "sharply peaked" in the same RPM range. This is just high school physics.

 

I'd take the torque... Torque is a better reflection of how hard an engine really pulls. HP is associated with torque but it is better associated with how high an engine will rev. Why do you think that many cars top out before reaching their peak HP RPMs... it's because, in many cases, the engine has run out of the necessary torque to keep weight of the car accelerating.
However as it relates to this topic i.e. the 2004 vs. 2005, or any comparable scenario, it all depends on where the torque is located on the bowerband. In this case, my beleif is that the 04/05 will pull better throughout most of the powerband except @/near higher revs/redline because of the reduction in lower-end torque

2003.5 G35C 5AT
Premium Package
Tire/Wheel Package
K&N Filter, Z-Tube, EGK

 

Torque is where it's at.

I don't know how to post a picture, but I'll try to describe the graph in front of me.

based on 260 hp, and 260 lb/ft (2004 sedan model)

HP is linear from 0 RPM to 6000 RPM going from 100 HP up to 260, then it takes a small dip down to 245 HP at 7000 RPM's

Our Torque curve is very nice, but not as nice as a HEMI engine.
Linear from 0 RPM's to 2000 RPM' from 100 lb-ft to 250 lb-ft, then from 2000 RPM's to 5000 RPM's it goes from 250 lb-ft to 260 lb-ft (very flat). After 5000 RPM's it takes a nose dive to 175 lb-ft at 7000 RPM's.

The 'formula' is based on a simplistic motor design, not one like ours with variable valve timing which changes the aspects of our engine. Thus a torque curve will never match the HP curve.

High torque means High Acceleration
High HP means High Speed.

I'd rather be able to accelerate faster than achieve 150MPH which I might only do a couple of times (safely), HP does come in handy if your trying to race someone up a hill though.

 

ArtofAWD wrote
<blockquote><font class="small">In reply to:</font><hr>


High torque means High Acceleration
High HP means High Speed.


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In a loose sort of way, I agree with your second statement. However high torque does not necessarliy imply high acceleration.

I can bench press 200 lb. Suppose I stand three feet away from a fulcrum with a rigid iron bar and push with 200 lb of force. I'm now exerting (200 lb)*(3 ft) or 600 ft-lb of torque. So I'm capable of exerting 600 ft-lb of torque -- almost three times that of the G35C. Does that mean I can propel a 3400 lb car to 60 MPH in 5.5 sec? Of course not.

The ratio of HP to weight has an almost perfect correlation with the acceleration potential of a car. A car with low torque that can operate at high RPM can out-accelerate a car with high torque operating at lower RPM.

 

The problem is you are assuming there will be 10 more lb-ft or torque at 1500 RPM's. The decrease in torque that we know of so far is ONLY at the torque peak. With variable valve timing on both sets of cams, the engineers would likely have used different cam profiles to broaden the torque curve. The ability to vary cam timing in relation to the cylinder's position and each other can make a huge difference in an engine's flexibility. Losing 10 lb-ft of torque at say 4800 RPM does not mean you will lose the same at all other RPM. Or even at all. From the HP rating, if it occurs at 6700 RPM(I'm not sure of where the torque and HP peaks take place in the new VQ off the top of my head) it is making 233.5 lb-ft of torque. The current VQ makes 237.2 lb-ft. Since HP generally rises to the peak, it might be safe to say that the new VQ will be making more torque at 6500 RPM than the current one. The current VQ at redline will be making less than 280HP. Yet to have 280 HP at 6500 RPM, you need 226.2 lb-ft of torque. Torque levels also generally decline after the torque peak. The New VQ will likely have a bit more torque at 6500 RPM than it has at 6700 RPM or so. In fact, I wouldn't be surprised if it made up the 10 lb-ft you lost at the torque peak here. While this area of the new VQ's powerband is easier to speculate on, we shouldn't assume we have lost anything at the low-mid RPM's at this point either. I say just wait and see.

As far as preople's preferences as to where they would like to see more torque, it's all subjective. Most people will find more low-end torque to be a bit more comfortable, but how often do you floor it at 1500 RPM? You're likely not going to be using all the available torque at that RPM most of the time. And for the most part if you're at 6000 RPM, you are more likelty to be at WOT and actually using all the torque available. So then the question to you would be what does 10 lb-ft of torque equate to at 1500 RPM? IMO, a whole lot less than it does at 6000 RPM.

 

I say we consider then, a motor that is closer matched to the VQ in design. The Current M3 uses a 3.2L I-6. It also has variable intake and exhaust timing. With .3 Liter less displacement it puts out 261 lb-ft of torque at 4900 RPM. Yet with 333 HP on tap at 7900 RPM, it is still putting out 221 lb-ft of torque at 7900 RPM. And accroding to an article I have, BMW claims that 80% of the peak torque is available as low as 2000 RPM. Having that much of it's available torque from 2000 RPM to 8000 RPM is pretty damned good. And given that the VQ's range is smaller, it may show a higher percentage of it's peak torque earlier on as it has no need to extend itself to the 8000 RPM that the M3 does. Of course this has more to do with the possibilities, but we really know more as we start seeing the dynos appear.

 

AlanP,

In reply to your post about gaining only 2.9 HP at 1500 rpm - Although your math may be correct, think of it this way....At 1500 rpm, you may be only making 50-60HP, so an additional 2.9 HP is actually 5% more power (HP). Making 20 HP more at 6000 rpm (where the old motor was making 280 HP) is a gain of 7%. So the percentages are not far off. Of course, in your example you aaume that the additional 10 lb-ft of torque is available at 1500 rpm, which we will not know until we see some torque curves.

I think everyone has added some insight to this topic, and in some resepcts everyone is right to some extent. I will just add that if this thread was meant to compare the performance of the pre-2005 models to the 2005 model, then all this talk about HP and Torque is useless without taking into consideration the weight gain (70 lbs or so) over the 2004 models. The question is - will an additional 20 HP be enough the overcome the weight gain, and what effect will the weight gain have on the handling of the vehicle? My prediction is that you will see a slightly beter 1/4 mile but nothing that will make a difference in everyday performance. But the already hefty G getting heftier is where I see a major flaw.

 

<blockquote><font class="small">In reply to:</font><hr>


The question is - will an additional 20 HP be enough the overcome the weight gain, and what effect will the weight gain have on the handling of the vehicle? My prediction is that you will see a slightly beter 1/4 mile but nothing that will make a difference in everyday performance. But the already hefty G getting heftier is where I see a major flaw.


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Yes, I agree with you that the weight of the G is a problem already. However adding 20 HP will more than offset an extra 70 lbs. You would have to add about 250 lbs before you begin to lose the benefit of adding 20 HP. Adding 20 HP will provide a noticeable improvement in HP-to-weight and therefore acceleration.

<blockquote><font class="small">In reply to:</font><hr>


At 1500 rpm, you may be only making 50-60HP, so an additional 2.9 HP is actually 5% more power (HP). Making 20 HP more at 6000 rpm (where the old motor was making 280 HP) is a gain of 7%. So the percentages are not far off.


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If you are driving your grandma to the library and you don't want to wake her by revving your car over 1500 RPM-- then I agree with you. I bought a G35, not a golf cart. Personally, I'll take 20 HP @ redline over 2.9 HP @1500, any day

 

The essential issue is not 20 additional horses and 10 less torque. It's those figures in relationship to a 2005 G35 and a 2003-4 G35. Follow me for a moment---

Let's compare the 2005 to a 2003-4 with a Z-tube (a mod so cheap--$80, and easy--10 minutes, that everyone should do this). We now have a 2005 with 298 HP/260 torque vs. 2004 Z-tubed with 287 HP/274 torque. The 2005 buys you an increase of 11 HP (4%) at redline with a decrease of 14 torque (-5%) at 4800 RPM. Lastly, the 2005 has a 70 lb. weight penalty (2%). Let's reasonably presume that the torque curve is flattened in the 2005 to achieve the extra HP at the expense of a lowered peak torque. This means that HP across the RPM range should roughly equivalent in both models until you get to higher revs with a 5% edge given to the 2004 at a moderate 4800 RPM. Since HP is the equivalent of force (M=mass X acceleration), as mass goes up accel must go down to keep force or HP the same. In other words, at a given HP, more mass equals less acceleration.

With these assumptions, the 2005 gains 4% HP vs 2% increased mass--at redline. This is clearly favorable because of the equation F=m X a. But only at redline. As HP drops off below redline (as it must because less torque has to equal less HP at any given RPM) mass, of course, never changes. When the added HP for the 2005 equals 2%, the power-wieght ratio becomes a wash compared to the 2004. Below 2% increased HP, the 2005 starts to lose out to the 2004. A 4800 RPM, the 2005 acutally loses 5% HP while maintaining the 2% weight penalty. As F (or HP) = m X a, acceleration = F/m. At 4800 RPM, HP (or force) is 5% lower and mass is 2% higher. This equals a loss in acceleration of 10% at 4800 RPM (but a bit less of a loss below and above 4800 because of a flattened torque curve).

At redline, the 4% increase in HP for the 2005 is at the expense of 2% increased mass resulting in a 2% gain in accelration at redline.

So, with a 2005, you gain 2% acceleration at redline at the loss of 10% acceleration at around 4800 RPM. This is a very unfavorable relationship for most kinds of driving.

 

While it is probably certain the original post had to do with the changes coming in th 05 models, I don't see that he asked about what we thnk of the weight. And I don't think anyone really put much thought into that aspect in their posts. I think it really just deals with the preference in motors.

However, if we want to bring weight into the picture, a simplified way to look at this is to compare the HP to weight ratios.

03/04 - 3435/280 = 12.26
05 - 3512/298 = 11.78

Almost a 4% increase. And while this is a siomplified way of looking at things, you'll find it will be a pretty good representation of how quick a car will be.

 

AlanP,

The 2004 Motor has 10 more lb-ft of torque at 4800 rpm. At that rpm, the old motor is producing 245 hp. The new motor at that rpm is producing 236 HP. Driving your car at 4,800 rpm will most likely wake up grandma. The 2.9 HP lead for the old motor at 1500 rpm, grows to 9 HP at 4800 rpm. The increase in HP for the new motor happens way up in the rpm range where you will get more acceleration, but perhaps not enough to make up the lost power from 0-4800 rpm (and I would guess even higher as I bet the gains with this motor is that they were able to flatten the curve slightly above 6,000 rpm where the old motor seemed to have a decent drop). I say it's still up in the air whether or not the new 2005 will be any faster than the 2004. I would be excited about the extra 20 HP even at the expense of torque if only the 2005 lost some weight rather than gained weight. A 3300 lb G with the new motor would have been a nice improvement.