Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!





Acura RL

18687899192235

Comments

  • jeff88jeff88 Posts: 94
    Has been difficult to keep up...

    was reading about 300 posts ago about the octane discussion and maybe missed this but this is one thing I've noticed.

    When running premium gas, the shifts were smoother than running 87. It appeared to me that the retarding of the spark prior to shifting wasn't as well timed with 87 as it was with 93. Upon occasion, my wife would accidentally fill the rl with 87 when driving it since that is the grade for her ride. It was noticeable to me afterward.
    -----------------
    other comments were about the looks of the pre-'05 rl; I have always thought it to be a very pleasing look inside and out but then again, I'm biased.
    -----------------
    someone wrote that their I-4 in their accord felt to a passenger like a 6; my impala company car has a v6 that feels like a 4...

    ...or as a friend once said, it ain't the size of the boat, it's the motion of the ocean.

    Think he may have been describing something else.
  • saugataksaugatak Posts: 488
    J35A is also the perfect example to illustrate that output isn’t necessarily dependent only on compression. There are more ways to getting it done. Odyssey & Pilot have the 3.5/V6 rated at 240 HP, and while using same compression (10.0:1), the version in MDX is rated at 265 HP. That’s using simple tweaks to the intake and the valve heads.

    Are you sure this is the case? I've run my MDX on regular fuel and I can feel the loss of HP, might even be 20HP or so which would bring it down to the level of the Ody or Pilot.

    Is it possible that Honda used the EXACT same engine for the Ody, Pilot and MDX and just tweaked the software in the Ody and Pilot so that it could not take advantage of premium fuel? That would seem to be easier and cheaper than tweaking intake and valve heads.

    Aah, the benefits of variable valve timing & lift, and multi-stage intake! I’ve observed Honda engines enough to bet that it will deliver more than 90% of its peak torque from about 2000 rpm.

    Honda's engines are impressive, but not in regards to developing low end torque.

    IMO, Nissan's engines alwasy felt way more torquey than Honda's engines.

    GM's LS1 develops abut 295 ft.lb. of torque (or about 80% of max torque) at about 800 rpm and hits 90% of peak torque below 2,000 rpm.

    http://www.gm.com/automotive/gmpowertrain/engines/gmpow/images/ls- - 1curve.jpg

    The Hemi produces 80% of peak output at around 1,200rpm and 90% of peak output at 2,000rpm. Here's a small and barely readable torque curve chart of the Hemi.

    http://www.popularhotrodding.com/tech/0403phr_hemi/

    GM's upcoming 3.9L OHV v6 (which also has VVT) produces peak 245 ft.lb. of torque at 2,800 rpm, so it's a safe bet that it'll produce more than 90% more torque at 2,000 rpm.
  • lexusguylexusguy Posts: 6,419
    Nobody is going to argue that OHVs dont make serious torque down low. They do. The problem with OHV (aside from its general low techness) is the sheer size it has to get to make competitive power to a SOHC or DOHC engine. The LS6 is pushing 6.0L. A 3.9L six that only makes 245ft.lb of torque is hardly what Id call efficient. I bet its hp figures cant match modern DOHC either. I seriously think the OHV 6 is on its death bed. How large would an OHV 6 have to be to match the horsepower of Acura or Nissan's 300hp 3.5L engines? 4.5L? 5.0L?
  • saugataksaugatak Posts: 488
    The point is that OHV engines are actually SMALLER than comparable OHC engines. Whereas OHC engines have cams sitting on top, the OHV engines have a "cam in block" architecture and so have one cam sitting within the valley of the V, which would otherwise be wasted space.

    DOHC V engines in particular are very large. Compare the size of 4 cams on top vs. 1 cam nestled in the V.

    While a 3.9L v6 sounds like a HUGE v6 engine, it's not. It fits in comfortably in the upcoming Pontiac G6 which is a FWD car.

    You're focused on specific output (HP/L of displacement) as a measure of efficiency. Another way to determine efficiency is HP/volume of engine size, and by that measure, OHV engines are just as, often more efficient than, comparable OHC engines.

    Another example is the 5.7L Hemi, which is a pushrod. It fits not only in trucks, but also in cars, because it's not a big engine for the amount of displacement it gets.
  • saugataksaugatak Posts: 488
    BMW gets even more horsepower than the RL from a smaller displacement inline in their M3.

    I've love to see a torque curve chart of BMW's inline 6's b/c when driving them, I always felt they had more low end power than any OHC v6's I've driven.

    Theoretically, a good inline 6 should have more HP and torque than a v6 b/c the I6 doesn't have a balancer shaft robbing it of power, whereas a v6 does.

    There are also reliability issues. While the M3 straight 6 produces gobs of torque and power, it's had some reliability issues.
  • lexusguylexusguy Posts: 6,419
    Well, to a certain extent that has to be expected, considering how hard BMW has pushed that engine in order to not have to resort to forced induction. Hat es einen Turbo? NEIN! sind wir BMW!
  • saugataksaugatak Posts: 488
    Aah, the benefits of variable valve timing & lift, and multi-stage intake! I’ve observed Honda engines enough to bet that it will deliver more than 90% of its peak torque from about 2000 rpm.

    You mention VVT and multi-stage intake as 2 factors enhancing low end torque.

    I'm wondering how much VVT actually helps low-end torque? I always thought the extra valve lift was beneficial at higher rpms so that the engine could suck more air. I'm not sure how extra valve lift will help at lower rpms.

    For example, the Hemi and LS engines don't have VVT, but they do have multi-stage intake manifolds (pretty high tech for those low tech pushrods), and they're getting 90% peak torque at 2,000 rpm.

    GM's upcoming 3.9L OHV v6 adds VVT to a dual stage intake manifold and gets 90% of peak torque at 1,800 rpm. GM's engineers indicate that it's the dual stage manifold that is responsible for a broader torque curve.

    http://www.auto-report.net/index.html?gmpt05.html

    The variable intake manifold is a significant low-speed torque 'enhancer' for the 3900. It gives the 3900 a broader torque curve that retains higher specific torque output across the engine speed range.

    As far as I can see, multi-stage manifolds are mainly responsible for enabling engines, whether OHC or OHV, to hit 90% of peak torque at around 2,000 rpms.
  • saugataksaugatak Posts: 488
    Excellent post, as always.

    I read through your post carefully again and 3 things struck me right off the bat:

    1. How creative Honda engineers are in tweaking their I4 engines to achieve the desired HP and torque/powerband.

    2. No matter what the Honda engineers did to boost power, they're still limited to a max. torque of around 160 ft.lb.

    The 2.4L I4 Accord with a compression ratio of 9.7:1 gets 160HP and 161 ft.lb.@4,500 rpm, the 2.4L I4 TSX with a compression ratio of 10.5:1 gets 200HP and 166 ft.lb.@4,500rpm.

    So a 0.8 increase in compression ratio yielded a whopping 5 ft.lb. of extra torque. Wow.

    I guess if the RL takes the MDX engine and boosts compression ratio to 11.0:1 (which is the same compression ratio as the TL), it may get to 260 ft.lb. We'll have to see.

    3. We're making a big deal out of getting the torque curve as flat as possible and as low down the powerband as possible, saying things like "90% of peak torque available at 2,000 rpms." But still, 90% of 160 ft.lb. is only a measly 144 ft.lb. of torque.

    At some point, you have to bump up displacement to boost max torque. It looks like multi-stage manifolds help flatten out the torque curve and broaden the powerband, but there is still no replacement for displacement (except supercharging perhaps) when it comes to increasing torque and low end power.
  • ksomanksoman Posts: 590
    >>>
    3. We're making a big deal out of getting the torque curve as flat as possible and as low down the powerband as possible, saying things like "90% of peak torque available at 2,000 rpms." But still, 90% of 160 ft.lb. is only a measly 144 ft.lb. of torque
    <<<

    GEEZ mang! If 144 is measly, then basically 160 is measly too. On a comparitive basis, 90% is a lot and very close to 100%.

    The fundamental reason to try to bring the torque curve flat (oxymoron) is try to bring torque as lower in the rpm range as possible. For big bad engines, they have a huge torque advantage in the lower RPM range purely because of size, not because of brains.... whereas for the small engines, they have to be smarter. I think the whole purpose of raw torque against raw HP is because torque really is what helps you break the coefficient of resistance of the myriad things that are at rest when a vehicle is at rest. Once you start spinning, the use of torque starts to lessen (not eliminate, diminish). That is where high RPM & screaming engines come into play, basically the reason why the s2000 is not the fastest from the readlight, but when its spinning, it can whoop anybody's "ahem", rear! Also, on that logic, just getting more and more torque is not necessary.

    Lets say Engine A is pumping 400 lb-ft of torque max, at 4500 rpm, and 120 lb-ft at 2000 rpm
    Enginge B is pumping 250 lb-ft of torque max at 4200 rpm, and 180 lb-ft at 2000 rpm
    Obviously engine 2 is better in my dishonest opinion. It is more capable of breaking resistance and getting the fat pig rolling. As the car speeds up and the gearing controls where the car can keep in the powerband, you are good to go. If you still can't get your car moving fast, one of two is likely, you either are incapable of shifting your gears if its a manual or if it's an auto, the computer controlling the shift points was just designed by morons and that car company needs to shutter down yesterday!

    couple of comparitive notes:
    the starter motor on your car, its a DC motor, cuz it pumps loads of torque up front, right of the bat... that's to break the resistance of non-moving parts quickly.
    the huge electric locomotive engines, they use DC motors, not AC motors. DC motors have a huge torque advantage in the lower RPM, where as AC motors have better torque later in the RPM range. Considering how much mass the locomotive is pushing or pulling, and that too on smooth steel wheels on a smooth steel rail, you want the torque up front to overcome the coefficient of resistance as quickly as you can. Have you seen a electric locomotive spin its wheels? Yes it actually does do that at times.

    ksso
  • varmintvarmint Posts: 6,326
    Without a VVT system, the engine must accept a compromise. There are three choices.

    1. Allow the engine to breathe freely at higher RPMS (producing good horsepower) and sacrifice the low end torque.

    2. Allow it to breathe efficiently at the low end (producing good torque) and sacrifice the high end horsepower.

    3. Pick a middle ground that does both well enough, but neither of them particularly well. Most engines would fall into this category.

    With a VVT system in operation, the engine can change breathing apparatus to match the situation (high or low rpm). In other words, the engine can have its cake and eat it too.

    In the past, Honda has used VTEC so that it produced the greatest amount of horsepower. Horsepower was the priority for cars like the NSX and Integra. The lower rpm intake cams were designed to function more like a number 3 engine. They serviced both the low end and the middle ground. Meanwhile the upper rpm intake was designed to get the most from the high end. So the second set allowed the top end to function like a number 1 engine. Honda still takes this approach with cars like the S2000.

    This approach spawned the myth that VTEC is only good for the top end. Truth is, those engines made decent torque down low for an engine of their size. It's just that most other cars were using bigger engines or forced induction.

    Anyway, it doesn't have to be that way. VTEC can also be used to make an engine work both as a number 1 and a number 3. It could produce good torque down low and hold it through the middle range. The original MDX engine was a decent example of this.

    What about an engine that works like a number 1 and a number 2? Why not build an engine that focuses on both the high and low ends? Well, the technology is good, but it's not the answer to everything. Such an engine would have a weak mid-range. That hurts driveability and smoothness. Remember, there is more to a good engine than just power output. There's also NVH, fuel economy, emissions, reliability, cooling, and a host of other considerations to juggle.

    With the addition of VTC, Honda is working out how to correct for problems with a smooth power curve. The addition of VTC is yet another way to manage air flow which can compliment VTEC. The combination is called i-VTEC in Honda speak. All three of the 2.4L engines I mentioned earlier use i-VTEC to produce what is essentially a very broad torque curve for an I4 engine. I mean, the torque curve for the TSX's I4 doesn't look as good as BMW's I6, but it's pretty darn impressive for a 4 banger.

    Okay, now imagine all this being applied to a 3.5L V6... Right now, none of the J series engines makes full use of the technology Honda has developed in recent years. Probably because of the expense. With cars in the price range of the RL, cost becomes less of a priority. So it's possible we'll see a fully blown V6 in the RL.
  • robertsmxrobertsmx Posts: 5,525
    Honda's engines are impressive, but not in regards to developing low end torque.

    Well, I don&#146;t expect a 2.0-liter engine to match the torque output from a 6.0-liter engine. Do you? In RL, the rated peak can be expected to be about 260-265 lb.-ft. Is that lack of torque compared to other engines with similar displacement?

    And it is not just the peak torque either, we have been talking &#147;range&#148;. If RL&#146;s engine gets 260 lb.-ft and provides 90% of it (about 235 lb.-ft) or more between 2000 rpm and 6500 rpm, I would say that it is not only high for the displacement, it is also a very broad torque curve!

    As for the OHV versus SOHC/DOHC debate, let us use the thread that exists for the purpose.

    BMW gets even more horsepower than the RL from a smaller displacement inline in their M3.

    RL isn&#146;t supposed to get its peak power at 8000 rpm. Its 300 HP will likely arrive around 6000-6200 rpm range (pretty much where everybody else is rating the peak power these days), and red line at 6800 rpm or so.

    That said, it is unfortunate to not see Honda use its engine expertise in high performance sport coupe/sedans. The last time I heard about something along the lines was the NSX GT-R that participated in Honda&#146;s 50th anniversary parade, powered by a 380 HP version of its 3.2-liter V6. This engine was used in Real Time Racing NSX for World Challenge GT Class, before they switched to a supercharged version.

    So much for Honda not being able to get &#147;enough&#148; HP/liter out of its engines. :-)

    I'm wondering how much VVT actually helps low-end torque?

    I&#146;ve a perfect illustration for you. Japanese Accord 24TL (AKA Acura TSX in North America) and American Accord use variations of K24A engine. The dynographs (below) would be helpful.

    Honda Accord 2.4
    Acura TSX 2.4

    Accord&#146;s engine produce 90% of its 161 lb.-ft (about 145 lb.-ft) or more between 2500 rpm and 5800 rpm, while the TSX version produces 90% of its 171 lb-ft (abut 154 lb.-ft) or more between 2000 rpm and 6800 rpm. Obviously, TSX not only has a higher torque curve, but it is broader as well.

    The TSX version does have additional tweaks, besides VTEC being applied to intake as well as exhaust side whereas in Accord it is at the intake side only.

    That said, the basic idea behind variable valve timing systems is to enhance low-end torque without compromising the same at the top end, and vice versa. It would be possible to get 200 HP out of a 2354 cc I-4 without I-VTEC, but try to imagine the shape of the torque curve.

    A basic engine can be tuned to develop most of its torque at low end, and the output will taper off quickly past the mid-range. If you had a secondary cam profile that got activated in the mid-range, the output will stay up in mid range and above (broadening of the torque curve) instead of tapering off.

    To understand the impact, superimpose the two versions of Northstar that existed. Northstar used single cam profile, one tuned to produce a little more torque at a lower rpm (300 lb.-ft @ 4000 rpm/DTS) and compromised a little at the top end (rated 275 HP@ 5600 rpm). The other compromised a little at the lower range (295 lb.-ft @ 4400 rpm/STS) to gain a little on the top end (300 HP @ 6000 rpm).

    If it were possible to keep the better low end output from the DTS version while retaining the better top end output from STS version, we wouldn&#146;t be talking about compromising one for the other. And that&#146;s where variable timing would come into play.
  • ksomanksoman Posts: 590
    good points.

    ksso
  • varmintvarmint Posts: 6,326
    "No matter what the Honda engineers did to boost power, they're still limited to a max. torque of around 160 ft.lb." - Saugatak

    Yeah, that's true. But I think that has more to do with the fact that they are working with an I4 engine displacing only 2.4 liters. I know of no other petrol 2.4L that produces significantly more torque without resorting to forced induction.

    "I guess if the RL takes the MDX engine and boosts compression ratio to 11.0:1 (which is the same compression ratio as the TL), it may get to 260 ft.lb. We'll have to see."

    Everything is speculation at this point. But, unlike the 2.4L I've mentioned, we are now dealing with 3.5 liters in a V configuration. I don't think it is unreasonable to expect a larger boost of more like 10-12 lb-ft with that engine. And there's always the chance that Honda will add something like VTC to the RL's block, which is not found in the MDX, TL, or Pilot.

    So, I think 260 or 265 are both reasonable estimates. But my original point was while these peak numbers may come at 4,000 rpms, that does not mean there is no torque in the bottom end.

    "At some point, you have to bump up displacement to boost max torque. It looks like multi-stage manifolds help flatten out the torque curve and broaden the powerband, but there is still no replacement for displacement (except supercharging perhaps) when it comes to increasing torque and low end power."

    Ultimately, yes, I think you are correct. There is a limit to how much torque can be produced by a given displacement. But what I'm expecting from Acura is a V6 that provides as much torque as the other V6s in this class and horsepower that is closer to the V8s. Assuming the car is priced like the other V6s, how is that a problem?
  • robertsmxrobertsmx Posts: 5,525
    How creative Honda engineers are in tweaking their I4 engines to achieve the desired HP and torque/powerband.

    Not just Honda, just about any engineer is expected to be creative. And why just I-4, you see it in the V6 as well. Don&#146;t you?

    No matter what the Honda engineers did to boost power, they're still limited to a max. torque of around 160 ft.lb.

    Putting this in perspective, 161 lb.-ft to 171 lb.-ft from a 2354 cc engine is quite good. And especially considering that at least 90% of the peak torque is available for a range of (almost) 5000 rpm!

    Do you not agree?

    We're making a big deal out of getting the torque curve as flat as possible and as low down the powerband as possible, saying things like "90% of peak torque available at 2,000 rpms." But still, 90% of 160 ft.lb. is only a measly 144 ft.lb. of torque.

    So, are you suggesting that it is better to not have a flat torque curve from an engine producing 160 lb.-ft? For that matter, any engine regardless of the output?

    At some point, you have to bump up displacement to boost max torque.

    Undeniable fact. But, how is it better to increase displacement every time torque has to go up? To put this in perspective, for couple of years, a version of Honda 3.5/V6 produced 229lb.-ft. In case of RL, we&#146;re now &#147;talking&#148; 260 lb.-ft. Should Honda have bumped up the displacement to almost 4.0-liters to achieve 260 lb.-ft? To me, it appears, engineers managed to get more from the same and I can never associate that with being a bad idea. Technological advancement is the obvious answer!

    Now, if we were talking 300 lb.-ft or more, I don&#146;t see how a normally aspirated 3.5-liter engine could achieve that, in which case, the displacement will have to be bumped to 4.0-liter or so (a &#147;really good and efficient design&#148; typically gets about 75 lb.-ft per liter displacement), unless the efficiencies of the engines suddenly changes. Even in racing forms, the engines are barely hitting 90 lb.-ft per liter at max.
  • markcincinnatimarkcincinnati Posts: 5,107
    At some point, you have to bump up displacement to boost max torque. -- back to the old no replacment for displacement axiom?

    Generally the replacement for displacement is better breathing and better breathing via some form of forced induction seems to be very effective and very efficient. Further gains can be achieved via ultra high compression ratios (12:1, e.g.) and direct (or fuel stratified) injection. The technical tricks that are coming soon to an engine near you are quite impressive.

    And, we've also talked about the max torque available @ 0 RPM's of an electric DC motor -- the main reason for the low down torque, as noted herein by severl of us, is off the line acceleration (perhaps [improving] the 0 - 62 sprint is enough [of a range] that the assist could be kept, mainly, to achieve that goal).

    In any case the "new" Acura/Honda 3.5L with twin turbos and enough "beefing up" to make reliability not an issue, would get them where they "want" to be with little fuss or muss. Torque would jump impressively and HP should surpass 400HP, which in the RL ought to be plenty for both bragging rights and absolute performance and efficiency.

    I know, "not gonna do it," "wouldn't be prudent."

    I can dream, can't I?
  • varmintvarmint Posts: 6,326
    Uh-oh, the engine boys are in town... =)

    Yes, I don't think their is an ultimate limit to how much torque can be provoked from a given displacement. In the year 2025 someone may find a way to get 110 lb-ft per liter. The envelope is always being pushed. The goal posts are always moving farther away.

    I think the trick in speculating about the RL is trying to "keep it real". We do that by guessing within the parameters of what Honda is already capable of doing today. Hence all this discussion about other Honda engines.

    All this makes me wonder how the others will respond. It's all fun and games to compare numbers like this, but it's the market that will determine how much power is needed. Maybe people won't care about the RL's horsepower advantage. Or maybe the others will be forced to adjust their 6 cyl offerings in either price or output.
  • markcincinnatimarkcincinnati Posts: 5,107
    IMO, people will indeed care about the HP number from Acrua -- @ nearly $50K? You bet!
  • robertsmxrobertsmx Posts: 5,525
    Another technical trick that Honda has developed and is offering in a model in Japan is its own version of DI, dubbed &#147;I-VTEC-I&#148;. But, will it happen with the V6? We shall see. But it is probably more about improving fuel economy than anything else.
  • saugataksaugatak Posts: 488
    GEEZ mang! If 144 is measly, then basically 160 is measly too. On a comparitive basis, 90% is a lot and very close to 100%.

    Yes, that's exactly my point. I'm not denying that Honda is great at doing a lot with a little, but this is America, the land of no displacement taxes.

    Why can't Honda just bump up displacement and use its VCM technology so that we can get both power and decent gas mileage?

    Lets say Engine A is pumping 400 lb-ft of torque max, at 4500 rpm, and 120 lb-ft at 2000 rpm

    Enginge B is pumping 250 lb-ft of torque max at 4200 rpm, and 180 lb-ft at 2000 rpm
    Obviously engine 2 is better in my dishonest opinion.


    Not disagreeing with you, but who says the best technology needs to be used on smaller, less powerfu engines? Why not use the same technology on the bigger engine and get the same flat torque curve?

    The RL is supposed to be Honda's flagship. I can't see Honda skimping on the technology front for the RL's engine.

    As the car speeds up and the gearing controls where the car can keep in the powerband, you are good to go. If you still can't get your car moving fast, one of two is likely, you either are incapable of shifting your gears if its a manual or if it's an auto, the computer controlling the shift points was just designed by morons and that car company needs to shutter down yesterday!

    But in city driving, you're going fro 0 to 40 mph A LOT. The fact is, unless you're racing, low end grunt is usually a lot more useful than high revving HP. Also, isn't the RL supposed to be a luxury car, not a sports car? This class of car is supposed to have low end grunt so that you can accelerate smoothly without making the engine scream, which is bad for NVH, an important consideration in luxury cars.
  • robertsmxrobertsmx Posts: 5,525
    Have you figured out yet, how much low end grunt is &#147;needed&#148;?
  • saugataksaugatak Posts: 488
    I'm familiar with the theory of VTEC and I know it helps out at all rpm ranges. However, it seems pretty clear from the data that it helps out most at high end rpms.

    Non-VTEC OHV engines with multi-intake manifolds such as GM's LSv8s and DC's Hemi hit 90% peak torque at 2,000 rpms. The DOHC I4 in the Accord has 161 ft.lb. and 160HP, the higher compression version in the TSX gets 166 ft.lb. and 200HP. A pretty minimal increase in torque, but a significant increase in HP.

    By comparison, the only OHV engine with both VVT and dual-intake manifolds hits 90% peak torque at 1,800 rpm, so it seems like VVT accounts for approximately 200 rpms.

    With the addition of VTC, Honda is working out how to correct for problems with a smooth power curve. The addition of VTC is yet another way to manage air flow which can compliment VTEC. The combination is called i-VTEC in Honda speak. All three of the 2.4L engines I mentioned earlier use i-VTEC to produce what is essentially a very broad torque curve for an I4 engine. I mean, the torque curve for the TSX's I4 doesn't look as good as BMW's I6, but it's pretty darn impressive for a 4 banger.

    I'm familiar with VTC and i-VTEC and I agree it flattens the torque curve and Honda's 4 bangers are impressive for a 4 banger, but it's still a 4 banger.
  • lexusguylexusguy Posts: 6,419
    That seems to be Toyota's position, as all of their latest engines put out more torque than HP.
  • saugataksaugatak Posts: 488
    Toyota ain't #1 for nothing. Toyota probably realizes that your average driver cares more about torque than HP.

    Enthusiasts (like us) aren't representative of the average car buying public IMO. We LIKE to rev that engine and blast it, but seriously, most people don't and the high end HP just ends up becoming a marketing ploy.
  • ksomanksoman Posts: 590
    99.973% of the drivers out there should not be touching a steering wheel...
  • saugataksaugatak Posts: 488
    So much for Honda not being able to get &#147;enough&#148; HP/liter out of its engines. :-)

    I never complained about Honda's specific output. I am merely pointing out that no matter how good the specific output, the TOTAL OUTPUT is not that high with limited displacement.

    Accord&#146;s engine produce 90% of its 161 lb.-ft (about 145 lb.-ft) or more between 2500 rpm and 5800 rpm, while the TSX version produces 90% of its 171 lb-ft (abut 154 lb.-ft) or more between 2000 rpm and 6800 rpm. Obviously, TSX not only has a higher torque curve, but it is broader as well.

    The TSX version does have additional tweaks, besides VTEC being applied to intake as well as exhaust side whereas in Accord it is at the intake side only.


    I think your numbers are off b/c the TSX only gets 166 lb-ft. Wouldn't you agree that all the extra tech. in the TSX engine is producing a pretty paltry return in terms of extra torque?

    I agree that VTEC can help broaden the torque curve, but how much is it really helping? OHV engines w/o VTEC have just as broad and flat a torque curve.

    That said, the basic idea behind variable valve timing systems is to enhance low-end torque without compromising the same at the top end, and vice versa. It would be possible to get 200 HP out of a 2354 cc I-4 without I-VTEC, but try to imagine the shape of the torque curve.

    Isn't that another way of saying VTEC helps increase max. HP at higher RPMs? If you start off with an engine that has good low end torque and add VTEC, it helps raise the HP. If you start off with an engine that has high HP but a non-flat torque curve, VTEC can help flatten the torque curve.

    I'm aware of how VTEC works, and I think we're all using different words to say the same thing.

    But no matter how good VTEC is, it can't make create torque where it doesn't exist. Look at the TSX engine vs. the Accord I4, all that extra VTEC raises max. torque by 5 lb-ft.
  • saugataksaugatak Posts: 488
    Putting this in perspective, 161 lb.-ft to 171 lb.-ft from a 2354 cc engine is quite good. And especially considering that at least 90% of the peak torque is available for a range of (almost) 5000 rpm!

    First, it's not 171 lb-ft, it's 166. Second, the 5,000 rpm range (covering from around 2,000 rpms to around 7,000 rpms) is misleading. The rpm range from at least 5,000 rpms to 7,000 rpms are unusuable, so who cares?

    You think Honda automatic trannies aren't going to upshift by 4,500 rpms? And you'd have to want to waste your engine pretty bad if you're going to upshift at 5,000 rpms regularly in a manual.

    So, are you suggesting that it is better to not have a flat torque curve from an engine producing 160 lb.-ft? For that matter, any engine regardless of the output?

    You're missing the point again. I'm saying no matter how flat the torque curve, 160 ft-lb is not a lot. It's appropriate for a small car like the Civic USED to be.

    With the Civic and Accord getting larger, and the CR-V being an SUV, that 4 banger is really straining, especially with a full load.

    how is it better to increase displacement every time torque has to go up? To put this in perspective, for couple of years, a version of Honda 3.5/V6 produced 229lb.-ft. In case of RL, we&#146;re now &#147;talking&#148; 260 lb.-ft. Should Honda have bumped up the displacement to almost 4.0-liters to achieve 260 lb.-ft? To me, it appears, engineers managed to get more from the same and I can never associate that with being a bad idea. Technological advancement is the obvious answer!

    Sometimes technology can provide the answer and sometimes it doesn't. Witness all the extra technology in the TSX I4 for a measly 5 lb-ft. increase in max. torque. Also, adding more tech can add costs, reduce reliability and raise repair costs.

    Besides, this is not an either/or situation. I'm not advocating ditching the tech and going with displacement only. Why can't Honda offer more tech and more displacement? The U.S. doesn't have silly and artificial displacement taxes like Europe and Japan do.
  • robertsmxrobertsmx Posts: 5,525
    It does help deliver more peak power, but it also helps down low! Most people do not realize that the benefit of having a second (aggressive) cam profile triggering somewhere in the mid-range (in most applications) allows the flexibility of having a &#147;low rpm&#148; cam profile!

    Let us assume we have engine A that is tuned for low-end power. The fixed cam profile isn&#146;t going to be able to do much in the top end, resulting in lower peak power.

    We want to develop engine B, using engine A, but now we want more peak power. We don&#146;t have a choice, but to use a fixed cam profile. This time, we choose to compromise some low-end power in favor of letting the engine breathe better at higher rpm, hence producing higher peak power than in engine A. Mission accomplished.

    To put this in real life, that GM&#146;s 4.6/V8 used in DTS (275 HP) can be considered engine A, and the STS version (300 HP) would be the engine B. To get the additional 25 HP, GM engineers seem to have fiddled with the single cam profile that was available and forcing the engine to breathe better 400 rpm higher (peak torque moved from 4000 rpm to 4400 rpm and peak power moved from 5600 rpm to 6000 rpm).

    If something like first generation VTEC were to be used, we could start with engine A, the basic cam profile tuned for low-end power. After 4000 rpm, the torque output would taper off. But now, VTEC provides us a second cam profile that will take over, and push the torque curve back up again and help deliver greater peak power.
  • robertsmxrobertsmx Posts: 5,525
    Assume two engines, each displacing 2.0-liter with the following outputs:
    A: 120 HP @ 5200 rpm, 125 lb.-ft @ 4000 rpm (90% of peak torque available at 2000 rpm)
    B: 140 HP @ 5500 rpm, 140 lb.-ft @ 4500 rpm (90% of peak torque available at 2500 rpm)

    Does this mean engine B lacks low-end torque compared to engine A since &#147;90% of peak&#148; arrives 500 rpm later? A simple math reveals that engine B produces 126 lb.-ft at 2500 rpm, which is greater than the peak torque from engine A!

    At 2000 rpm, engine A will be producing 113 lb.-ft, and unless engine B has a real lousy torque curve below 2500 rpm, it is likely producing better than 113 lb.-ft.

    To use real examples, let us use couple of Honda&#146;s V6 engines.
    C35A: 225 HP @ 5200 rpm, 231 lb.-ft @ 2800 rpm (3.5/V6 in current RL)
    J35A: 265 HP @ 5800 rpm, 253 lb.-ft @ 3500-5000 rpm (3.5/V6 in current MDX)

    I have not seen dyno plot for the C35A, but let us assume the engine produces 95% of its peak torque at 2200 rpm. And that would mean…
    About 220 lb.-ft at 2200 rpm
    Peaks at 231 lb.-ft at 2800 rpm
    Tapers just a little to 227 lb.-ft at 5200 rpm (to develop 225 HP).

    This engine doesn&#146;t use VTEC, so it is using a single (fixed) cam profile, but has a reasonably flat torque curve (between peak torque and peak power engine speeds which are 2400 rpm apart, the torque output is dropping by only 4 lb.-ft).

    OTOH, this dyno plot for J35A suggests that the engine develops…
    300 Nm (220 lb.-ft) at about 1200 rpm!
    By 2000 rpm, the engine is developing about 235 lb.-ft (which is already better than the peak in C35A)
    Continues to develop more until hitting the ceiling at 3500 rpm (253 lb.-ft) and maintains the peak for next 1500 rpm
    And, finally, starts to taper off to 240 lb.-ft (still 95% of its peak torque) at 5800 rpm.

    While J35A also appears to hit its &#147;95% of peak&#148; mark at about 2200 rpm (about 325 Nm/240 lb.-ft), retaining this 5% over a range of engine speed from 2200 rpm to 5800 rpm is far more impressive because it is harder to maintain a higher percentage of high specific output than it is to maintain the same percentage of lower specific output.

    To put this in &#147;numbers&#148;,
    C35A has a maximum specific torque output at 66.5 lb.-ft per liter compared to 72.9 lb.-ft per liter for the J35A. 95% (or 90% or any percentage) of 66.5 lb.-ft per liter would be easier to retain compared to the same for the 73 lb.-ft per liter engine.
  • robertsmxrobertsmx Posts: 5,525
    Not really. Using the example from above, C35A has torque &#147;number&#148; higher than power &#147;number&#148; and the opposite is true for J35A. This does not mean C35A is tuned for low-end torque and J35A is not.

    J35A ends up producing more HP because it has a broader torque curve that continues to hold itself past the magical 5252 rpm mark in the formula…

    HP = Torque (lb.-ft) * Engine Speed (rpm)/ 5252

    If, instead of producing 240 lb.-ft at 5800 rpm, the J35A were producing 226 lb.-ft, then the engine would be rated as 250 HP @ 5800 rpm, 253 lb.-ft at 3500-5000 rpm! But since it develops more torque, it ends up developing 265 HP.

    The same will be true for RL, which will have to have its torque curve just a little higher and just a little wider, to get the additional 35 HP.
  • saugataksaugatak Posts: 488
    Uh-oh, the engine boys are in town... =)

    Heh.

    Everything is speculation at this point. But, unlike the 2.4L I've mentioned, we are now dealing with 3.5 liters in a V configuration. I don't think it is unreasonable to expect a larger boost of more like 10-12 lb-ft with that engine. And there's always the chance that Honda will add something like VTC to the RL's block, which is not found in the MDX, TL, or Pilot.

    Making the RL's engine an i-VTEC might do the trick, but I'm not sure the extra displacement will necessarily improve incremental gains.

    For example, the 2003 TL Type-S had a 3.2L SOHC v6 making 260HP@6,100rpm and 232 lb-ft@3,500 rpm with a compression ratio of 10.5:1.

    Boosting the compression ratio to 11.0:1 in the 2004 TL raised HP to 270HP@6,200 rpm (have to rev 100 rpms higher for the extra 10HP) and 238 lb-ft@5,000 rpm (an extra 6 lb-ft @ 1,500 rpm more is not that great an incremental gain).

    So, I think 260 or 265 are both reasonable estimates. But my original point was while these peak numbers may come at 4,000 rpms, that does not mean there is no torque in the bottom end.

    Oh I agree. Assuming 260 torque and 90% peak at 2,000 rpm, that's 234 ft-lb at 2,000 rpm which isn't bad. As long as the RL isn't too heavy, it'll probably be enough.
Sign In or Register to comment.