Last post on Nov 05, 2013 at 12:08 PM
You are in the Acura RL
What is this discussion about?
Acura RL, Sedan
#2893 of 7386 Re: robertsmx [saugatak #1444]
Jun 23, 2004 (6:29 am)
Honda's engines are impressive, but not in regards to developing low end torque.
Well, I don’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 “range”. If RL’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’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’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 “enough” HP/liter out of its engines.
I'm wondering how much VVT actually helps low-end torque?
I’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’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’t be talking about compromising one for the other. And that’s where variable timing would come into play.
#2894 of 7386 Re: The VTEC Myth [varmint #1452]
Jun 23, 2004 (6:31 am)
Jun 23, 2004 (7:04 am)
"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?
#2896 of 7386 Re: Varmint #1439 [saugatak #1450]
Jun 23, 2004 (8:38 am)
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’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’re now “talking” 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’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 “really good and efficient design” 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.
#2897 of 7386 Hear that sound. . .whoooooshhhh!
Jun 23, 2004 (9:27 am)
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?
Jun 23, 2004 (9:31 am)
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.
Jun 23, 2004 (10:28 am)
IMO, people will indeed care about the HP number from Acrua -- nearly $50K? You bet!
Jun 23, 2004 (11:18 am)
Another technical trick that Honda has developed and is offering in a model in Japan is its own version of DI, dubbed “I-VTEC-I”. But, will it happen with the V6? We shall see. But it is probably more about improving fuel economy than anything else.
Jun 23, 2004 (11:27 am)
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.
#2902 of 7386 Re: [saugatak #1461]
Jun 23, 2004 (11:49 am)
Have you figured out yet, how much low end grunt is “needed”?