6mtV6

Are there any reviews on the TL's engine that I can read? I know Ward's has a review on the Accord's V6, which is very similar to the TL's.

Legend2TL

There have been many great posts here detailing the differences between SOHC and DOHC heads. One compromise that was missed is very important, sparkplug location. With the slightly offset center cam location of the current Honda/Acura SOHC heads, the sparkplug is postioned more toward the exhaust valves, not the optimum location but Honda engineers have made it work there effectively for power and emissions. The common cam is positioned closer to the intake valves. Both intake and exhaust valves use roller rocker arms to actuate the valves. On most DOHC engines the sparkplug is located directly in the center of the cylinder head, the best location.

As many people have already posted it's all about compromise mostly involving cost and requirements, A DOHC setup allows individual phasing of the cams (variable valve timing typically just adjust the intake cam pahsing). The SOHC setup is typically smaller and allows a smaller overall engine package.

FWIW, Mercedes has gone back to DOHC 4 valve heads on the majority of their engines, they went to SOHC 3 valve (2 intake, 1 exhaust) 2 spark plug heads in the mid/late 90's on their modular engine design. Interesting was the dual plugs had two ignition coils to fire the sparkplugs independently, allowing non-symetrical flame propagation in the head. Yes a Mercedes V12 back then has 24 ingition coils!

MB's engine designer said in some interview back then that the 3 valve head was optimal for the typical MB driver since it gave bettter low end torque than the previous 4 valve design and matched the typical MB owner driving charactoristics. A couple years ago I read another article stated that thye've gon back to 4 valve heads for the power wars that seem to be in vogue with the Euro automakers.

Yet another FWIW, Honda's jump to 4 valve heads wasn't from 2 valve, they went to 3 valve first (2 intake and 1 exhaust) in the early 80's. Some were actually 4 valve (3 big intake, 1 CVCC intake, and 1 big exhaust). These were great engines, compact, light, but had excellent power band and torque. I owned a 86 Prelude Si and it was a great engine.

SouthernBoy

To ONAGER;

Excellent analysis and writeup, my friend. I commend you. But I wish to add two things.

The Ford 302 cubic inch (5.0 liter) pushrod engine as used in the former Mustangs weighted 537 pounds. I know, I had on in my 1988 Mustang LX. Their newer series of 281 cubic inch V8's (4.6) used in the Mustangs are quite a bit lighter than this when all aluminum, though they've gone back to iron blocks with aluminum heads from what I understand.

Anyway, fine job.

ONAGER

true when the engine is all aluminum but the standard 4.6 gt sohc motor had an iron block, cobras got the aluminum ones. the weights i quoted were taken from muscle mustangs and fast fords in an article comparing the 5.0 to the 4.6. this article is older when the 4.6 couldnt hold it own to the 5.0. when ford fans wanted a return of the 5.0, circa 96 or so

ONAGER

http://www.mbusa.com/brand/index.jsp

check this website MB engines are all still primarily SOHC with 3 valves per engine 2 intake 1 exaust. the only engines that are not are their 4 cylinders. these are DOHC 4 valve per cylinders..... every other v-6, v-8, or v-12 all have sohc. even their 604 hp 738lb tq v-12 amg sl65 is a SOHC 36 valve engine.

so no, MB has not moved back to DOHC, and considering their success i dont for see them going back at least any time soon...

and they also still have and use 2 spark plug per cylinder technology

AND HERE PEOPLE COMPLAIN ABOUT OUR $35,000 DOLLAR SEDAN ENGINE NOT BEING ADVANCED, WHEN A $180,000 MB GETS ONE LESS VALVE PER CYLINDER!!!! THE SHAME

Now back to hondas (because who wants a MB anyway? ) the spark plug may be slightly closer to the exaust valves (this i still dont know if true as i have no first hand experiance with a sohc honda head. ) but what i do know from my research and the lovely cut away drawing from above, is that the spark plug is still in the middle of the combustion camber between all four valves. flame travel length/path is why this is so important, you want all the fuel to burn as quickly and as evenly as possible. but considering they offset the cam, why would they offset the plug location? they freed up the room by moving the cam.... the only issue that i can see is that the spark plug is canted to ride along at around the angle of the exaust valves, and this wouldnt effect flame travel or length in anyway..... any one have removed heads and a micrometer?

onager--

Legend2TL

http://www.caranddriver.com/article....&page_number=4

Check out the new SLK350 engine. This is the first in the series of MB modular engines. It is 4 valve per cylinder with DOHC V6. Also notice that both the intake and exhaust cams are variable (and probably not the same timing). Retooling a car manufacturers production engine line cost billions of dollars or euro's so it does not happen in a year. The remainder of this new generation of engines will be phased in over the next several years. And they are also moving away from 2 spark plugs per cylinder. They always stayed with 4 valve head for their 4 cylinders.

There are some pictures of the Honda/Acura V6 heads in Japanese tuner magazines and the plugs are offset slightly. I recall reading a article stated it also and a very slight flame propagation performance reduction. This is offset by the fact that the cam timing is slightly different for the two valves which induces more swirl in the combustion chamber.

Legend2TL

In terms of the spark plug location, the cam is located to the inside of the intake cam. Due to the size of the components and ability to remove the sparkplug without removing the cylinder head cover the spark plug is angled slightly toward the valves. It terms of sparkplug location and it's overall effect, engine designers spend countless hours analyzing it. The issues are not simple enough for novices like us to look at and understand to say it shouldn't have much effect. I've read some SAE journals once in a while and they are very different reading than automagazines, I don't even get half the acornyms.

mrsteve

iTrader: (1)

It's far from that simple. The motor in the NSX is VERY different than the motor in the TL. It would be a very simple and popular swap if the NSX motor would fit in our cars... hell, even if the cylinder heads would fit the J32A2, but they don't.

Legend2TL

This was out of Autoweek, it appears that the future MB engines will also use direct injection.

"Power will come from a new line-up of modular V6 and V8 gasoline engines. Among the more significant developments is a switch from three-valve to four-valve cylinder heads and the adoption of Mercedes' Twin Pulse direct-injection technology as seen on the carmaker's four-cylinder powerplants. Allowing finer metering of the fuel supply than today's conventional sequential-injection engines, it contributes to a more efficient combustion process, with moderate power increases, lower fuel consumption and reduced emissions. Secrecy surrounds the exact makeup of the new S-Class engine lineup, though AutoWeek sources say there will be a base 3.5-liter 272-hp V6, a 4.7-liter 325-hp V8 and a 5.5-liter 410-hp V8. Topping the lineup will be a 5.5-liter 500-hp twin-turbo-charged V12."

Bitium

Honda is also using direct ignition. Talk about the i-CTDi accord (TSX) disel (turbocharged) that produces 140hp and 340 torque while increasing fuel economy to over 60mpg

http://world.honda.com/HDTV/news/2003-4030226_1a/

then there is the awesome Honda DOCH i-vtec I with 65:1 ratio. You could see the cams work

http://world.honda.com/HDTV/news/2003-4031127a/

Don't forget the best DOHC V8 in the world: I hope it makes it to prodution cars some day, maybe the next NSX.

Honda HI4R Engine

Normally aspirated, fuel-injected, aluminum alloy cylinder block V-8
Displacement 3.5 liters (213.6 cubic inches) Valve Train Dual overhead camshaft, four valves per cylinder
Crankshaft Alloy steel, five main bearing caps
Pistons Forged aluminum alloy
Connecting Rods Machined alloy steel
Engine Management Motorola
Ignition System CDI
Lubrication Dry sump
Cooling Single water pump

Ken1997TL

The NSX motor (being a C block) wont even trade heads or ANY other parts with other C32 engines, not to mention a J series which is 60 degrees. The C block is 90 degrees (like most V-8's are)

aw1

imo, i really would like to have a TL with DOHC which means more power/torque...but im not complaining since this SOHC TL makes 270 hp... other manufacturers have bigger engines with DOHC and makes about the same or even less...

mrsteve

iTrader: (1)

The guy I quoted stated J32 + DOHC = NSX. Implying that the DOHC heads from the NSX motor was the only difference between the two motors.

Legend2TL

Cool, I didn't realize Honda was that far along in their direct injection gasoline engine developement. Thought only BMW and MB have or were bringing out engines with direct injection.

Bitium

No problem. did you see the videos? they are pretty cool.

Legend2TL

Yeah, pretty neat.

You gotta wonder how many CGI artists there are out there who specilize in creating engine video's showing internal workings of engines wheither for car companies, oil manufacturers, ...

PandaBear

You guys forgot one important detail: do you want the power and torque to be in low end or high end.

The more air you get, the higher the power band location. You see all the low end tuned engine and you will realize they have the common points:

longer runner intake/exhaust
smaller valve diameter
less valves

This is a V6 for a luxury car and you don't expect people to rev it up to 8000rpm like a modified integra. Most people don't want this car to sacrifice bottom end for top end power. Thus you see SOHC and the car is tuned for low end torque. Same theory goes for Odyssey engine, why the hell you want a minivan to go 8000rpm instead of staying at 2000-3000?

Vtec try to address this, I am sure the way this engine is tuned is to use the SOHC alone to satisfy the low end and combine with Vtec to satisfy the mid range. If you have DOHC then you will get good mid and high end and sacrifice low end, not what you slow old folks would want in a luxury sedan, right?

Some will say you can tune a DOHC to do low end, but if it isn't as reliable as SOHC and is overkill, why bother?

avs007

That's not true at all.

The Odyssey has:
255hp @ 5750 rpm
250 pound/ft torque @ 5000 rpm (or 4500rpm if you have EX)

Infiniti FX35 3.5 DOHC V6 has
280hp @ 6200 rpm
270 pound/ft torque @ 4800 rpm

So it looks like the FX's DOHC engine has better low end AND top-end, than the SOHC 3.5 in the odyssey. Or if you wanted to be a luxury purist, the Acura MDX has 265 hp and 253 pound ft of torque.

PandaBear

Of course, there are other things that can determine why one engine has more power than the other at a certain rpm. In your example you can clearly see that the peak power of FX35 is at 6200rpm vs. 5750rpm of Odyssey. Torque is 4800rpm on FX35 vs 4500rpm on Odyssey EX. It is clearly that the Odyssey's power come earlier, and the peak is lower.

However, what people in general refer to low end is BELOW 3000rpm no engine in this class will tell you 4500rpm is low end. I don't have access to the Dyno chart but I am fairly confident (not willing to bet my $ on but have seen many in this case) that the Honda SOHC will have a lower rpm power band than a "compariable" DOHC design. By comparible I mean same volume, same parasitic lost, and similar fuel economy (this is very important as one can easily tune an engine for economy vs power).

Honda in general has the best engine technology in the world and their engineers are not stupid. They won't just slap a bunch of parts together without optimization to push the time to market, expecially in the TL. If you already find out what kind of power band you want by running simulations, the kind of volume, the kind of emission, etc, you will find out what kind of intake and exhaust flow volume and velocity, then you know what kind of valves and diameter you needed.

With this you decide whether you want DOHC or SOHC, and what kind of vtec profile you want. Then everything will make sense.

Repecat

I don't think having DOHC precludes higher torque at a lower rpm level. My last car had a DOHC V6 of 3.0 liters which developed 200 BHP @ 5000 rpm. More importantly, it developed 229 lb-ft of torque @ 2100 rpm and up. That car was a blast to drive on freeway on-ramps from 30 to 75 mph. The TL is also fun, but by the time I am getting into the peak torque, I am far exceeding the legal limit. Just some thoughts..........

Ken1997TL

The NSX's motor is a DOHC and for its displacement it makes a good amount of torque not only downlow but throughout the entire powerband. Its a VERY flexible motor.

Repecat

The NSX torque peak is over 5000 rpm. Do you know how low at least 90% of that torque is developed?

Ken1997TL

About 3000 rpms.

In fact, 90% of the torque curve is available from 3000 rpms to 7200 rpms.

At 2000 rpms, 85% is available

Repecat

That's still pretty good. I be it's a blast to drive.

Ken1997TL

It sure is. I've driven the older ones that had a 5 speed manual.. absolute joy to drive. Reasonably comfortable too, especially for an exotic. I imagine the 6 speeds with an extra 20 hp and .2 liters of displacement are even better

Legend2TL

One factor that is also very important to a engines's performance is the piston bore, crankrod stroke and the ratio of those two in the engine.

Most racing engines are very over-square bore/stroke ratios, meaning the bore diameter is greater than their stroke length. Typically this allows higher RPM since the piston velocity is lower. They typically have better top end power and less low-end torque.

A square motor is when the bore and stroke are identical and under-square is when the bore is less than the stroke.

Long stroke undersquare motors are typically better are at low end torque (all other factors being the same) and suffer from lower top-end power. Compare the bore/stroke ratio's of a diesel truck engine to a Formula One racing engine and it's pretty.

This is yet another area in engine design where the designers have to make a compromise. Although it also has little to do with SOHC versus DOHC.

F23A4

You all make some valid points but, true to the original poster is the fact that SOHC motors simply less costly than their DOHC counterparts.

I havent seen any evidence that DOHC setup lose any low-end to their SOHC counterparts. If anything, the DOHC maintains SOHC level low-end but has the virtue of added mid-range/high-end.

Thinking aloud: The comparison between the VQ35DE (FX35) and J35 (05 Odyssey) is a very interesting one (if not touch and go). The VQ35DE is a DOHC 24v V6 with CVTC on the intake cam but no variation on lift or duration. The Odyssey's J35 is an SOHC 24v V6 with a VTC (the 'i' in iVTEC) that adjusts valve lift and duration on the intake valves as well as continuous valve phasing.

Where Nissan's DOHC/CVTC setup is definitely biased towards low end performance with high end abilities, Honda did pretty well with their SOHC/VTC setup in the Odyssey so that it'll gain some high end prowess (though not DOHC) but have strong low end.

IMHO, the benefits of either setup probably have more to do with ECU tuning and bottom end setup (like Legend2TL posted) than the head setup.

Good discussion, nonetheless.

AcuraVic

Great Discussion!! Although I have nothing to add, I have read every post.
Who needs 'Car and Driver', 'Road and Track', and 'Motortrend' when you have 'Acurazine'

cpurick

My take -- what the heck, everybody else is just guessing:

DOHC offers two advantages:
1. Lighter valvetrain components (when accompanied by four valves per cylinder).
2. Valve timing can be regulated by advancing or retarding camshaft rotation. Since intake and exhaust benefit from different offsets, this is only possible when separate cams are responsible for intake and exhaust.

Honda uses SOHC because:
1. Four valves per cylinder deliver advantage #1.
2. VTEC manages the cam profiles instead of a variable valve timing system.

Both VTEC and variable valve timing schemes address the same high-speed inefficiencies. You can combine both technologies for maximum gains, but there's a diminishing return with each additional solution. Each approach may be worth 25HP, for example, but in combination they might only be worth 30HP total. Apparently Honda prefers VTEC in applications that use only one technology.

GunnmeTaLCURA04

ok so lets say our TL's 3rd Gens came with DOHC.. how many ponies.. HPs? or torque... alot more of not really? just a guesstimate..???????

ONAGER

although they both address the same situation vtec is a much more flexable (powerful) solution.... vtec allows two seperate and completly different cam profiles to be used within an engine. a low speed cam profile, and a high speed (racing cam profile). it literally will switch between the 2 while driving. cams have by far the greatest impact on a na car performance because they alone change almost everthing about the engine (powerband, emissions, torque curve) emissions in this case being probably the most important (because of the laws in place, and standars manufacturers have to meet). vtec allows a low speed profile to maximize torque down low, produce good emmisions, and overall driveability (idle quality). then when rpm warrents the change, a change to a high rpm (racing) profile. this profile is heavily biased towards high rpm horse power, with fewer if any consestions towards emissions or low rpm torque. its like having two different tuned motors under the hood.... s2000 is the example below vtec changeover the car is smooth, drivable, dare i say docile? above that the cars character changes completly. it becomes a fire breathing moster of a 2.0l, it rips to redline at an unbelivable rate. it becomes the worlds highest hp/L NA production car. when you add variable cam timing to the mix it can only get better. however this is a very complex system when you add all this up BMW has a similar system known as vanos.

with nissans setup they dont have variable lift only timing control.... so the same cam profile at low rpm is the same one at high rpm. they have to make consessions when it comes to emissions and idle quality. (anybody remember an old cammed muscle car? and the distinctive "lope" as it fought to stay idling, some went as far to raise the idle if the cam got to wild) nissan cant get to wild as emissions will suffer and so will low speed drivability. they have to choose an all around cam.... one that will be ok down low and ok up high. you dont want to kill the top end to much with a low rpm biased cam. what there system does allow is the variable phasing of the cam to put the cam they have chosen in the best position for the rpm the engine is at. this helps improve (fatten) the power curve improve drivabilty and emissions. however not anywhere near the extent of what vtec is capable of providing

ONAGER

with no other changes to the engine? probably none at all. unless you change the intake manifold, add variable cam timing, larger valve size, different cam profile or any other variables you will see little to no change.... if all other factors are equal you will see little to no difference. dohc has the ABILITY to be tuned to a greater extent.

F23A4

Correct. That's how Nissan's CVTC works.

Spazz

This has got to be one best threads i have every read hands down

Ken1997TL

Maybe. But Nissan's engines sacrifices some refinement for a bit more torque. I'm willing to bet the J35 has a pretty broad torque curve that is nearly as strong.

Not to mention, lets keep in mind that Honda seems to be underrating their J and K series engines.

Roadmaster

I believe that everyone is missing one big reason why the J-series engines are SOHC motorts; size and space. I've pulled a handful of B-series engines apart and even a B18C at 1.8 liters has a huge head. I honestly don't believe that a DOHC VTEC J-series motor would fit in the current configurations of the cars. The heads would be huge.

Now, some will ask - well Nissan has DOHC V6's, likewise Toyota, Porsche, Hell even GM. However, all of those head designs are much different in size and configuration. In fact, if you have ever looked at a Nissan 300's VE30 motor, the heads are huge, there is no room in the engine bay. However, the Maxima's VQ30 (also DOHC) has a much smaller head design.

Also, the statement about DOHC being less reliable than SOHC; where is your proof? I have yet to see why H22's, B16's, B18's, K20's, even NSX C30's and 32's would be any less reliable than a SOHC D16 or J-series.

Likewise, the statement about DOHC motors being lacking in lowend torque where SOHC motors are better for low end torque is misleading as well. Your torque output has nothing to do with whether or not you are using two cams per bank or not; it has to do with the lift and duration of your cam profiles as well as the bore and stroke of the motor.

You could easily tune a DOHC VTEC cam to produce tons of low end torque below say 4,900 and then cut the high lift cam to produce screaming top end power. The problem is the change over between low and high cam profiles would be much more noticable and that is not something Honda wants.

In the end, you certainly can't go wrong with the J-series being SOHC, would I like variable timing on the exhaust side? Certainly, but I don't have it and I will just stick with what I have.

Dustin

SouthernBoy

Very good, people.

"Cammers" from the earlier "muscle cars" ( I much prefer the term supercars) always referred to overhead cam engines of which there were almost none on the street.

As for Nissan's VQ series of engines, I can only speak of the VQ35 in the 2002 Altima. This car was starving for intake freedom. If you installed a decent after-market intake, you would immediately notice that the engine had two distinct power hits. The majr one occurred at 4000 RPM when their "VTEC" cut in. The second one came on at around 4200-4300 RPM and was the secondary intake runners opening up.

What this means as far as the TL is this. If you keep an Altima (or Maxima) stock, the felt in-the-butt acceleration is a little more pronounced with the TL. Apparently, Acura (Honda?) has done a better job of controlling power delivery with the TL engine than has Nissan.

Jirzlee

iTrader: (1)

VTEC cut in at 4000rpm? I thought the engine had variable cam timing, not variable lift/duration that would come from multiple cam profiles like that from a GSR B18 4cyl. If its just cam angle that it adjusts there shouldn't be any pronounced steps in the power delivery.

Ken1997TL

I believe there is no variable valve lift, just timing.

avs007

Some of nissan's 4 cylinder engines have Variable Valve lift. All the engines that have the "VE" moniker, have Variable Valve Lift Control. Most of those engines were JDM only though. The VQ35, is VQ35DE, so as previously pointed out, it has continuously variable valve timing, but no variable lift.