JerryG

To the engine gurus:

From an engineering design standpoint, it seems like many of today's "average" and HiPerf engines are DOHC. What criteria prompted the 3.2 TL engine to be designed with SOHC? Other than lower cost? this is a relatively high-end car, after all. Glancing through today's car section, even the Scion is listed as DOHC, for pete's sake. An obvious conclusion is that two is not necessarily better than one.

UglyPsycho

If the TL came with a DOHC, it will take out the competition.

SouthernBoy

"An obvious conclusion is that two is not necessarily better than one".

Our TLs already have two cams. You mean 4 vs 2. Anyway, I've heard that Honda's engineering believes that their SOHC engines operate better with their VTEC systems.

Can anyone confirm this??

Xpditor

Neighbor: If this were true, why do they put DOHC on the NSX?

Save your Confederate money. The South will rise again!

-XP

JerryG

Yes, I meant two per bank vs one.

rets

We have discussed this topic millions of times, SEARCH will bring up some threads if you'd like to get further info...


Simple words: Advantages to having a DOHC engine over a SOHC is that the engine has twice as many intake and exhaust valves as a SOHC motor. This makes the engine run cooler and more smoothly, quietly, and efficiently. But the downfall is that DOHC engines cost more for repairs.

2K2SilverTL-S

Simple answer:

J32+DOHC= NSX

Repecat

Remember, the DOHC NSX and the SOHC TL each have 4 valves per cylinder. The cams actuating the valves in the SOHC are more complex, but in the V6 there are only 2 and not 4 camshafts.

JerryG

Millions of times? Interesting, if you do SEARCH on SOHC you get 24 hits - none of which have SOHC in the Subject. Yes, there are some snippets hidden here and there, but you exagerate.

Also, someone else has pointed out that your answer RE valve count (in the case of TL) is actually incorrect?

Also, if a result is more efficiency, why do many other engines with more of an eye toward economy use DOHC?

Still haven't heard a good plausible answer.

JCastag

EASY!!!

Its cheaper to design, build, assemble!!


Thats it.

F23A4

It's really that simple.

Bitium

NO NO... VTEC is better on DOCH which is called i-vtec. i-vtec engines are DOCH. SOCH one cam shaft controls both intake and exhaust valve, it has nothing to do with how many. DOCH (dual) cam shaft uses on cam for each the exhaust valves and intake valves. Dissavantages of DOCH like other people mention is cost, complexity, and TAKES more SPACE since they are two cams instead of one.

Since i-vtec controls timing/duration on both intake/exhasut valves it shoud be easier on a design stanpoint to use DOCH, at least I see to believe so.

Bitium

It dosn't have twice as many valves, it just have 2 cams instead of one. You still have the same amount of valves, but the intake valves are control by one cam and the exhaust valves are control by another.

KT88

Bitium stated it perfectly. Although I woul add, as some have surmised, you can have a cam drive one valve or two at the same time, as in the case of say four valves per cylinder driven by two camshafts.

DOHC - the reason for dual cams is that the valves on a single overhead cam are usually both on the same side of the cylinder head, this makes for a less than optimim combustion chamber shape. Dual cams allow the valves to be positioned 90 degrees opposite each other in a hemispherical combustion chamber with the spark plug placed between them directly in the center of the "hemisphere", which is potentially a more efficent, and hence more powerful, engine for a given size. Yes, there are many more "Hemis" out there than Dodge would have us believe. It's just one of many engine design techinques to squeeze more out of less. The Italians have been doing it for years.

There are engines that have a single overhead cam and also a 90 degree valve position, but then rocker arms are required to reach from the camshaft over to actuate the valve. Positioning the cam directly over the valve eliminates a lot of moving parts

JerryG

Possibly so, but the TL is an upmarket car, not downmarket.

There are many cars costing half of the TL that use DOHC engines. If cost was a primary advantage, you would think they would use SOHC as well. Apparently, the advantage outweighs the cost in these lower displacement engines.

.

Road Rage

There are some advantages to SOHC as implemented by Honda, and Mercedes. DOHC puts some practical limitations on intake valve size, intake charge dynamics, swirl, and ands mechanical complexity. I would surmise its parasitic losses are higher as well in many cases. Given the power, emmisions perf, and smoothness Honda gets out of SOHC, there is no overriding driver to go DOHC just because many others do. VTEC was an engineering breakthrough that obviated the "necessity".

The NSX (and S2000 for that matter - I have owned both) is designed for hi-RPM use, and there the extra breathing and lower reciprocating mass of the "smaller" parts of a DOHC make a lot of sense - plus who would spend $90k for "only" a SOHC?

SouthernBoy

To Bitium;

It's SOHC and DOHC, not SOCH and DOCH. Easy typing mistake, I'm sure.


To KT88;

You wrote, "the reason for dual cams is that the valves on a single overhead cam are usually both on the same side of the cylinder head".

This is almost never the case with overhead cam engines, but IS very common with in-the-block-cam engines (the nearly single exception being the famed Chrysler Hemi engine design).

Also with modern overhead cam engines, the valves are usually not 90 degrees apart, but more like 60 degrees. And most modern overhead cam engines, be they SOHC or DOHC, do not have hemispherical combustion chambers since most are 4-valve per cylinder engines. With 4-valves per cylinder, a hemispherical head design would not only be extremely expensive, but incredibly complex. What they are is called a pent roof combustion chamber.. and this is the design of our TL heads, which are not hemis at all. What this means is that there are very few hemi head engines in production.

"There are engines that have a single overhead cam and also a 90 degree valve position, but then rocker arms are required to reach from the camshaft over to actuate the valve"

Except for the fact that out TL engines don't have valves angled at 90 degrees from one another, this statement describes our engines' valve operation. We do have roller rocker arms which open and close the valves by riding on the cam lobes.

Not a flame or such.. just a little clearing the air.

Bitium

Yeah of course. Single Over Head Cam; Dual Over Head Cam. sorry about that.

Xpditor

You took the words right out of my mouth, Bubba.

The previous correction that said DOHC doesn't have more valves is correct. It doesn't (necessarily). The main advantage as stated by both Southernboy and Road Rage is LESS reciprocating mass because you don't need rocker arms. That allows more power at higher RPMs. Another advantage is that you can have V-tech on both the intake and exhaust. We only have it on the intake.

Also right on is the explanation of hemispherical combustion chambers. They were a breakthrough at a time when most cars had cam-in-block push rods and inefficient flow of the fuel charge. Some cars, like flat heads, even had the valves in the block.

Hemis are still pushrod engines but, then again, so are Corvettes. They don't get anywhere near the HP per cubic inch that out Acura engines get. If they did, they would be outrageous road burning machines. Imagine 5.7 litres putting out about 481 HP in the same naturally aspirated state as our TL?

Today, "Hemi" is a marketing ploy. The concept is actually a technical backward step when compared with current state-of-the-art valve technology. (IMO)

SouthernBoy

A few manufacturers have taken a further, more advanced approach to DOHC engine design. The Ford SVT Contour (I had a 2000 version) had a 152 cubic inch V6 DOHC with hollow cams and beehive valve springs. Hollow cams have serveral advantages. The obvious is that they're much lighter. But they also run cooler as well.


To Xpditor;

Some of the earlier American V8's got some huge horsepower-per-cubic-inch numbers. The L88 427 Chevy was rated at 430 HP but was actually pushing 580 HP. And the ZL-1 managed 610 actual street ponies. Granted, these were rare, especially the ZL-1, but this has happened before. And the soon to be released new Z06 will be rated at 500 HP.. we don't know yet what engine will reside under the Z06's hood, though.

Road Rage

I really don't care about power with less cubic inches, provided the bigger engines do not compromise weight, reliability, emissions, or fuel economy. The fact that the LS6 Corvette engine is large does not make it less formidable a performer, and in fact quite the contrary. Comparable Euro cars witrh a similar performance profile get a fraction of the Chevy's fuel economy. The new Z06 will be simply dazzling in that regard, at a svelte 7.0 liters.

While I admire and love the 2.2L "racing" engine in my S2000, and its lightweight and mid-engine config figure prominently in its performance capabilities, let's also consider that it weighs only 200 pounds less than the "huge" Corvette. The SB Chevy is nearly 50 years old, but has the greatest racing history of any engine design, be it OHV, SOHC, or DOHC. The Euros who once laughed at its "primitive" technology now laugh as it blasts past them. The C5R's performance in the ALMS is proof positive that NO given engine configuration has it all over another.

rets

JerryG, you could bite me anytime you want. "Millions" means a lot. Do you ever say "wait a minute" then spend more than 60 seconds? (Plus, you're right, SEARCH cannot get all threads out of database)

My theory seems not to put the up-to-date technology into modern OHC engine design. I'm sorry. I just simply describe what's difference btwn "S" vs "D" over this OHC engine.


I did say DOHC is more efficiency, didn't I? Check again, please.

Repecat

Valve configurations are kind of a fun topic. Do any of you remember the rather short-lived Willys "F" head engine in the Willys Aero? It had the intake valve in the head and the exhaust valve in the block. I think they were both actuated from the same camshaft in the block. Odd arrangement.

kosh2258

The other issue is packaging. DOHC heads, by necessity, are wider than a SOHC head since that extra cam requires more space. So to keep the overall width of an engine down, SOHC heads have an advantage. And the narrowest engines are generally OHV engines that use pushrods to run the valves.

OHV is compact, but it also pretty much sacrfices the ability to do VTEC type stuff like variable valve timing and so on - part of how these smaller displacement engines squeeze more torque and hp out for their size. About all OHV can do effectively is cylinder deactivation which is done by depressurizing the valve lifters so they can't open the valve.

The issues of cost and increased complexity of DOHC have been covered by others in the thread.

Repecat

I think the Aero was produced about 1953, give or take a year or two. My memory is failing.

F23A4

FYI: The new Odyssey has an SOHC iVTEC motor.

SouthernBoy

Well said, Road Rage. I admire a lot of different things in and about cars and their engineering. At various times, a host of companies have had engine designs that were excellent for their times. And a few have managed to span numerous generations of design.
Such is the small block Chevy and its copies (the Ford small block comes to mind here as well, but the Chevy is still King). The small block Chevy does just about everything right and is like the Everready battery.. it keeps going and going and going.

But I am consistently surprised, amazed, and delighted with the power and performance of the small V6 which resides in our TLs. Folks, this is NOT a large or even a medium sized 6-cylinder engine (although by today's standards, that could be argued). 196 cubic inches is small.. especially when one considers that it hauls around a 3500 pound sedan.. and does so very conpetently. Still, I would love to see Honda punch this engine out to 220 cubic inches for the TL for a bit of a power increase. That would really ice the cake.


So Road Rage. You say the new Z06 will sport a "7.0 liter" engine (God, I hate the term liters here in America). Is this just a big inch small block or a rebirth of the famed semi-hemi 427 Chevy (also made in 396 and 454 configurations for those not fully familar with this baby)? Or is Chevy introducing a completely new engine for the Z06?

MR1

Back to SOHC vs DOHC. I think I missed something. I know Honda has produced both for the same car recently & perhaps now.

My 1993 DelSol Si has a SOHC Intake only Vtec, 125 HP
In 1994 my car was also available with a DOHC w/ Intake & exhaust Vtec, 160 HP

Similar options were available for some Intergas. These were all small 4 cylinder inline engines. They share with our motor a certain relative lack of low end power.

Citing the above, I don't see how it's a cost or space consideration only. Looks to me like more power is available from our engine in our car, DOHC and or (full) Vtec. Please enlighten me.

avs007

Not necessarily. If I remember correcty, GM is introducing a 3.9 litre pushrod V6, which actually has 3 valves per cylinder, and variable valve timing.

EleVatE

It seems to me in my newbie way of thinking that if you theortetically had a DOHC that had an intake that was Vtec and an Exhaust that wasn't, you would get less power than if both were controlled by Vtec. And it seems to me that that is sorta what happens in a SOHC Vtec... the Exhaust, being controlled by the same Cam that controls intake, misses because there is only the SOHC to control both intake and exhaust. So a question I have is how much power can you actually lose by not having a Cam controlling the intake and exhaust? It doens't seem like it could be that much.

I dunno maybe I am completly missing it here but if thats the case... then I dont see why the TL wouldn't have DOHC.... which no one has answered.

To me, saying 'cheaper, easier to fix' is not an answer, because people who buy the TL aren't looking for a cheaper more economical (relatively) option, they want performance. And even if it was the 'cheaper easier' route, there are cheap cars that use DOHC so that doesn't make any sense.

Now I love TLs and will be looking at getting one next year, but the SOHC has been something that I questioned for a while.

avs007

I'm going to go out on a limb, and say that maybe it's the packaging. I always thought Honda/Acura had quite the petite engine compartment. I think a DOHC head, would significantly increase the dimensions of the engine.

If you compare the TL to other FWD V6 cars that have DOHC heads, I think those other cars have "bigger" front ends. Like the Lexus ES330 for example. The front end looks kind of porky to me, compared to the TL.

Xpditor

OK. Let's focus on your question. Why doesn't Acura put DOHC in the TL?

Various posters have said that it is because of cost. There is truth in that. But not only in original cost of design and production, but the cost of space and weight and the cost of smoothness and economy.

Apparently, Honda (Acura) has determined what they believe to be the line of diminishing returns on valve operation. They have decided that vtech on the intake side can give them, say, 60% of the gains of a DOHC set up without the added weight, complexity, cost and size. For them to try in pull in the remaining 40% potential power is offset by the factors mentioned.

Also, this is not a purebred racing/performance vehicle. It is a sporty luxury sedan for carrying 5 people in comfort and quiet while returning good gas mileage. That always calls for compromises in the engine bay.

Balancing the needs of such a car with high performance expectations, limits what you want to do with the engine. You still want it to idle smoothly at a stop light.

So, IMO, the answer to your question is: It's a compromise.

Bitium

You are right. Is the newest honda V6 in the states. It was realeased on the honda inspired over a year ago. I knew, but sorry I did not recall it. But yes It is SOHC i-vtec V6 with VCM. When i-vtec first was introduced it was design to work with DOHC, I guess I just needed a litte reminder. Thanks.

Honda DOCH i-vtec (all inline 4 engines)
CRV
civic Si
Element
accord

Honda DOCH vtec
S2000

Honda/Acura DOCH i-vtec
TSX
RSX

SOHC i-vtec (V6)
Odessey


Here is the picture of the engine you brought up.

kosh2258

AVS007, you're referring to the LZ8 3900.

I've read the blurb, but it fails to explain how GM is doing "variable valve timing" off a single cam. It talks about DOD, a recently revived concept, and variable intake runners, which is nothing new in the world.

VTEC uses two different cam lobe profiles to get variable valve timing. I suppose you could do that with a single, OHV cam. But that would imply a pair of push rods and lifters working off seperate lobes and then some mechanism at the rocker arm level, probably a vee shaped rocker arm, and, using the DOD tech, depressurizing one of the lifters, to determine which push rod and lobe profile is activating the valve(s). To deactivate a cylinder would require DOD to depressurize both lifters to a valve.

The LZ8 has only two valves per cylinder according to the press release, for now anyway, with a 3 valve design following up. That should make for an interesting geometry lesson.

On the face of it, that seems like an awfully "busy" method to achieve what Honda does with SOHC. And the more cylinders you add, the busier it becomes. Yes, you do eliminate one cam, but you add back 1 push rod per cylinder and a lot of reciprocating motion into the mix.

I've always felt that a OHC is more physics friendly than pushrods for translating rotational motion into reciprocating motion (distance being the issue). But, that's just me.

fast-tl

you don't have tho these days. NSX resale's in the toilet!

F23A4

On a similar note, it'd be kinda cool if they went IMA with this motor (i.e. Accord Hybrid).

Ken1997TL

Why not DOHC?

Simple, because Honda CAN do quite a bit with a SOHC motor. Why add the complexity if its not needed? If you can get away with a reliable 300 hp motor with only 3.5 liters and SOHC...

Now.. just imagine if Honda decided to go with a DOHC V6 (like the NSX's C30 and C32B engines)

JerryG

However, the Nissan 3.5L VQ is DOHC and if I'm not mistaken uses variable valve timing. It's also used in FWD models eg Maxima (also, of course, in the RWD G35's). I've not noticed a rough idle in those models and they have noticeably more low-end torque (which may not necessarily be a good thing with FWD).

I also wondered if the physical space considerations of the engine bay played an important factor. However, the TL doesn't strike me as smaller than a Maxima, for example, but that kind of thing is hard to eyeball.

Ken1997TL

Nissan engines generally are somewhat less refined, however they DO make a lot of torque for their size. Its all about trade offs. Refinement, emissions, cost and power.

ONAGER

my key board is going to hate me tonight...

this quote best sums it up..... TRADE OFFS

where to begin.... down to the most elemental level its not cost efficient, our motor is part of the j series family (shared with the accord, odyssy, pilot, mdx, rl) when you share engineering cost over many cars its much more affordable to do so. many have mentioned nissan, there development cost are spread even wider with the vq family (350z, altima, maxima, pathfinder, g series sedan, murano, quest, fx 35). since the money has already spent, why not use it to power the whole line of vehicles (minor updates are far cheaper the designing a new engine from scratch) plus the basic j series motor has been around since the 90s. and NO DEVELOPMENT TIME NEEDED TO BRING IT TO MARKET

what we all have to look at is the big picture. what would honda get out of a new engine family? lets take a peak
1. the tl already meets ulev2 standards (thats really clean in engine talk).
2. it has 270hp and 238lb tq.
3. refinement that has been applauded by car magazines the world over.
4. cost has already been diluted thru time and other vehicles.
5. smaller overall engine size
6. lighter total weight (although rotational weight is probably up).

1. all manufacturers are having to meet tighter and tighter emissons standards, ulev2 is one of the best one right now, an honda has several vehicles that meet this mark. so the engine is clean. emissions killed mazdas former rotary engine (a complete and costly redesign has brought it back from the grave)

2. granted the nsx makes more hp (although with additional timing the tl would probably put down closer to 285 hp towards redline, only a chip will tell) but the nsx only makes 224lb tq. and it makes it a a higher rpm what does this mean to us? in a 3500lb sedan torque is king higher and wider the torque peak the better. with further development the j series motor is stout, look at the rl 300 hp, 260lb tq. at the level with most of these other "dohc motors"

3.the tl revs freely, is super smooth (but still not on level with the king of sixes, bmw, in smoothness) has nearly instant throttle response. from idle to redline the tl purrs. my moms old pathfinder or my friends current maxima couldnt say the same thing (although they are still very smooth). 1 test i recall, the editors of the magazine kept hitting the redline because of how smooth the tl reved up, i know that i have when im not careful.

4. again with cost, when an engine family is created its extremly expensive and time consuming.... it literally takes years to design and build a new series of motor. to assume that kind of cost its only smart to break the cost down as far as you can. which is why all manufactuers use engine familys over a wide variety of cars and sometimes even different companys. take for instance aston martin. there production 6.0L V12 was nothing more then 2 ford 3.0L V6s grafted together!!!! fords modular engines share many components to drive down cost. also development time kills, new engines have to be tested over and over and over again to meet production standards. and then tested again in all particular cars to makes sure no body interactions effect the way they perform. most of hondas development time has already been paid for... and there using that to there advantage

5. smaller engine packaging, simply put an ohv engine of similar displacment will be smaller then an sohc and the largest will be a dohc. this is really important as the cams are towards the top of the motor and any additional height up here spreads the v out even further and on both sides. when trying to design cars around crush zones, packaging issues and cosmetic issues, a smaller engine is a designers best friend

6. weight... who knows what a fully trimmed ford 5.0 weighs? 480lbs. now this is a lowly ohv engine with an IRON BLOCK. now who knows how much a ford 4.6 weighs fully trimmed? 600 lbs. thats a difference of 120 lbs!!!! same holds true for a sohc vs a dohc, sohc comes out lighter as there is significantly less material in the heads to hold those extra cams. and remeber all that weight is up high in the car.

as you can see the benifits of a dohc vs sohc, dont really pan out for the change. its just not economical and the benifits arent that great. corvettes pushrod engines are unbelivable in their power production, reliability, and fuel economy (at TWICE our cars displacment, it gets the same gas mileage!!!) and that design is supposed to be out dated.... yeah .... NO

now there are some additional benifits to a dohc design (and no valve count is not one of them) dohc main benifit is that the cams can be phased independantly of one another, ever hear of cam timing/degreeing? on a sohc car if you change the degree of the cam you change it for both the intake and exaust. vtec works without relation to the # of cams, oil pressure locks rocker arms together to follow a higher cam profile, weither its a sohc or a dohc principle is that same and will work on both. dohc motors will have the basic ability to flow more air. thats why this is the choice of high winding motors (honda s2000, ferrari f360). but that airflow comes at a price, poor slow speed performance, ever look at an s2000 power curve? its dead below 6000.