OverHead Valve vs. (Dual)OverHead Cam

I am a firm believer that both of these designs are just as good as each other. I am a bit of a throwback to the oldschool OHV however... tried and true, and impressive as ever.

Instead of beating random technical data and other mumbo-jumbo into your head, I'll just show you the numbers that matter.

GM's LS3 = 6.2 Liter V-8 436hp/428ft/lbs 18/28 mpg OHV

GM's LS7 = 7.0 L V-8 505/470 16/26 mpg OHV

Lambo Gallardo = 5.0 L V10 513/396 11/17 mpg DOHC

911 GT3 = 3.6L B-6 415/298 15/23 mpg DOHC

911 Turbo = 3.6L B-6 480/457 15/23 mpg Turbo DOHC

Ford GT500 5.4 V-8 S/C 500/480 15/21 Supercharged DOHC



The numbers don't lie. The OHV V8s use a larger displacement to get their higher power numbers, this is true. However, they still match or exceed the DOHC power numbers overall, and heres the kicker: Those low-tech huge V8s get the best gas mileage. Interesting huh?

If you want to get an idea of a new "high-tech" performance motor that matches the GM V8s mileage, heres the new BMW TT Inline 6....

BMW 335i = 3.0L I-6 300hp/300ft/lbs 20/29 mpg Twin-Turbo DOHC

So we finally have one that beats their MPG... it however uses 2 turbos, and still makes 136 less hp.



So, in conclusion, I've changed my mind. Go OHV!!! Go GM!!!


Feel free to argue with me =)

OHV and DOHC have completely different sorts of power bands. OHV tends to make more torque and power and be lighter (it's also externally much smaller), but DOHC makes power in the upper revs and has a flatter power curve. This isn't universal obviously but it's a good rule of thumb to keep.

A good example is the manual tranny 2200 LN2 in my Sunfire VS the 1.8 Toyota engine in the Corolla. The Corolla I drove was heavier, automatic and only made 15 hp more, yet it felt like it was making 50 more just because of the way it could find power throughout the powerband while the LN2 gets tired around 4000rpm.

DOHC, like a lot of modern engine innovations (Fuel Injection and computer controls are others) doesn't help make more power. It helps make smoother, more refined power. Because the engine can have an economy cam and a power cam. So when you're just putting about around town it's sipping fuel and when you nail the pedal it switches to the other cam, opens up and just goes like stink. OR you can have both cams geared towards power. One towards torque, the other towards high revving power.

I guess what I'm trying to say is that it doesn't matter if it's OHV or DOHC. Both are fine designs with advantages to both. OHV is simple, strong, torquey, cheap and can be set up to mimic almost anything a DOHC can do. It doesn't have the flexibility of the DOHC design but it doesn't matter if you know how to build it right.

And just so you'll know, the reason for a lot of those low MPG numbers you posted is that those engines aren't geared towards fuel efficiency because they're installed in low volume exotic supercars. The Corvette is built in higher numbers and sort of has to adhere to the CAFE laws. You'll also notice that most of the cars you posted have very similar city mileage and then extremely crap highway mileage. That's what big super sticky tires, massive downforce created by wings and bodykits, and a transmission that never lets the engine rev under 7000rpm will do to your fuel economy.

Actucally, Knox, you're referring to VVT. DOHC is a different beast altogether.


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[quote=Keeper of the Light™]Actucally, Knox, you're referring to VVT. DOHC is a different beast altogether.

Isn't it a DOHC too? Either way, it's an amazing engine.

Not always. I know the 3.9l used in the G6 is VVT, but is a OHV configuration. For the 00 vintage, the Civic EX used a VVT configuration (Known by most as "V-Tec") in a SOHC configuration.

The LD9 and the ecotec are both engines that are DOHC, but aren't VVT. They basically have the same cam profiles across the RPM range. The biggest difference between OHV and DOHC is that for OHV and SOHC, there's 1 cam per bank of cylinders (or possibly just 1 cam, for the OHV engines in a V configuration--correct me if i'm wrong on that), that controls both the intake and exhaust valves--and usually means that there's a single valve for intake and exhaust in each cylinder.

DOHC has 2 cams per cylinder bank, and because of this, has 2 valves for intake, and 2 valves for exhaust.

Generally, OHV get's beter low-end torque because with the single valve per cylinder for intake/exhaust, it can't suck in high volumes of air, and you have parasitic losses because of the pushrods and the like at higher RPM's. DOHC's can suck in more air and expell it, and because of their design, have a natural "pentroof" design that is very sim,ilar to the hemispherical combustion chamber. They tend to be better suited for more higher RPM applications. Compare the peak HP and Torque at RPM's for the 2200 and Ecos used in J's for an example of this.

Their drawback is their relative complexity.

Personally, i prefer DOHC. However, for an accurate comparison, you'd have to take a similar-archirtectured DOHC and OHV engines, at the same displacement, and compare their numbers.


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Fords have that kind of setup with the 4.6L DOHC, and roughly similar 5.0L OHV.




Transeat In Exemplum: Let this stand as the example.

A good comparison is Ford's various 2.3 engines. There's the OHV HSO and the OHC Lima and the DOHC Duratec.

Here's Ford HSC engine that was in the Tempo/Topaz and Taurus FWD cars:

1988 - 1991 2.3L HSO : MPFI
Bore: 3.68 in (93.5 mm) Stroke: 3.3 in (83.8 mm)
100 HP @ 4400 rpm
130lb-ft @ 2600 rpm
Compression ratio 9.0:1

Here's the specs for the Lima OHC engine in the Mustang/Ranger:

1987 - 1989 2.3L Lima: MPFI
Bore: 3.78 in (96.0 mm) Stroke: 3.13 in (79.5 mm)
88hp @ 4000 rpm
132lb-ft @ 2400 rpm
Compression ratio 9.5:1

See? Barely any serious difference between the two designs. It's not the OHV/OHC that makes the difference in power. It's the number of valves.

Just look at the Duratec DOHC to see what I mean. Notice how high it revs? That's the second cam letting the engine breathe more.

2005 and up 2.3 Duratec DOHC engine: SFI
Bore: 3.40 in (87.5mm) Stroke: 3.7in (94.0mm)
151 hp @ 5750 RPM
154 ft·lbf of torque @ 4250 rpm
Compression ratio 10:1

Personally I prefer than engine that revs because it's simply more fun to drive if you don't have much power.

im not gonna argue with u OHV V8 FTW!!!!

Knoxfire wrote:
And just so you'll know, the reason for a lot of those low MPG numbers you posted is that those engines aren't geared towards fuel efficiency because they're installed in low volume exotic supercars. The Corvette is built in higher numbers and sort of has to adhere to the CAFE laws.

I'd like to bolster his argument, then...

Honda S2000 = 2.0L 4 Cyl 240hp/153 ft·lb 18/24 mpg DOHC

Mitsubishi Eclipse = 3.8L V6 263hp 16/25 mpg SOHC

Nissan Altima = 3.5L, 6 cyl 270hp 19/27 mpg DOHC

GM's LS3 = 6.2 Liter V-8 436hp/428ft/lbs 18/28 mpg OHV

GM's LS7 = 7.0 L V-8 505/470 16/26 mpg OHV


Personally, I appreciate any engine that makes power and can make the car perform. Who cares what config it is?


---

AGuSTiN wrote:

Knoxfire wrote:
And just so you'll know, the reason for a lot of those low MPG numbers you posted is that those engines aren't geared towards fuel efficiency because they're installed in low volume exotic supercars. The Corvette is built in higher numbers and sort of has to adhere to the CAFE laws.

I'd like to bolster his argument, then...

Honda S2000 = 2.0L 4 Cyl 240hp/153 ft·lb 18/24 mpg DOHC

Mitsubishi Eclipse = 3.8L V6 263hp 16/25 mpg SOHC

Nissan Altima = 3.5L, 6 cyl 270hp 19/27 mpg DOHC

GM's LS3 = 6.2 Liter V-8 436hp/428ft/lbs 18/28 mpg OHV

GM's LS7 = 7.0 L V-8 505/470 16/26 mpg OHV


Personally, I appreciate any engine that makes power and can make the car perform. Who cares what config it is?

first of all, you don't know how to make a fair comparison......you are comparing a family car against a sports vehicle....WTF? of course the sport car will perform better

(directly from cars.com)
Nissan Altima = 3.5L, 6 cyl 270hp 19/27 mpg DOHC

Chevy Impala= 3.5L 6 cyl 211hp 21/31mpg OHV

Hyundai Sonata= 3.3 6 cyl 234hp 20/30 mpg DOHC

Saturn Aura= 3.5 6 cyl 224hp 20/29 mpg OHV


now what cars has more power???

PWNED!!!

Travis C wrote:

first of all, you don't know how to make a fair comparison......you are comparing a family car against a sports vehicle....WTF? of course the sport car will perform better

(directly from cars.com)
Nissan Altima = 3.5L, 6 cyl 270hp 19/27 mpg DOHC

Chevy Impala= 3.5L 6 cyl 211hp 21/31mpg OHV

Hyundai Sonata= 3.3 6 cyl 234hp 20/30 mpg DOHC

Saturn Aura= 3.5 6 cyl 224hp 20/29 mpg OHV


now what cars has more power???

PWNED!!!

WTF you say? I was comparing MPG. Read what I quoted. I wasn't even talking about power. I was refering on how a 7.0L OHV V8 has better MPG than much smaller DOHC's. What you posted doesn't dispute this, either.


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i think we can all agree the ls7 is an amazing motor

and we all wish we had a vehicle with one in it

i wouldnt mind driving a new z06

Yes it is...although i'd love to see someone shoehorn that badboy into a Solstice.

I look at it like this, though:

Pontiac G6 and related vehicles:

the 3.9l OHV has less horsepower and worse gas milage than the 3.6l DOHC


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Dammit, I forgot MPG in my last post:

1988 - 1991 2.3L OHV L4 "HSO" : MPFI
Bore: 3.68 in (93.5 mm) Stroke: 3.3 in (83.8 mm)
100 HP @ 4400 rpm
130lb-ft @ 2600 rpm
Compression ratio 9.0:1
MPG City/Highway: 21/28

1987 - 1989 2.3L SOHC L4 "Lima": MPFI
Bore: 3.78 in (96.0 mm) Stroke: 3.13 in (79.5 mm)
88hp @ 4000 rpm
132lb-ft @ 2400 rpm
Compression ratio 9.5:1
MPG City/Highway: 23/29

2005 and up 2.3 DOHC L4 "Duratec": SFI
Bore: 3.40 in (87.5mm) Stroke: 3.7in (94.0mm)
151 hp @ 5750 RPM
154 ft·lbf of torque @ 4250 rpm
Compression ratio 10:1
MPG City/Highway: 22/31

I know a lot (well... everyone) ignored my last post, but I think that the above engines are about as close as you can get to the differences between OHV 2v, SOHC 2v and DOHC 4v. Also take note that the fuel economy ratings were each taken from the lightest cars available with those engines in those years. The HSC was from a 1990 Tempo, the Lima was from a 1989 Mustang coupe and the Duratec is from a Focus. All were in the 2400 to 2900lbs range.

Ideally, though, Knox, what we'd want to do is compare 2 engines--same diplacement, with the same bore, stroke, and compression ratio.

Also, the years with the technology would make a difference: It's like comparing the 2200ohv to the 2.2 ecotec. One engine is a lot older than the other, with a different bore, stroke, and compression ratio.

Per your last two posts: what i can derive is:

The longer the stroke, the more power
The more the compression ratio, the more power
SFI gets better numbers than MPFI

All of those are independent of the valvetrain mechanism.

The best comparison i can come up with negates OHV, but it should help:
Saturn SL/SC/SW series:

DOHC 1.9l I4
Gas City/highway: 24/34
HP/TRQ: 124 @ 5000/122 @ 4800

Can't find Bore/stroke/compression info, but i'm assuming it's similar to the SOHC engine:

SOHC 1.9l I4
Gas City/Hoghway 29/40
HP/TRQ: 110 @ 5000/114 @ 2400




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^^ 1998model year, same bore/stroke for both.

Bore and Stroke
82.0 mm x 90.0 mm

Compression Ratio
SOHC (L24) - 9.3:1
DOHC (LL0) - 9.5:1

Horsepower
SOHC (L24) - 100 hp at 5,000 RPM
DOHC (LL0) - 124 hp at 5,600 RPM

Torque
SOHC (L24) - 114 lb ft at 2,400 RPM
DOHC (LL0) - 122 lb ft at 4,800 RPM

Then all we'd need to do is increase or decrease the C/R for them to match each other and we have a very accurate comparison.


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More valves mean you can utilize more of the head to breathe in and out, which leads to a higher VE. But a large reason for the differences comes in the intake, cam, and exhaust design. For instance, the 4.7 in the Toyota Tundra is DOHC, but puts out great lowend torque because of the cam selection and intake design.

O noes!

On paper a SOHC should be the best. It has the least valve train loss. BUT, paper isn't always right in the real world.
DOHC should be second and OHV should be third. The issues don't really hinge on just the came/valve design but the entire engine layout. When you consider the entire engine there are pluses and minuses for all types and it's next to impossible to say one is definitely better than the others.

The market has room for all of them. I personally prefer big bore, short stroke, OHC engine with high compression. I like the sound they make, I like the quick, bursty, twitchy power delivery. They are no fun to drive in traffic at all and are not at all practical.

PAX


PS: This is what part of the alphabet would look like if Q and R were eliminated
- Mitch Hedberg (RIP)

^^^On paper, camless technology should be the best. No valvetrain losses from the engine itself, and infinte cam profiles avaliable.

The downside is getting it to work correctly.


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The only thing every single person from every single walk of life on earth can truly say
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2 strokes with reed valves.. Poof, problem solved.. New problem? Breathing...


PAX


PS: This is what part of the alphabet would look like if Q and R were eliminated
- Mitch Hedberg (RIP)

Nah, in that level 2-stroke diesel is the way to go.

It would actually be intresting to see if someone could make a 2-stroke diesel engine small enough to fit in a car.


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The only thing every single person from every single walk of life on earth can truly say
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They could probably do it now except the metals would probably be highly exotic and expensive.


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Erm, I'd like to add that DOHC vs SOHC has nothing to do with 4v or 2v.... Take hondas D-series motor... they are almost entirely 16v(or 2 intake 2 exhaust). And OHV motor can be made 4v too.... its not imposible due to the design. Just not cost effective... so instead the LS7 has an intake valve thats almost as big as a honda piston =)

Ace140 wrote:OverHead Valve vs. (Dual)OverHead Cam
I am a firm believer that both of these designs are just as good as each other. I am a bit of a throwback to the oldschool OHV however... tried and true, and impressive as ever.

Feel free to argue with me =)

Do some research and you'll find that the DOHC engine isn't nearly as new as everyone think it is.


-Chris