Pushrod or OHC

[Slicks]

THIS is where I think you're missing the key fact.

WHY are they not reaching the speed ? Smaller gear + higher revs = laonger gear and lower revs.
I tihnk this is where you're getting it twisted and making the wrong conclusion.

They are the same engine remember, and the smaller the gears the less speed you will reach in that gear.

So they've actually switched the same numebr of times
You're position had been that they needed to change gearrs more often, I dont' see how you have described that at all
You want to try again or just drop it ?

Think if they were switching at the same RPMs though. And on top of that @50 the smaller geared car would switch up, where as the longer geared car would not.

[Slicks]

And guess what desingers do to increase compression ?
THEY increase valve size and gas flow !
To do that you have to go multi-valve and/or larger openings to do THAT you go OHC.
QED.

Larger openings do not = OHC. Also valve shape and "smoothness" counts for better airflow.

Where did you come up with that ?
According to Ford, the 04 was 20/29 or 17/25 and the 05 is 19/28 17/25
BUT look closer and you see the 05 model is running on 62 versus the 04 59 tred wheels. SO the extra rolling resistance will soak up an easy couple of mpg THAT was a marketing choice by Ford on what to use the oomph of the engine for

Uhhh, you just said it.
04 Mustang V6 gets 20/20
05 Mustang V6 gets 19/28
Bad comparison though, I know. Almost totally different cars.

http://www.fordvehicles.com/cars/200...eatures/specs/
http://www.fordvehicles.com/cars/200...eatures/specs/
So it doesn't REALLY get better mileage under the same setups
AND it's 1mpg different on ONE test of ONE engine. Wow you can be pedantic can't you
BTW, the 04 Mach 1 used DOHC and returned the same 19/28 consupmtion

I know, I was just giving you trouble :P
On Fords site they site the 04 Mach 1 as 17/25 mpg. Wheres the 19/28?

We've gone through this before and you cite US examples with worse consumption and I cite Eureopan examples with better consumption and you dont' care

Because the European example are not in the same weight and power. You site mostly very light cars with small power. Im talking about 3000lbs cars with 300-400hp. Like the BMW M3 for example, 16/24. And these are not just EPAs ratings, the magazines come out with the european cars still getting worse mpg than the american cars.

HOWEVER, I DID notice a VERY important point on consupmtion especially motorway. You listed earlier that it's 48mph over in the US. In Europe its 55mph. So 2 things. First, reading Eureopan consumption figures for motorway and mixed will make Eureopan figures read worse as they are at a higher speed. SECONDLY designers DO try to make their cars look better consumption-wise and European setups will be better at 55 than at 48. So unless they are willing to do a complete gear setting and engine remapping they WILL return worse figures underthe TESTS but no difference in the real world.
Worth remembering when "slagging" Eureopan cars as a test is NOT the real world. Equally too for US cars over here.

True, but like I said, its not just EPA whos getting the worse MPG in the European cars.

[Matra et Alpine]

They are the same engine remember, and the smaller the gears the less speed you will reach in that gear.


Think if they were switching at the same RPMs though. And on top of that @50 the smaller geared car would switch up, where as the longer geared car would not.

Wait I thought we were comparing SIMILAR engines one with a wider power band !!

if you keep constraining things then it's pointless Liek changing at the same revs. No difference, so you're then only comparing a well-matched set of gears for an negine with a poorly matched set

[Matra et Alpine]

Larger openings do not = OHC. Also valve shape and "smoothness" counts for better airflow.

No it doesn't.

There is a "perfect ratio" for valvel opening size, and valve lift.
You need to keep in the sweet spot.

So as the valve opening NEEDS to get bigger then you ahve to go to more valves to remain in the "sweet spot".

Uhhh, you just said it.
04 Mustang V6 gets 20/20
05 Mustang V6 gets 19/28
Bad comparison though, I know. Almost totally different cars.

and did we read where I said 1mpg difference can easily be attributed to the TYRES ?
It was made clear

I know, I was just giving you trouble :P

See above the figures spokefor themself

On Fords site they site the 04 Mach 1 as 17/25 mpg. Wheres the 19/28?

Don't know, as the site is clearly 17/25 !! Read it wrong, sorry, as I'd said I was using that site as first time reference

Because the European example are not in the same weight and power. You site mostly very light cars with small power. Im talking about 3000lbs cars with 300-400hp.

Old GROUND again, Slicks
Does anyoen go in to buy a 3000lb car ?
NO, they go in to buy the seating, performance and luggage space !!
So like I said, YOU switch it to big heavy cars and compare cos then biog lazy V8s ALWAYS will look 'good'. BUT as a vehicel, it's the overal performance and mileage. Who gives a toss about the WEIGHT ??

Like the BMW M3 for example, 16/24. And these are not just EPAs ratings, the magazines come out with the european cars still getting worse mpg than the american cars.

The top number you're quoting is the crusing isn't it ?
The BMW does 24mpg on urban mixed cycle.
It does 33mpg on cruising.
Are you/we comparing like with like ??
So for a 4 seater with luggage space that can show it's heals to a few sports cars it doesn't seem too bad
You got me on it being 1-2 mpg worse than the 'vette, probably about the weight of those rear seats worth
Anyway, can you confirm the US mileage as it seems odd that the US BMW doesn't quote the Eureopan cruising figure of 33mpg !!

True, but like I said, its not just EPA whos getting the worse MPG in the European cars.

Well it's safe to assuem the EPA's 48mpg is chosen as an "average" figure and so woudl suggest that's what everyone else woudl chose around.
NOT seen any official Eureopen cycle fuel consumption for the Corvette so hard to compare.
BEST I can do to try to illiminate the issue for you is to compare the Chrysler 300C.
Same car for sale in US and UK.
So UK consumption is
Combined Cycle 27.2 mpg
Extra Urban Cycle 37.2 mpg
Urban Cycle 18.3 mpg
US consumption is
!!!!!!!!!!!!!!!!!!
JEEEEESUS, now I know why you guys don't care about consumption !!
Teh UK page on the 300C was 3 buttons pressed and I had the fuel consumption. Just spent 5 mins goign over the Chrysler US page and STILL no sign of fuel consumption !!!!

Can you either find the official figures or the standrd 300C to compare above OR find a car sold in UK and US to use to enlighten on the differences. Differences which we've already said can make a car look good or bad dependant on wher eit's being sold !! It needs to be an officially imported car or it won't have the official Eureopan consumption test.

[Quiggs]

[Matra et Alpine]

EXCELLENT

Is he swinging that club OVERHEAD or just PUSHing it ???

[Matra et Alpine]

PS: for the "anoraks" the EU directive for the measurmenet of consumption figures is fully described at http://www.vcacarfueldata.org.uk/inf...onsumption.asp

[Slicks]

Old GROUND again, Slicks
Does anyoen go in to buy a 3000lb car ?
NO, they go in to buy the seating, performance and luggage space !!
So like I said, YOU switch it to big heavy cars and compare cos then biog lazy V8s ALWAYS will look 'good'. BUT as a vehicel, it's the overal performance and mileage. Who gives a toss about the WEIGHT ??

LOL!
Im talking about in the US market. Most of our cars are right around 3000lbs. And the performance cars sold here are right around that figure too.
Im comparing "big heavy" cars because its FAIR. You CANNOT compare gas milage of a 2000lbs car with a 190hp 4 cylinder to a 3000lbs car with a 400hp V8. Thats why I say compare cars around 3000lbs that have 300-400hp, like the M3, Audi RS4, Ferrari 360(yea right), Jag XKR, many MBs, Maserati Coupe, Porsche 911, etc.

The top number you're quoting is the crusing isn't it ?
The BMW does 24mpg on urban mixed cycle.
It does 33mpg on cruising.
Are you/we comparing like with like ??
So for a 4 seater with luggage space that can show it's heals to a few sports cars it doesn't seem too bad
You got me on it being 1-2 mpg worse than the 'vette, probably about the weight of those rear seats worth
Anyway, can you confirm the US mileage as it seems odd that the US BMW doesn't quote the Eureopan cruising figure of 33mpg !!

The 24mpg figure is the highway mpg. Is the 33mpg the european consumtion figure? Because it only fair to compare cars mpg when doing the same test. BMW US doesnt quote the EUROPEAN figure because its a different test, driving at a different speed from what our test is supposedly done at.

Well it's safe to assuem the EPA's 48mpg is chosen as an "average" figure and so woudl suggest that's what everyone else woudl chose around.
NOT seen any official Eureopen cycle fuel consumption for the Corvette so hard to compare.
BEST I can do to try to illiminate the issue for you is to compare the Chrysler 300C.
Same car for sale in US and UK.
So UK consumption is
Combined Cycle 27.2 mpg
Extra Urban Cycle 37.2 mpg
Urban Cycle 18.3 mpg
US consumption is
!!!!!!!!!!!!!!!!!!
JEEEEESUS, now I know why you guys don't care about consumption !!
Teh UK page on the 300C was 3 buttons pressed and I had the fuel consumption. Just spent 5 mins goign over the Chrysler US page and STILL no sign of fuel consumption !!!!

LOL! Dont you hate that!
Chrylser.com>300C>Performance
The Hemi is 17/25, the 3.5L V6 is 18/28 and the 2.7L V6 is 21/28.

I cant find consumption of the Corvette in europe, but ill keep looking.

[culver]

This comparison is for V block motors. Many of the pushrod benefits are less significant on an in line motor

The general advantages of a pushrod motor over an OHC motor are:
-For a given displacement the pushrod motor is more compact (smaller height and width)
http://www.vorshlag.com/pictures/motor-4.6-4V-004.jpg (Ford 4.6L mod next to the old 5.0)
http://www.vorshlag.com/pictures/BothRight.jpg (GM LS1 next to a Mazda Miata 1.8)
-For a given number of cylinders a pushrod motor is cheaper to construct
-For a given displacement a pushrod motor will be lighter assuming similar construction (ie all alloy or iron block and alloy heads)

The general disadvantages of a pushrod motor over an OHC motor are:
-Extra valve train mass limits high RPM work
-Generally limited to two valves per head which tends to limit high RPM breathing.
-This is not always true as shown by GM’s XV8 concept motor
http://www.carcraft.com/techarticles...GM/index3.html
-Generally limited to a single cam shaft thus cam phasing must be applied to both intake and exhaust profiles. Twin cam can be done as shown in GM’s XV8 motor.
-Perception

Hp/L, why should we care?

Compared to an OHC motor, the fewer valves and heavier valve train mass of the pushrod motor limit it’s ability to work at high RPM. High RPM is the way to get the most power out of a given displacement without forced induction. Basically pushrod motors are at a real disadvantage in the HP/L game.

But why do we care about it? Some racing series like F1 run displacement limits. In that case they don’t care about HP/L, they care about getting the most power with in the rules. If they could get more total power by running a 2.0L motor instead of the 3.5L they would.

Production cars are different. Some countries have displacement based taxes. These taxes started way back at the dawn of automotive time when the French were trying to figure out how to apply taxes to cars. A standardized dyno (adjusted for temp, humidity, pressure etc) hadn’t been invented so the French government simply said displacement=power and applied taxes accordingly. We of course know this isn’t true but it has stuck. In countries with displacement based taxes it makes sense to get as much power out of a 1.6L motor because I don’t want the extra taxes of a similar power 1.8L.

However in the US and other countries that don’t have displacement based taxes we can just opt for the larger engine with more torque. A pushrod motor will allow me to get a lot more displacement into a given engine bay (note that a Mustang 5.0 fits under the hood of a 1.8l Miata quite nicely).

BMW M5 V10 vs Corvette Z06 LS7
Both of these engines are 500hp monsters:
BMW 5.0L 500hp, 390lbft, 530lbs
GM LS7 7.0L 500hp, 475lbft, 485lbs
Yes, the LS7 displaces more but it weighs less. Should BMW be applauded for producing 100hp/L if the final engine weighs more than GM’s torquier 500hp motor?

but aren’t smaller (displacement) engines more efficient?
Not really. Of course we should expect a small 1.6L Civic to be more efficient than a 6L Corvette. However when we start talking similar size and power smaller isn’t necessarily better.

Lets look at high Hp/L motors first. Generally the tricks used to get a motor to produce over 100hp/L are not the same tricks you need to maximize fuel economy. Notice that the high mileage HX Civics (ignoring the hybrid Civic) have lower Hp/L figures than the Si or even the more pedestrian Civics.

Smaller displacement also can sometimes hurt mileage. Larger engines typically can run at lower revs and still generate sufficient power to move the car. The last generation BMW 530 actually got better mileage than the 525 because the 3.0L was geared longer so it spun slower on the highway. The 2.5L could have been gear the same but then it would have very poor passing power. The Corvette’s impressive 28MPG highway figure comes from a very long 6th gear. The Corvette has the torque to drive it so why not use it.

Lets look at it from a more technical view. A large engine spinning slowly can be just as efficient as a small engine spinning quickly. At low RPM, part throttle conditions the extra breathing ability of a multi valve head really isn’t used. We have already choked the engine by having the throttle at less than wide open. The larger engine takes more force (well torque) to spin the crank but it spins slower.

Comparing a C5 Z06 motor to a 2.0 Honda S2000:
The Honda turns about 4000 RPM at 75mph. The Corvette turns about 1800 at 75mph (these may be a bit off, I’m doing this from memory). Lets assume the parasitic friction in a motor is only due to moving the pistons up and down (there is more than that but for illustration’s sake). Lets assume the friction of a piston is equal to its circumference; ie each inch of cylinder wall imposes the same amount of drag on the piston regardless of bore. Thus it takes more force to move a large Corvette piston one inch and a small Honda piston 1 inch.
In physics terms, work equals force* distance. So it takes the same work to move a small force a long distance or a big force a short distance. The work it takes to turn the crank one rev will be circumference of the piston* stroke length *2 (up and down) * the number of pistons. Now the small S2000 motor clearly has the edge. It takes a lot less work to turn its crank one time.
In physics terms, power is work over time or work/time. The Honda has to turn it’s crank 4000 times a minute at highway speeds. The Vette turns its crank 1800 times. When I multiply out the work per rotation times RPM the Corvette ends up with a slight edge. In other words, given the speeds the engines are turning, the Corvette actually looses slightly less power to friction than the S2000. That is how a large slow turning engine can have lower frictional losses than a smaller faster turning engine.

It’s similar with pumping losses. The largest part of pumping losses come from choking the engine with the throttle. The closer you can run a motor to WOT the better. Infact BMW said the most fuel efficient way to accelerate in their cars is 80% throttle (most cars have a more aggressive, less fuel efficient fuel map at WOT) and shift at ~2500 RPM. At these low revs and open throttle conditions the motor is running in its most fuel efficient condition (that is power generated per fuel consumed). You might have the same rate of acceleration at 40% throttle and 5000RPM but you would have increased pumping losses and higher friction losses because the engine is spinning faster (see the Vette vs S2000 comparison above).

With a large displacement motor I can easily run it at these low revs and still have reasonable drivability. More so when the low cost of a pushrod motor allows me to add two extra cylinders (say a V8 for the price of a V6 or a V6 for the price of a I4). The extra power pulse of the extra cylinders help the engine stay smooth at low revs. A 2.5L V6 is smoother than a balance shaft equipped I4 under low RPM load. While the balance shafts make the I4 “inherently” balanced as a total system, there is no escaping the fact that the V6 fires 50% more, 3 times per revolution vs 2. According the Consumer Reports the Chevy Malibu V6 actually got better mileage than the Accord or Camry I4’s despite being significantly more powerful. A bit more embarrassing for GM is the V6 Malibu returned better mileage than the I4 Malibu.

So what we have is a valve train design that can allow us a lot more displacement with no weight or dimensional size penalty. We can maintain good mileage by taking advantage of the extra displacement and running the engine slower. With more advanced designs (XV8) we can get variable valve timing and more valves while still maintaining the size and weight advantages.
The drawbacks: Well many people know just enough about engines to have perception issues with pushrods. Lots of people mistake displacement for engine size and say, “only 200 hp out of 3.5L (or 400hp out of 6L or 500hp out of 7L), other companies are more efficient.” Finally, in my opinion, smaller engines can feel more sporty. The 2.5L SVT Contour motor is less powerful than Mazda’s 3.0L Duratec derived engine. I still think the 2.5L is more fun to drive.

For reference: I’ve only owned 1 car with pushrods. That was my first car back in high school. It used a 1.6L Ford Kent motor. The rest of my cars have been OHC or DOHC, all 4 pots except for my SVT Contour V6. I used to think pushrods were only for junky left over engine designs. The C5 Z06 motor really got me thinking about the issue. After looking at it in detail I saw the benefits.

[Matra et Alpine]

Variable cam technoloigy removes the issue once held with a performance cam being 'peaky' and no low end torque

[targa]

my car weights 1188lbs

[henk4]

Thanks culver for this well thought out contribution.
A few remarks though.
Obviously the pushrod engine gets its power out of displacement. (there is no replacement for cubic inches) and it is always compared to DOHC engines with less displacement. Just wondering what the same displacement DOHC engine would give.
The pictures of the two V8's are revealing but what is being compared? It appears that also the block of the DOHC engine is much larger (which need not be) than that of the 302. What you to find is a pic of two similar blocks where one has an OHV and the other has 4 OHC's.
The XV8 engine puts out a mighty 300 hp from 4.2 litre. Not very impressive, (perception again??) given all the technology that goes in there which certainly has a price. (interesting comment about the interest that the average reader has about the efficiency increase of the XV8).

Small correction: F1 now runs 3.0 litre engines and is indeed interested in getting as much HP out of litre as possible (about 300 these days), and don't blame France for the displacement tax, Germany and Italy are the main culprits here.

The issue on fuel consumption is a bit blurred and greatly depending on the gear ration in the speed area where these standard mileage figures are calculated (48 mph in the USA if I am not mistaken) If you don't use the bigger engine to its full capabilities it will be less stressed than a smaller one to reach the same performance. However, is the bigger engine being offered at the same price? No, so you pay more for the same performance if you want to economise on fuel. That is not what you bought the bigger engine for, you want the power, you want the grunt and up go your mileages figures, otherwise what's the use of a big engine.

Finally do you really think a S/DOHC inline four is more expensive to build than a pushrod V6? Would like to see that being supported by some facts and figures

[werty]

Does anyone have internal pictures of the pushrods and OHC and DOHC?

You know those drawings that show the internal parts.

[johnnynumfiv]

Here's a pushrod:

DOHC:


I couldn't find a good SOHC diagram.

[Slicks]

Thanks culver for this well thought out contribution.
A few remarks though.
Obviously the pushrod engine gets its power out of displacement. (there is no replacement for cubic inches) and it is always compared to DOHC engines with less displacement. Just wondering what the same displacement DOHC engine would give.

All about control right? Limit air flow = limit displacement. So both engines must have the same amount of air flow, and same revs. They would be making the same amount of power.

Finally do you really think a S/DOHC inline four is more expensive to build than a pushrod V6? Would like to see that being supported by some facts and figures

Thats unfair and you know it. Why not compare a OHC V6 to a OHV V6? Because you know that the OHV will be cheaper, so you drop two cylinders, and go to a I block design, thats so even now isnt it?