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[Martin_1962]

OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
 

In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?

I personally feel that OHV is old hat.

That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.

Rolling road setup helped immensly

If that was the case then the 1.3 endurance engine from Ford (built until 2005 with full sequential EFi and DIS spark) would be excellent but, its not, its a crock of ......

To many disadvantages with pushrods....period......and we havn't mentioned valve guide wear yet either....

But that is a bodge of an engine though, it is a mangled and ruined XFlow I think.

As to valve guide wear - can't see why they would wear much worse than any rocker type system.

[Marks DTM Calib]

OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
 

In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?

I personally feel that OHV is old hat.

That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.

Rolling road setup helped immensly

If that was the case then the 1.3 endurance engine from Ford (built until 2005 with full sequential EFi and DIS spark) would be excellent but, its not, its a crock of ......

To many disadvantages with pushrods....period......and we havn't mentioned valve guide wear yet either....

But that is a bodge of an engine though, it is a mangled and ruined XFlow I think.

As to valve guide wear - can't see why they would wear much worse than any rocker type system.

Modern OVC setups dont have rockers at all so its a nice direct up down motion on the valve....

[Martin_1962]

OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
 

In answer to your post, if this is the case, why is there not an OHV engine in regular production, used in most euro shopping trolleys, that is capable of 45mpg and over 100bhp?

I personally feel that OHV is old hat.

That is not due to OHV vs OHC but to modern engine management systems, and the greater prevalence of 5 speed gear boxes, I could scrape 30mpg out of my Sunbeam on an A road run, and that was on twin carbs, and a four speed box, that would red line in top at around 120, yet it would pull talling gearing if it was available (some people ran 5 speed Ford boxes and got pretty good consumption). Best economy was 35mpg on the motorway at rep speeds and it was definately over 100bhp - it had 90bhp at the wheels.

Rolling road setup helped immensly

If that was the case then the 1.3 endurance engine from Ford (built until 2005 with full sequential EFi and DIS spark) would be excellent but, its not, its a crock of ......

To many disadvantages with pushrods....period......and we havn't mentioned valve guide wear yet either....

But that is a bodge of an engine though, it is a mangled and ruined XFlow I think.

As to valve guide wear - can't see why they would wear much worse than any rocker type system.

Modern OVC setups dont have rockers at all so its a nice direct up down motion on the valve....

OK with twin cams but not so good on stuff like the Austin Rover O & S series.

DOHC actually makes it easier to design a head - just took a long time to become popular in cars, multivalve engines were common on bikes years before cars.

But then I have done the tappets on a 16v head with twin cams and 8 small forked rockers - Suzuki design.

[Ford Prefect]

OHC engines are capable of much closer valve/piston clearances than the OHV/pushrod engines, hence incresing power output and efficiency.
 

Rubish I am afraid... Take a look and the old bristol engine as used in the AC Ace before Carol Shelby molested it.

OHC engines main reason in racing is to reduce the reciprocating masses, there are no push rods or rockers to accelerate/decellerate on each cycle, as for the production engine this can't hurt, but the OHC design also significantly reduces the number of parts that need to be made and thus makes the engine cheaper to build. Hoever and SOHC design either has to have the valves all in a row (like the 8V engine) which is not so good for gas flow, ideally you want inlet and exhaust valves each side of the head, this can be done, but you can either add a set of rockers, as BMW and Triumph did (truimphs version being as woudl be expected a far more elegant solution!) or add a second cam.

Stewart

Not totaly correct either, its not a reciprocating mass you are reducing, it the valve train weight.

In addition, with SOHC there are simple ways of offsetting the valves and again the GM 4 pot is a good example with a hydraulic lifter at one end of a rocker, the valve at the other and the cam working on the upper surface....

It is totally correct, the rockers and pushrods are all reciprocating masses. All the other parts are there on both OHV and OHC. By introuducing a rocker you have added a reciprocation mass, and lost some of the advantage of the SOHC design. Although Mercedes did it on the M110 DOHC engine.

Stewart

[MaxV6]

Q:  Overhead cams , why??


A : they're  bloody uncomfortable to sit on.






I miss my Duplex Chained Straight 6

[HerefordElite]

One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir?  8-)

Kevin

Damn i thought that was my invention   - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait

[Kevin Wood]

One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir?  8-)

Kevin

Damn i thought that was my invention   - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait

Problem is the forces required to accelerate the valves are considerable, and not easy to achieve with a solenoid. Some sort of electro-hydraulic setup might work, but it would be very expensive compared to a lump of cast iron with some lobes ground on it, and has the potential to be less reliable.

IIRC it's been played with by someone - one of the F1 teams perhaps (where the problems are compounded by very high revs).

Edited to say: Cam and crank sensor reliability achieved by VX would really ruin your day too as you'd have mangled valves as well.

Kevin

[Vamps]

Too technical for me, bring back the side valve.

[Martin_1962]

One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir?  8-)

Kevin

Damn i thought that was my invention   - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait

It is being worked on - it may even be used in test cars

[Martin_1962]

One day someone'll invent a cost effective actuator that will allow the ECU to directly control valve opening and closing events and we'll eliminate the cam completely, and have some real fun. How lairy would you like your cam today, sir?  8-)

Kevin

Damn i thought that was my invention   - it can't be that hard to do now surely? it's only a fast acting solenoid valve.
change engine timing at the flick of a switch i can't wait

Problem is the forces required to accelerate the valves are considerable, and not easy to achieve with a solenoid. Some sort of electro-hydraulic setup might work, but it would be very expensive compared to a lump of cast iron with some lobes ground on it, and has the potential to be less reliable.

IIRC it's been played with by someone - one of the F1 teams perhaps (where the problems are compounded by very high revs).

Edited to say: Cam and crank sensor reliability achieved by VX would really ruin your day too as you'd have mangled valves as well.

Kevin

I think they are all looking at it - free power too as the engine is not driving a bunch of cam shafts

[Kevin Wood]

I think they are all looking at it - free power too as the engine is not driving a bunch of cam shafts

I think whatever system of actuation is used will be quite power hungry though. The biggest advantage will be a continuously variable cam profile dependant on speed and load - so you can have the holy grails of good low down torque, bonkers high red line and economy when you're not hoofing it. 8-)

Kevin

[Martin_1962]

I think they are all looking at it - free power too as the engine is not driving a bunch of cam shafts

I think whatever system of actuation is used will be quite power hungry though. The biggest advantage will be a continuously variable cam profile dependant on speed and load - so you can have the holy grails of good low down torque, bonkers high red line and economy when you're not hoofing it. 8-)

Kevin

If electrical powered - run the alternator only when braking, free power.

I reckon there are a few places to get free power from. Oil pump, water pump, valve train. Could help an F1 car quite a bit.

[Pitchfork]

Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?

[zippo]

Ah Ha!!
But 2 strokes don't have valves so why not 2 stroke engines in cars?

weren't early Saab's 2 stroke, sounded like wet farts

[albitz]

Some Desmodromic I.C valve-train systems do away with belts, chains and valve springs; with those (and many more engineering and operational advantages) why aren`t they more popular?  :-? ......

Have you never heard a Ducati? They sound like a bag of spanners.    

thats because they use a dry clutch,but the desmodromic valvetrain gives much more control over valve movement,hence an engine which revs higher and produces more power than you would expect from a v twin 8-)