Topic: Discussion: Would this be a terrible engine?

[rrocket]

I was having a discussion with a friend.  He seems to think that a great engine would be a 2.4L (or smaller) turbo engine.  But not any engine.  Here are the specs:

-No DOHC
-No VVTI
-No 4 valves
-2 valves, pushrods.
-Turbo

His reasons were as follows:  "May as well go pushrod, tune it for low to mid range favoring low end and let the turbo handle mid range and above, any of the minor loss in efficiency in flow can be made up in boost pressure anyway..... seems pointless to go with all of the added complexity.  Much less complex, cheaper to build, lighter, better weight distribution and more reliable"


I disagreed immensely.  His idea sounds good on paper.  But reality is a different matter IMO.  First of all, this engine wouldn't meet CAFE fuel economy standards.  While I agree that it would be lighter and less complex, it would suffer greatly in efficiency...particularly when off boost.  The advantage of the 4 valves and VVTI combo is primarily for efficiency and off boost performance when combined with a turbo.  Second, I think the drive ability of his engine would be just horrible.

He also seems to think that no company "wants to take a chance" on an engine like this.  I said the reason no one would take a chance is because they've already simulated such an engine in the design lab and it sucked.  If carmakers could make an engine that was cheaper, more reliable, same power, same fuel economy and lighter...they would have done so long, long ago.  I said they would have done it long ago for the greater profits alone....let alone everything else.

What does everyone else think?  And yes,...this is a real convo I had. 

[initial_D]

 ... so how many cigars were smoked?

Not a techie, but did read on Car&Driver when everybody switch their 4 cylinder engines to DOHC / multi valve designs. The advantage of DOHC have over ohv is less friction, and the valves themselves are smaller, its related component system is smaller and less weight, can operate efficiently at much higher rpm. Together with a turbo charger, seem like the obvious logical choice. Not even sure if an ohv engine can rev smoothly at high rpm, like 6500+, let alone be reliable and produce high horse power.

For a high output engine, your friend's idea would suck. For a car that is the equivalent of a small tractor, it might work well. 

[tpl]

  Most modern cheap and simple cars are the equivalent of a tractor.   Turn on, drive relatively slowly from a to b turn off. repeat a zillion times.  No high speeds, no stresses.  Over 90% of these engines have an automatic transmission.  So a simple reliable engine with sufficient torque will always do the job.   Why do you need to rev to 6500 rpm in the real world?


Isn't the current Corvette engine still OHV cam in block?     The DOHC, VVTI, 4 big valves is useful for good breathing at high rpm but with a turbocharger why bother with the high rpm? 
Direct injection not mentioned but I think that IS a step forward for economy and emissions.

If you were prepared to have some complexity, Desmodromic valves, 2 per cylinder, controlled directly by the ECU might be the way to go but complexity and reliability both are good reasons that has not been employed in a modern road car. Same goes for  the electric motor assisted turbo  F1 style, it would work in a road engine... but the complexity comes back again.


I suggest that the truly modern gasoline engine would be configured like a modern diesel...lots of low down torque and let the transmission do the work either with lots of DCT gears or even a CVT.

[Snowman]

Would of like to be part of that conversation as this is the best car engine:

[tpl]

AHA!  Your picture is obviously of a device that uses the energy of the vacuum to produce rotation at the output shaft with no fuel required.  Your pic is just a small one that only manages 100,000 lbs/ft at 1000 rpm.   Useful and I don't think anyone has patented it yet... Maxwell's Demons are natural phenomena and cannot be patented.    

[Fobroader]

Your buddy sounds like he wants the old 2.5 Iron Duke GM 4 banger put back into production. While maybe that would be ok in the 3rd world, I mean look at cars like the Tata, there would be no way to make it worthwhile here. Yeah, it will run forever and if kept simple enough it would cost pennies to fix, but since every has a hard on for mileage and crap, I doubt you could sell it on the cheap and reliable pitch.

[Triple Bob]

It sounds like a redneck engine.  Would be harsh, great for relaibility, simple to maintain, but low revving and crappy fuel economy.  It would have been a great engine 50 years ago.

[Fobroader]

It sounds like a redneck engine.  Would be harsh, great for relaibility, simple to maintain, but low revving and crappy fuel economy.  It would have been a great engine 50 years ago.

What does your average driver of an appliance need revs for??

[Sir Osis of Liver]

I don't think he's necessarily wrong. A long stroke, slow reving engine would have lower pumping and mechanical losses, but would need a turbo to maintain manifold pressure, to maintain efficiency. I'm not sure it those lower losses would be offset by the higher losses with a OHV arrangement.

A decent explanation regarding keeping engine revs down:

http://www.hddeo.com/DownsizingandDownspeedingofDieselEngines.html

[tpl]

RR's buddy was describing  a 'simple' engine.     Doesn't need to be like the Iron Duke just needs to be a basic efficient powerplant. 
As Sir O says, a turbo to overcome the less good breathing of just two valves per cylinder.  Pushrods and OHV work perfectly well up to 5-6000 rpm but I ask: How often do you rev out to 6000 rpm on the street?  Not often I bet so a long stroke is ok.   Single cam in block and push rods work well enough.   Now this engine should be of modern construction for lightness, strength and good thermal performance. Should have Direct injection for economy and a good torque and power curve.    While you are at it have the water pump, cam and oil pump all external and driven by an easily accessible chain.  Careful design should make for a very short and light engine...sort of a 4 cylinder version of Fords 3 cyl eco boost.

[Triple Bob]

It sounds like a redneck engine.  Would be harsh, great for relaibility, simple to maintain, but low revving and crappy fuel economy.  It would have been a great engine 50 years ago.

What does your average driver of an appliance need revs for??

I'm just not a fan of low revving engines, I prefer high revs.

Admittedly I don't drive like that all the time, but I used to hit 8,500RPM in the Exige about 30-40 times a day on my commute.

[Fobroader]

It sounds like a redneck engine.  Would be harsh, great for relaibility, simple to maintain, but low revving and crappy fuel economy.  It would have been a great engine 50 years ago.

What does your average driver of an appliance need revs for??

I'm just not a fan of low revving engines, I prefer high revs.

Admittedly I don't drive like that all the time, but I used to hit 8,500RPM in the Exige about 30-40 times a day on my commute.

Yeah, but you drove an Exige, not a Kia Rio, you are an "enthusiast"

Sent from my Galaxy S3

[Triple Bob]

It sounds like a redneck engine.  Would be harsh, great for relaibility, simple to maintain, but low revving and crappy fuel economy.  It would have been a great engine 50 years ago.

What does your average driver of an appliance need revs for??

I'm just not a fan of low revving engines, I prefer high revs.

Admittedly I don't drive like that all the time, but I used to hit 8,500RPM in the Exige about 30-40 times a day on my commute.

Yeah, but you drove an Exige, not a Kia Rio, you are an "enthusiast"

Sent from my Galaxy S3

Exactly, I can only comment from my needs/wants.

Would this be a terrible engine for me, yes.

[aquadorhj]

...didn't exige have Toyota Celica engine?   no wonder you rev'ved to 8500 rpm!  you needed all those revs to make any power!   

[wing]

Regular people rarely see above 4000.   Heck my co-worker says he never goes higher than 3000 in his 4cyl mazda6    I look at him funny when he says this.

[Triple Bob]

...didn't exige have Toyota Celica engine?   no wonder you rev'ved to 8500 rpm!  you needed all those revs to make any power!   

Yep, different cams though.  190bhp ain't to be sniffed at in a 1,000kg car.  The kick in the back when the second cam came on at 6K was delicious! My hour long commute was like driving at Le Mans.

[Snowman]

  Geez..perhaps the people who actually design, build, and comply with standards in the automotive industry might know what they are doing

[Fobroader]

It sounds like a redneck engine.  Would be harsh, great for relaibility, simple to maintain, but low revving and crappy fuel economy.  It would have been a great engine 50 years ago.

What does your average driver of an appliance need revs for??

I'm just not a fan of low revving engines, I prefer high revs.

Admittedly I don't drive like that all the time, but I used to hit 8,500RPM in the Exige about 30-40 times a day on my commute.

Yeah, but you drove an Exige, not a Kia Rio, you are an "enthusiast"

Sent from my Galaxy S3

Exactly, I can only comment from my needs/wants.

Would this be a terrible engine for me, yes.

I agree, I regularly rev all the vehicles I drive to the redline....why....because I can.

[Great_Big_Abyss]

  Most modern cheap and simple cars are the equivalent of a tractor.   Turn on, drive relatively slowly from a to b turn off. repeat a zillion times.  No high speeds, no stresses.  Over 90% of these engines have an automatic transmission.  So a simple reliable engine with sufficient torque will always do the job.   Why do you need to rev to 6500 rpm in the real world?


Isn't the current Corvette engine still OHV cam in block?     The DOHC, VVTI, 4 big valves is useful for good breathing at high rpm but with a turbocharger why bother with the high rpm? 
Direct injection not mentioned but I think that IS a step forward for economy and emissions.

If you were prepared to have some complexity, Desmodromic valves, 2 per cylinder, controlled directly by the ECU might be the way to go but complexity and reliability both are good reasons that has not been employed in a modern road car. Same goes for  the electric motor assisted turbo  F1 style, it would work in a road engine... but the complexity comes back again.


I suggest that the truly modern gasoline engine would be configured like a modern diesel...lots of low down torque and let the transmission do the work either with lots of DCT gears or even a CVT.

Back to the original topic at hand, why does it have to be OHV Cam-in-block?  Why can't it be a single overhead cam?

One of the reasons why corvette engine is still and OHV push-rod engine is for compactness.  You have smaller heads and therefore an overall smaller engine which can fit under a low hood easier than a DOHC V8 can.  THAT and OHV is still king for low-end torque.

ANYWAY, back to the question at hand, instead of just doing cam in block, why not just do a SOHC with no VVT?  You get rid of the complexity of having a pushrod and rocker arm valvetrain, replace it with an overhead cam and a timing chain, and you don't have the complexity of a VVT system.  it's the best of both worlds, and functionally, wouldn't have too much different from a cam-in-block 4-cyl.

[tpl]

Sure.   SOHC works.   The Corvette engine surely is a perfect example of:  if it works don't mess with it.