In reply to NickD :
True, but how many 1.5l turbos have a manual transmission behind them? I can't think of one we have.
One marketing thing that turbos have brought is this enormous focus on "low end torque"- when it's in an area where combustion tends to really be poor. But that's a totally different project and thread direction.
To expand (or contract) upon the simpler/more complex thing, I own and operate two SOHC engines that do not have rocker arms or screw adjusters. The other side is the BMW / Bristol inline 6 with 18 pushrods, 18 rocker arms, and only 12 valves. The only legitimate reason for a pushrod engine is compact dimension/ low CG
Alfa driver your parts count is off (albeit in a minor way) you left out the 4 caps per camshaft the retain the camshaft in the head, a DOHC has 45 parts, whereas a OHV the cam simple slides into the block. The number of parts are nearly identical. In the Nissan A-series there is retainer to locate the camshaft so that makes 43 parts. Fewer parts doesn't necessarily make something simpler; a square 4 two stroke (Suzuki RG500) only has 14 moving parts in the entire engine but they are not simple to set up.
My point being set up and maintenance (for me at least) factor into a motor being simple or not. Read I can pull the head, adjust the valves, change water pump and do several other tasks quickly versus some DOHC that may require pulling the cams to adjust valves and removing the timing belt to change a water pump.
So back to the original topic my answer is still no on new push rod I4s; modern twin cam motors make it easier to meet emissions/efficiency goals than a single cam motor. In theory one could design a twin cam in block push road motor but that doesn't make a whole lot of sense when starting from scratch. The 10-15lbs of weight savings (only advantage I can think of beyond some maintenance tasks) would hardly be worth it.
In reply to Tom1200 :
Fair point for the bearing caps.
But I will also say that you are making a assumption of OHC cars being harder to work on- I think it more depends on what the engine IS vs. how the valvetrain is laid out. Like I can change the water pump on my Alfa without doing anything other than take the fan belt off. Also, it can be pointed out that my Alfas barely require adjustments to the valve clearance- as there are fewer things that move that could even make it go out of spec. Personally, I think it's even simpler if you have to do less maintenance.
A lot of OHC engines slide the cams into the head, no caps.
Some OHC engines integrate the cam caps with the valve cover.
Pushrod engines are easier to R&R the head on, true. Although, if ease of head removal is a priority, there are other issues. (Reminds me of the argument that carbs and points are superior, because you can fix them on the side of the road with a screwdriver, or a worn silver dime)
@alfadriver it does indeed come down to design but comparing modern DOHC 4s against the push rod version, the more modern motor is more complex. Obviously this is down to the modern DOHC motor having to make good power, get good gas mileage and meet higher emission standards.
@knurled (keeping in mind I do contract for a living) it's all down to priorities; from a standpoint of fixing a car on the side of the road with minimal tools carbs and points are better. So while yes you can fix the points on the side of the road you are more likely going to need to do so. As for carbs other than a bad float needle I've seldom had issues with them (including ones with leaking throttle shafts). I get your argument; it's the same thing as when people who've only dealt with FI state they'll automatically make more power than carbs, even though they won't, the difference is F.I. isn't going to need adjustments on an hourly basis to get the most power out of an engine. Read I'm going to be rejetting between the morning and afternoon sessions, who would actually do that on a road car.
With all that said I am contemplating putting a twin cam motor in my Datsun at some point...................let's face they are a superior design to my beloved push rod motor.
In reply to cdeforrest :
I had a Mercury 470 (1/2 of a 460). 470 was just Mercury's motor & outdrive#.
Traded an old van & an old camper for it. Amazing motor & Cuddy cabin. Didn't know what it was until I went the Mercury dealer to get a book & tune up parts & there was an old salty mechanic that explained all about that motor & said the only problem I would ever have would be the water cooled voltage regulator. He was right. Put a single Chevy alternator on it & was then awesome.
It had a Chevy bell housing on it so I'm sure someone put one in a car.
Zussman said:I think yes, why not? :)
That's some pretty good insight on a year and a half old thread....
It's like a weird (canoe) sub hunt around here lately. Periscopes popping up randomly...
And this thread has already gone on for several pages of good reasons about why pushrod fours are not likely to make a comeback, too.
Just for fun, what's the most recent new design in four cylinder, pushrod gasoline engines? I'm thinking the AMC 2.5 from 1982, which was a purpose built light truck motor.
In reply to MadScientistMatt :
AMC 2.5 was just a shortened six, no?
Kind of like the Ford HSC 2.3 from 1983 or 1984, which was largely based on the Ford 250 (maybe 200) to minimize tooling expenses.
Ahem. 
Does the Chevy 2.2 count an all new engine or just an evolution of the 1.8/2.0 engine?
Pete. (l33t FS) said:In reply to MadScientistMatt :
AMC 2.5 was just a shortened six, no?
Kind of like the Ford HSC 2.3 from 1983 or 1984, which was largely based on the Ford 250 (maybe 200) to minimize tooling expenses.
Ahem.
Does the Chevy 2.2 count an all new engine or just an evolution of the 1.8/2.0 engine?
The Cavalier/S10 2.2 sure looked different to the 1.8/2.0. I think I'd call it all new. Certainly completely new cylinder head design.
I guess it depends on how fussy you want to be around your definition of "new", but I can't really think of one if the 2.2 came up from something else. AMC 2.5 was a cut down 4.0. Tempo was a cut down 6. Iron Duke was a cut down small block v8. I suppose, based on that, we could ask whether there has been a "new" pushrod 4 cylinder in the last hundred years.
They still make brand new pushrod fours. Just not for ground pounders.
This was released in 1996:
Knurled. said:ProDarwin said:I would say its more likely to see a cam-less 4 cyl than a new pushrod design.
Although... if you were to do a V4, the packaging advantages over a DOHC would still exist. And a V4 LS motor would leave room for lots of transmission (and electric motor)
Although IIRC the only thing it actually shared with an LS1 was the timing chain.
While the Motus was heavily inspired by the LS I don't belive it shares any parts with it.
In reply to MadScientistMatt :
Nissan A-series engines were in new cars up until 2007. They were used in Nissan 1200/1400 utes in South Africa.
Tom1200 said:In reply to MadScientistMatt :
Nissan A-series engines were in new cars up until 2007. They were used in Nissan 1200/1400 utes in South Africa.
I'm wondering when the last time somebody came up with a new production design (counting the amount of work to shorten a six to a four, but not minor updates to an existing four banger), though. So far, I think the Ford HSC engine is in the lead at 1984, with the GM 122 series (1.8 / 2.0 / 2.2) and AMC 2.5 both rolled out in 1982. If truncated sixes don't count, GM's 122 series holds the lead, as it seems like it was designed from scratch.
In reply to MadScientistMatt :
The Nissan A-Series ran from 1971 through 2007 and while there were a few updates it was pretty much the same engine the whole time............so yeah it was pretty much a 36 year old design when the production run ended.
I'd still like to put an A-series in an Exocet as it would take another 175lb off the car versus a Mazda powered Exocet.
You can buy a brand new flathead pushrod 4 aircraft engine.
Tom1200 said:In reply to MadScientistMatt :
The Nissan A-Series ran from 1971 through 2007 and while there were a few updates it was pretty much the same engine the whole time............so yeah it was pretty much a 36 year old design when the production run ended.
I'd still like to put an A-series in an Exocet as it would take another 175lb off the car versus a Mazda powered Exocet.
Ah, the era when an engine would last more than 5 years.... good old days.
my tercels make a E36 M3 ton (relative) of torque and it all comes down to cam profile and intake manifold.
Considering most "pushrod torque" motors are large displacement, low revving engines with overall low air flow. Think about it...older 2.0 and 2.2 Cavaliers were making what...125hp? Meanwhile all their OHC competition was making similar to more numbers with less displacement. Yeah they may not of made the same off idle torque, but they make more everywhere else and with less fuel.
In reply to malibuguy :
It's generally true that DOHC make more off idle torque than any 2 valve, because the larger and better shaped valve curtain area (less percentage of it is shrouded) means you need less duration, so you are closing the intake valves earlier, and IVC pretty much defines how much low end torque you get.
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