Why No Pushrod Modern 4's and V-6's?

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May 12, 2019
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Can anyone tell me why there is no company making pushrod 4's or V6's? I ask for these reasons:
1. GM's LS/Vortec series of V8's are competitive with OHC and DOHC V8's of competitors.
2. Pushrod engines make more torque lower in the rpm range where MOST American drivers drive their vehicles.
3. Pushrod engines are more compact which leads to lower hood lines and most likely better aerodynamics.
4. Pushrod engines are simpler in design and don't have rubber timing belts or looong timing chains.
5. There is a privately made LS 4 cylinder racing engine that is basically half an LS V8 that is dominating right now.
6. Ford replaced the OHC V10 with a new pushrod engine.

Supposedly DOHC and OHC engines are more efficient or economical but by how much? The old GM pushrod motors were generally crap due to GM's cost cutting and shoddy engineering(like Dexcool eating pushrod V6 intake manifold sealant and causing coolant to get into crankcase) but the 3800 series of engines are famous for lasting 200-400K miles without issues. Heck, the old 2800/3100/3500 V6's were known to have racked up 300K plus mileage if the owner was lucky and stayed on top of maintenance.

It just seems to me that pushrod engines have more upsides than downsides compared to OHC engines. Any engineers or anyone with "the knowledge" that could shed some light on this mystery?
 
I thought the big push to go OHC to begin with was to free up the ability to make your intake and exhaust ports any shape you wanted, because you didn’t need any holes for pushrods?

I imagine some other reasons might be that cam in the block makes the block heavier, and it’s probably more difficult to do VVT, but I presume someone could overcome that.
 
Still in development; the marketing team pushed it aside at the PRI show. Many people still believe if it doesn't have eight cylinders, it isn't worth having.

340-HP 3.6-Liter Four-Cylinder LS-Headed Crate Engine

 
So sick of people thinking the valve configuration has anything to do with where an engine makes its peak torque.

The arrangement of the valve actuation has NOTHING to do with the power curve. Yes, OHC engines may be able to rev higher, but the torque and power curves are dictated by bore, stroke, and cam PROFILE.
 
Because pushrod engines have poor power density compared to any even remotely well executed 4-valve per cylinder engine.

1. Compared to a 4-valve/cyl engine? Only if the LS has a significant displacement advantage

2. No they don't - method of valve actuation has zero impact on where any combination makes it's power.
Power-band is dictated by factors such as intake manifold design (runner length, cross section, etc.), intake port design (cross section/runner volume/valve angle), valve events, valve area to displacement, etc.
It just so happens that most pushrod, in-line valve engines tend to be valve area limited (for the bore diameter) with smaller ports and longer intake runners that enhance low-speed power production relative to their less valve-area limited OHC multivalve alternatives.
It's very easy to design a "torquey" OHC engine or a rev-happy pushrod.
It's just that OHC engines are inherently superior high revvers.

3. This is the pushrods ONLY advantage from the perspective of the end user

4. "Simpler" with more moving valve-train mass

5. What is it dominating? It will never match the accomplishments of the OHC Honda K20.

6. Godzilla is suffering the same lifter/cam problems the rest of it's pushrod competition has been for 20 years.
 
...
3. This [compact size/shape] is the pushrods ONLY advantage from the perspective of the end user
...
I can think of one more: overall weight. All else equal, a pushrod engine seems likely to be lighter than OHC, especially DOHC. That doesn't matter much for most cars since the engine usually makes up on a small % of overall weight.

Yet for aircraft engines, weight matters. For example a Lycoming O-360 is a 360 ci engine that only weighs about 260 lbs. Aircraft engines can't rev high because the propeller bolts directly to the crankshaft so you have to keep it below about 2800 RPM for the tips to stay subsonic. So you need to make a lot of power at low RPM, which sounds like diesel would be ideal. But you also need to be lightweight, so no diesels. And you need to be durable and reliable. And you need to be compact size/shape that fits inside the cowling. Thus we get horizontally opposed 4 and 6 cylinder engines of large displacement, air cooled, gasoline powered, with pushrods.
 
The above LS 4 cylinder does not have 350HP without a turbo. More likely a touch less than half of a LS engine due to tuning and frictional reasons. I expect a real world 180HP.
 
There is an LS-based pushrod V6 now that came out a few years ago. It is 4.3L, 3/4 of the LS1, making 285 hp. It's is the standard engine on GM's full-size vans. They just stopped using it in the Silverado/Sierra. Too bad they don't offer it in the Colorado/Canyon :unsure:

Too bad there is no cheap I4 pushrod, though. The 122 is cheap and simple.
 
I can think of one more: overall weight. All else equal, a pushrod engine seems likely to be lighter than OHC, especially DOHC. That doesn't matter much for most cars since the engine usually makes up on a small % of overall weight.

True
 
The above LS 4 cylinder does not have 350HP without a turbo. More likely a touch less than half of a LS engine due to tuning and frictional reasons. I expect a real world 180HP.
You have proof of that accusation?
 
Its a fuel efficiency thing,

with a pushrod engine its kind of hard to equip it with variable valve timing which helps with fuel efficiency and different cam profiles that assist in achieving said fuel efficiency and efficient powerband at given rpm for many engines.
 
Most of the current pushrod engines do have VVT.

In more displacement limited 4 and 6 cylinder applications I believe it really does come down to power density more than anything.
 
Thanks for all the info. So my follow up question: since it isn't valve train design that determines torque why dont the engineers engineer the overhead cam engines to generate more torque lower in the power band instead of so much higher in the power band?

Oh, GM built and put in production the first variable valve timing V6 pushrod engine in the last generation of the 3500.
 
What i like about pushrod engines is their heads are usually more compact. Especially the older era of engines.
 
Thanks for all the info. So my follow up question: since it isn't valve train design that determines torque why dont the engineers engineer the overhead cam engines to generate more torque lower in the power band instead of so much higher in the power band?
Because power moves the car, and power is torque * RPM. The higher RPM at which you can produce torque, the more power it produces, the better performance. Put differently, torque at the rear wheel is torque at the crank * overall gear ratio. If the engine B produces the same torque as engine A, but at twice the RPM, a car with engine B can use twice the gear ratio to get twice the torque at the wheel at the same speed, which is twice the acceleration as a car with engine A.

So high RPM is good for power and performance but low RPM is good for efficiency. So ideally if you want both, the engine needs a flat torque curve over a wide RPM range. That requires variable valve timing and intake geometry, which many engines have. Also, many gasoline engines use variable valve timing to simulate Atkinson cycle to achieve peak efficiency under low demand, then automatically shift to Otto cycle under heavy load.
 
... Because power moves the car, and power is torque * RPM. The higher RPM at which you can produce torque, the more power it produces, the better performance. Put differently, torque at the rear wheel is torque at the crank * overall gear ratio. ...
... times transmission efficiency.
Why rear wheel? That same equation applies if front wheels are driving, or both ends are.
 
... times transmission efficiency.
Yes. But the point is that power is conserved and torque is not. If your drivetrain efficiency is 85%, then power at the wheels is 85% of power at the crankshaft. But torque at the wheels could be anything: maybe 20x greater than at the crankshaft, maybe 1.5x. Depends on the gear ratio. Gearing swaps torque for RPM but their product, power, remains the same.

... Why rear wheel? That same equation applies if front wheels are driving, or both ends are.
Sorry, by "rear wheel" I simply mean "drive wheel(s)". That's just my old school bias showing.
 
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