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

[nthach]

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.

Yea, the vaunted Ford Vulcan 3.0L made 150-155hp in its final years - the OHC Japanese and 2.7L Mopar competition made more. Same thing with the Mopar 3.3/3.8L, Ford Essex 3.8L/4.2L and GM 3800(no blower)/3.9L, the Japanese competition used on the Odyssey/Sienna and the later Quest still made more power with less displacement.

However, the American pushrod motors have more of a torque emphasis, the Japanese V6s for the exception of the Nissan VG30/33 non-DOHC/turbo versions have more of a high-RPM horsepower bent.

 

[Cujet]

You have proof of that accusation?

The company states that 300 to 360hp and 500 foot pounds of torque are possible with a turbo. I don’t see anywhere where they publish normally aspirated HP numbers.

Really a 3.6L 2 valve 4 cylinder engine can be tuned just like any Chevy pushrod V8 to make good power with enough compression and cam. But why? That makes for a miserable beast. We tuned all sorts of 2.3 and 2.5L 4cyl Ford engines. The HP in practical form was never impressive, always around 150.

A normally aspirated tractor engine with an LS head is not going to compete well with today’s 4 valve engines. It will make Nissan Altima levels of power

I can’t think of any streetable 7L Chevy V8s that make 720HP in normally aspirated form.

 

[tyman]

The company states that 300 to 360hp and 500 foot pounds of torque are possible with a turbo. I don’t see anywhere where they publish normally aspirated HP numbers.

Really a 3.6L 2 valve 4 cylinder engine can be tuned just like any Chevy pushrod V8 to make good power with enough compression and cam. But why? That makes for a miserable beast. We tuned all sorts of 2.3 and 2.5L 4cyl Ford engines. The HP in practical form was never impressive, always around 150.

A normally aspirated tractor engine with an LS head is not going to compete well with today’s 4 valve engines. It will make Nissan Altima levels of power

I can’t think of any streetable 7L Chevy V8s that make 720HP in normally aspirated form.

So…..no, you don’t have any proof to the contrary. Got it, thanks!

 

[Skippy722]

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.

Chrysler’s 3.6 for instance makes 90+% of peak torque starting at 1800rpm and maintaining that to 6,350. The “PUG” 3.6 is slightly better below 3,000 (they claim an over 15% improvement).

GM’s 3.6 V6’s are the same way. They just quote peak numbers and rpm though.

 

[Cujet]

So…..no, you don’t have any proof to the contrary. Got it, thanks!

Horsepower calculator

Estimate horsepower output from any engine type (4-stroke, 2-stroke, any fuel type, turbo, blower, Wankel, etc.).

hpwizard.com

at typical numbers I come up with 170 to 205hp. Not far off my guess. Of course, making a full race engine will get ya a bit more


To answer the question above, engineers do design for as much torque as possible where it is needed. Today’s engines with variable valve timing and tuned intakes come darn close to what’s possible. Higher compression and direct injection can help. The idea that something significant is missing is generally not correct.

 

[IndyIan]

Chrysler’s 3.6 for instance makes 90+% of peak torque starting at 1800rpm and maintaining that to 6,350. The “PUG” 3.6 is slightly better below 3,000 (they claim an over 15% improvement).

GM’s 3.6 V6’s are the same way. They just quote peak numbers and rpm though.

I don't really know why now though? If we were running the old 3 speed autos, then sure its nice to have a flat-ish torque curve, but everything has 6+ speeds now so why bother?
Half an LS makes more torque at lower rpms, so gets better fuel efficiency with less engine weight and complexity, but then needs a many speed automatic to avoid having to rev out as much. With DI and a small turbo it could be optimized to work even better as it can build even more torque at low rpms and still have no need to rev up?
With a CVT you could have a turbo engine that can be optimized to run in a tiny rpm range and just use boost to meet increased power demand.

 

[Skippy722]

I don't really know why now though? If we were running the old 3 speed autos, then sure its nice to have a flat-ish torque curve, but everything has 6+ speeds now so why bother?
Half an LS makes more torque at lower rpms, so gets better fuel efficiency with less engine weight and complexity, but then needs a many speed automatic to avoid having to rev out as much. With DI and a small turbo it could be optimized to work even better as it can build even more torque at low rpms and still have no need to rev up?
With a CVT you could have a turbo engine that can be optimized to run in a tiny rpm range and just use boost to meet increased power demand.

People have this thing against their transmission “shifting all the time”, a nice broad torque curve can help prevent that complaint. My Chrysler 300, with its 2.62 axle and 8 speed, would be turning 1200rpm at 60 for example.

Blueprints “half a LS” is based off an industrial engine intended for industrial applications, so it should be nice and tough. But 4 cylinder engines have an issue with secondary imbalance, which is why we don’t see “large” gas burning 4 cylinders in road going vehicles which makes me wonder how Blueprint plans to tame that. Unless you give it a low peak redline to keep that in check?

As for weight, Blueprint says the 3.6 comes in “around” 300lbs. Chryslers 3.6 V6 comes in at 330lbs.

I don’t think there’s an automotive CVT available today that won’t either instantly grenade itself or live a relatively long reliable life if fed 500lb ft of torque. So you’re back to a conventional auto/manual, in which case you need to be able to rev unless you want a dull lifeless driving experience, the exact opposite of what anyone buying a “performance engine” is looking for.

Don’t get me wrong, I think this thing is super cool and I hope it succeeds. I just have my reservations given the current super limited information on it.

 

[Graham Piccinini]

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

Blueprint’s New LS-Headed Four-Cylinder Crate Engine Prototype

We check out Blueprint Engines’ LS3-headed 3.6-liter four-cylinder, with the potential to make well over 300 hp—and even more with power-adders.

www.motortrend.com

My Hyundai Accent needs this. Oh boy, how my toes tingle thinking about it....

 

[meep]

Seems like I recall reading that the typical “toyota profile” where there’s less torque down low also provides either an improvement in efficiency or emissions, I can’t remember which. Remember the chrysler 3.7? Early versions moved Ram 1500s around daily… plenty of torque. Latter versions were barely adequate in the unit body grand Cherokee. It wasn’t by accident.

pushrod designs with one cam can’t do independent timing sweeps between intake and exhaust. They also have higher moving mass in the valvetrain.

man… it’s been a long time. I think the only pushrod motor I own is in my lawn mower.

 

[John105]

Wonder how much is/was dictated by marketing? I think to myself, look at how "premium" has been associated with "V6." right off the bat in my mind, balance comes to mind. As in, lack thereof. Same with the I4.

 

[John105]

Seems like I recall reading that the typical “toyota profile” where there’s less torque down low also provides either an improvement in efficiency or emissions, I can’t remember which. Remember the chrysler 3.7? Early versions moved Ram 1500s around daily… plenty of torque. Latter versions were barely adequate in the unit body grand Cherokee. It wasn’t by accident.

pushrod designs with one cam can’t do independent timing sweeps between intake and exhaust. They also have higher moving mass in the valvetrain.

man… it’s been a long time. I think the only pushrod motor I own is in my lawn mower.

Your lawnmower is not DOHC 4-valve? j/k mine is OHV too It wouldn't surprise me if many can't envision what OHV looks like. My first car had a Volvo B20F. I remember replacing the timing gears on it. I also remember I missed SOHC by a year

 

[PimTac]

The one thing I remember about pushrods is that they would get bent. Back in the day it was common to have a bent pushrod.

 

[ESP9935]

... times transmission efficiency.
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.

RWD = right wheel drive

 

[SC Maintenance]

The Japanese can build a torqy OHC - the Nissan VQ40DE has 288 Ft.lbs of torque and 266 HP, and I can assure you it has lots of torque off idle - I own 2. They put them in Xterra's and Frontiers from 2005, Its still lowish compression / MPFI and has VVT only on the intake side. The primary difference from it and say the VQ35 is the 4.0L has a much longer stroke.

 

[OVERKILL]

The Japanese can build a torqy OHC - the Nissan VQ40DE has 288 Ft.lbs of torque and 266 HP, and I can assure you it has lots of torque off idle - I own 2. They put them in Xterra's and Frontiers from 2005, Its still lowish compression / MPFI and has VVT only on the intake side. The primary difference from it and say the VQ35 is the 4.0L has a much longer stroke.

The 2V Modular engines were quite torquey too, Ford did well with camshaft selection for those. And, like a pushrod engine cammed similarly, they didn't rev to the moon.

 

[Stumpy]

Thanks for all the input guys. I learned a lot.

 

[dumkid]

4v pushrod engines are quite common. any 24v Cummins is a pushrod engine with 4v per cylinder, and same with many ford psd. i don't need revs to be happy, as long as it has enough torque to accelerate at low rpm. most engines nowadays are smaller and more rev happy than their distant ancestors, and that's because a smaller engine will get better mileage when cruising around, but has to rev alot to make the same power as a larger engine at lower rpm. vvt and variable intakes and especially turbos have helped little engines make torque at the bottom end. my 3.5 v6 using technology from the early 90s (sohc, 4v, no variable anything) makes good power above 3000 rpm, and revs to 6000, but that only gives me 3000 rpm of useful area, while a diesel redlines at 3500 it also has torque off of idle so it has the same useful rev range as a gas engine. slightly less power though, because it has less rpm. for offroading and towing, low speed torque is nice, even if high rpm HP will get you better acceleration and maybe better mileage

 

[Cujet]

4v pushrod engines are quite common.

I always liked this design on the Honda v-twin CX500 and CX650 motorcycles. Very long lifespan too. Although this specific layout would be difficult with any inline bank of cylinders.

 

[xgmad]

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.

it is still expensive in the sense that the way of manufacturing versus marginal scale in cost does not make it practical. And the VVT is still limited in what it is able to do. The pushrod engines being made are still compensated in overall café targets because if i am not mistaken are made in limited quantities? I could be wrong on limited quantities.

 

[barryh]

I always liked this design on the Honda v-twin CX500 and CX650 motorcycles. Very long lifespan too. Although this specific layout would be difficult with any inline bank of cylinders.

I can remember when the CX500 was first introduced and it came as quite surprise that Honda had made a relatively low tech pushrod V twin when OHC in line 4's had become near universal for a Japanese bike at the time. It must have been a consideration that a pushrod engine would keep the width down on an across the frame V twin. It did the job very well and was refined into the bargain. Very much a confirmation that push rod engines could still be the appropriate choice.

I can think of another example of a pushrod engine being still fit for purpose and that was the Rolls Royce 6.7 litre V8 that was in production from 1959 until 2020. They did some major upgrades to it during that time and had the opportunity to go to OHC 4 valve but a push rod 2 valve design proved to have the lowest noise levels so they kept producing it.