Feasibility of pushrod/cam-in-block engines in Formula One [OHV/overhead-valve]

[JordanMugen]

Pushrod/OHV/cam-in-block advocates are always pushing the advantages of pushrod engines... That they are physically more compact, simpler, lighter (though crucially not the valve-train reciprocating mass): they say they "just work" and are pretty much all-round great!

Given this, what is the feasibility of a pushrod engine in Formula One? When was the last pushrod engine in Formula One (60's? or was it earlier or later than that, I have no idea)?

Is the Mercedes-Illmor 500I 1.8 bar turbocharged 16-valve 3.43L V8 (supposedly 1024 bhp @9800rpm, max 10,500rpm) the last modern purpose-built racing engine with a pushrod design (aside from production-derived racing engines like the Ford Windsor BOSS, Chevrolet small-block and so-on including the purpose-built Toyota NASCAR engine made to similar specifications)? Or are there others?



Likewise how about in CART/USAC? I notice that Indy racing was long dominated by the DOHC Offenhauser engine just as Formula One was (later) dominated by the DOHC Cosworth DFV engine. [Where were there advantages exposed by pushrod engines advocates when Offys and Cossies were winning everything? ]

With regards to the engine speed limitations, I recall reading here that innovative well-manufactured valve springs allowed production-based larger capacity NASCAR Cup engines to push-up towards 10,500rpm (from a former 8000rpm or so in about 1998), albeit this has since been restricted by the rules if I understand right.
https://www.popularmechanics.com/cars/a ... r-6643778/

Also, if pushrod/cam-in-block engines have all these advantages, how come most modern ICE road cars -- small hatchbacks, medium SUVs and so on (which let's face it are all about being built as economically as possible by the manufacturer, like the reasonably-priced Dacia Sandero and mostly all the others too) -- use overhead-cam engines of some description (albeit chain or belt driven overhead camshafts, rather than gear-driven overhead camshafts like a racing engine)?

[ I put both terms as the title, as it seems like some people object to calling pushrod engines "OHV" engines since OHC engines are also OHV, so it's an imprecise name for identifying cam-in-block engines. ]

Toyota isn't making any OHV engines anymore

Seriously?? You mean they went back to flat heads?
Overhead cam (OHC) engines are overhead valve (OHV) engines. OHV means the valves are in the heads.
OHC only refers to how the valves are actuated.

ok ok, Toyota isn't making pushrod engines anymore (expect for nascar, where they are mandatory)

I knew you knew,,, I just couldn't resist.

Out of interest's sake here is said Toyota engine:
Cutaway: https://i.ytimg.com/vi/Oo8DoRitG6U/maxresdefault.jpg
Complete: https://www.speednik.com/wp-content/blo ... cingv8.jpg

While this is the more common production-based Ford alternative (a V8 Supercar example which allows intake trumpets and eight throttles): https://media2.speedcafe.com/wp-content ... 4e91_k.jpg

And for comparison's sake a production-based Nissan DOHC engine built of the same capacity built by the same V8 Supercars racing team, showing the larger physical size of the overhead cam layout: https://d3lp4xedbqa8a5.cloudfront.net/s ... ne-(6).jpg

[gruntguru]

Pretty sure the rules have always allowed pushrod engines.

[Tommy Cookers]

the last pushrod engine in F1 ?
remember ERAs and Talbot-Lago won in 1948-1954 F1
remember 1952-3 WDC was for F2 so had Cooper-Bristols etc (developed BMW engine)
and there were many non-championship F1 races until c. 80s (eg 22 in 1962)

certainly in F1 in UK - Bob Gerard's rear engined Cooper-Bristol in 1957 WDC (and 1958 in non-WDC)
in F1 in Australia - Brabham's pioneer rear engine Cooper-Bristol Reg Smith then Max Stephens owned it
https://en.ascottcollection.com/coopert40-fr
NOTE 'Black Jack' Brabham so called after his early striking black beard and hair combo
the car won the Australian GP in 1956 and raced there in 59 - but this GP was always FLibre not F1
https://primotipo.com/tag/cooper-t40-bristol/

1961-65 1.5 litre saw a lot of F1 pushrodding (many races in SA - afaik for the national championship) ....
eg 1962 Rand GP (non-WC but many WC entries)
Brausch Niemann's 127 mph 1958 Lotus 7 (shortened to F1 rules) with 1.5 pushrod ohv Ford finished 10th (on the road)
famously slipstreaming Jim Clark's V8 Lotus
https://grassrootsmotorsports.com/forum ... 225/page1/
the engine was the UK 1340 cc '109E' Ford bored to 1475 (with 65mm stroke plausible against 1961-2 Climax F1 4cyl 72 mm)
like the 1100 FJunior Ford/Cosworth etc (a bored out '105E' 1000) - the blocks were identical ie 109E replacing 105E
BN then drove a Lotus 22 FJ 109E getting good places in non-WC F1 GPs Mozambique and Pietermaritzburg etc
and qualified for the WC SA GP at the end of 1963 (pushrod cars dnq'd the next SA GP - in Jan 1965)
others in 109E engined Lotus FJ cars in SA included Bernie Podmore and Dave Charlton
other FJs used 'twin-cam' (dohc) 'Lotus' Fords as did Hawkins & Prophet Brabham BT10s SA GP 1965
(some wrongly call these 109E - though a twin-cam is a 1.6 on a pushrod 116E block so 1.5 tc via a 109E block is conceivable)

1961 (UK/US invented) Intercontinental Formula allowed 3 litre ohc/dohc vs 5 litre pushrod - only IC 7 races held

2.5 (but not 4.5 litre) UK Daimler pushrod hemi V8s did hillclimbs but eg as 2.5+ never F1 used even as 1966 stopgap
similarly Armstrong-Siddeley had in later 50s pushrod hemi 4s and 6s (tried in a race sportscar)
Riley and Lea-Francis hemi 4s somewhat earlier

canted valves were unknown until GM evolved them (by accident having invented the ball-mount rocker for other reasons)
though Rudge race and even road motorcycles had heavily canted ie 'radial' valves in the early 30s

[Maritimer]

OHV hemis might work with the current rules since they could be run close to 12K and flow best at those higher revs, and with F1 not allowing VVT/VVL. But the example of the Merc CART engine is maybe disingenuous as its advantage was being much larger than the quad cam engines, the pushrods were just a clever work around of the old stock block rules. I dont know if the added reciprocating mass would outweigh any reduction in internal loss from bearing drag.

[bill shoe]

If engine rules limit power by displacement, then rpm will be very fast and there will be no pushrod engines. If engine rules limited power by airflow or fuel flow and without regard to rpm, then large-displacement and low-rpm pushrod engines probably become the best solution. Race engine architecture is a function of rules and nothing more.

[Jolle]

If engine rules limit power by displacement, then rpm will be very fast and there will be no pushrod engines. If engine rules limited power by airflow or fuel flow and without regard to rpm, then large-displacement and low-rpm pushrod engines probably become the best solution. Race engine architecture is a function of rules and nothing more.

Even if such rules rules would be used (we almost have them now, with a turbo canceling our displacement), a DOHC or a OHC setup to any pushrod engine would improve efficiency so much, that it would counterbalance any weight penalty. Thats why every racing engine since the 50's is a (D)OHC engine if the rules don't specify a pushrod setup.

Pushrod engines are a traditional thing, like 911's still having the engine in the back. It gives a certain character but it's not the best solution for performance (and that's why Porsche has a racing version of the 911 with a mid engined motor and Chevy racing a DOHC Corvette)

[Rodak]

I don't think comparing the Ilmor pushrod engine to the OHC cam Indy engines is a fair comparison. The Ilmor had a displacement of 3.43 liters vs the 2.65 liters of the OHC and was allowed a boost of 1.86 bar vs 1.52 bar; this was allowed to try and equalize the pushrod engine so I suspect if you compared a pushrod 1.6 liter engine, even with four valves (the Ilmor was 2 valves by regulation) with a four cam engine at the same boost OHC would win. The Ilmor valve gear was very complex and a four valve version would be even uglier. There's a good book about the Penske engnine that's worth a read, 'Beast' by Jade Gurss. And on that note I am really glad Penske took over the Indy series; a real racer who will hopefully get the series back to what it was. The CART-Indy debacle sure ruined open wheel racing in the States.

Edited to add: And let's not forget the engine life requirements......

[PlatinumZealot]

Well think of all the finer reasons why they did not continue to be used.

How does it go with wear?

Can four valves be actuated easily with that design? Two valve have interesting charecteristics but not as balanced as four valves.

Backlash In quick throttle changes?

Might be some reasons why....

[Hoffman900]

The engine doesn't care how the valve is actuated. It doesn't know whether it was done via pushrods or multiple camshafts.

The Illmor Penske engine was more about equalizing 2 valve vs. 4 valve. The pushrod part of it was to allow for production based American engines in, but they exploited a loophole to build a purpose built engine. The boost / displacement advantage was again, about 2 valves. As you all know, a 4 valve engine can fit much more valve area for a given bore size.

NASCAR builders were able to see in excess of 10,000rpm, for 500 miles (plus qualifying, plus practice sessions, so 750miles or so). These engines have 2.20 +/- a tenth or two intake valve diameters (with a minimum weight that I forget) and are running in excess of 1.000" valve lift. The valvetrains are variable in the sense they they use controlled lofting of the valves (through lobe / pushrod / spring design) so they gain valve open area with rpm. These are very sophisticated pieces of equipment, and my sources told me Cosworth engineers were blown away when they were taught how to do this just a few years ago.

Of course, NASCAR engines are more limited now through a gear rule.

When the NASCAR Cup cars switched from flat tappet to roller lifters, they didn't gain any more power. Why? Well they used very high rocker ratios (2:1+) so when you multiply the lobe values through that, they were already at the acceleration limits of what a conventional valve spring could do. Switching to rollers just meant they used less rocker and more aggressive lobes, but the metal valve springs is still the limit. NHRA Pro Stock also is the same in this regard.

One thing racing series here in the States do not allow are pneumatic valve actuation. Del West campaigned to get this in NHRA Pro Stock in the early 2000s, with no bites. Builders would love it, but the rules makers like the frozen in time rule sets as it uncomplicates things.

Pneumatic valve actuation would again change the whole game with pushrod engines and it would allow for some awesome performance. With that, you're not limited by the valve spring (like mentioned above).

The push rod engine's biggest downfall, is that it does not give you a clean slate for port location as you are always have to accommodate push rods passing by the intake port. Furthermore, purpose built pushrod race engines have the cam moved very far up the block (to shorten the pushrods) and thus lose valley clearance that could be used to intake manifold packaging.

Given the current rpm limits, with pneumatic valve actuation, I think a multi-valve/cylinder pushrod engine could work very well from a CoG POV. However, the compromises that would have to be made in port location / design as well as the ability to package the top of the engine in the valley (intercooler, runners, etc) is its Achilles heel in this type of racing.

[Rodak]

Well think of all the finer reasons why they did not continue to be used.
How does it go with wear?
Can four valves be actuated easily with that design? Two valve have interesting charecteristics but not as balanced as four valves.
Backlash In quick throttle changes?
Might be some reasons why....

Two weeks after the race USAC reduced the boost from 55 inches to 52 inches for purpose built pushrod motors. Four months later Tony George, the owner of the Indy track started the IRL and began the CART/IRL wars. He changed the rules to allow only 2.2 L turbo V-8 engines from 1996 and changed qualification so that the top 25 IRL teams would be guaranteed entry to the 500 regardless of qualification speed....... For the 1995 race boost was reduced to 48 inches, effectively killing the pushrod motor. Ilmor had orders from 17 teams for engines for 1995 and had started production when the new boost levels were announced; they had a lot of scrap castings....

[Jolle]

The engine doesn't care how the valve is actuated. It doesn't know whether it was done via pushrods or multiple camshafts.

The Illmor Penske engine was more about equalizing 2 valve vs. 4 valve. The pushrod part of it was to allow for production based American engines in, but they exploited a loophole to build a purpose built engine. The boost / displacement advantage was again, about 2 valves. As you all know, a 4 valve engine can fit much more valve area for a given bore size.

NASCAR builders were able to see in excess of 10,000rpm, for 500 miles (plus qualifying, plus practice sessions, so 750miles or so). These engines have 2.20 +/- a tenth or two intake valve diameters (with a minimum weight that I forget) and are running in excess of 1.000" valve lift. The valvetrains are variable in the sense they they use controlled lofting of the valves (through lobe / pushrod / spring design) so they gain valve open area with rpm. These are very sophisticated pieces of equipment, and my sources told me Cosworth engineers were blown away when they were taught how to do this just a few years ago.

Of course, NASCAR engines are more limited now through a gear rule.

When the NASCAR Cup cars switched from flat tappet to roller lifters, they didn't gain any more power. Why? Well they used very high rocker ratios (2:1+) so when you multiply the lobe values through that, they were already at the acceleration limits of what a conventional valve spring could do. Switching to rollers just meant they used less rocker and more aggressive lobes, but the metal valve springs is still the limit. NHRA Pro Stock also is the same in this regard.

One thing racing series here in the States do not allow are pneumatic valve actuation. Del West campaigned to get this in NHRA Pro Stock in the early 2000s, with no bites. Builders would love it, but the rules makers like the frozen in time rule sets as it uncomplicates things.

Pneumatic valve actuation would again change the whole game with pushrod engines and it would allow for some awesome performance. With that, you're not limited by the valve spring (like mentioned above).

The push rod engine's biggest downfall, is that it does not give you a clean slate for port location as you are always have to accommodate push rods passing by the intake port. Furthermore, purpose built pushrod race engines have the cam moved very far up the block (to shorten the pushrods) and thus lose valley clearance that could be used to intake manifold packaging.

Given the current rpm limits, with pneumatic valve actuation, I think a multi-valve/cylinder pushrod engine could work very well from a CoG POV. However, the compromises that would have to be made in port location / design as well as the ability to package the top of the engine in the valley (intercooler, runners, etc) is its Achilles heel in this type of racing.

A valve is on an engine is not a digital “on off” thing. Cam profiles are very important and one is one of the big differences in performance. A DOHC engine can run much hotter cam profiles with less friction by default then a pushrod engine, just for the simple fact that valves and (the absence) of rods are always lighter then a pushrod engine. On top of indeed flow and two vs four valves.

I think the cog doesn’t even change that much. If you look at a racing engine, cams and belts doesn’t weigh that much and only put a few cm of extra hight to a block. Those few cm of a higher cog are easily offset by the extra performance at lower size.

[63l8qrrfy6]

Surely you are missing the main point ?
On a pushrod actuated valve the spring has to control the inertia of the valve plus everything up to the cam lobe. That's easily double the inertia of an equivalent direct acting valvetrain.

For the same cam profile, direct acting = smaller spring force = more power. Or alternatively, direct acting = higher allowable valve acceleration for the same spring force = more power, whichever works best.

[Mattchu]

This is probably as good a place to ask as any Does anyone think that electronic actuators [as seen on the recent Koenigsegg via freevalve] will become seen in F1 engines any time soon?
From all accounts they look to be the next big thing when it comes to engine advancement and with F1 now having to satisfy the green agenda [nothing wrong in that btw] should the technical regs be changed to allow this inovation to become something that the big engine makers can promote.

Any thoughts on why or why nots?

I personally would love to see it, F1 should be about pushing the technology boundries with new stuff that could filter down to road cars, this seems to hit a home run!

[Jolle]

This is probably as good a place to ask as any Does anyone think that electronic actuators [as seen on the recent Koenigsegg via freevalve] will become seen in F1 engines any time soon?
From all accounts they look to be the next big thing when it comes to engine advancement and with F1 now having to satisfy the green agenda [nothing wrong in that btw] should the technical regs be changed to allow this inovation to become something that the big engine makers can promote.

Any thoughts on why or why nots?

I personally would love to see it, F1 should be about pushing the technology boundries with new stuff that could filter down to road cars, this seems to hit a home run!

Any flexibility in an engine or a car in general, like shift cams for instance, is very helpful for street cars because of the large operating window. A racing engine only has to be performing at a very small power band. So if there any other advantages then flexibility, possibly, but otherwise not.

[Hoffman900]

Surely you are missing the main point ?
On a pushrod actuated valve the spring has to control the inertia of the valve plus everything up to the cam lobe. That's easily double the inertia of an equivalent direct acting valvetrain.

For the same cam profile, direct acting = smaller spring force = more power. Or alternatively, direct acting = higher allowable valve acceleration for the same spring force = more power, whichever works best.

Not necessarily.

A direct acting, cam on bucket valve train is inherently stiffer, but it is velocity limited by the diameter of the bucket. Also, it's a 1:1 lobe to valve profile, and as such, the extra acceleration at the lobe due to the system stiffness is needed because the lobe isn't being multiplied by a rocker, and needs the acceleration to get the same valve lift profile over one with a rocker multiplying the lobe profile.

Finger followers provide the best of both.

Again, the engine doesn't care how the valve is lifted. It only sees the valve lift profile. With the push rod system, there is some disconnect between the lobe profile and the valve profile through the rpm range, due to system stiffness, this is all measurable and compensated for, and in NASCAR's case, it is used to their advantage through controlled loft that gains open valve area with increasing rpm. Regardless, top pushrod racing engines are valve spring limited, not anything else.

We're talking pushrod actuated cam systems here. Pushrod does not have to mean 2 valve per cylinder.

A SOHC like Honda's CRF450, provides a narrow / compact top end like a pushrod actuated system does over DOHC, but with the system stiffness of a OHC platform as well as rocker multiplication through finger followers: