H8, X8 - Some Future Engine Ideas for Subaru

[evolutionmovement]

So I read they want a 5-series competitor built off the Tribeca chassis, but they have no engine. In this class, a large displacement 8 cylinder engine would impress more than a turbocharged smaller one. This is tough to achieve with the drivetrain and engine architecture. Either way, the Tribeca nees a bigger engine.

So I figure about 4.4 litres would be good and could probably make about 330 HP. It just so happens that would be the same displacement as 2 2.2s so I did some measurements. For 9.25 inches more length, the EJ22 could be stretched into an EJ44 or whatever they want to designate it. That's actually not that bad length wise for a bigger platform vehicle (especially an inherently clumsy one like an SUV). Overhnag could be reduced with thinner profile fans and radiators with weight compensation coming from battery relocation (as many German cars do). Another thing I was thinking to reduce length would be to stagger the cylinders in each bank both above and below the center line so that the block length could be reduced, yet the low CG would be retained. This would more resemble an 'X' with an extremely small angle between the cylinder centerlines on each bank. Experimenting with cancelling forces and moments would be costly, but I thought it would be an interesting idea.

I'd also like to see servo-motor actuated rotary valves. A gear off the crank could run the water pump and a T-belt would be eliminated. Very high flexibility as far as valve timing goes only surpassed by indivdual solenoid actuated valves, but then airflow characteristics of the rotary valve vs. the poppet valve may be superior in terms of flow potential. There would also be 0 chance of interference of any kind and reliabilty would be high. I read about 2 companies that have solved the sealing issue of rotary valves. This is the kind of innovation Subaru needs to stay on top of the assmonkeys that are all jumping on the AWD bandwagon. And with tis kind of action, their design direction won't be so important.

Me, I'd just like to get a hold of a rotary-valve flat 8 with displacement on demand to force feed into an old Impreza or the back of some custom mid engine car (while I'm dreaming) ...

Steve

[THAWA]

I do believe flat engines larger than 6 cylinders are dimensionally larger than v versions with the same cylinders. I can't remember where I read that though...

[G-reg]

Ok gear heads, why wouldn't an X engine work? Assume you get past the obvious crank/block/head configuration problem. With everything floating around in my head I’m thinking it’s just too complicated for any gain it would produce. Would something like a “Siamese VR6” two narrow angle Vdubs sharing a crank, or a why not a + engine….naah too many intake/exhaust problems. But all that being said the H6 makes more power and torque and runs smoother (according to one of the mag articles I read) than the I6 in the X5 and aside from the M motor is the biggest 6 in a Bimmer IIRC. The A6/5series would be a good target for Suby but I see a “big block” H6 or something with Turbo’s…like the A6. In 5 or 6 years a wicked E55/M5/RS6/ and a STi H6TT comparo….an STi H6TT wagon of course

[entirelyturbo]

Why wouldn't an X engine work?

It would be absolute hell to design the oil system for it, as you now don't have an oil pan on the bottom.

Now there is an engine called a radial engine which has 9 cylinders going all the way around, so a design where cylinders facing straight down can be done, but I still wonder just how that engine is lubricated...

[evolutionmovement]

I think I explained it wrong - there would be two banks of cylinders as on a boxer with a common head for each bank just that half the cylinders would be a little less than the 180 deg a true boxer would have while the other half would be at a slightly greater angle. The opposing bank would have the higher cyls 180 from the lower cylinders on the other side and vise versa for the lower cyls (greater than 180 deg angle). Looking at this engine it would look something like a large bore boxer from the outside, not like an X. I jjust used X to signify the four bore centerlines. The whole reasoning is to reduce the length a small amount of the engine since it overhangs the front axle.

Cam set up would be a nightmare or have poorly optimized breathing, hence my idea to combine it with rotary valves which also allow the engine to be narrower (much less room required than poppet valves and cams) and intake could also be greatly simplified (or about the same depending on if you'd use the open end of the rotor to fill with air like a fuel rail or introduce air through top ports as on a poppet valve head).

Steve

[AWD_addict]

Why wouldn't an X engine work?

It would be absolute hell to design the oil system for it, as you now don't have an oil pan on the bottom.

Now there is an engine called a radial engine which has 9 cylinders going all the way around, so a design where cylinders facing straight down can be done, but I still wonder just how that engine is lubricated...

I don't remember how radials are lubricated, but old aircraft radials from the '50s use a lot of oil. A radial with a 5 gallon oil capacity will go through about a gallon of oil a day. I'm sure this could be improved with modern tech, but the radial design would be so wrong for a car space-wise. There was a car that used a radial, I think it was a quick failure.

An X configuration is an interesting idea.

[evolutionmovement]

I think it was the Velocar that had a radial and a propeller. It was built in the thirties. Doubt it would pass Euro pedestrian safety standards now.

Steve

[THAWA]

I think I explained it wrong - there would be two banks of cylinders as on a boxer with a common head for each bank just that half the cylinders would be a little less than the 180 deg a true boxer would have while the other half would be at a slightly greater angle. The opposing bank would have the higher cyls 180 from the lower cylinders on the other side and vise versa for the lower cyls (greater than 180 deg angle). Looking at this engine it would look something like a large bore boxer from the outside, not like an X. I jjust used X to signify the four bore centerlines. The whole reasoning is to reduce the length a small amount of the engine since it overhangs the front axle.

Cam set up would be a nightmare or have poorly optimized breathing, hence my idea to combine it with rotary valves which also allow the engine to be narrower (much less room required than poppet valves and cams) and intake could also be greatly simplified (or about the same depending on if you'd use the open end of the rotor to fill with air like a fuel rail or introduce air through top ports as on a poppet valve head).

Steve

I see what you mean. Like two v4's mated together boxer stlye. that sounds huge honestly. I mean as much as subaru will say how short boxers are they are actually pretty tall. But to add more height to it now you're getting into v height, and a v8 would just be an easier and cheaper engine to produce. Honestly a 6 cylinder engine is quite enough for most things. If subaru finally wakes up and starts adding forced induction there's no need for anything larger.

[evolutionmovement]

People who buy premium cars want multiple cylinders. One of the reasons I think Saab doesn't do well is that it doesn't have multi-cyl engines. To have a 6 turbo and try to sell as premium looks like a tarted up cheap car to your uppity consumer who already is suspect of the badge to begin with. There are advantages to large displacement anyway, especially with a large vehicle, and even further with one that may be required to tow stuff.

This would not be like two V4s. I never should have designated it 'X'. The angle the cyls on one bank would be apart would be, like, 15 degrees, only half of that angle would add to block height. The cylinders would overlap for perhaps half their diameter - not separated like a V. I'd bet it would be barely taller than a 2.5. And a boxer is low - it's Subarus intake system on top that makes it look tall. Cut the sump down and you get it even lower. With rotary valves, the intake could be as low as the intake rotor if supplying air as in the fuel rail method and there's nothing to dictate the high rise spider that Subaru uses now. Intake and exhaust pulses would also change (and could be modified by the valves as well as the intake. This top end design has huge possibilities).

Picture something like the below for the front view:

:>-<:

Steve

[THAWA]

Well no I understood what you meant about the cylinders, but I didn't think it would have been fitting to say two vr4's together. Not the mitsu vr4 but a 4 cyl version of a vr6. If that makes any sense. I wasn't thinking you meant like a 90 degree crank angle. I knew it was small but that is still going to add height to the engine no matter which way you slice it. As far as a boxer being short, I consider the engine, sump, intake, etc, all part of the engine. so thats the engine height to me. Yes I know inlines are much taller but still an x engine would be around as tall as a v. About the extra cylinders, porshe seems to be doing quite alright with 6 cylinders. They've used 6 cylinders for how many years?

[BAC5.2]

I do believe flat engines larger than 6 cylinders are dimensionally larger than v versions with the same cylinders. I can't remember where I read that though...

I dunno, I'd like to know where you heard that also!

I mean, a Flat Plane V8 would be no larger than an H8, I would think. The crank layout would be almost identical.

[entirelyturbo]

People who buy premium cars want multiple cylinders. One of the reasons I think Saab doesn't do well is that it doesn't have multi-cyl engines.

I agree with this entirely. My grandfather rented a Saab 9-5 2.3T around Thanksgiving last year when he had a minor accident in his Caddy CTS. He told me he couldn't believe how much balls that Saab had. When I told him it was a 4-cyl barely bigger than the one in my Legacy, he almost didn't believe me.

Me personally, I prefer a smaller 4-cyl engine that is built up, rather than a huge V8 which is powerful no matter what. I think it's because I feel prouder of the small engine when it hauls ass

[evolutionmovement]

The H8 would have a lower CG than a V8 no matter what. The problem isn't that an H8 takes up more space, it's the space that it takes up. V8s can fit the frame rails or suspension under the heads, so width isn't as much a concern. Intake and sump can be designed according to package concerns - ever see a flat 12 Ferrari race car (not a Testarossa or BB with the transmission underneath)? The engine is low, the intake (which is light and contributes very little to the CG) is low, and the sump is dry.

Porsches are bought by staunch traditionalists, which is why they bore me. They can barely accept a water-cooled engine, much less a flat 8. They flipped when they went to a 6 for the 911. An H8 would be too much overhang over the back of a car anyway, and developing an engine like that would be expensive with Porsche's volumes especially when combined with their customer base. So why a V8 for the Cayenne? Because they can thin development costs by sharing it with other companies, they have V8 experience, V8s are a common engine type with lots of known development work, and the engine went into a planned high-volume, high-margin vehicle that appealed to non-traditional Porsche customers. Besides, why shouldn't Subaru do something different than Porsche? Their cars are nowhere near the same class or segment.

With GMs backing (with the agreement to share the rotary valve idea), I'd love to see Subaru take the reuigns on innovation. I don't think they have much choice.They should do that to Saab, but GMs to stupid and wants high volume instead of pushing Saab's reputation for innovation and aerodynamics by using them as a base for luxury hybrids and things like variable compression engines. And how cool would a new aero Saab hybrid styled like their earliest vehicles be? Well, anyway, Subaru needs to innovate to ompete with all the AWD bandwagon jumpers and to increase their reputation, but uppities won't care about the innovation (because they don't understand it) unless it has 8 or more cylinders on the top model.

Steve

[scottzg]

Porsches are bought by staunch traditionalists, which is why they bore me. They can barely accept a water-cooled engine, much less a flat 8.

Very true- rear engined is a terrible design for the street, imho, but thats what most porsches are bought for. However, for the same thinking, why shouldn't subaru just develop a v8?

A new engine shape and rotary valves is cost prohibitive, esp. for a low volume vehicle with a low volume manufacturer. R&D would kill, plus all the tooling and certs for production. Yeeoouch. I'd say that their best bet would be a very large 6 with a very effecient CC. Sure, it wouldn't have the top end potential of something with more cyls, but thats not the market they would be going for.

[evolutionmovement]

I don't think the problem is development as much as 'not invented here' syndrome. There are two companies who have developed rotary valves and solved the sealing issues. If they could buy out or license that technology and share it with GM, I think they could afford it. The problem more would be developing the H8 as it would be low volume and the X8 would be even worse cost wise - at least the H8 could be a modular type design.

The problem with a V8 would be the same as the H8 (except a lot less development work would be needed), but dynamically the V8 would be inferuior due to the lower CG. That or Subaru will have to go to an assymetrical AWD design. Something's got to change, and though I'm not averse to a V8 or assymetrical drivetrain, Subaru would then be just another car (and an arguably uglier one) and a lot of their brilliant engineering would be lost. Hell, they wouldn't have to develop a V8 at all - GM has a few of them, though the LS would be the most likely option (cheaper than the Northstar). Maybe an LS6 with a DOHC head ... Hm, maybe a V8 wouldn't be so bad.

Steve