How 'bout a 45 degree V-8 for fwd vehicles?

[jlsaylor]

Alright, sorry this is getting up so late, but pondering the future of Ford Motor on the internet, unfortunately enough, doesn't pay the bills so this got squeezed in when I could manage it. That said, I've recently wondered why nob automaker has produced a 45-degree V-8 with a 90-degree crankshaft for use in fwd cars?

 

The advantages to this design are many...let me explain. First, the packaging advantages of a 45 degre desig should be obvious, especially in a transverse arrangement. The designw ould be 15 degrees narrower than a V-6 but no longer than an L-4, which means it would fit easily into just about anything you might take a mind to stuff a V-8 into. Torque production should be somehwat aided by the narrow 45-degree angle as well, something which would be useful on an engine which seems likely to be on the small side of the V-8 equation.

 

On to what could be wrong with it. Despite what some may think primary and secondary balance should actually be pretty good for this engine. Effectively what we would have is a narrow angle take on a 90-degree V-8. The 90-degree crank provides for even firing accross the cylinders while still leaving the slightly uneven fire from bank to bank that gives the American V-8, as well as 90-degree V-8's from other countries, it's much loved lopey idle. While it might seem that secondary balance would be problematic with a 45-degree bank angle, as best as I can tell with my admittedly quick and sloppy calculations balance should work out pretty well here too, if not quite as nicely as it would on a standard 90-degree cross plane V-8. In fact, it should be at least as good and likely better, than most of the 60-degree V-6 designs currently on the market.

 

This really shouldn't be too surprising as we can see examples of good balance achieved in much the same way with other mills as well. The 60 degree V-6's we see in so many mid-sized sedans employ a bank angle which is optimum for a V-12, not a V-6. (note: for those who may not know..divide 720 by the number of cylinders employed in a V engine design and you'll get the optimum bank angle for that number of cylinders...in a 4 stroke engine of course) These engines do typically employ 120 degree crankshafts to achieve even firing. The reason these engines employ a 60 degree bank angle is obvious, since a motor with the V-6's ideal 120 degree V angle would make for an utterly impractical package in most applications. But, while the above 60-degree V-6 design is not the ideal setup, it does work and can achieve very good balance and smoothness if properly designed.

 

In fact, I actually became curious about a possible 45-degree V-8 design when I began to notice that the above is something of a trend. That 60-degree V-6 mentioned above, employing a bank angle which is more appropriate for an engine with twice as many cylinders, works just fine with a split pin crankshaft providing even firing. Likwesie, a 90-degree V-4, an engine employing a bank angle more appropriate for a V-8, works just fine, and arguably better than an L-4, when utilizing split pins to keep the firing even. I knew that Marmon and Cadillac, among others, had built 45-degree V-16's back in the day, a bank angle which works out to be ideal for a V-16 engine. Would the same thing that holds true for a V-4 and a V-6 also then hold true for a 45 degree V-8 as well? Would cutting that V-16 in half and, producing a 45-degree V-8 with a 90 degree crankshaft, work out here as well?

 

In the end it seems as though it does, if not for the reasons I initally thought. And, it is worth mentioning that a 45 degree V-8, just like it's 90 degree brethren, possesses some inherent advantages in terms of simplicity and manufacturing over the above mentioned V-4 or V-6 designs. Let me explain.

 

Any V-6 engine, in order to achieve even firing, is forced to employ a split pin crankshaft, as is a V-4, a reality which most of you are likely aware of. This weakens the crank and increases production costs on what is essentially the most expensive part of an engine to begin with. A 45-degree V-8 would employ the same 90-degree crankshaft design virtually every other V-8 produced does...meaning no split pins and a simpler crank design saving money and improving durability.

 

Also, don't forget the advantage that a greater number of cylinders, not to mention an even number of cylinders on each distinct bank, provides in terms of balance. More cylinders gives an engine greater opportunity to balance out second order vibrations by better dealing with kinetic energy, etc. This is obviously a disadvanatge for the V-6 and V-4 relative to a V-8. Also worth mentioning is that an even number of cylinders per side, a design feature which ensures each cylinder on a given bank has a partner on that same bank with every pair reaching TDC simultaneously, also allows for better second order balance. This is obviously a problem inherent in the V-6 design since it only employs 3 cylinders per bank.

 

Another factor worth mentioning in light of the fact that this engine would almost certainly be on the small side for a V-8 are the advantages gained by employing an oversquare design, which seems appropriate here. This is worth mentioning because shorter stroke engines typically see lower piston speeds than their longer stroke relatives do improving durability and further improving the balance equation for this engine. Finally, the fact that 90-degree V-8's use counterweights to achieve their balance, something which is often criticized as shortcoming of the design desite the torque this system helps to produe, also makes it that much easier to achieve good balance in a 45 degree design.

 

I think this design makes sense and works well...I can find no fault in it. But, to be honest, I am not an engineer so if anyone out there who is decides to run calculations, which would certainly be more accurate than mine, I'd welcome it and would be quite curious to see what they come up with.

 

And before somebody mentions it, yes, I know that 45 degree V-8's have been attempted before and that they were bona-fide paint-shakers. But, while I could be wrong about this engine, the problems those engines encountered don't translate since every example of which I am aware predates the modern, 90-degree V-8 design....and before that era virtually every V-8 was a paint-shaker to some extent. Those engines were built on totally different principles.

 

All of that said, I wouldn't mind seeing a motor which ran from about 4.4L (with something like a 4inch bore making the stroke about 2.67inches or so) down to about 3.8L for large and premium car fwd duty. Hybrid suv's, possible future mini-vans should Ford change their mind, entry level Lincolns like the MkZ and cars like the 500, or even the Fusion, could make good use of a compact V-8.

 

And of course, the possibility that a four cylinder engine could be based on this, either in inline form utilizing the cylinder head from either bank of this design or by halving this motor and creating a 45 degree V-4. Either of these could take over duties on the smaller side of Ford's four cylinder market and help amortize development of both mills. A 45-degree V-4 would be a uniquely compact engine design to be sure. And while that engine would certainly need a split-pin crankshaft, and possibly even a set of balance shafts, to achieve good balance it would possess many advantages over a similarly sized L-4 with such an engine making for a very small package indeed.

Edited December 8, 2006 by jlsaylor

[68fastback]

Very interesting and thought-provoking post, JLS.

 

I'm not an engineer either, but I think you raise some good points. Such a V8 would be approximately the length of the '60s 289/302 (4.0 x 2.67/3.00?). A possible problem is that the 4.0" bore makes for an engine that is likely considerably longer than, for example, the 3.5 V6 .

 

I'm also wondering about the feasibility of a 22.5-degree V8 analygous to Audi's 15-degree V6 (at least I believe they have one coming).

 

Anyhow -- thanks for your good thoughts.

 

-Dan

[jlsaylor]

Very interesting and thought-provoking post, JLS.

 

I'm not an engineer either, but I think you raise some good points. Such a V8 would be approximately the length of the '60s 289/302 (4.0 x 2.67/3.00?). A possible problem is that the 4.0" bore makes for an engine that is likely considerably longer than, for example, the 3.5 V6 .

 

I'm also wondering about the feasibility of a 22.5-degree V8 analygous to Audi's 15-degree V6 (at least I believe they have one coming).

 

Anyhow -- thanks for your good thoughts.

 

-Dan

 

Thanks for the reply. Wow, your definately way above my pay grade with that one. Halving the 45 degree to come up with a 22.5 degree V angle. It'd be seriously compact, but I can't say I have any idea how well balanced such a design would be. But I suppose it could work so long as everything fit into the block. And possibly, by being so narrow, it could end up like VW's narrow angle engines and take on more of the characteristics of an line design, avoiding most balance issues altogether. Heck, Lancia built a 20 degree V-4 once, even if it was just one liter.

 

I know that VW's VR6 employs a 15 degree bank angle, and has been employed by Audi from tiem to time. But that engine has been out for quite some time now. Is that the Audi engine to which you are referring?

[68fastback]

I'm fairly sure I read someting in the past 60 days or so about a 15-degree Audi V6 coming along, not in an historic context, but not certain.

 

I was wondering how that might actually "fit" since, at that angle, the bottom of the cylinders are likely getting a bit cramped. I had read no to long before that about a stress/strain analysis Ford had done on V8s in the context of valley ribbing to prevent cracking. In that article was a simulated deformation showing how both banks of cylinders want to distort away from the direction of rotation, i.e. piston power stroke sidewall forces, and how external ribs were also added on the outside of the (the alloy 5.4 Ford GT??) motor to manage that.

 

That got me thinking that there's really no reason that the centerline of the bore needs to point directly at the centerline of the crank mains -- they could be offset to reduce the bowing stresses that accompany maximum torque at the point in the power stroke where rod angles are most severe by effectively reducing rod angle of the power stroke.

 

So I was thinking that, on the assumption that if the Audi 15-degree was a 'balanceable' design, a very narrow V8 of 22.5 degrees ought to be at least as balanceable -- and possibly more so due to the inherently balanced pairing of reciprocating mass of 4 cylinders per bank -- and that angling the centerline of the bores to minimize the bowing forces due to long-stroke high-torque demands and short-deck heights mandated by low car hoods might work well together.

 

In theory, the bore centerlines could be offset enough to permit maximum torque to occur with the connecting rod nearly vertical (!!!), but deck height would have to so tall to permit rod clearance on the exhause/compression strokes as to eliminate any stress-reduction benefit (weight tradeoff). In the context of the 5.4 modular or LS7 (as two examples of relatively severe rod angles), not all that much offset would be needed to bring cylinder side-load stresses down to levels similar to the 4.6 mod or LS1.

 

I was also thinking that additional deck height might be aviodable if slightly asymetric connecting rods were also designed to ease the clearance problem caused by the bore offset on the exhaust/compression strokes (a really radical thought, I agree). This seemd a bit nutty at first and a long way to go, but as I thought through why the bottom of the connecting rod needs to spread at the crank journal -- to spread load AND to handle the added bending stresses of rotation-at max-torque that journal bearing friction produces -- I realized that some accommodation on the rod journal on the side away from the bore offset (the side that must clear the cylinder bottom on the exhaust/compression strokes) might be possible since bearing load on exhaust/compression is minimal compared to the power stroke. So some accommodation in rod design for cylinder-bottom clearance, as long as it does not affect compressive strength or power-stroke bending strength, might be possible with only very slightly offset rods. If not, then a slight increase in deck height might be unavoidable for adequate rod-to-borebottom clearance on exhaust/compression strokes.

 

To clarify, looking straight-on at the snout of the crank rotating clockwise, the bore centerlines could be offset slightly toward a point to the right of the crank centerline to reduce the stresses of short-deck high-rod-angle torque. Of course, that exacerbates the deck-height issue and/or piston skit length and/or bore length a bit, but a very narrow well-oversquare V8 with a approximately a 4" bore might permit a short enough deck height and offset bores even with conventional rods and the whole engine might then be narrow enough to tilt it significantly in the engine compartment such that deck height becomes a non-issue in any case (sort of like the old Plymouth slant-6.

 

That's where I was thinking from. I did a little research some time ago and found (to my surprise) that offset bore-to-crank centerline engines had been conceived before, but I was unable to determine if a production engine was ever built or if a very narrow V8 was ever designed or attempted. I could find no information on a narrow V8 with offset bores, but I don't see anything that makes it undoable.

 

But, as I said, I'm not an engineer so I could be overlooking something fundamental for sure.