30 replies to this topic

[mat1]

One of the claims to fame of boxer engines is the lower center of gravity, compared to for example in-line engines.

Last week I was at the IAA in Frankfurt, and looked down in the engine compartment of a Subaru Legacy diesel, which has 2 litre 4 cylinder boxer engine. And the engine seemed to lie pretty high in the compartment. It turned out the exhaust was (of course) partly under the engine. Which led me to the question: is there really a significant difference in center of gravity of a boxer engine when it is built in a car (accounting for exhaust space etc), compared to a four cylinder in-line engine, especially as it it possible to place te in-line engine at an angle.

Are there any data on this?

BTW, the benzine (gasoline) engine of Subaru seemed to lie somewhat lower.

Thanks in advance,

Mat

[kikiturbo2]

we had this disscussion recently..

I'd say, that if you had a dry sump boxer, you'd get pretty low COG and maybe not the greatest exhaust because you need a sharp bend right after the head... so in that respect you will be better than a inline 4... however, I think it is hard to beat a V8.. esp. a dry sumpped one.

looking at a normal boxer, I think that the biggest problem is not the exhaust but the wet sump... because you have cylinders lying flat, you do not want the oil sloshing around too much in the corners,.. so you end up with a deep sump..

[cheapracer]

The reason the exhaust is as it is, is because of overhead cam. Early Subs and of course VW have the exhaust exit from the 'ends' of the heads. Ideally a DOHC racing boxer engine may benefit from exhaust ports coming through the top of the head.

[zac510]

The issue that the rally cars have is that the gearbox has to be inline with the front wheels to not have excessively angled driveshafts and then that puts the engine outside of the wheelbase. Maybe this wouldn't be so bad if Subaru didn't also insist on having 4wd road cars!

[cheapracer]

The issue that the rally cars have is that the gearbox has to be inline with the front wheels to not have excessively angled driveshafts and then that puts the engine outside of the wheelbase. Maybe this wouldn't be so bad if Subaru didn't also insist on having 4wd road cars!

I have no idea why they do that because on a Sub RX Turbo rally car I pushed the engine and box 40mm back without any problems. I had to lengthen the shafts anyway for the wider track I did for it so what the hell, back she went. It may come down to CV life expectancy issues in production?

All under standard Group A regs of course

[kikiturbo2]

well, if Audi can hang 5 in line in front of the front axle, why should subaru worry..

[zac510]

I haven't seen any successful Audi rally cars for over 20 years!

[kikiturbo2]

that comment was "tongue in cheek" ... I haven't driven a really good Audi road car until the R8..

[gordmac]

How much of an influence on installed engine c of g height is the height of the centre of the driven wheels? If the crank height has to be the same, a boxer engine must have a lower installed c of g height than anything else.
The companies that have used boxer engines generally have had the engines longitudinally and at the same end as the drive (eg Porsche with the Beetle and 911, Subaru) and have perhaps considered the boxer design as much for being short as for c of g height. The other option is to have a "conventional" engine transversely mounted, above the gearbox with a c of g height penalty or in line with the gearbox which is now the normal way of doing it but with a lateral imbalance.
Sticking a big heavy cast iron lump out the front with an inline gearbox to get front wheel drive as Audi seem to prefer makes no sense to me, other companies with inline front wheel drive (Renault, Saab?) at least put the engine behind the gearbox.

[cheapracer]

Sticking a big heavy cast iron lump out the front with an inline gearbox to get front wheel drive as Audi seem to prefer makes no sense to me, other companies with inline front wheel drive (Renault, Saab?) at least put the engine behind the gearbox.

Renault only did it for a short time in the 60's then with the 12 went the VW/Audi way.

SAAB were on top of the gearbox with a very hi CG.

I'm fairly confident that the Boxer engine is chosen for it's length and don't forget the Lancia Gamma series, oh on second thoughts please forget them

From Wiki http://en.wikipedia....ki/Lancia_Gamma

"Lancia developed a unique flat-4 engine for the Gamma....
Ironically, it was the engine that caused the Gamma to have a poor name. It overheated far too easily, wore its cams, and leaked oil. The wishbone bushes wore out early, and, because the power steering was driven from the cam-belts, the car was prone to snapping the belts when steering was on full lock — with disastrous results"

Edited by cheapracer, 25 September 2009 - 13:21.

[PJGD]

Jowett Jupiter, front engine, RWD, and as gordmac says the crankshaft is essentially at the center height of the road wheels.

Tubular steel chassis, arguably underpowered, but won the 1.5L class at Le Mans three years running in part due to its good road holding.

By my estimate, the C of G is at about 15" high.

PJGD

[McGuire]

One of the claims to fame of boxer engines is the lower center of gravity, compared to for example in-line engines.

Potentially lower CG but otherwise the packaging sucks. It won't fit between the front wheels without seriously compromising the suspension layout and turning circle, so it's only suitable for mid-engine rwd layouts -- or more commonly, hung out over the front or rear axle.

[PJGD]

The engine mass overhanging the front axle and the implications on polar moment of inertia is a valid concern, although arguably only when you are cornering at the absolute limit which one rarely has the chance to do in normal motoring. Thus I don't see this as an impediment for most platforms.

Likewise, the suspension may be slightly different, but I don't think that it has to be compromised. In the case of the Jowett Jupiter, the chassis is exceptionally stiff in the area of the suspension attachment points and this contributes to its good handling. At 31 feet, the turning circle is average I would say. In a head-on crash, the engine can be arranged to submarine beneath the passenger footwell.

I recall that somewhere circa 1990, it was reported in Wards or Automotive Industries that Chrysler were considering the development of a FWD powertrain comprising a boxer engine over the top of the transmission, conceptully very much like the Issigonis Mini. Obviously nothing came of it.

PJGD

[carlt]

The engine mass overhanging the front axle and the implications on polar moment of inertia is a valid concern, although arguably only when you are cornering at the absolute limit which one rarely has the chance to do in normal motoring. Thus I don't see this as an impediment for most platforms.

Likewise, the suspension may be slightly different, but I don't think that it has to be compromised. In the case of the Jowett Jupiter, the chassis is exceptionally stiff in the area of the suspension attachment points and this contributes to its good handling. At 31 feet, the turning circle is average I would say. In a head-on crash, the engine can be arranged to submarine beneath the passenger footwell.

I recall that somewhere circa 1990, it was reported in Wards or Automotive Industries that Chrysler were considering the development of a FWD powertrain comprising a boxer engine over the top of the transmission, conceptully very much like the Issigonis Mini. Obviously nothing came of it.

PJGD

Issigonis designed something like the Jowett layout for his Morris Minor .
Seeing your pic above , even the lever arm shockers ? [I see teles as well ] and uprights bear a resemblance to the Minor

Edited by carlt, 26 September 2009 - 21:43.

[PJGD]

True, Issigonis did design the Morris Minor for a flat four engine, but it never made it into production; he was obliged to use an existing engine since there was no money for new tooling. Also, the Minor had torsion bar springing IIRC, as does the Jupiter.

However, those are not lever-arm shocks, those upper arms were designed by Roy Lunn, later of Ford and Jeep. This view shows that area of the chassis and suspension slightly better:



PJGD

[McGuire]

The engine mass overhanging the front axle and the implications on polar moment of inertia is a valid concern, although arguably only when you are cornering at the absolute limit which one rarely has the chance to do in normal motoring. Thus I don't see this as an impediment for most platforms.

Likewise, the suspension may be slightly different, but I don't think that it has to be compromised. In the case of the Jowett Jupiter, the chassis is exceptionally stiff in the area of the suspension attachment points and this contributes to its good handling. At 31 feet, the turning circle is average I would say. In a head-on crash, the engine can be arranged to submarine beneath the passenger footwell.

In the Jowett the engine was not installed between the wheels but hung out over the front spindle CL, as shown in the photos. The engine would never fit between the wheels without seriously compromising the suspension layout and turning circle, just as I said.

Engines hung out over the axles work well enough with lightweight pea-shooter engines ala Porsche and Subaru but are not such a good idea with say, a V8/O8. When all is said and done there is a limited selection of packages for which an opposed engine is suited and they have pretty much all been done. I wouldn't be looking for more of them. The Jupiter shows just what can be gotten away with in a light enough car with little enough engine. Maybe Tata could have a look at it. Their engine could go in the glove box or on the roof rack without causing undue problems.

[PJGD]

Hey Mac, not so fast! An overhung engine as shown must restrict turning circle more than if it were mounted on the front axle center line. The fact that one can get a reasonable turning circle with an overhung engine; an engine which BTW is long stroke and thus wider than optimum, should not inhibit the selection of a boxer engine. Yes, the chassis tubes as shown would be somewhat different if the engine were on the axle CL, but the suspension itself need not be different.

Since the future belongs to down-sized, boosted and down-speeded engines with or without hybridization, you could also have observed that we should not be looking for any more V8 engines. What we should be looking for are engines that package well after the electric motors and battery pack have been located in the chassis. In-line and Vee engines may have been the best choice for vehicles with conventional powertrains, but that may not hold for the future where different criteria apply. For instance, in the past we have got away with 4-cylinder in-line engines of ~2L capacity without balance shafts. Given the more robust reciprocating components, modern down-sized highly boosted engines in that size range require balance shafts to achieve acceptable NVH (for example Mercedes OM651). Boxer engines avoid the need for balance shafts, so now the cost differential between in-line and boxer is diminished. Little engines are the future! They just need to have a construction that can withstand the high cylinder pressures that go with high boost.

PJGD

[Tony Matthews]

Their engine could go in the glove box or on the roof rack without causing undue problems.

[gruntguru]

Maybe Tata could have a look at it. Their engine could go in the glove box or on the roof rack without causing undue problems.

No those spaces are both allocated for additional passengers.

[cheapracer]

Firstly a little sad at the passing of the great Pentti Arikkala and I was just reading an interview from last year relevant to this thread...

"Subaru is dead. It is dead. The problem is the same as Audi had - and still has. The engine is in the wrong position. It is too far forward relative to the front axle and unless they change the engine location they are not going to do very well. I have driven all of these cars and having too much weight in the front makes the car understeer. It doesn't change direction as quickly as other WRC cars where the engine is less on the top of the front axle. There is a big difference. Subaru is saying it is great because the engine is so low. But I don't buy it. You have to have a weight transfer that is very fast in World Rally cars. You don't need it in F1 cars, but the cars without wings, like rally cars, they have to have a weight transfer that is very quick. To achieve that you have to put the weight high up in the car and then you can change direction very quickly. Look at the switches they have now-a-days in WRC cars - the indicators, the windscreen wiper switch and the change of brake balance - they are all down in the floor. Everyone knows that is the wrong thing to do. Guess what I won't be very popular for saying all this will I!"

[gruntguru]

Firstly a little sad at the passing of the great Pentti Arikkala and I was just reading an interview from last year relevant to this thread...

"Subaru is dead. It is dead. The problem is the same as Audi had - and still has. The engine is in the wrong position. It is too far forward relative to the front axle and unless they change the engine location they are not going to do very well. I have driven all of these cars and having too much weight in the front makes the car understeer. It doesn't change direction as quickly as other WRC cars where the engine is less on the top of the front axle. There is a big difference. Subaru is saying it is great because the engine is so low. But I don't buy it. You have to have a weight transfer that is very fast in World Rally cars. You don't need it in F1 cars, but the cars without wings, like rally cars, they have to have a weight transfer that is very quick. To achieve that you have to put the weight high up in the car and then you can change direction very quickly. Look at the switches they have now-a-days in WRC cars - the indicators, the windscreen wiper switch and the change of brake balance - they are all down in the floor. Everyone knows that is the wrong thing to do. Guess what I won't be very popular for saying all this will I!"

It is easy to raise the CG of a rally car - or any car for that matter - just raise the whole thing! (and get a bonus increase in ground clearance). Lowering the CG on the other hand, is not always so easy - ground clearance is a conflicting requirement. So it makes sense to arrange everything (including switches and brake balance knobs) for the the lowest possible CG and raise the ride height (or the drivers seat) if you decide a higher CG is needed.

Interesting that he starts off talking about front engine overhang and the effect on understeer, and seamlessly transitions to CGH, weight-transfer (I assume F-R) and their effect on yaw response.

[gordmac]

Sad to hear of his passing. Pentti was a good driver, not so sure about being a good vehicle dynamicist though.

[TDIMeister]

CoG should be evaluated in reference to the crankshaft centreline position. The two side-by-side pictures above are hardly a fair comparison.

Edited by TDIMeister, 05 October 2009 - 19:10.

[gruntguru]

CoG should be evaluated in reference to the crankshaft centreline position. The two side-by-side pictures above are hardly a fair comparison.

It is always possible (with gearbox design) to move the drive up or down to meet the axle height requirements. The final say on CGH of an engine will always come down to ground clearance.

[TDIMeister]

Fine, then a boxer will always have the lowest CoG. Thanks for agreeing with me.

[gruntguru]

Fine, then a boxer will always have the lowest CoG. Thanks for agreeing with me.

You're welcome.

[cheapracer]

Fine, then a boxer will always have the lowest CoG. Thanks for agreeing with me.

Theres many a picture of F1 Ferrari flat 12 race cars from the early 70's with the engine and exhaust system clear to be seen - check them out and you will see the issues.

[TDIMeister]

Well, I agree with you, except F1 is a whole other ball game when it comes to packaging/aero requirements, etc. Besides, there's absolutely no rule that states that the exhaust has to be on the underside of a boxer layout.

[kikiturbo2]

Well, I agree with you, except F1 is a whole other ball game when it comes to packaging/aero requirements, etc. Besides, there's absolutely no rule that states that the exhaust has to be on the underside of a boxer layout.

well, you could have both intake and exhaust on top, but you'd be loosing quite a lot of volumetric efficiency that way...
I still stand by my point that boxer engines are first and foremost limited by the sump height and the need for dry sumps in order to have low COG... once you throw that cost into consideration , a small V 8 or V6 engine might be a better solution, but that is strongly dependant on the overall package..

[mat1]

Are there any hard data on CHG of cars with boxer engines and cars with other types of engines? I would not be surprised if the difference, if any, is very small.

mat1

[Greg Locock]

Are there any hard data on CHG of cars with boxer engines and cars with other types of engines? I would not be surprised if the difference, if any, is very small.

mat1

I doubt it-and if there was the difference would be small. Say the engine weighs 100 kg, and the rest of the car 500, then if you dropped the CG of the engine by 30 mm (a damn good effort) then the CG of the vehicle would drop by 5 mm, which on rigs I've used is about the limit of repeatability.