Flat Engines

[Edmonton]

What are the advantages/disadvantages of these in racing?

[Richy_Rich]

Low center of gravity would be the main advantage, I think.

[imull]

I think that Subaru struggle for power in their boxer engines.

[KC]

The only problem I see with a boxer style motor is that it can be hard to package between the suspension components on a road car. Porsche has pretty much solved the horsepower issues with the design over the last 30 years. With most car designs ther eis more room front to back than side to side. Of course, FWD setups favor a shorter engine when mounted inline with the axles.

Biggest advantage would seem to be low center of gravity and low overall height. Easier to package under a low profile shape. This can also be a challenge if the engine is wide enough to be in the way of suspension mounts.

[chunder]

A few manufacturers still use them.
Alfa used them for a while with some success, but like an earlier thread said, they struggle foir outright power I think.
Subaru also make a flat 6 I reckon.
And Porsche have so much experience that they have got all the problems licked, using different types of cooling and turbos for the power.

[cannardd]

The main reason for Porsche switching to water cooling is emissions, for which you want a constant(ish) controllable engine temp and it is very difficult to do that with air cooling.

It also has an added benefit of being quieter, which helps them in the EU drive-by noise tests.

A flat-4 is an ideal setup for a front engine 4WD car though.

[GTV27]

Why are there any power issues associated with a flat engine (I've not previously heard of it as an issue)?

As an admirer of the Alfa and Subaru boxer engines (not to mention Porsche and Ferrari), I'd appreciate if this could be elaborated on.

[imull]

the inlet/exhaust tract is a bit tricky to do due to the length and complexity I would guess. That would probably affect torque and power is a function of torque (or is it the other way round :confused: )

Dont they also have to use a lot of balancing weights in a flat 4 which would affect throttle response I guess...

[avsfan733]

Ya thats definitely a problem. Especially once you go the turbochargin route. you have to run one set of primaries all the way accross the engine then run the intake back.
I thought that part of the reason for flat engines was there inherent balance though?

[imull]

porsche used balancing shafts in their engines didnt they.

engines really arent my thing. enjoy them but havent really studied them too much () so am groping in the dark.

[KC]

I think they only used balancing shafts in the 968 massive four cylinder engine. I don't think the flat 6's needed any additional balancing other than a harmonic balancer on the crankshaft.

[imull]

ah that would make sense.

[graham bahr]

a flat 4 is far better balenced than an inline 4 due to the fact that the pistons and rods always have an opposite number travelling in the exact opposite direction.

[alfasud]

Exhaust problems are not impossible to solve.... just difficult at times - my Alfasud has 4->1 exhaust.... just don't look too closely at the ground clearance (or lack). Of course with a turbo it's extra difficult and may result in some undesirable compromises being made.

However, when compared to an inline four, a four cylinder boxer has another advantage - the very short crankshaft has 3 main bearings, instead of 5 in an inline 4. So less friction and the potential for more power rather than less.

[imull]

Surely the surface area of the bearings will be similar though as it still has to withstand similar peak same gas forces acting upon it?

[graham bahr]

i'm not so sure on that one, in a normal inline engine all the load is taken by the lower bearings because the crank is being pushed down onto them, but in a flat engine, both sides of the bearings take the load, so you dont actually need as bigger a bearing, as its the area that takes the load thats important not the actual bearing size.

[imull]

The engine must still fire one cylinder at a time so the crank is still effectively going to be pushed away from the burn.

I am probably missing something but cant see how the crank can exert a force on the bearing on the 180 degrees facing up the bore :confused:

[StephenRae]

A 4 cyl. boxer engine is essentially two x two cylinder blocks bolted together. Surely this must be inherantly stronger than having big end caps?

[imull]

the big end caps only take the load when at TDC on the exhaust stroke.

unless the crank journal is pushed through the rods big end there will still be big end bolts allowing the con rod to be removed from the engine...

[graham bahr]

yes the crank is pushed away from the burn, but the burn is in two opposing directions, so the load is spread.

the flat 4 alfa engine has conventional rods and bigends, its the main caps that are different, the two cylinder blocks are joined on there bottom sides by the lower half of the main bearing which is turned through 90 degrees compaired to a normal main, and the cap is fitted through a hole in the top of the crankcase, and is tied unto the rest of the engine by the head bolts in a similar manor to the rover k series engine.

[BugEyed]

Flat engines fell out of fashion in racing when under-car aerodynamics were used to provide downforce in the '80's. In F1 at that time Ferarri were running their Flat 12, but they were unable to successfully exploit the downforce available because of the width of the engine, whereas the relatively narrow DFV allowed the use of full length venturis. They subsequently went to a 90 degree V6 for their F1 turbo before going 72 degree V10 for their normally aspirated engines. Modern race engines now tend to run very narrow V angles to make the engine as narrow as possible (despite the inherent imbalance involved) to allow the best possible aerodynamics.

Duncan

[imull]

I must be missing something Graham but I still cant figure out how you get this "burn in two opposing directions" bit.

Surely there is only one cylinder firing at once...?

[noodles]

Bugeyed, interestingly, the initial turbo V6 ferari engines were 120 degrees ,as in the 126 series of cars (i.e Pironi & Villeneuve etc. cars) before moving to a 90 degrees for the 1987 season.

[alfasud]

I'm not sure I'd like to claim any expertise in engine design theory, but in practice, the three main bearing boxer-4 engines do tend to have less overall bearing area than a 5-main bearing inline-4 cylinder engine. Reduced crankshaft flex probably helps.

Interestingly, I remember reading about the Ferrari flat-12. For sports prototype racing, these had 7 main bearings, but when they began developing the engine for 3.0L F1 engines, they used 4 main bearings, for reduced friction.

http://www.ddavid.com/formula1/fer312b.htm

[eclectic]

Boxer engines? Lovely things I have one in my Citroen 2CV 1964, 425cc! Last week it seemed to be even slower than usual, traced to a loose spark plug, amazingly it was still able to take two adults up the hill out of my village, albeit at snail's pace in 1st!