More Cubic Inches-engine architecture

The following is a series of options looking at the packaging aspects of various engine architectures for mid engined implementations. The title indicates that I am trying not to steel the thread on "Hey Ferrari....Use More CUbic inches!!!"

I made the comment that a 120 degree V12 would make a better road car than either a 60 degree V12 or a 180 degree V12. The first 12 entries in this thread discuss one engine architecture each.

But to start, let us take the F355 engine as a starting place. A) because I have the users manual, and B) because I have a scanner. We start here because this enging has good breathing properties, and if we are to discuss alternate engine architectures, we should start with the notion that each enging should be in a similar state of tune.

On top of the bitmap from the scanner, I have composited building blocks that allow me the creator and you the reader to follow along as we distort the 90 degree V8 architecture along with its breathing so that each engin is in the same state of tune. Or comment about the state of tune when it is not.

On this engine we can see that the inlet track is very straight, and the exhaust header is considerably straighter than the typical american V8 header. Aroud the critical engine components I have drawh a box that outlines the minimum area this engien can occupy. In subsequent figures, this box will stay the same but be filled with a grey background. This box will allow us to reason about the packaging and center of gravity issues facing the engine bay architecture.

 

This is the figure that was supposed to be on the first entry:

 

This next figure shows the F355 engine essentials sitting between the rear wheels. The astute reader will see that there is little room under the headers for a venturi thus limiting downforce. In addition, the reader can see that the rear suspension lower a-arm runs over the venturi area allowing for a long a-arm and thereby lower camber change with respect to body roll.

 

This next figure shows the modifications made to the engine breathing as it sits in the F360 engine bay. The headers are rearranged to allow for larger venturies and the suspension arms have been shortened to allow maximum use of the venturi area and smooth airflow. The intake tract has been reshaped with a straight in inlet tract for high RPM operation, while a second inlet tract has been added to increase torque in the lower part of the RPM band.

 

This next figure shows how much a better center of gravity that can be accomplished when money becoms no object. The engine remains the same size as the F355 starting point. Notice that the exhaust headers are straightened out for better exhaust breathing, and that this increases the ability to place large ventruies under the rear of the car.

Notice how much lower the engine can be placed (ignore the suspension stuff on this figure).

I have shortened the inlet stacks to represent shifting the RPM band from 8500 to 13000 RPMs (ala 1978 F1 engine). I have also straightened out the exhaust manifolding in the head and in the header. this will increase exhaust breathing efficiency.

 

Now let us look at incarnations of V12 designs. I will keep the same cylinder, bore and stroke dimensions for clairity and practicality as this represents a 5.75 litre V12.

The first thing to recognize is that bending the 90 degree V8 into a 60 degree V12 has surprising packaging implications. Its a lot smaller! and not particularly taller, and should be easy to package. Even the conventional header location provides plenty of room for venturies.

The second thing to see, is that the top of the block where the two banks connect is a lot stronger in the 60V12 than in the 90V8. It appears to me that ther is no CG advantage, and amybe a very small loss.

The only drawback is the position of the ancillaries will be to the side and bottom and not in the bay between the cyclinders (this also cancels any CG penalty).

 

Now in road car formal, it is common to bend teh air inlet tracts for better packaging (e.g. a lower hood) however, this is not as useful in a mid engined alyout.

 

Now lets look at a 120 degree V12 arrangement.

Just unbending a 90 V8 into a 120 degree V12 has some interesting implications. A) all the breathing stuff works ok (intake and exhaust), B) the venturi area is comprimized, C) the CG is definately better than the 60DV12 and the 90dV8.

All in all this is a surprisingly small package.

 

If the designer faces a height problem he can allways fold the sir intakes around as follows, at some cost in breathing efficiency at high RPMs.

This makes for a very small package with lots of CG advantages.

 

Now let us unfold the 90 degree V8 into a 180 degree V12. The first engine shows a reasonable arrangement of a flat V12 (ala Porshes)

An issue the flat 12 has that the flat 6 engine does not is that the 3 extra header tubes may actually cause the engine to be higher in the chassis. This is an interesting (but solvable) packaging issue.

Under the engine there is not much room for venturies, and although it has great CG value (and thus dominating the late 1970 F1 racing) the lack of room to put venturies was a handling issue the flat 12 could not overcome.

 

An all out race car would go even further with the center of gravity with the flat V12

 

Now, finally the Boxer/Testarossa implementation.

I have bent the air inlets around to match TR style. This will end up hurting top end performance as bent air passages have higher resistance to airflow than straight inlets.

With the transmission under the engine, there is room for the headers and medium sized ventruies (not shown), but notice the CG is at a disadvantage (engine to engine) with respect to the 90 degree V8 implementation. On the F355, the transmission is at the same height above the road surface as is the transmission in the Testarossa so there is no advantage or disadvantage. However, a V12 is much heavier than a V8 so the CG advantage is in the F355 direction. Notice, also that the total height is equal to the V8.

Bottom line: these two architectures package up about the same.

 

Now, finally, let us see what an american V8 would package like.

I have scalled the engine up to 5.7 litres and rearranged the inlets like the LS1/LS6 Corvette engien, and rebent the exhaust headers in Vette style. The Vette headers have to contend with the steering and front end suspensions, whereas out configuration contemplates a mid engined design point. I also changed the engine back to a wet sump system and placed it at 4.5 inches of ground clearance just like the rest of the figures.

The interesting thing to notice is that the LS1 packages into a slightly larger area than does the F355 or F360 engine. The smaller Ferrari engines can utilize multiple cams, intake systems, straight inlet tracks, and good header geometry BECAUSE the engines are SMALL. And because they are small, these engines will deliver a lower center of gravity and the handling benefits that go along with the lower center of gravity. This does not detract from the advantages of a BIG V8, TQ, TQ, and more TQ, with out sacrificing HP.

 

All done--fire away.

 

I thought it might be fun to compare a 3.5 litre V8 against a 3.5 litre V12. The first figure shows the 60 degree V12. At the same displacement the 60 V12 is much smaller than a V8 of the same displacement.

 

The trend continues with the 120 degree V12

 

The trend is complete with the 180 degree V12

So the V12 is a lot longer and a lot more compact in cross section. I can see why Porsche likes the flat 6 as the engine. the packaging above the engine itself is rather open, extremely low center of gravity without having to dry sump, even better when yo do. A 120 degree V12 has similar packaging and center of gravity advantages as the 180 degree and that the 60 degree does not.

 

Finally, a flat 180 degree V6 (ala Porsche)

 

I can see several reasons

A) Headers are heavier than the air inlets leading to a lower CG
B) Getting a positive pressure to the lower air inlets would be an interesting airflow challenge.
C) the welders schedule was already filled.

But I think B is the right answer, cold air at high pressure is easier to obtain just above the drivers head at the top of the vehicle, and once obtained it is easier to duct into the cylinders if it does not have to turn around several corners.