8 replies to this topic

[richdubbya]

Have any of you that have seen inside an F-1 engine measured the amount of cylinder offset from

the crankshaft centerline? A measurement from an older engine would be helpful along with

approx stroke, rod length and rpm range. If not, has anyone heard any rumors or discussions of

bore offset? Does anyone have a good picture of an upper cylinder case? Thanks guys.


Richard

[perfectelise]

The line drawing on the right illustrates what you're talking about.. only in a VR6 though ;)

Why would a V engine with two cylinder heads need 'cylinder offset'?

[Greg Locock]

I'm glad you found a diagram. The advantage is a slight reduction in cgZ. The disadvantage is a huge increase in piston sidethrust. I don't think they'd use this.

[richdubbya]

Thanks perfectelise, i cant tell from the illustrations. This is a road engine?



Greg, im not familiar with what cgZ is? Cylinder offset does increase piston side thrust, but also


increases the length of the effective power stroke, both in crank degrees and in time, and


increases the cylinder pressure at the point it is needed the most, both of which will show


gains in power especially at very high rpm. I realize it's a trade off (just like pistons with


no skirts), that's why im interested to find out.

[J. Edlund]

I think you guys thinking of different "offsets". Since a F1 engine is basicly two I5 engines in an angle with an I5 style crankshafts the cylinderbanks are offset so they can share the crankshaft.

The other "offset" is what also can be achieved with an offset piston pin, that is, the piston will not be at TDC when the crankshaft is at this position. If any F1 engine uses this I don't know but I would imagine that it would lead to larger friction losses, and since F1 engines use such high engine speeds this would probably be a problem.

[Fat Boy]

I would guess that this is something they play with when designing a new engine. There are certainly gains to be had. SAE paper 2003-01-0983 can give you a little insight on the numbers and mechanics of this particular trick.

Among the conclusions are these:

3. If a piston side force is below a certain level, piston friction becomes independent of the piston side force. Thus, it is important to design the psiton skirt so that the piston side force is maintained below the certain level.

5. Crankshaft offset of more than 10mm is not effective to reduce the piston friction in the test engine because the piston side force no longer is a factor of the piston friction during the expansion stroke. Piston friciton increased during the compression stroke is not a factor.

Fat Boy

[richdubbya]

Thanks J. Edlund, i guess i didnt make that clear. I'm not talking about the degrees of offset

between cylinder banks in a v type engine. I mean the distance between the cylinder bore

centerline and the centerline of the crankshaft main journals. I agree that friction becomes very

important at 19,000 but the amount of time to advance the flame front is greatly reduced also.

Does anyone have any idea what the total ignition advance in degrees is for these engines?

[desmo]

Ignition advance in an F1 engine will probably be in the range 0f 50-55 degrees. This and indeed the answers to most of your other questions can be found by searching the Tech Forum archives.

[Greg Locock]

I was wrong about cgZ (height of the CG). When you offset the pistons like this you are effectively delaying TDC, so the left bank is lifted up, and the right down, so there is no net change in cgZ.

For a simple model, using a coefficient of friction of 0.01, which is reasonable, but may be too good for a piston skirt, I get an increase in friction power from 13.4 kW at zero offset to 16.7 kW with 10 mm of lagging offset.

ie not really measurable in practice.

This gives you about 3 degrees of extra expansion time, eyeballing it from the graph. Is that good? My old copy of Taylor doesn't seem to mention it.