Is the Combustion Chamber Volume for a Lamborghini Aventador Really That Small?

[mastermechanic]

I was analyzing the Lamborghini Aventador's tech. specs. and it is given Bore x Stroke 95mm x 76.4mm and compression ratio 11.8:1. Then I calculated the volume of displacement and it's 541.5 cm^3 for each cylinder. Then I know the compression ratio as $$\frac{V_1 + V_2}{V_2} = C.R$$ $$ V_1=Displacement,$$ $$ V_2 =Combustion Chamber$$

So V_1 = 10.8 V_2 and from here I found the V_2 as 50 cm^3 and divided it by 70.9 cm^2 ( area of the piston) to be able to find the approximate height of combustion chamber. And I got 0.71 cm.

It seemed weird to me, I grabbed a ruler and it's really really small. I couldn't imagine that a combustion chamber can be such small. There is no place even for manifolds to open and close. Where did I make mistake?

Thanks.

 

[JBA]

That is not necessarily a mistake because there is essentially no clearance required as long as the valve timing insures that both the inlet and exhaust valves are closed at the piston TDC (top dead center).

 

[mastermechanic]

That is not necessarily a mistake because there is essentially no clearance required as long as the valve timing insures that both the inlet and exhaust valves are closed at the piston TDC (top dead center).

Yeah, but even though there is not, 0.7 cm is pretty small, isn't it? If there is no mistake, Lamborghini engineers did a good job.

 

[Ranger Mike]

CR=(D + PV + DC + G + CC) / (PV + DC + G + CC)

you have to find the piston volume, Deck clearance volume, gasket volume as well.
this only works with flat top piston. any piston dome or piston reliefs ( eye brows) will add / subtract from this formula.

 

[JBA]

Or take the quick and dirty route. Assuming flat piston head:

 

[jack action]

Yeah, but even though there is not, 0.7 cm is pretty small, isn't it? If there is no mistake, Lamborghini engineers did a good job.

And that is an average. The closest parts are probably closer to 0.10-0.15 cm apart. And that is cold, with no inertial forces pulling on the piston/connecting rod/crank assembly. The piston is probably almost touching the combustion chamber or valves when in motion.

More info on Quench Quest - Squish, Quench, and Piston-to-Head Clearance

 

[Ranger Mike]

Jack is correct
Aluminum flat top piston with steel or cast iron connecting rod should have 0.15 cm or 0.060" clearance. Les will kiss the cylinder head. I built "quench" head engines running this close with no failure but this is the minimum you can use. Aluminum con rods will require more clearance as they will stretch. Do not forget you have two different materials with thermal expansion rates and the physically will " grow longer" due to heat. I ran this combo at 7000-7500 rpm daily with zero failure.

 

[HowlerMonkey]

 

[CWatters]

Yeah, but even though there is not, 0.7 cm is pretty small, isn't it? If there is no mistake, Lamborghini engineers did a good job.

7mm isn't that small. Bit more than 1/4 inch.

 

[HowlerMonkey]

Knowing the piston to deck height is also important as more than a few engines have pistons "proud" of the deck.

 

[Rx7man]

Howler, true, but usually that will just make up for head gasket thickness.

I'd be fairly certain these heads have quench areas, which are quite close to the piston at TDC... that gives a lot more room everywhere else.