Turbo vs NA

[NetWareHead]

If the engine put out 450 instead of 200, that would make the drivetrain hella expensive. Tranny and everything else connected to it would need to be a lot stronger.



In any event, NA cars are flat as well. first google image result for a honda civic torque curve. The second spike is the vtec kickin in, yo

Also, I started a thread like this a while ago. Turbo is better than NA because high compression NA is high compression all the time. Turbo is more dynamic. It can run at low compression or it can spin up and run high compression. That range gives a lot of flexibility.

Not necessarily ALWAYS high compression all the time. That statement simply does not always hold true. Just like turbos are variable in boost pressure, so is actual compression ratio. The physical dimensions of a combustion chamber are unchanging but it is the cam that controls the valves and for how long they stay open, and therefore the ultimate compression ratio. There are numerous examples of engines with high compression ratios (13-14:1) and they can idle and even do some light driving on pump gas. At low RPMs the valves stay open for a long time (over-simplifying) and some of the compression gets bled off before the valves seal shut. At racing and high loads/RPMs, more of the compression is retained in the chamber and therefore higher octane gas is necessary.

 

[ShawnD1]

At racing and high loads/RPMs, more of the compression is retained in the chamber and therefore higher octane gas is necessary.

Sounds like vtec, yo! (yo)

 

[JCH13]

Not necessarily ALWAYS high compression all the time. That statement simply does not always hold true. Just like turbos are variable in boost pressure, so is actual compression ratio. The physical dimensions of a combustion are unchanging but it is the cam that controls the valves and for how long they stay open, and therefore the ultimate compression ratio. There are numerous examples of engines with high compression ratios (13-14:1) and they can idle and even do some light driving on pump gas. At low RPMs the valves stay open for a long time (over-simplifying) and some of the compression gets bled off before the valves seal shut. At racing and high loads/RPMs, more of the compression is retained in the chamber and therefore higher octane gas is necessary.

This is not correct. The compression ratio of an engine is solely determined by the ratio of the geometric volume of the combustion chamber at its smallest volume (TDC) and largest volume (BDC): CR = Vsmall/Vlarge. This is independent of the valve timing, adjustable or not.

Also, there are numerous engines, specifically motorcycle engines, in the 13:1-14:1 compression range that run just fine on pump gas, even under high loads without VVT.

As far as I know SAAB was the only manufacturer to play with variable compression engines, which are VERY different from engines with variable valve timing, VVT or similar technologies like V-Tech.

 

[NetWareHead]

This is not correct. The compression ratio of an engine is solely determined by the ratio of the geometric volume of the combustion chamber at its smallest volume (TDC) and largest volume (BDC): CR = Vsmall/Vlarge. This is independent of the valve timing, adjustable or not.

Also, there are numerous engines, specifically motorcycle engines, in the 13:1-14:1 compression range that run just fine on pump gas, even under high loads without VVT.

As far as I know SAAB was the only manufacturer to play with variable compression engines, which are VERY different from engines with variable valve timing, VVT or similar technologies like V-Tech.

True, my terminology use was incorrect and comp ratio never does change. What I meant was combustion chamber pressure levels are determined by the cam profile which have a direct impact on fuel choices. I was not aware of motorcycles running with such high ratios.

 

[PlasmaBomb]

This is not correct. The compression ratio of an engine is solely determined by the ratio of the geometric volume of the combustion chamber at its smallest volume (TDC) and largest volume (BDC): CR = Vsmall/Vlarge. This is independent of the valve timing, adjustable or not.

Also, there are numerous engines, specifically motorcycle engines, in the 13:1-14:1 compression range that run just fine on pump gas, even under high loads without VVT.

As far as I know SAAB was the only manufacturer to play with variable compression engines, which are VERY different from engines with variable valve timing, VVT or similar technologies like V-Tech.

I think what he was trying to say was that the dynamic compression ratio of an engine isn't the same as it's static compression ration.

Lotus also did some work with variable compression engines.

http://www.lotuscars.com/engineering/en/omnivore-research-engine

The interactive version is good -

http://www.lotuscars.com/engineering/en/omnivore-interactive