How does the 2018 GS 450h V6 engine differ from the 2018 GS 350 V6 engine?

 

Honestly probably the same, just de-tuned for efficiency. The hybrid power train makes up for the lower hp output of the engine. On paper total system hp of hybrid is more powerful, but it's also several hundred pounds heavier.

 

Yeah, just about the same, just different cams, pistons, crank, combustion cycle... :P

 

That's what I was curious about. How sure are you about the 450h engine having different cams, pistons and combustion cycle?

I suspected the 450h engine probably had different fuel mapping, ignition timing, VVT valve timing to improve fuel efficiency. Even a slightly different exhaust routing could be a factor also.

 

My understanding is that the 2GR-FXE is a version of the older 2GR-FSE, just tuned to run the Atkinson cycle. So I think it's pretty closely related to the 350's engine from model years 2013-2015.

 

Sure enough that the EPC confirms everything but the combustion cycle - that's explained by the "new car info" section... and every single literature piece on the car. The engine (as stated above) overexpands (i.e. uses a simulated "atkinson cycle", using late intake valve closing to expel some of the intake charge). The RX400h, 3rd gen GS hybrid (first gs350h) and the LS600h are the only Lexus hybrids that don't overexpand (i.e. use regular "otto") - hence their poor fuel economy, relative to their peers at least. Just about all somewhat modern engines overexpand to an extent, but the hybrid engines are usually cranked up to the point where they can't afford not to (too high static compression, the cam profiles, etc). Exhaust gasses leave the manifold at basically atmospheric pressure.

Don't suspect, look things up. There is a ton of information out there on these cars and you don't really have to dig into anything.
https://en.wikipedia.org/wiki/Toyota_GR_engine#2GR-FXE
http://australiancar.reviews/2GR-FXE-engine.php
First two results

 

Rated at 292 HP (for the V6 engine alone less the traction motor) with a 13:1 compression ratio.

I'm surprised by the different pistons in the engine for the GS 450h making the higher compression...

I'm not sure what to make of Toyota/Lexus feeling the GS 450h engine needed the higher compression.

 

Lwerewolf - Do you have any thoughts on the needed purpose of the higher compression in the engine for the GS 450h?

 

All Toyota/Lexus hybrid engines have higher compression ratios than their ICE only counterparts. It’s for fuel efficiency.

 

Yeah, a higher compression ratio is beneficial because the higher ratio allows for an engine to extract more energy from the combustion process due to better thermal efficiency. Higher compression allows the same combustion temperatures to be achieved with less fuel.

Strange because I'm more familiar with big block Chevy 396/427 L78/L88 engines with higher compression actually being less fuel efficient than their cousins with lower compression, but fuel efficiency was not an important factor with those high-performance engines with 850 cfm double pumper Holley carbs at the ready.

Anything around 11.5:1 to 12.5:1 compression ratio was considered 'crushing'! So crushing that sometimes you didn't know if a new battery could turn the engine over enough to get it started. You could hear the pistons squeezing the air as the engine started turning over. Now we have 13:1 compression ratio in a Toyota/Lexus 3.5L V6 engine...and the engine turns over like it has no compression thanks to technology advancements such as the release valve mechanism at startup...

 

Might have something to do with the actual compression ratio being lower due to the intake valves staying open a bit into the compression stroke (hence the expansion stroke "overexpanding" relative to the compression, which is where the actual fuel efficiency gains come from. Please read the links). 3GS didn't have that (same -FSE as the GS350). 4GS does.