I noticed on the FJ cruiser with the 1GR-FE engine, it had VVTI which applied to the intake valves and produced 239hp @5200rpmm 278lb-ft@ 3700rpm with Premium, 236hp @5200rpm 266lb-ft @4000 RPM with Regular and has a 10:1 compression ratio. This same engine is also used in the Tundra and Tacoma trucks.

For the 2010 model year, Toyota added Dual VVTI to the 1GR-FE which means there is now variable valve timing for the Intake and Exhaust valves. But also made another change and that is they bumped the compression ratio to 10.4:1 as well. This engine now makes 259hp @ 5600rpm and 270lb-ft @ 4400rpm with REGULAR gasoline. So now I'm wondering, how was the addition of variable exhaust timing able to allow Toyota to bump up the compression ratio of this engine? Does anyone want to elaborate or explain their theory as to why this allowed for a bump up in compression ratio?

The reason I ask is because I'm kinda dumbfounded as to how engines today have been getting such high compression ratios on 87 gasoline compared to engines of just 10 years ago. I mean sure we could claim better materials but back in the 60s, 70s and 80s, there weren't any really bumps up in compression ratio for cars that run on 87 until fuel injection was introduced. Then in the late 80s to early 90s, the CR was able to be bumped up again with the introduction multi-port fuel injection. Now supposedly, we're able to bump up the compression ratio because of variable valve timing? I don't see how an engine starved of air and fuel wouldn't be able to attain the same CR as one that isn't.

I mean the Geo Metro 1L engine I believe had a Compression ratio of 11:1 and that didn't have variable valve timing. Is there something to this?

Shouldn't we be able to chronologically explain for each increase in CR for consumer engines that run on 87 gasoline?

 

There are alot of things that determin how much compression you can reliably run on lower octane fuels.. Port shape, combustion chamber design, injector placement, quality of atomization, tuning strategies, piston design, engine geomerty, exhaust and intake manifold design, advanced EGR strategies..

They probably just raised the CR to get a little bump in power, its not really that big of a deal. The dual VVTI mainly allows for a broader power band and more control over smog at low speeds and idle, the cam angle can and does affect dynamic compression ratio, but I doubt they added Dual VVTI just so they could raise compression, they probably could have raised it even without it.. I think they were just aiming to build a better overall motor.

 

I just looked up dynamic compression ratio and while I was familiar with the term, I hadn't thought of it too hard. I specifically looked at this page:http://www.empirenet.com/pkelley2/DynamicCR.html for more information.

Actually I do believe they would add variable valve timing in order to increase the compression ratio since they could top off the cam timing at the high end to just the point before detonation. The thing is though, they added EXHAUST valve timing, so now I'm wondering how could exhaust valve timing affect dynamic compression ratio? Or are you saying that it wouldn't?

 

It can and will affect compression, any time you change the valve timing in relation to piston movement, you will affect dynamic compression.

To keep it simple, generally the later you close the exhaust valve more compression stroke goes out the exhaust. But the lowered potential of detination is probably less affected by the lower compression and more affected by the fact that longer overlaps tend to allow more hot gas to be moved out of the cylinder due to scavenging. But this changes in relation to RPM also, obviously there a point where reversion will occur and push exhaust back in and this and that.. Honestly this is a can of worms lol..

But I seriously doubt that they added Dual VVTI just so they could bump compression .4 .. There is much more to gain from dual vvti like a much broader power band, and better emissions control..

 

That's because static compression ratio has never had anything to do with whether an engine will detonate. This is just a myth that has been spread by uninformed journalists over the last 30 years. An engine could run 15:1 static compression ratio and still not detonate assuming its intake valves closed late enough. This would limit it's effective compression ratio, the ratio measured beginning at the point the intake valves close, which is the one that really counts when it comes to detonation. You'll notice that peak torque and power are made higher in the rpm band in the new engine. This is the effect of running a higher static compression ratio.

 

Ok...well then how about this, they added Dual VVTI because of what you just said above and consequently, because of the addition of Dual VVTI they were able to bump up the compression ratio?