Vvt - Fuel Economy, Hypermiling, EcoModding News and Forum

Arragonis · 08-19-2011, 09:05 AM

I'm trying to get a handle on how VVT actually works - basically so I can work out how to exploit any advantages it seems to have - and also try and work out what exactly the version George has.

As I understand it the VVT system allows the timing of the valve opening to be varied. Conventional cam timing is a compromise between driveability at low speeds and top end power so this VVT system allows the best of both worlds. The variation in early versions was based on engine speed and later based on throttle opening as well. Also it allows the valves to remain open after they should close - e.g. the exhausts staying open for part of the induction stroke (for EGR) and the inlets for part of the compression stroke to reduce pumping losses.

I came across this which has a comparison of the first system against the Honda VTEC versions. Plus of course there is the entry in Wikipedia which contains some details.

George's engine is the 1KR FE unit. The link referring to VVT-i from here goes to the VVT-i link in Wikipedia, but I'm not sure which version it should be - is it VVT on both sides, or just the inlet side. I assume it is the later version based on throttle position.

I'l like to know more and wondered if anyone had any other details ? I'd really like a BSFC map (wouldn't we all for all of our cars

) but I can only find ones for 4 cyl VVTs.

Daox · 08-19-2011, 09:35 AM

Well, I did a little digging and couldn't find anything about the 1.0L's VVT. My guess is that the Aygo engine only uses VVT on the intake cam since its a lower priced model and it is more expensive to put it on both cams. Only real recent models (past couple of years max) have been using VVT on intake and exhaust cams.

As far as using it there really isn't much to it. Its all automatic and no real way to take advantage of it more so than just driving.

Ryland · 08-19-2011, 09:53 AM

VVT-i - Wikipedia, the free encyclopedia

It sounds like if it's just the VVT-i then it's just the intake side.
Before VVT in Toyota's, Toyota had a set up where some of their 4 cylinder engines had 8 intake runners, one for each of the 8 intake valves, one of the intake runners on each cylinder had a butter fly valve, so that even tho the valves were all opening only one of them at lower speeds was getting fuel/air so it was more like having two intakes on the car, one for low rpm's and one for high rpm's.

Arragonis · 08-19-2011, 01:37 PM

Thanks for the replies, I think you are correct in that the VVT system on George is the 'i' system - inlet only - although I'm basing this on looking at an exploded view of the engine and trying to spot the parts involved and of course I am an expert engineer

What I'm wondering though is what affect the inlet VVT system has on whether the engine is running its best at WOT vs part throttle. One thing that has surprised me about George is that he can pull from low revs - anything over 1000 rpm on the flat, and anything over 1500 on a hill. There is a "shift" in the power delivery around 3-4000 rpm - not sure exactly where.

I'm experimenting with P&G (engine on) but I'm not sure what rev range to use. Its the old BSFC search...

Daox · 08-19-2011, 02:17 PM

I'd probably just keep the rpms centered around 2000-2500. It really isn't going to matter that much if you are off 1000-1500 rpm because high load the efficiency is so much better than at low loads.

Daox · 08-19-2011, 02:21 PM

Here are a few sample gas engined BSFC maps. If we look at them, you can generalize quite well what rpm band you should use. Generally around 2500 is where most engines seem to peak. But, if you keep increasing the RPM, there isn't a big penalty at all compared to lower load levels.

Nevyn · 08-19-2011, 03:04 PM

In my Elantra, it's done with oil pressure and has 4 modes. Toyota's system I'm mostly unfamiliar with, except for a little experience with VVTL-i on an 03 Celica GTS. In that case the "i" stood for intelligence, not intake.

Ryland, the system you mentioned is similar to what the 97-02 Escorts had in the 2.0L Split Port Induction CVH series engine. I had one, and when that second intake runner opened, you could definitely feel it.

I'm attempting to find the CVVT info for my car to post - I should be back with that data soon.

Old Tele man · 08-19-2011, 06:25 PM

Arragonis -- have you seen this article?

The CityBug Blog: The 1KR-FE engine of the CityBug

...it says the 1.0L engine is designed by Daihatsu and includes an engine power curve graph.

...and, from something Toyota:

http://www.toyota-global.com/sustain...pdf/eco_02.pdf

...and, a visual:

http://www.youtube.com/watch?v=Lb433kj6Cbk&NR=1

Arragonis · 08-20-2011, 10:15 AM

Quote:

Originally Posted by Nevyn

In my Elantra, it's done with oil pressure and has 4 modes. Toyota's system I'm mostly unfamiliar with, except for a little experience with VVTL-i on an 03 Celica GTS. In that case the "i" stood for intelligence, not intake.

Ryland, the system you mentioned is similar to what the 97-02 Escorts had in the 2.0L Split Port Induction CVH series engine. I had one, and when that second intake runner opened, you could definitely feel it.

I'm attempting to find the CVVT info for my car to post - I should be back with that data soon.

I understand the i does stand for "Intelligence" on all of them

The VVTL-i does lift as well I think, according to Wikipedia.

Old-Tele - I had seen the items from Toyota but the video is useful. The City Bug Club article is a copy (I think) of an article I read when searching last week. There is a guy in Holland who chip-tuned his bug with no benefit whatsoever except that the rev limiter was raised. He had a similar article on his blog but if course I never kept the address

Daihatsu is owned by Toyota and they use this engine in some of their smaller cars too.

So looking at the maps there is a sweet area around 2-3K, so assuming I'm doing P&G then I should use WOT at those speeds or go for peak torque which is (I believe) 4000 although the article linked suggests 3600.

Just about the time George was made the factory made a small ECU change which dropped he CO2 slightly which makes tax cheaper in a few markets so the tune may be slightly different. Maybe.

Peter7307 · 08-21-2011, 12:19 AM

Just a comment on some of the BSFC maps above...
Given the island for lowest consumption ranges down as far as 1 500 RPM in some examples (Saturn 1.9 for instance) it seems to make more sense to aim for the lower end rather than the exact centre.

In other words revving at a constant 1750 RPM or so should give the same BSFC spot as 2500 but with lower friction from using fewer revs.

Just an observation.

Peter.