Variable Compression DVVT Turbo EF?

So as I’m pondering what to do with my assortment of EF engines and L200 Miras that need to go slightly faster I stumbled across something interesting that has me curious about many things.

While trying to find an image of an EF-VE Piston to compare to an L5 EF-EL Piston (an option I’m considering for high compression) I ended up on Japanese Google and found this Japanese blog with a lot of obscure information.

Most interesting is this blog here (you’ll need to google translate it)

About the engine in this car:

EF-VE+DET hybrid engine combining the N/A 10.5 high compression pistons and Variable Valve timing head of the EF-VE with the Turbo setup and I assume block of the EF-DET (oil squirters, turbo drain etc) with variable 8-10 compression ratio?

How would that work? I’m guessing it somehow uses the variable timing to drop compression under boost and then bring it back to high compression when off boost?

One thing really lacking in my L2 TR-XX EF-JLs performance was the off boost time, you could really feel the bog of the low compression until it spooled up. (The thrashing I gave that motor also really did not help the compression…)

So in theory this could eliminate that and give it better low rpm snap and no / low boost performance and then more room to run higher boost once it gets into it?

Aside from my high compression, Triumph ITB N/A ideas I’m still also contemplating boosting the tits off the EF-DET with a bigger turbo but that would just increase the bog and lag that I already don’t like about my tiny turbo EF-JL.

This could be an interesting way to make a very snappy, very powerful engine but I don’t have enough engine knowledge to know if that’s actually how it works or how I would go about setting it up.

These engines really haven’t been explored much here in Australia so information is pretty limited but it’s super interesting to find stuff like this.

ITBs look cool but such will reduce tuning options. You will find them to be really hard to tune esp without a plenum feeding them.

The L5 ef-el piston is a dome shape. It has poor squish. Upon spark the combustion flame for most available fuels has a long way to travel before the piston gets pushed down. When these pistons are pushed for power the limit is found quickly and it is typical that they get to a point of needing huge timing advance to get the flame burning and give it time to travel around the dome before making max pressure to push down. Now a Mazda Skyactive has a dome but it has remarkable squish with the majority of the dome coming within a fraction of a mm of the combustion chamber. But it works because they put a small pocket in the to where combustion occurs and the spark is fired really close to TDC. The EF-VE is basically a flat top piston. For NA this is the way to go. In looking into this I was going in the direction of using a motorcycle piston from a GSXR 600 as the are strong, forged, light and have thin rings and thus can be revved and have little friction so “more power”. Plus they are short so you can use a long rod for a good stroke to piston ration in the EJ-DE block I was going to use. Alas life got in the way and it never came to fruition.


There are no variable compression Daihatsu motors that I know of, only DVVT or variable cam timing.

“Snappy” will need high compression or a way of getting the turbo spinning at low revs. My experience is that a high level of spark and fuel control along with a closed loop feedback system is critical to controlling and maximizing what is happening. So #1. the electrics and a sophisticated ECU with data logging for the tuner will be essential. #2 choose a turbo for response. I’d be trying a RHV4-VJ38 as they are a common variable vane turbo that is not stretched until over 180hp stock or move with billet inducer and some other mods. These are a common diesel turbo where low down grunt is needed and I’ve been able to get excellent boost from them just off idle.

There are plenty of direction you could go, but above is a few quick thoughts.


I consider Mr Gormsby to have the correct solution to your dilemma. A boosted engine will provide more power over a broader rev range, however i also love naturally aspirated engines for the raw sound that comes from an engine starving to breathe deep enough to produce decent power.
The opinion I am giving you in a nut shell - I believe it is better to have a lower power engine that is open 100% of the time vs a higher powered engine that is at maximum power 25% of the time. (It’s something I am beginning to regret - having a cylinder head that is past the point of N/A tuning, when I could have been just driving the car for fun).

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I get the L2 EF-EL Piston is rubbish for performance and I’ve already tried using EF-RL Pistons and shaving the head for compression on my EF-EL but that didn’t work too good.

So for my EF-DET I’m thinking of running it N/A with L5 EF-EL Pistons as they’re a different dome (would probably suit your idea of machining a pocket) than the L2 Piston and seem to do a good job in my L5 Engine and EF-VE Pistons are basically unobtainable on this side of the globe.

I was mainly curious about these blogs as tuning the EF-VEs variable timing is a complete unknown here and seems to go against common sense changing a turbo engine to the high compression parts of the N/A variant.

The shape still won’t work for good flame travel. The dome has to match the combustion chamber shape perfectly, with the sort of accuracy done by scanning the combustion chamber, CAD and then CNC machining.

I think this Japanese guys using the DVVT mechanism to almost like bleed off compression once it reaches a certain boost level while keeping the compression of the N/A Pistons when DVVTs disabled. Does that make sense?

Maybe I’ll have to try hunt down some EF-VE Pistons if I go the N/A route. I’ve never even seen a set for sale haha
Maybe Daihatsu still have some?

Can’t see it working as you seem to think. It would be detrimental to inlet flow if it could bleed off. What is happening there is not a bleed off of compression but continued cylinder filling providing a denser charge and not reduced pressure. The static images do not convey the dynamics of thermodynamics.

Those EF-VE are the sort of things you want. Look at some pics of the tops of Cosworth NA images of 4 valve 2000cc engines. I’d recommend reading up a bit on the early work of Cosworth on squish, tumble and vertical or down draft port geometry.

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Well I don’t know enough about variable valve timing to know how this works but this guy is definitely altering compression with the DVVT system. It’s fully aftermarket ECU stuff but I would really like to know how that works. Also there is pages full of melted pistons so maybe I shouldn’t dig too far into this :rofl:

So after reading up on it a bit I’m pretty sure he’s using the DVVT to really hold the intake valves open under boost so when they close the pistons only compressing about 80% of what it normally would and he’s running about 20psi of boost to compensate for it pushing it back through the valves. Sounds like a tricky way to run a boosted engine but if it would allow you to keep the N/A response off boost I could see it being very fun to drive. I need to read a lot more stuff on how engines work before I come to any actual conclusions on what to do for engine projects. All my engines are in storage and 1 of my Mira’s is broken so I’m getting restless to tinker again…