Toyota MR2 with "variable Valve Timing"?
 

I was looking at the intake manifold for a 1987 toyota MR2 today, and noticed that even tho it is a 4 cylender engine, it has 8 intake ports on the manifold, one for each of the 8 intake valves, and every other intake opening had a butterfly valve... alowing half the intake valves to go unused even tho they were being opened, or so I can only assume.
I thought this was a great way to keep the air velosity high at low RPM, and still alow it to rev high, and with much lower cost then a VVT head, imagine the number of engines out there that could simply have their intake manifold replaced, and alow them to get better mileage at lower engine speeds.

Mazda does something very similar... Although, it's been called all sorts of things :p It was called VRIS (variable resonance induction system - I think) in the v6 626 and ford probe (mazda engine). The newer 6 has it too, but it's called something else. It's basically just butterfly valves that open at specific rpms to change the runner length ;)

Yup. ACIS for Toyota. I believe VVT-i is better for mpg because it'll allow a change in intake valve timing, increasing low end torque and moving the BTE peak lower w/o hurting high end power w/ the same cam profile. Dual VVT-i allows for internal EGR, which simplifies things a bit, and VVT alone is just Toyota's version of VTEC. There's also VVT-ie or something which is a combination of mussing wit the valve timing and having VVT/VTEC. I swear to god, every manufacturer has a group of different names for the same basic things that don't really follow any convention. Nuts... :rolleyes:

Mmm-hmm, you are correct. A nice simple solution, huh? If they had wanted to, they could have even put a different cam profile on those high-rev valves - maybe they did.

Nissan uses a system called swirl control. There is a half butterfly that covers the intake port. Its RPM activated.

I have owned the 16v version of my Peugeot 405 and that 4-cyl motor was stunning. Massive and long intake runners and 8 little exhaust pipes that swirled from 8 to 2 to 1. It was a work of art. Man could that motor scream!!! But, I wish I could find another one in good shape!!!


My Mazda MPV has the butterfly deal. It has the Ford Duratec 3.0 liter V6 motor which is a near constant source of problems for the van. The intake manifold has to be removed in order to change the spark plugs. Real sweet. Thanks to the bone-head who made that decision, obviously 1) does not keep his/her vehicles too long and 2) would not do the work anyway.

Hooray American Auto Engineering :thumbdown:

My VW is somewhat the same... I need a special tool to remove the plugs because the IM wraps over top... Makes the package very compact (to fit in small platforms like the beetle), but really makes things interesting to work on... It's not as bad as that Noble I posted a little earlier though -- rivets everywhere :p

The nearly identical Mazda V6 motor with a similar manafold has openings for the rear spark plugs, that would have been nice. It is on the brain because I am really close to changing the plugs on the van. It is starting to run a bit rough at idle and it is approaching the mileage limit as well.

It is not a bad motor otherwise. Except for the cooling system issues.

My '94 Jetta has the motor that started that trend in 8V VW's, it is a nightmare to change plugs, plus all the dirt and grim seems to collect under there. I spend more time cleaning the impossible to access area to get to the plugs than changing plugs. I usually get a platinum plug and forget about it for a couple of years!!!