What is that butterfly system called in the inlet manifold on the 6VD1 DOHC engines. I saw it in some photos of the gasket replacement, and I have seen the actuator coming from the rear of my manifold. What does it do and how is it controlled?

I can find no reference to it in any manual or parts listing.

Andrew.

Engine control valve? I would have called it a throttle body, but myisuzuparts.com labels it the engine control valve. I hope I'm reading your question right...

Not that one. It's two shafts that run through the inlet manifold with a butterfly on each cylinder inlet duct. There is some kind of actuator on the back of the manifold in front of the fire-wall.

Andrew,

Thats a type of port tuning device that is common these days. By opening or closing the valves, the PCM can optimize the tuning of the ports to help cylinder filling and increase power across the power-band.

That sounds like the one. I can't find any reference to it, including myisuzuparts.

Andrew.

They affectivly change the size of the intake runners as Tom said. HERE (http://forum.planetisuzoo.com/viewtopic.php?t=15937) is a post about it recently on planetisuzoo.

Here's the relevent replies about it..

I think that engine has dual length intake runners...long ones for torque at low rpm and short ones for hp at high rpm...I forget the break point where the butterflys change over, might be around 3000 rpm.
HEY STEVE ,YOU ARE CORRECT IN THAT THE EARY DOHC ENG DID NOT HAVE DUAL RUNNERS , JUST DUAL INLET INTAKES , THAT UNTILL ABOUT 3600 RPM THEY STAYED CLOSED , AND THEN OPENED TO LET MORE AIR IN , UNTILL THAT RPM ONLY HALF OF THE INTAKE VLV ARE RECEIVING AIR ,FROM THE PLENUM TO HELP WITH LOW SPEED DRIVEABILITY, AND TORQUE, ODD PART, THE SOHC ENG USED THE SAME NO OF VAVLES AND DIDNT USE THE AIR CONTROL VLVS, AT ALL THEREBY RECEIVING AIR IN ALL 12 VLVS ALL THE TIME , ON THE 98 AND LATER ENGS THEY DID GO TO THE DUAL INLET RUNNERS , AND THEY WORK JUST AS YOU SAY, LONG RUNNERS UP TO ABOUT 3600 RPM AND THEN SW TO SHORT RUNNERS FROM THERE ON HI TORQUE AT LOW RPM AND HP AT THE TOP END , POOR MANS SUPERCHARGER , PIONERED BY CHRYSLER WITH THE RAMCHARGERS ENG IN 1960 , EXCEPT THEY DIDNT USE THE LOW AND HI SPEED RUNNERS , LIKE THE LATER ENGS , LONG RUNNERS FOR THE BIG CARS AND THE SHORT RUNNERS FOR THE DRAG CARS . THOSE LONG RUNNERS HAD AN EFFECT IVE LENGTH OF ABOUT 44 IN LONG JERRY