Discussion: blacktop 20v: the road beyond 200HP

[BenR]

Right....interesting topic.

Put quite simply, the downfall of the 20v engine is the fact that it is 20v.

And as with all engines, the ultimate ability of that particular engine to perform is the cylinder head.

ALL varients of 20v that i have seen are apalling. Sure you can squeeze a whole shed load more valve area into a certain bore size, but valve area is only one part of the equation.

Ignoring the bottom end assembly as its quite easy on any engine to sort out any issue that it has, but the 4age doesnt have any really.

Product support for the 20v is limited because its not wanted, the limits of the 20v are too low compared to the 16v to bother with high levels of support.

Now the 20v solution is a mass production one, its easier to gain raw cylinder head flow using an extra valve. Simpler and cheaper castings, inexpensive design phases, high port volume etc etc. It was easier for toyota to bung in another valve than to piss about developing an efficient 16v head.

However this provides problems to those who want to tune to the extreem upper limits. The ports are just terrible. There is no control of flow down to or between valves, the port volume is massive........all in all, a horrible show for port efficiency, and thats the name of the game when were trying to maximise the efficiency of the valve area we have available.

The 20v has comparable area to a 16v head with 32.5mm inlet valves, which in itself is enough for about 240-250bhp without straining too hard.

Christ, i dont even know where to carry on with the poor points. Staggered included valve angles mean poor cylinder filling and high tumble values.

To efficiently modify the head to use the available valve area would take considerable modification. To this date i've yet to see anybody modify a 20v head to any decent level, which is why they all sort of cap themselves at 200-210bhp. To make use of the setup i would start with a BT simply because its all hogged out from stock and gives me the space to do what i need to do. Your going to have to strip the whole head of all material which isnt part of the parent casting......then break out the old tig welded and mini torch as your going to have to fill that port something crazy. You want to build up the floor of the port, and bring up the bifurcations between valves to at least halfway up the port. That in itself will be a terribly difficult job due to the limited space, in some cases you might be limited to working with a liquid ally or epoxy if you dont care about what it looks like.

With the base sorted you can modify the head to a much better shape........what this shape is another subject in itself.

Port filling is becoming a popular trend among racing engines where manufacturers use large valve area and large port volume to increase efficiency, and variable valve technology to help with the associated low engine speed torque issues that arise.

Then you have the chamber issues, its large with zero usable quench, even in the ST. Poor combustion and thermal efficiency........basically wastes alot of the burns energy in timing. Subceptable to det because of far off end gasses etc etc.

I wouldnt bother worrying abuot anything else until you sort the heads basic flaws.

As for a 1.6 20v generating 206bhp at the crank, i highly highly doubt it.