Delica Canada | Mitsubishi Van Club

Hey all, I have an 89 I'm buying a head for. My memory is telling me that it's a protruding valve type but want to make sure; the head manufacturer wants me to confirm. I don't have the engine apart yet.

1989-1993 used protruding valve type (pistons have two large recesses the same size as the valves, covering most of the piston top- sometimes referred to as "cloverleaf" but it's a mutant cloverleaf if you ask me).

1993-1999 used flush valves (pistons have a small figure-8 shaped recess on one half of the piston top only).

I've heard you can use either flush or protruding head with the earlier, protruding head style pistons (though I haven't tried it!), but you must use a flush head with flush style pistons. In theory using a flush head with protruding pistons would lower your compression ratio, allowing higher boost for more power, but reducing efficiency off boost and maybe making starting harder. The precombustion chamber outlet port is also a different shape, which might not work well with the protruding-valve piston. It's probably not something to experiment with unless you have no other option.


That said: your van is 27 years old, who knows what sort of life it's lived. The only way to be sure is to pull the head off and look at the pistons.

Thanks. Spent hours last night searching the net, trying to find the answer. Amazing how something so critical is so hard to find, especially given how often the heads get swapped. Doesn't help that there are so many versions of that engine in so many manufacturer's cars over so many years.

I was sure I knew, but I double-checked by looking up the parts listings- there are two pistons listed, 1988-'93 (MD103308) and '93-'99 (MD304847). throwing the part numbers into Google Image Search showed the difference between the two- here's the best picture I found, early (pre-'93) protruding valve piston on the right (obviously):
Recessed/Flush valve piston----------Protruding valve piston

Interesting.. Is there more horsepower in the engine from 93-99? Looks like a higher compression piston..
TLWF

Given that the valves are recessed in the head, nope. I believe they're both 21:1 CR

Even chasing down part numbers didn't help me, as wherever I went they'd show both kinds of heads, and most didn't even indicate the kind of valve. Finding a relationship online between head, part number, valve style and model year Delica, was well nigh impossible and I'm good at online searching. Even when few forum threads talked about it, they just mentioned the two kinds but didn't define which went with what year. Eventually I was able to parse it together through various vague sources, but it wasn't easy. Should be a sticky somewhere, although hopefully THIS thread shows up for the next poor bastard wasting his time.

Both engines have the same compression ratio. The later engines *do* make more power, but that's because they have an electronically-controlled injection pump with more flexible control over timing and quantity of fuel. (Bosch call it EDC. It's not common-rail though, just an upgraded version of our Bosch VE pumps). Flush valve engines usually have intercoolers. I believe the change to flush valves was to smooth out the combustion chamber- fewer sharp edges means fewer hot spots and more predictable combustion, allowing the ECU to advance the timing a lot more without melting a piston. Flush valve engines also received a water-cooled turbo. Flash.

Lots of nerdtastic info in the Bosch VE pump technical manual here: http://gnarlodious.com/vanagon/bosch_pu ... _Pumps.pdf

Good idea about the sticky- I'll move this thread into the FAQ when it falls off the first page.

Here's what the two styles of head look like:

Pre-93 Protruding valves, uses the piston with the larger "cloverleaf" cutouts. Post-93 flush valves, uses the piston with the smaller figure-8 shape cutout.