hi, this is a fairly often asked question but i think this is abit different.

 

i have a 3k bigport with out the compression chamber/ recess bit.

if i put that onto a dished piston 4k what will my comp be like?

will it be too high to turbo?n and will i need a decomp plate?

hi, this is a fairly often asked question but i think this is abit different.

 

i have a 3k bigport with out the compression chamber/ recess bit.

if i put that onto a dished piston 4k what will my comp be like?

will it be too high to turbo?n and will i need a decomp plate?

 

A dished piston 4K,???

 

A 3K bigport head without the chamber,????

 

MAybe the 3K head has been machined a lot to bring the comp up on a 3K but it would be unusual to see a 3K bigport head without a chamber as you put it.If you put the two together i would ASSUME that t5he comp RATIO would be around 9:1 dependimng on how big the dishes are in the pistons.

Measure it.

 

I can't remember off the top of my head, but there was something like 16cc's in the piston of a dished 4k (twin squish type). Depends on what pistons are in it as there are 2 different types of 4k dished pistons.

 

You would probably end up with something around 8.0:1 with a bigport 3k head. Couldn't say for sure. As I said measure it.

Edited March 23, 200719 yr by Felix

this it what i mean

Pretty sure the head with the recess is an auto head... Lower compression.

Which pistons are in your dished 4k?

 

In the pic below, the ones on the left are 4ku, the right ones (twin squish) 4ke.

i havent got my dished piston 4k yet, still waiting for nickz to ask his brother about selling it

 

I'm guessing its just a 4kc

If it is a 4kc it is just a normal flat top motor.

 

The dished piston motors mainly came in through jap importers over the last 15 years or so.

ill see nick tomorrow and see what it is

just talking to him and there was abit of confusion sorry guys, nick has had some dished piston 4k's but he isnt suure of the one he has left, i sound dumb now lol

 

is it hard to find a set of dished pistons?

this it what i mean

 

Use either of those heads and you WILL need some sort of dished piston, not sure how hard they are to get .

Think I worked out previously that if I put a skimmed 3k bigport head (non recessed type), on my dished 4k (with twin squish pistons), it would have had around 7.8:1 CR. Great for high boost.

 

The dished pistons are not available off the shelf in australia, you can get rings though which are thinner than normal 3/4k ones. Maybe you could get some pistons from japan, or some other country that had the dished piston motors as a standard production model. USA?

 

The dished piston 4k motors are easily identifiable by the heads having cast protusions under no1 and no4 spark plugs (like on a dished piston 5k). They share the same head. Have a look in the pic below so you know what to look for in the wreckers and such.

ok i see, looks like the hunt for a dished piston 4k is on!

some of the early lite ace vans had the dished piston 4 and 5k engine.

you could try Garrmax international here in brisbane, they may beable to get some new ones.

number is 07 38811692.

Looks like I got myself a dished piston 5K going by that pic that Felix posted.