Hey all.

Slowly collecting parts for a 5k turbo build. Will be running a 4k head with some work done to it which leads me to the question of which pistons to run? I'm assuming if I run d dish I'm going to have super low compression? Which could be good for boost but bad for lag... But would this be required if I was aiming on 15-20psi? Will be street driven so don't want an absolute pig to drive

Some 5k's came factory with flat top pistons and chambered heads, not too sure if you can buy them (pistons) new, only other option would be to get a 5k head to up the compression back to where it suppose to be.

 

cheers!

have a 4ke manifold/tappet cover for sale if interested pm me

Cheers. I have a 5k head but do want lower compression.. but just not sure if it will be too low... As for the 4ke gear cheers for letting me know but already have 7k gear

Mine has 22cc D's. When I first put it together I had a pretty well stock 4k head on it, c/r worked out at a touch over 7:1....which was far too low really. It did drive fine on boost. 100 thou shave later and c/r was up to 8.5:1, bit better off boost drivability and economy. Ideally I'd like to go higher again but that head is pretty much shaved to its limit now. Only option is to start again with a 3k head.

I would highly suggest you learn from my mistakes/experience and go 3k head (not 3kbp cause the stem seals are shit) not 4k and aim for at least 9:1, hell even the original c/r which iirc is 9.5:1. That way being a daily you're still going to retain good off boost drivability and fuel economy, make good power and probably spool slightly quicker. It'll just come down to full noise timing. I run about 28° @ 16 psi...which is rather high for a turbo engine, most skyline's etc would run around 11°. To me realistically this says that my c/r probably is too low!

 

I'm going to have to start charging a consultancy fee soon! Lol ;)

Ohh forgot to say if you already have a 4k head to use maybe crunch the numbers for 6cc O dish and see what you come up with. From memory I've got a few volumes etc in my projects thread a few pages back when I was doing the fore mentioned head shave.

 

Just checked for you, stock 4k head was 33cc, then 23cc post shave.

Edited June 19, 201511 yr by Taz_Rx

Cheers man... I'm thinking o dish may be the way to go..

I would use spool h beam rods and 4age pistons and stud the mains and the head be very strong then

 

So I was bored...and interested myself: 5k, stock bore, 33cc (4k) head, 6cc piston, 1mm gasket thickness = 9.4:1

Nice... Sounds like that should be decent... Compared to super low compression... Pistons are quite cheap so it may just be trial and error... But would prefer to get it rite first.. to save where I can

Off topic.. but any idea on what size pipe is ideal for the jpipe??? :)

Can't seem to find any large diameter steam pipe

1.5 would probably do. The outlet of the manifold probably wouldn't be any bigger.