IDI to TDI, a few questions

[lord_verminaard]

Say I have an AAZ block, and I acquire a 1z TDI head, would I be able to use ALH TDI pistons in the AAZ block?  Or would 1z pistons be my only choice?

Thanks-

Brendan

[410]

You can use the alh pistons but there is one issue.  Since the top ring groove on the alh piston is higher than the aaz piston, the ring can catch the ring groove in the cylinder wall.  Even the ahu or 1Z pistons have a higher top ring groove than the aaz but not quite as high as the alh pistons.  If there is no ring groove in the cylinder wall or you've bored to the next size then your fine.  I'm sure you know this but you also need tdi delivery valves, injector lines and valve cover to make it all work. 

[rallydiesel]

This is all assuming you are going mtdi. If you want to run an ecu, you will need a tdi block as it has the casting to accept a crank position sensor.

[lord_verminaard]

Awesome.  Just the information I was hoping for.  Thanks!

So rods.  Some use AAZ rods with the TDI pistons, can I use TDI rods on the AAZ block?  Since I have a set of those too that I won't need for my Scirocco TDI build. 

I do plan on MTDI for the AAZ to-TDI conversion, not aiming for a ton of HP, just double what the car came with in the 1.6. 

Thanks folks-

Brendan

[MJF]

130+hp PD rods has larger big end, so those won't fit, but all othes will.

[jimfoo]

And if you don't use TDI delivery valves???

You can use the alh pistons but there is one issue.  Since the top ring groove on the alh piston is higher than the aaz piston, the ring can catch the ring groove in the cylinder wall.  Even the ahu or 1Z pistons have a higher top ring groove than the aaz but not quite as high as the alh pistons.  If there is no ring groove in the cylinder wall or you've bored to the next size then your fine.  I'm sure you know this but you also need tdi delivery valves, injector lines and valve cover to make it all work. 

[410]

And if you don't use TDI delivery valves???

I don't know what happens if you don't use tdi delivery valves but I do know they are different.  The tdi ones have a bleed port and the idi ones are designed to leave a bit of pressure in the injector lines.  I remember reading about it in my Bosch manual but I lent it to a friend so I can't reference it right now.  The other issue is if they are a different length, so the lines don't fit so nicely!

[oldpoopie]

I think I've got a set of TDI delivery valves lying around.

[jimfoo]

Well, I guess I have been running mine with AAZ delivery valves since '07, although my pump never has become a full M-TDI pump yet. I got a kick out of reading my original IDI to TDI thread, although it made me realize I have forgotten a lot! Well, now that the overheating is finally fixed, maybe I can slowly return to where I left off on my pump mods, where ever that was.....

[jimfoo]

Good to hear. That way I have one less thing to worry about