bore out 1.9 to 2.0

christi

Top Post Dawg
Joined
Feb 22, 1999
Location
Ruislip, Middlesex, UK
TDI
Peugeot 806, 607
I was just doing some dreaming here...

Pistons from a 1Z motor are 79.5mm diameter.
Pistons from a five cylinder 2.5 TDI (AAT) are 81mm diameter.

Early 1Z and AAT both use the same part number for the circlip (that holds rod pin in piston).

So maybe an AAT piston could fit on a 1Z conn rod...

Now, going from 79.5mm to 81mm is a 3.80% increas in surface area.

That takes a 1Z motor from 1896cc up to 1968cc.

Unanswered questions:-

1. Will an AAT piston fit on a 1Z conn rod?
2. Is an AAT piston shorter or taller than a 1Z piston? If its a little shorter then we might be able to reduce compression ratio too

3. What other rods might fit? The bearing shell for the big end are different though...

What we need is a piston from a scrapped Audi 100 TDI to compared with a 1.9 TDI.
 

Davin

Top Post Dawg
Joined
Jan 4, 2001
Location
L.A.
TDI
2001 Golf GLS 5spd blk/blk
Interesting. What about the combustion bowl? Same design?
 

tdi rs

Veteran Member
Joined
Sep 23, 2000
Location
England
TDI
mk2 16v tdi
Guess what i'm in the middle of doin!!!
i've got the pistons and the blocks bored out.
The piston are the same as a 1.9tdi but with a slightly bigger bowl in the top.
 

christi

Top Post Dawg
Joined
Feb 22, 1999
Location
Ruislip, Middlesex, UK
TDI
Peugeot 806, 607
...which will give a lower compression ratio I guess


Are you using 1.9 conn rods? Do they fit straight onto the 5 cyl pistons?

Where are you going to get a head gasket from?
 

therabbittree

Veteran Member
Joined
Feb 20, 1999
Location
Red Hook, NY USA
TDI
B4 passat, 2000 Golf, 2003 Allroad tdi
ok i have a ?..the 1z engine's pistons do not have the bronze reinforced pin bores or the teflon skirt coating that the alh '98 A3 tdi engine has..what style pin bore do the aat 2.5 tdi have?..if they are bronze pin supports and teflon skirts i'm gonna order a set...any idea..tdi rs your doing it waht have you found?
thanks
Deo
ps does any one remember hereinga about a 99mm crank a few years ago from ottenger or eurospec? etc
that would be cool 99mm crank and 81,5 mm tdi pistons heheh in a a# TALLdeck tdi block!
 

tdi rs

Veteran Member
Joined
Sep 23, 2000
Location
England
TDI
mk2 16v tdi
As far as i can find out the rods are the same.
And they have brass inserts on the gudgeon pin inserts.I have opened up the bowl in the top of the piston and cut deeper valve pockets by 2.5mm.
 

tdi rs

Veteran Member
Joined
Sep 23, 2000
Location
England
TDI
mk2 16v tdi
Yup i'm kinda forced into it really,i think the compression will drop a little too much but i'll be able to run more boost then!!
 

rwolff

Veteran Member
Joined
Mar 10, 2002
Location
Lesser continental mass, Tosev 3
TDI
None yet
Sorry to rain on your parade, but the pistons aren't the only things to consider. Going from 79.5 to 81 mm pistons works out to roughly a 0.060 overbore (all material I've read about hot-rodders boring out engines was in inches).

Back in the "bad old days" of loose manufacturing tolerances, cylinder blocks had thick walls to allow for core shifting. Even then, boring 60 thousandths over was pushing things. With newer (a.k.a. mid-'80s) engines, going over 0.030 risked getting the cylinder walls too thin. All this is from "big 3" V-8 engines, which are gassers. The higher cylinder pressures of a diesel make boring a riskier proposition.

Someone already bored their block? I hope they checked the specs for minimum cylinder wall thickness and verified (probably using an ultrasonic tester) that they had enough "meat" to play with - otherwise they turned a perfectly good engine into scrap metal.
 

tdi rs

Veteran Member
Joined
Sep 23, 2000
Location
England
TDI
mk2 16v tdi
It was 1 of the things i considered but i thought the place where its gonna be the weakest is lower down the bore as the top is very thick.But i'm using s/h parts so if it does turn ****ty it hasnt cost much!!
 

Micwal

Veteran Member
Joined
Dec 11, 1999
Location
USA
If you do bore out the block, you might want to try an old drag racers trick. There is a compound that you can buy to pour in the water jacket that hardens/cures hard. It is used to stiffen the blocks and bores. You do not fill the block, just the lower half. The upper half of the block is still cooled and if done right the engine is still streetable. As most heat is generated in the upper half of the block, this may have limited effect of overheating.

If I remember right, I think Oldman used to build engines professionally, and may be able to give you a better insight into this. I have not had the heads off of a tdi yet, if it has an open upper block like a honda, you can weld a plate from the exterior of the cores to the sides of the block to stiffen the upper bore area. It is a shame that no hipo blocks are made by VW like GM makes bowtie blocks.
 

[486]

Top Post Dawg
Joined
Mar 1, 2014
Location
MN
TDI
02 golf ALH
17 years later and you're still better off upping the boost, as the dismal extra displacement doesn't gain you much airflow while the 81mm bore limits your head gasket choices and significantly reduces cylinder wall thickness

actually, 1z uses the older head gasket than alh, so maybe there's some solution there for 81mm bore, but I kinda doubt it
 
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Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
Northern MD (HAGERBUSH)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
Old thread!
I've been going back and forth on my ahu build. 82mm bore with a 100mm stroker crank. Makes it s 2.2L
I'd rather go machined pistons with 100mm crank vs more bore. Current build goal is 350hp but 450 with some crazy injection
 
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Jazer3

Active member
Joined
Feb 14, 2016
Location
California
TDI
05 tdi golf 12 tdi golf
Cylinder wall thickness is not at all an issue. All 1.9 and 2.0 tdis have the same distance between piston center points. I actually just put these same pistons in a brm direct swap to existing rods. I used a bhw head gasket. I also had to relocate the piston oil reliefs
 
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