# mk4 2.0 pistons in jh block?



## ShaggyMutt1 (Jun 19, 2012)

would this work? mk4 has same pistons as 3a 8v. 82.5mm Would these fit as a upgrade?


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## WaterWheels (Aug 14, 2005)

The question can be answered real simple as it is stated, no. But you really can't answer it correctly unless enough details are given if there is more to it then trying to stick them in a JH bottom end. The block can be bored out to allow 82.5mm pistons but crankshaft throw (stroke)and which rods are being used make a huge difference. So maybe you would be well off to supply some details of your plans for a better answer.


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## ShaggyMutt1 (Jun 19, 2012)

I talked this this guy that owns a vw shop.He said mk4 pistons are same as found in the Audi 80 3a "bubble block"" He told me that you can use these pistons to get 1915cc out of the jh. I realize it would not be 2.0 w/o the the longer stroke crank.


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## ps2375 (Aug 13, 2003)

Unless you sit one of each piston on the table and measure piston crown to wrist pin distance, I would be skeptical. Or if someone has the piston specs...


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## WaterWheels (Aug 14, 2005)

ShaggyMutt1 said:


> I talked this this guy that owns a vw shop. He told me that you can use these pistons to get 1915cc out of the jh.


The owner of the shop didn't tell you anything wrong, he just didn't explain in detail and you're not asking enough or providing enough for a one word answer. You can use *any* piston in any motor, within reason of course. If the motor can be safely bored large enough, if the compression height is correct or can be corrected by using different rods and/or crankshafts and if there is no piston contact with valves or surfaces then things will work. So just what is the question or why the question if someone has already said you can do it and you understand that other parts of the motor also need to be changed?


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## ShaggyMutt1 (Jun 19, 2012)

WaterWheels said:


> The owner of the shop didn't tell you anything wrong, he just didn't explain in detail and you're not asking enough or providing enough for a one word answer. You can use *any* piston in any motor, within reason of course. If the motor can be safely bored large enough, if the compression height is correct or can be corrected by using different rods and/or crankshafts and if there is no piston contact with valves or surfaces then things will work. So just what is the question or why the question if someone has already said you can do it and you understand that other parts of the motor also need to be changed?


He also said max bore on JH is 84.5mm :screwy: I don't know about that!


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## rhussjr (Aug 7, 2000)

Regardless the fact that the pistons will fit the block if bored to fit, they will not work unless you stroke the block or install a set of custom rods to compensate for the change in compression height. 1.286" of the 1.8 minus 1.174" of the 2.0 equals 0.112" or 2.84 mm which is 15ccs of extra combustion chamber that means lower compression, lower power and hard starting.


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## ShaggyMutt1 (Jun 19, 2012)

rhussjr said:


> Regardless the fact that the pistons will fit the block if bored to fit, they will not work unless you stroke the block or install a set of custom rods to compensate for the change in compression height. 1.286" of the 1.8 minus 1.174" of the 2.0 equals 0.112" or 2.84 mm which is 15ccs of extra combustion chamber that means lower compression, lower power and hard starting.


Huh the 2.0 and 1.8 both have same stroke and both use 144mm rods??


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## ps2375 (Aug 13, 2003)

With an 82.5mm bore, the stroke has to be longer to get near 2.0L, to be "called" a 2.0L motor. VAG is usually generous in rounding up, but not that generous.

82.5mm bore with 86.4mm stroke and 4 cylinders = 1847cc


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## rhussjr (Aug 7, 2000)

ShaggyMutt1 said:


> Huh the 2.0 and 1.8 both have same stroke and both use 144mm rods??


As mentioned above, the 1.8 has a stroke of 86.4mm and the 2.0 has a stroke of 92.8mm. They are not the same. They only share the same block height 220mm as long as you are Mk4 and Mk2. Mk3 have a 236mm block height.


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## ShaggyMutt1 (Jun 19, 2012)

I only want to know if those pistons work i the jh block


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## Rheinland Technik (Apr 2, 2010)

The definative answer is no.


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## ShaggyMutt1 (Jun 19, 2012)

Rheinland Technik said:


> The definative answer is no.


So whats the compression height on the aeg piston?


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## ShaggyMutt1 (Jun 19, 2012)

Rheinland Technik said:


> The definative answer is no.


I dont get it they both use same stroke, have 20mm pin etc


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## rhussjr (Aug 7, 2000)

They do not use the same stroke

1.8 = 86.4 mm
2.0 = 92.8 mm

Compression height on an AEG is roughly 1.174"
1.8 engines are 1.286"


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## ps2375 (Aug 13, 2003)

ShaggyMutt1 said:


> I dont get it they both use same stroke, have 20mm pin etc


As already stated 2 or 3 times, they do not have the same stroke, even though they share the same connecting rod dimensions. That is not the same thing.


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## ShaggyMutt1 (Jun 19, 2012)

ps2375 said:


> As already stated 2 or 3 times, they do not have the same stroke, even though they share the same connecting rod dimensions. That is not the same thing.


then how are AEG pistons the same as 3a pistons?


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## rhussjr (Aug 7, 2000)

AEG motors use a 220mm deck height, which is the same as the 3A deck height and share the same 92.8 mm stroke and 144mm rod length and 20mm wrist pin diameter. Hence, they pistons, though not 100% identical, will interchange.


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## ShaggyMutt1 (Jun 19, 2012)

rhussjr said:


> AEG motors use a 220mm deck height, which is the same as the 3A deck height and share the same 92.8 mm stroke and 144mm rod length and 20mm wrist pin diameter. Hence, they pistons, though not 100% identical, will interchange.


3a has the 86mm stroke!


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## ps2375 (Aug 13, 2003)

ShaggyMutt1 said:


> 3a has the 86mm stroke!


Everywhere I've looked, the 3A has 82.5 bore and a 92.8 stroke.

Look here:

http://forums.subdriven.com/showthread.php?5694062-2.0l-16v-block-to-8v-(9a-to-3a-specs)&p=77482944

http://techtonicstuning.com/main/in...ducts_id=383&zenid=mr3rjv8qk579prlh6i7fjmtja5

http://forums.vwvortex.com/showthread.php?705318-audi-3a-or-vw-aba-specs-HP

http://www.audifans.com/archives/1998/11/msg00890.html


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## ShaggyMutt1 (Jun 19, 2012)

ps2375 said:


> Everywhere I've looked, the 3A has 82.5 bore and a 92.8 stroke.
> 
> Look here:
> 
> ...


damn thats crazy how does it use that stroke w/0 being a tall block?


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## ps2375 (Aug 13, 2003)

By having the shorter connecting rods. Just like the 9A does it. And the AEG....


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## WaterWheels (Aug 14, 2005)

I'm not here to make friends nor is this a social function as far as I am concerned so I'll do the nasty (about time I think). 

Get a few books on Volkswangen engines and automotive design and engineering in general and then read them. Read them until you understand what is written and don't just look at the pictures. Stay away from Hot Rod or Carcraft or any other American iron performance book. Heck, spend some time at the computer and using the Internet will work also if you're serious. I don't post this to be rude or above you in any way, but please. People have tried over and over to point some things out to you and you just don't seem to understand. Yes, you can swap those pistons into a JH block. No, they are not a direct replacement part. The height of the cylinder block really does not mean a thing so long as there is enough room for whatever parts are installed to function and their demensions are correct for whatever is being built. If the idea of installing these pistons in your own engine, sounds like what you want to do, pleases you then may I suggest one or two routes: either pay someone who knows what they are doing to build your engine or bring up your knowledge base until you yourself can do the task. Stating over and over that you don't understand is just a waste of time and energy.


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## rhussjr (Aug 7, 2000)

There is a TV commercial for insurance that has the girl that says they can't put anything on the internet that isn't true, which she read on the internet and is dating a French model.....

Here is a fact: The 9A 16V uses crank shaft part number 053 105 101 H. This is the same part number used in the Audi 3A 2.0 found in the Audi 80 & 90. ABA used 053 105 101 H from 1993 - 1995 and the 1.8 AAC engine found in the Canadian cars used 026 105 101 F, which by the first three digits makes it a 1.8 part and an 86.4 stroke. Parts with 051 and 053 are 2.0 and all 2.0s are 92.8 stroke. 

The 3A (which is a 220mm block or short block when referenced against an ABA or tall block) is noted on the internet as the "bubble block" and came before the ABA (2E, ABF, AJE and a number of other codes for 2.0 engines from around the world and was Audi's first attempt at larger displacement in this block design. Audi had a 2.0 years before in the Audi Fox (100) and it was nothing more than the 2.0 from the Porsche 924, which is not related to the 9A, 3A, PG, PL, RV, GX or any other engine found in a 1974-1999 VW.


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## ShaggyMutt1 (Jun 19, 2012)

ok 1 question? It says online the 9a and 3a use 86mm cranks! So what pistons can I use to make the JH into a 1.9l with out spending alot


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## ShaggyMutt1 (Jun 19, 2012)

ok 1 question? It says online the 9a and 3a use 86mm cranks! So what pistons can I use to make the JH into a 1.9l with out spending alot :vampire:


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## ShaggyMutt1 (Jun 19, 2012)

rhussjr said:


> They do not use the same stroke
> 
> 1.8 = 86.4 mm
> 2.0 = 92.8 mm
> ...


which 1.8 engines have this compression height?


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## ps2375 (Aug 13, 2003)

If a 1.8 motor had that compression height, it's CR would be very low. The compression height is a factor along with the geometry of the rest of the motor. The reason the 3A has that compression height is partly due to the stroke.


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## ShaggyMutt1 (Jun 19, 2012)

Damn I guess Ill try putting 3a pistons in 9a block. Good?


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## ps2375 (Aug 13, 2003)

ShaggyMutt1 said:


> Damn I guess Ill try putting 3a pistons in 9a block. Good?


With the 9A crank and an 8V head, you just made yourself a 3A clone.


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## WaterWheels (Aug 14, 2005)

ShaggyMutt1 said:


> ok 1 question? It says online the 9a and 3a use 86mm cranks! So what pistons can I use to make the JH into a 1.9l with out spending alot


Where on-line does it say that a 3A or 9A use 86mm crankshafts? An answer to this might help to steer you away from reading that site and get you pointed towards some correct information. 3A and 9A both use a 92.8mm stroke crankshaft. If you want a 1.9L displacement engine with your 86.4mm stroke crankshaft you will need pistons with a diameter of at least 84mm. Sorry to repeat what someone else already said. So you are looking at custom parts and the term "without spending alot" becomes a matter of how much money you have in the bank. It would be far cheaper to just grab a used 2.0L bottom end. But really, where are you getting this 3A/9A has a 86mm stroke?


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## ShaggyMutt1 (Jun 19, 2012)

well how much hp can I get out of a streetable 3a?


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## ps2375 (Aug 13, 2003)

ShaggyMutt1 said:


> well how much hp can I get out of a streetable 3a?


More than with a 1.8. The term "street-able" is very open to interpretation.


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## ShaggyMutt1 (Jun 19, 2012)

ps2375 said:


> More than with a 1.8. The term "street-able" is very open to interpretation.


150hp out of yet another frankenstein engine 9a 83mm pistons (cast) 8v big valve head, 268 cam, etc I don't really want a knock sensor but hey I guess I gotta go that route


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## ps2375 (Aug 13, 2003)

ShaggyMutt1 said:


> 150hp out of yet another frankenstein engine 9a 83mm pistons (cast) 8v big valve head, 268 cam, etc I don't really want a knock sensor but hey I guess I gotta go that route


The CR will be very high with those pistons, and that cam won't get you there and the head will need major port work. And that hp number might be at the crank not the wheels. And 100+ octane will be needed, ya, street-able.


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## ShaggyMutt1 (Jun 19, 2012)

Sorry I meant 3a pistons in 9a block


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## ps2375 (Aug 13, 2003)

OK, but not going to be anywhere near [email protected] But will be fun to drive in any mkI/II.


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## ShaggyMutt1 (Jun 19, 2012)

Guy at machine shop told me it would cost 1100 bucks to make 8v head out flow 16v head


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## Rheinland Technik (Apr 2, 2010)

Just use 3A [AEG] pistons in a 3A block if you are staying 8V, unless you plan on running a crossflow head, then use the 9A block or just drop in an ABA bottom end. If you did use an 8V head on a stock 9A bottom end, the compression ratio would be around 12.5:1. If you were going to go 16V head, then you could even opt to run 9a pistons in an AEG bottom end. Options are almost endless.


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## ShaggyMutt1 (Jun 19, 2012)

Rheinland Technik said:


> Just use 3A [AEG] pistons in a 3A block if you are staying 8V, unless you plan on running a crossflow head, then use the 9A block or just drop in an ABA bottom end. If you did use an 8V head on a stock 9A bottom end, the compression ratio would be around 12.5:1. If you were going to go 16V head, then you could even opt to run 9a pistons in an AEG bottom end. Options are almost endless.


3a is super hard to find 

How can I lower compression w/0 using a copper head gasket


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## ps2375 (Aug 13, 2003)

ShaggyMutt1 said:


> Guy at machine shop told me it would cost 1100 bucks to make 8v head out flow 16v head


Sounds like he is fishing for work.


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## ps2375 (Aug 13, 2003)

Do you have 3A pistons? If not, you are going to have to buy pistons and this whole build will be $500-600 more.


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## Rheinland Technik (Apr 2, 2010)

www.car-part.com 

Audi 80 & 90 from 88-91 year models.


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