# TECH: Differences between OBDI & OBDII heads and blocks



## tdogg74 (Mar 1, 2002)

*The difference in the top end is as follows.* 

*Throttle body:* 
-OBDI had a dashpot while OBDII does not.
-OBDI has the external ISV (idle stabilization valve)
-OBDII has the TPS (throttle position switch) integrated eliminating the dashpot and ISV.
-OBDII has a different throttle bore shape than OBDI to increase air velocity at lower rpms.

*Intake manifold:*
-OBDI has the external ISV attached to the exterior of the upper manifold.
-OBDII has vanes immediately forward of where the individual ports begin in the upper manifold. Lower manifolds are identical for both OBDI & II.

*Camshafts profiles:*

OBDI camshaft measured @ .050" 
Advertised Duration: Unknown 
Duration @ .050": 211*/212* 
Valve Lift: .400" 
Lift @ TDC: Unknown 
Centerlines: 113.2* / 113.8* 
Lobe Center: 113.5* 
Valve Timing: -7.7/38.7 - 39.8/-7.8 
Valve Overlap: -15.5* 

OBDII camshaft measured @ .050" 
Advertised Duration: Unknown 
Duration @ .050": 210*/210* 
Valve Lift: .417" 
Lift @ TDC: Unknown 
Centerlines: 110.8* / 109.2* 
Lobe Center: 110* 
Valve Timing: -5.8/35.8 - 34.2/-4.2 
Valve Overlap: -10*

Pic of OBDII stock cam next to Techtonics 276* camshaft:









Pic of OBDII next to Techtonics 276* & 288* camshafts:









*Valve springs:*
-OBDI came stock with dual valve springs capable of lifts of .450" of lift. 
-OBDII came stock with single valve springs capable of lifts up to .432". 

OBDII valve spring assembly:









*Heads*
-OBDI & ODBIII heads are interchangeable.
-OBDI had provisions for EGR (exhaust gas recirculation)
-OBDII heads had SAI (secondary air injection) attached to the exhaust manifold
-Stock OBDI intake ports flow better than OBDII.
-OBDII intake ports were designed with shrouds immediately before the valve guide. This was to reduce intake noise and redirect the A/F mix to the top of the piston for increased efficiency. These shrouds became a hindrance at high rpms.
-It is important to note that during the 1995.5 and 1996.5 model years, there was sometimes a mix and match of parts. Some cars came with OBDII heads with OBDI valvetrain parts, ect. There is a ghost head out there. It's the OBDII "German" head. It has large OBDI ports (no shrouds), single valve springs, no spring seats, and smaller JH sized spring seat bores. In order to upgrade the valvetrain, you must machine the spring seats open to accommodate the dual springs seats. 


Here is a pic of a (ported) OBDI next to a stock OBDII intake port:









Here are cut-away shots of an ABA head:


















*The difference in the bottom end is as follows:* 

There are only 2 different blocks that the ABA could have... squirter or non-squirter. There is only one way to know exactly what's in there, and that's to take the oil pan off and LOOK.

Generally speaking, squirter blocks are the way to go if you're building a performance engine, however, I've used both for pretty intense buildups and I can't say I've noticed a difference.

There are a variety of internal combination that you may find as well, but let me preface it with a couple ABA LAWS.

All ABA's have forged rods
All ABA's have cast pistons
All ABA internals are interchangeable

That said, lets get down to the whole OBDI vs OBDII debate.

The general rules are...

OBDI - forged crank
OBDII - cast crank

But, knowing VW, there is a lot of gray in the middle. The only ones i can say for sure I've never seen deviate from the rule are 93-94 OBDI and 98-99 OBDII. Everything in the middle is hit and miss. Forged cranks are stronger than cast, but the power yield difference is much lower than people think, only about 35-50lb/ft.

The earliest ABA's also tend to have a full metal windage tray that forms the oil pan gasket, later ones had a little splash guard that snaps onto the oil pickup, the full metal tray is preferred.

There are also 3 difference sets of pistons you may find. They are also hit and miss, so the only way to tell for sure is to at least inspect them through the spark plug holes or remove the head. There is a smooth dish piston. These are generally OBDI "German" blocks, but they also made their way into later "Mexican" and "Brazilian" blocks. The later OBDII engines had what I call castle pistons. They look similar to the smooth dish, but have little castles that stick up on the front and back and also have a deeper dish. I assume the reason is to better direct the combustion downward but narrowing the combustion chamber at TDC. There are a handful of the elusive "unicorn" pistons out there as well. I have a set that I pulled from a "Brazilian" block and they are a mix of the other two but slightly a-symmetrical like a VR piston. Not sure what the reasoning was for them, but they clear a 16V head rather nicely.

Of the 3 pistons, for an ABA, I can't see either of the common ones making any difference, but I go with the smooth dish for because they seem to offer slightly more clearance for a large cam and decked head with large cam lift. For an ABA/16V build, the rare ones or the smooth are the more ideal.


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## MK2SnowPilot (Sep 8, 2005)

Great Tech as always Tdogg74!

Now you just need to answer the question everyone wants to know:

Which camshaft is better - OBDI or OBDII?

:beer:


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## tdogg74 (Mar 1, 2002)

OBDII.

Wider centerline
More lift
More overlap

If you think about it, the cam was re-profiled for the the OBDII head, which has smaller intake ports, to keep the same hp/tq figures as the OBDI head.


Did I also mention I have two of them for sale?


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## o2bad455 (Aug 22, 2003)

Thanks for the great info! In particular, that's an excellent description with pics of the ABA head differences, and I have to agree with your call on the cam.

I've got my ABA/16VT apart right now for another reason, and am very curious about the 3 different piston styles that you mentioned. I think I've got the smooth style from your description -- that is, I don't see any raised lands on rear (presumably for castle and unicorn styles) or on the front (presumably for castle style). To be sure, would you happen to have any pics of the three styles for comparison?



tdogg74 said:


> There are also 3 difference sets of pistons you may find. They are also hit and miss, so the only way to tell for sure is to at least inspect them through the spark plug holes or remove the head. There is a smooth dish piston. These are generally OBDI "German" blocks, but they also made their way into later "Mexican" and "Brazilian" blocks. The later OBDII engines had what I call castle pistons. They look similar to the smooth dish, but have little castles that stick up on the front and back and also have a deeper dish. I assume the reason is to better direct the combustion downward but narrowing the combustion chamber at TDC. There are a handful of the elusive "unicorn" pistons out there as well. I have a set that I pulled from a "Brazilian" block and they are a mix of the other two but slightly a-symmetrical like a VR piston. Not sure what the reasoning was for them, but they clear a 16V head rather nicely.
> 
> Of the 3 pistons, for an ABA, I can't see either of the common ones making any difference, but I go with the smooth dish for because they seem to offer slightly more clearance for a large cam and decked head with large cam lift. For an ABA/16V build, the rare ones or the smooth are the more ideal.


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## MK2SnowPilot (Sep 8, 2005)

Awesome info tdogg, thanks! So glad I took the obd1 cylinder head and intake manifold off the 93 parts car I just got rid of. Now I know when I get around to installing it 
I should put the OBDII cam in it and get a couple more ponies out of the motor without spending a dime


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## JDub8 (May 24, 2008)

tdogg74 said:


> OBDII.
> 
> Wider centerline
> More lift
> ...


Would an OBDII cam work in an OBDI head? I thought only 95~(pre obdII) 2.0's had forged rods. A guy who build up an aba 2.0T said OBDI bottom ends were stronger and VW weakened them at the OBDII transition because it was cheaper. Any truth to that? I like to dream about one day building my own 2.0 (mostly for fun) and I find it hard to find consistent info.

Note: When I say building my own 2.0 I don't mean building it up for crazy power or anything, just taking my time sourcing parts and building a "best of" of sorts. Hopefully maintaining the ability to pass emissions.


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## tdogg74 (Mar 1, 2002)

JDub8 said:


> Would an OBDII cam work in an OBDI head?


Yes. I have two OBDII cams collecting dust in the basement.

and...



> The general rules are...
> 
> OBDI - forged crank
> OBDII - cast crank


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## JDub8 (May 24, 2008)

I believe he was referring to the block itself - not the crank.


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## Svedka (Jul 4, 2008)

Is there a way to tell OBD1 and OBD2 heads apart from the numbers cast on them.


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## tdogg74 (Mar 1, 2002)

On the back of the head, there is a ring of numbers which tell the manufacturing date. There is also the big words GERMANY or MEXICO stamped on the head as well. 99% of the time, German heads are OBDI. 

The sure fire way to tell OBDI vs OBDII is to look in the intake ports. They will either have shrouds or not. ALL OBDII HAVE THE SHROUDS REGARDLESS IF ITS STAMPED GERMANY OR MEXICO.


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## cuesoccer24 (Nov 15, 2009)

tdogg...some good stuff on here man, makes much more sense now!!!!
i have a question for you though...if i wanted to install a short ram intake into my 96 jetta gls OBDII with a short ram intake from an OBDI, would that be possible?
would any problems with the air flow occur or bad things like that?


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## Rolands76xx (Sep 21, 2009)

OBDI head possible on a AEG block...?? Figured might flow better


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## tdogg74 (Mar 1, 2002)

Don'tt know why people think this is a question and answer thread. Its not. Its just an informational thread. 

If you have a question on something specific, search the archive first, and then start a thread if you don;t find your answer.


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## A3 jetta* (Nov 18, 2010)

really important info!:beer:


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## Rolands76xx (Sep 21, 2009)

tdogg74 said:


> Don'tt know why people think this is a question and answer thread. Its not. Its just an informational thread.
> 
> If you have a question on something specific, search the archive first, and then start a thread if you don;t find your answer.


Just figured if u answered the question, itd be useful information to the rest that might need the same info... Since its an information thread... Have tried searching for the answer, no luck... Thought u might know since u know alot... But thanks anyways


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## dkashbmx (Apr 17, 2009)

so i have an OBD1 engine and car! i have a spare head but is OBD2 i want to keep my autotech cam and cam gear that was in my OBD1 head. Am i going to see a loss or gain of power when i switch the head over from OBD1 to OBD2? remember just the head and what ever else i need, (i shouldnt because it looks like it just bolts right up) 

thanks,:beer: 
Happy st. Pattys Day!


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