# aba/20v compression ratio question



## Forty-six and 2 (Jan 21, 2007)

I have built a aba bottom end, intending to use it with a 16v head. To compensate for the loss of compression with this setup, I went with 10.5:1 aba pistons. The aba bottom with a 16v drops compression 1.5 points from the stock aba motor. By choosing the piston that I did, it would have dropped my comp ratio to 9:1. 

With that being said, can anyone comfirm the compression ratio of the aba bottom end, with "10.5:1" piston and a 20v head bolted to it?

I know this has been done before, but can't seem to find the answer to my question with any thread found by searching.

Will this piston combination yeild a usable comp ratio with a 20v head and a turbo?


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## V-TEC this!!! (May 4, 2003)

I see you are still considering building a motor for the corrado? 

I did a quick search on google and came up with:

16v head cc 42-45cc's
and a 20v head is 45 so I think it would be safe to say that the compression would be about the same for the 16v as the 20v. But do not quote me on it. Ask sdezego he will know for sure.


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## Prof315 (Jan 5, 2009)

OK... here's the deal. Stock ABA bottom end and virgin 16V head: 8.0 to 8.2 to 1

Stock ABA bottom end and virgin 20V head: about 8.5 to1

ABA with Wiseco 10.5 to pistons and virgin 20V head: around 9 to 1 maybe as high as 9.3 to 1

Stock 1.8T: 9.3 to 9.5 to 1.

Always always always cc your motor during the assembly/test fitting process. Especially a hybrid it's the only way you'll know for sure what your compression is.


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## Forty-six and 2 (Jan 21, 2007)

Hey what been going on man? How is the build going?

I talked to Shawn about it for a little while, but we couldn't come to a solid conclusion.

I am out of the Corrado game now. Life changes forced them out. I am looking to pick up a MkI TT. I still have my bottom end, and wouldn't be able to get much money for it, so I want to put it to use. The 1.8t bottom end is weak, so I am looking to drop in the aba I have. 

I have read conflicting info about needing valve recesses in the piston even with a 16v head. Are they necessary with either? Prof315, you have convinced me to check the clearances with clay, but I am just wondering if I should be prepared to have them machined.


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## sdezego (Apr 23, 2004)

Yea, I would need to sit down and do a lot of calcs, but as Jeff says, that still won't tell you about valve clearances



Forty-six and 2 said:


> I have read conflicting info about needing valve recesses in the piston even with a 16v head.


16v on OBD1 pistons is usually fine. 16v on OBD2 pistons can hit the small bump ups)

Add cams and anything is possible.


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## Forty-six and 2 (Jan 21, 2007)

I am running Wiseco's for the aba. They are originally entended for a high compression N/A setup. 10.5:1 with a slight dish.

http://www.intengineering.com/Wiseco-835MM-Bore-ABA-p8801837-1-2.html











The obdI aba uses 10:1 comp ratio pistons, so my _guess_ is, yes they will end up needing recesses. :thumbdown: This sucks, not only because the motor is assembled, but an added cost.


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## sdezego (Apr 23, 2004)

Can you post a pic with a piston at TDC?


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## sdezego (Apr 23, 2004)

To give you what 9.25:1 20v looks like in the ABA (much like a stock 1.8t actually)


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## Prof315 (Jan 5, 2009)

Forty-six and 2 said:


> I am running Wiseco's for the aba. They are originally entended for a high compression N/A setup. 10.5:1 with a slight dish.
> 
> http://www.intengineering.com/Wiseco-835MM-Bore-ABA-p8801837-1-2.html
> 
> ...


I'd be willing to bet you'll be fine. The only place where hitting the piston with the valve is an issue is on the raised portion of the piston out at the edge. OBD2 "castle" pistons actually stick out of the bore about .005" and still have .070 clearance with an unmolested 20V head bolted on. 

Shawn is absolutely right as far as cams go but since you can make well over 300whp with stock cams and lots of boost why bother.


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## rhussjr (Aug 7, 2000)

The compression ratio will roughly be 8.46:1, which will be suitable for turbo. That is using a 0.065 thick head gasket. If the gasket is thinner, the compression will be higher (8.77:1 using a 0.045" thick gasket).


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## Forty-six and 2 (Jan 21, 2007)

sdezego said:


> Can you post a pic with a piston at TDC?


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## sdezego (Apr 23, 2004)

Wow, those look nothing like the pic you linked to:











Your's def look like stock OBD2 pistons :screwy:

Edit: I just re-read your posts... I thought you had ordered the Wiseco pistons from IE for the 16v on ABA. After searching that P# I see that those are 8v ABA replacement pistons (http://www.wiseco.com/ProductDetail.aspx?AppID=&ItemID=6609M835&ModelYear=&ModelID=181) and as I mentioned those are OBD2 style.

I am pretty sure you would have had big issues with the 16v on those regardless.

S


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## Forty-six and 2 (Jan 21, 2007)

I noticed that too. I ordered the ones from IE that I got that picture from. Im not sure whats up with that then...


I just checked IE's site and they picture two different pistons. They use the picture you posted and the picture I posted for the same part.

http://www.intengineering.com/Wiseco-835MM-Bore-ABA-p8801837-1-2.html


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## Prof315 (Jan 5, 2009)

That is a definate check with clay situation. I agree with Shawn that they are OBD2 style forged pistons. I had .070" with stock OBD2 pistons/block and an untoched head but those castles look taller. I'd check.


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## Forty-six and 2 (Jan 21, 2007)

Defenitely. This is kind of a disapointment. 

I appreciate the help fellas. :beer:


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## sdezego (Apr 23, 2004)

Got a router?  j/k (kind of)


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## Prof315 (Jan 5, 2009)

sdezego said:


> Got a router?  j/k (kind of)


Actually I was thinking more like a mini D/A and some 150 grit. Follow that up with a couple af cans of brake cleaner and I'll bet things would be fine.


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## V-TEC this!!! (May 4, 2003)

take them out, bring them to a shop and have them machine that bit off. It would be a straight forward operation for a shop to do. Taking it apart is the biggest pita.


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## Prof315 (Jan 5, 2009)

V-TEC this!!! said:


> take them out, bring them to a shop and have them machine that bit off. It would be a straight forward operation for a shop to do. Taking it apart is the biggest pita.


That's the best route for sure....and truly very easy.


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## V-TEC this!!! (May 4, 2003)

if I was at home and not overseas I would have suggested to send them to me and I would have machined them for you.  Unless you want to wait until july.


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## Forty-six and 2 (Jan 21, 2007)

I just picked up a head today. $50, but has 4 bent valve. Regardless it is a steal. I work next to a machine shop.  He can't machine the pistons though. 

I hope to have it ready before July, but who know! lol I will keep you updated and how it goes. :beer:


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## sdezego (Apr 23, 2004)

Forty-six and 2 said:


> I just picked up a head today. $50, but has 4 bent valve. Regardless it is a steal. I work next to a machine shop.  He can't machine the pistons though.
> 
> I hope to have it ready before July, but who know! lol I will keep you updated and how it goes. :beer:


 $50 Damn pick me up another core for that and I will machine your pistons on my Bridgeport for you


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## Forty-six and 2 (Jan 21, 2007)

There are a handful to choose from.. I may have taken the better of them. I can check the others out further if you are serious. :thumbup:

The one I grabbed wasn't a belt failure, but a busted pan. I am assuming the the valves that bent seized open or something else odd. It's the center valve on all four. The other's seem to be ok. I will know for sure in a few days.


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## sdezego (Apr 23, 2004)

yea. Bent valves are ok as long as the head is rebuildable.


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