OST-093: My, My, Mystery
07-25-2022, 06:34 PM
Post: #1
OST-093: My, My, Mystery
Current build, so not a "Catching Up" thread.

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


Essentially there are 3 types of 16V 4AG heads. There are 2 versions of the largeport, and of course the smallport.

The early largeport (1984-1987) was originally designed/built(?) by Yamaha, where the later ones(1987-1989) were changed and made by Toyota(?). You can see some of the changes in the following photos...



[Image: AEU86 AE86 - OST-093: My, My, Mystery]



If you watch Garage 4AGE's videos you may have seen the earlier head makes a bit more power. This is likely because at the bowls the earlier heads have a better shape as the bowl turns to the valve...

[Image: AEU86 AE86 - OST-093: My, My, Mystery]

... BUT there is more room in the floor of the later head (arrows).

I've come to the conclusion that the later heads were partially designed to better accommodate Formula Atlantic engine builders....... but that's another story...



The Mystery here is the head I'm working for OST-093. It appears that it is a mixed head, with some newer features, and some older features......

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


more to come...... Wink

Dan -

You can |Sad .... OR you can ask for help!!!

OST Porting service - http://hachiroku.net/forums/showthread.php?t=19991
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07-26-2022, 12:10 PM
Post: #2
OST-093: My, My, Mystery
I see you stamped OST-096 over 63. Does this mean you worked on this head before? Or was the 63 stamped by someone else?

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[Image: AEU86 AE86 - OST-093: My, My, Mystery]
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07-26-2022, 10:35 PM (This post was last modified: 07-26-2022 10:47 PM by oldeskewltoy.)
Post: #3
OST-093: My, My, Mystery
(07-26-2022 12:10 PM)banpei Wrote:  I see you stamped OST-096 over 63. Does this mean you worked on this head before? Or was the 63 stamped by someone else?

far more innocent... I mis-stamped it. Confused


(07-25-2022 06:34 PM)oldeskewltoy Wrote:  If you watch Garage 4AGE's videos you may have seen the earlier head makes a bit more power. This is likely because at the bowls the earlier heads have a better shape as the bowl turns to the valve...

[Image: AEU86 AE86 - OST-093: My, My, Mystery]

... BUT there is more room in the floor of the later head (arrows).

I've come to the conclusion that the later heads were partially designed to better accommodate Formula Atlantic engine builders....... but that's another story...


(from soon to be posted "Catching up thread")..... This is a later head now fitted with oversize seats for Atlantic valves.

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


more to come.... Big Grin

(07-25-2022 06:34 PM)oldeskewltoy Wrote:  The Mystery here is the head I'm working for OST-093. It appears that it is a mixed head, with some newer features, and some older features......

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


more to come...... Wink

So... what makes it a mixed head?

Please note that the front of the head is cast as a later type - albeit it isn't drilled/tapped

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


and yet the intake ports have the earlier shape

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


more to come...... Wink

Dan -

You can |Sad .... OR you can ask for help!!!

OST Porting service - http://hachiroku.net/forums/showthread.php?t=19991
Find all posts by this user
07-27-2022, 05:22 PM
Post: #4
OST-093: My, My, Mystery
(07-26-2022 10:35 PM)oldeskewltoy Wrote:  This is a later head now fitted with oversize seats for Atlantic valves.

[Image: AEU86 AE86 - OST-093: My, My, Mystery]

Do you replace the valve seat with an insert to mill a new seat? How does that work?
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07-29-2022, 01:52 AM
Post: #5
OST-093: My, My, Mystery
(07-27-2022 05:22 PM)decryphe Wrote:  
(07-26-2022 10:35 PM)oldeskewltoy Wrote:  This is a later head now fitted with oversize seats for Atlantic valves.

[Image: AEU86 AE86 - OST-093: My, My, Mystery]

Do you replace the valve seat with an insert to mill a new seat? How does that work?

What you wanted to know?

Dan -

You can |Sad .... OR you can ask for help!!!

OST Porting service - http://hachiroku.net/forums/showthread.php?t=19991
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07-29-2022, 02:29 PM
Post: #6
OST-093: My, My, Mystery
(07-29-2022 01:52 AM)oldeskewltoy Wrote:  What you wanted to know?
Yes, thanks!

How do you remove and install the seats? Are they press-fit?
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08-01-2022, 05:11 PM
Post: #7
OST-093: My, My, Mystery
While this is a mixed generational head, the intake casting was SUPERB.... note the bowl casting comes all the way out to the edge of the seat.

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


In all my years working these heads this is among a handful that were well cast..... well at least on the intake side......



The exhaust side... not so much

[Image: AEU86 AE86 - OST-093: My, My, Mystery]


more to come......... Big Grin

Dan -

You can |Sad .... OR you can ask for help!!!

OST Porting service - http://hachiroku.net/forums/showthread.php?t=19991
Find all posts by this user


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