OST-093: My, My, Mystery

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oldeskewltoy
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OST-093: My, My, Mystery

Postby oldeskewltoy » Mon Jul 25, 2022 9:58 am

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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...



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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...

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... 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......

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more to come...... ;)
OST Cyl head porting, - viewtopic.php?f=22&t=300

Building a great engine takes knowing the end... before you begin :ugeek:

Enjoy Life... its the only one you get!

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oldeskewltoy
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Re: OST-093: My, My, Mystery

Postby oldeskewltoy » Tue Jul 26, 2022 2:16 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


more to come...... ;)


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


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and yet the intake ports have the earlier shape

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more to come..... :)
OST Cyl head porting, - viewtopic.php?f=22&t=300

Building a great engine takes knowing the end... before you begin :ugeek:

Enjoy Life... its the only one you get!

Corey20v
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Re: OST-093: My, My, Mystery

Postby Corey20v » Wed Jul 27, 2022 11:43 am

Fun to see these mixed mfg method parts in the wild! Hopefully the engineers knew and approved :lol:
1986 SR5->20V ST (WIP!)
Other toys: 1993 S13 Coupe, 1993 NA6 Miata, 1996 Z32 300ZX

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oldeskewltoy
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Re: OST-093: My, My, Mystery

Postby oldeskewltoy » Mon Aug 01, 2022 3:15 pm

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.

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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

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more to come......... :D
OST Cyl head porting, - viewtopic.php?f=22&t=300

Building a great engine takes knowing the end... before you begin :ugeek:

Enjoy Life... its the only one you get!

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Rogue-AE95
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Re: OST-093: My, My, Mystery

Postby Rogue-AE95 » Sat Aug 06, 2022 7:11 pm

The first 4A-GE I bought was from a 1987 GTS coupe (built in 12/1986 from the VIN). It also has those untapped holes on the head (for the FWD stiffener bracket).

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'88 Corolla All-Trac x2 (manual, auto)