OST Cylinder Head Porting Services

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oldeskewltoy
Club4AG MASTER
Posts: 1793
Joined: Wed Jan 09, 2013 4:44 pm
Location: Portland, Oregon

Re: OST Cylinder Head Porting Services

Postby oldeskewltoy » Wed Aug 15, 2018 12:27 pm

OST-050: the Black Limited head half way through....

Image
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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flymat88
Posts: 1
Joined: Fri Jan 06, 2017 11:34 pm

Re: OST Cylinder Head Porting Services

Postby flymat88 » Fri Oct 05, 2018 1:44 am

Hello Oldeskewltoy,
I have read many threads all around the 4A-GE- engine and there are only a few people, spreading "good information" and you are definately one of them.
Thanks for sharing information and pictures about the head-work. I am doing it right now on my 16V bigport and I have some questions.

The most spreaded opinion in forums is, that the exhaust port is not optimal designed. The inner radius is to narrow or the turn is too sharp!?
Is there a benefit to widen up the sharp bend, to make it more smooth and widing up the port diameter in that area?
My feeling would say YES, because the pressure and velocity of the gases just leaving the cylinder, is hight?! So at the exhaust side BIGGER is BETTER?
(Different story at the intake-port, where you want to have velocity, achieving it by reducing the diameter...).
Do you have some advice here and maybe some numbers?

All this thoughts in respect to the these engine specs:
252 - 262 EX cams
8.5 - 9 mm lift
free-flow exhaust and custom header

Thanks for your reply!

User avatar
oldeskewltoy
Club4AG MASTER
Posts: 1793
Joined: Wed Jan 09, 2013 4:44 pm
Location: Portland, Oregon

Re: OST Cylinder Head Porting Services

Postby oldeskewltoy » Sun Oct 07, 2018 1:13 pm

flymat88 wrote:Hello Oldeskewltoy,
I have read many threads all around the 4A-GE- engine and there are only a few people, spreading "good information" and you are definately one of them.
Thanks for sharing information and pictures about the head-work. I am doing it right now on my 16V bigport and I have some questions.

The most spreaded opinion in forums is, that the exhaust port is not optimal designed. The inner radius is to narrow or the turn is too sharp!?
Is there a benefit to widen up the sharp bend, to make it more smooth and widing up the port diameter in that area?
My feeling would say YES, because the pressure and velocity of the gases just leaving the cylinder, is hight?! So at the exhaust side BIGGER is BETTER?
(Different story at the intake-port, where you want to have velocity, achieving it by reducing the diameter...).
Do you have some advice here and maybe some numbers?

All this thoughts in respect to the these engine specs:
252 - 262 EX cams
8.5 - 9 mm lift
free-flow exhaust and custom header

Thanks for your reply!


As to the exhaust side.....


negative space.....

oldeskewltoy wrote:It just doesn't get any simpler - view the exhaust port on the left as it goes from beastly to beauty........
Image




positive space....

Image



not opinion... flowbench tested many times now....




on to intake... while "velocity" is important, the velocity of WHAT is more important. Currently the velocity @ the valve seat is high because the valve is significantly larger then the seat opening. But because the opening is small, it doesn't create a great deal of bowl, or port velocity, as say a hole that would be larger. The current accepted "performance" ratio range is 85%-90% of the valves diameter is the throat of the seat. The 4AG seat sits @ about 83% - some room to grow. By carefully blending the seats, short radius, and the bowls into the port, more volume and more velocity can be generated.
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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