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Re: OST Cylinder Head Porting Services

Posted: Wed Aug 15, 2018 12:27 pm
by oldeskewltoy
OST-050: the Black Limited head half way through....

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Re: OST Cylinder Head Porting Services

Posted: Fri Oct 05, 2018 1:44 am
by flymat88
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!

Re: OST Cylinder Head Porting Services

Posted: Sun Oct 07, 2018 1:13 pm
by oldeskewltoy
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.

Re: OST Cylinder Head Porting Services

Posted: Wed Dec 12, 2018 7:51 am
by oldeskewltoy
most recently a complete restoration/rebuild....

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more to come.... ;)

Re: OST Cylinder Head Porting Services

Posted: Wed May 01, 2019 8:12 am
by oldeskewltoy
Largeport intake "under construction"

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Re: OST Cylinder Head Porting Services

Posted: Sun Oct 13, 2019 9:10 am
by flymat88
That looks absolutely fantastic!

I am not sure about the way to go...
At the moment, I would like to do the following:
I did cylinder head porting and combustion chamber deburring on my Bigport-head. Finally measured the chamber volume - all equal now.
I want to install some CatCams with IN 267° / OUT 262° or Poncams.
Full standalone ECU with Rev-Limit around 8.000-8.200 RPM, no turbo.

And here come my doubts:
I need new valves. I considered oversize valves, for example IN +1,5mm / Ex +2,0mm AND
I would love to have the Silvertop, or Blacktop ITB´s.
But with my Bigport-Head and bigger valves, I am not sure if the performance is even worse as with the standard valves, T-VIS and plenum...
I can´t image how the alterations may affect the mid-range performance...any suggestions for the way to go??
I guess the small-port head would be better?

Thank you in advance for your thoughts!
Have a nice week.