4age bigport head: port & polish

[BenR]

I would not be tempted to follow the N2 specifications, they are out dated and old theory. On the bigport heads i high advise NOT touching the port dimentions at the mouth of the port, it is already too large by a long way. Concentrate on the area from the valve seat to 0.5" infront of the valve guide..........THIS is where you will gain all your flow, anywhere infront of that will make no difference.

If you want to make them smaller then you will have to experiement with liquid aluminium since welding like i do is a very very expensive thing to do, there are many parts to do before you can use a head that has been welded. But also, you will have to spend alot of time on the flow bench and on the dyno to test the effects of making a port smaller. My advice would be to leave the port dimentions alone, you will see no gains by trying to make things smaller or bigger..........you will only cause yourself trouble in the long run.

And because you are running ITB's, you can run much wilder cam, i would be looking at 275-280 at least or you will be wasting the RPM potential of the 4age.

For the savenging, its all about exhuast header design. This depends on the head flow rates, valve sizes, port lengths and dimentions, cam specs aswell as installed cam timing, compression ratios, induction methods etc. Then you can calculate the exhaust header primarcy and secondary lengths, bore sizes, stepdowns etc etc. It is complex to get right, so most people will settle for a design that will work nicely, rather than perfectly. I would buy one of the already available manifolds unless you have £600-1000 to play with for headers.

Do not run a cat, run a de-cat pipe.

Os7213 Wrote:Haha nice thank alot!
Lol sorry for the maths think it was late when my math have been done

For rod stretch since im using OE con-rod from a Ae11 blacktop i think ill be good cause my engine will not rev 12000 so

For the splitter in front of valve guide you are totally right...my bad...havent think about the round diameter of the valve guide ive just see something in the port!!! Thank for the advise

I think the head will be perfect, im using the 4agze since i want "middle" power what the blue-top head cant provide... The only thing i need to think about is the perfect dimension of the port for "middle" power and high rpm almost near 9000rpm or more since my cam peak power is near 7500. Do you think this kind of combinason is possible!?Ive also think about a 264deg ext cam since im running itbs who good on high rpm. Ill trying to check the port size by begin with the N2 port size specs..I already know they are too big for my application so i need to make them smaller but how can i have the best port dimension?! Ill find something between the dimension of the stock port and the N2 specs I think it can work! Since i dont have to change port configuration i have all my time to check these meusures.If you have tips dont hesitate!!

For the scavenging effect i have only begin to read about it... The only thing i know is the exhaust manifold have a restricted volume but in fact that help!! The thing you need to check is for too much rapid restriction if i have understand right...Dont you think a simple porting or the headers can help a lot? I only know the cat-bak intern desing play an important role so a test pipe its not the way to go and since i dont want to "reshape" the interior of a cat i think i will just install one..Where im lost is the part of the exhaust line leight im not sure wich type of headers i can use, i suppose a nice smooth curved one no high rise... And the total leight of the exhaust im not sure i dont find proper infos about it...
Thank a lot to help a guy who want to lear and have poor english skills

Thank a lot in advance
Ugo