Flowing the bigport head

[robokill]

Hey,

been doing some research but reached the point where I wonder if anyone ever tried anything difrent.

I checked the bible for info. In the N2 spec info you see that they make the bigport intakes LARGER (yes bigger than they are) Off course this is for 215 HP which I probably won't be reaching.

But the question is. Did anyone eever try some flowing on spots not in the bible and did recieve some good experience about it.

I was gonne try to flow the entire combustion chamber. (instead of only the corners between the intake and exhaust)

Maybe enlarge the exhaust ports completly

[Apolan]

there was an extensive conversation on that exact subject about a year ago.. i think one of our members, who deals in racing with ae86's and also preps the cars had some interesting views on porting the head.. cant remember his name atm, but surely sombody will.. i think jamiemirror also had alot to say on the subhject, maybe ask him.

also i would suggest reading the motomans page, to open your mind a bit..

[robokill]

motomans page???? you mean from moto from club4ag?

[Apolan]

no i mean this guy

http://mototuneusa.com/thanx.htm

He wrote alot about intake porting.. i've read all the articles, and some are very controvert.

[a112]

That is motoman i think,and also check out the guy croft's page,maybe you can find something.

http://www.gcroft.com/page2.html

[thanhngo]

Only talking from research here:

Formula Atlantics & N2 specs look like they make bigports bigger - some atlantic pics i've gathered from surfing.





Make power above 6000rpm, they probably don't care about lowend?

Motoman talks about making ports smaller...

Heres something I noticed upon buying a 20v silvertop and had a smallport gasket around. Note the blacktop is meant to have even smaller intake ports (will confirm when that engine arrives ). Though the valves area are HUGE! picture a trumpet intake design.



interesting to see port evolution for 4age made by toyota/yamaha

[E-volve]

Don't forget that real flowing can only be done on a flowbench.
I'f you don't do it right you can easily fuck up the flow and loose power instead of making more.

A bit of portmatching is ok, but real flowing can't be done with only a dremel

[oldeskewltoy]

What are you doing with this engine??? What is the rpm range you desire? What power levels do you need? What will be your principle use for it??

90+% of the time porting done to 4AG heads does more damage than good.

IF you plan on using this as a well tuned street engine, producing a moderate boost over original(20%) while retaining the OEM intake... then there are 3 things of importance... (in my opinion)

#1) each port(16) at the transition point from horizontal flow to vertical flow has a minor casting flaw. The 4AG head was cast in 2 stages(from what I can see...) The two casting points meet at the port transition point. In all likelyness you will NOT see this, but once the valves are removed you CAN feel it... just run your finger up the port edge and it will FEEL obvious
#2) The TVIS plate adds low end torque, and as long as peak rpm doesn't go beyond the factory ECU rev cut, the TVIS plates add more in the bottom end then they rob in the top end(being in the air stream....) BUT there is a flaw in how the intake/TVIS and head assemble... or rather where the intake and TVIS assemble. If you have your largeport head bare you will see that two of the intake bolt holes are actually larger than the bolts... because they have dowels to make sure there is an EXACT fit between the head and the TVIS plate. Now look at the other side of the TVIS plate... where the manifold meets the TVIS plate. There are NO dowels! Although the differences in the stud as to the bolt holes in the manifold is small, it still can lead to manifold mismatching which can cause eddy points in the intake stream. What is needed is a dowel, or roll pins to lock the intake to the TVIS plate so all the air passages can be tapered to minimize eddy points.
#3) Once the valves have been lapped in and a final valve to valve seat depth has been determined (how far down inside the seat the valve face is from the combustion chamber) then and only then should you begin to measure and adjust combustion chamber volumes. Using a pipette you fill each chamber and measure its volume... once you have found the largest... you then CAREFULLY begin to remove material in the areas noted by TRD bible. Another note here is to do a MINIMAL TRD polish to the LARGEST chamber first... remeasure it and then proceed with the other chambers till they all have the same volume.

The most significant rule of thumb with largeport 4AG heads is minimalism... Don't do anything too much. The main idea is to imcrease port velocity, NOT to screw it up

[irishtwincam]

4ag combustion chamber




Have intake port pics somewhere, and short side radius.

This head made 199.7hp with ~290degree/10mm cams.
Made for rally. TRD do 320degree 12.5mm lift
Throw that in and see what happens

Mass flow does not equal meaningful flow.
Getting a fuel air mixture in fast and efficiently is important, then you need to burn the mixture properly. Everything from the piston up should be matched for power!

[apardal]

Beautiful headwork!