My 4AGE Story... (56k Warning)

[PazzaAE86]

Freshly carbostripped, hot tanked, stripped, degreased, TFR'd (yes TFR!), scrubbed, soaped and washed head just about to get attacked on the AWT porting bench. It really does take alot of cleaning to get a head to come up nice if your dont bead blast it.



The combustion chamber is std trim. Not ideal at all. Relatively small quench area (matched by the piston crown design) so mech octane is not superb. Actual chamber isnt too bad, nice and shallow, but horrid horrid machining around the valve seats which in std trim will really hurt the combustion process and provide pre-ig points and hamper flame propagation, hide end gasses yadda yadda yadda.

For a std engine, the valve seat configuration isnt too bad, a true 3 angle cut with 2 lead ins, so a simple bottom cut would effectively leave you with a 4 angle seat, a thin one none the less. However, on this application the seats will be all ground down and hand blended to form a compound radii from port to chamber, with only a very thin seat cut into it. The seat will be come part of the port and it wont be concentric or even round, it will be shapped to flow the best quality possible, although the seat will be concentric to seal the valve.

Chamber will be heavily modified to match piston crown and create a better shape for flame propagation to work in, allowing less peak ignition timing to be run, a faster burn under higher CR's with less knock sensitivity, wasting less energy from starting the burn too early.



Std inlet port. Its crap, volume too big, valves too small, casting quality is not great and there is alot of shift below the seats, horrible machining in the throats (visible at the back below seats). Port runner (manifold side) is actually offset and there are 2 port designs, one a left hooker, one a right, mirrors of eachother. So each valve has to have its half of the port designed and modified differently as flow reaching the bifurcation is comming from different entry angles (guide bosses give a clue).



Short side has nice amount of material to work with, this port will be running a flattened and widened short side turn to drop velocity over it. Each port will flow into the cylinder at different angles to promote swirl and mixture conditioning.



Exhaust ports arent too bad, just tiny! The work begins!



Just another pic of how bad the std ports are around the valve seats.....pretty apalling stuff.




Initial grinding starts around the bowl/short side and seats and this is what makes the port work. Blending of throat into seat and bowl, and bowl walls belnded into short side. It starts off looking pretty rough, and you have to be careful not to grind away areas where it will hurt flow, despite it not looking 'prety'. Not all areas of the port require touching, and this is down to core shift of the casting, primarily around the underside of the seats, you get little pockets, which if you touch destroy flow quality and quantity. Its very important to know what to touch and why.




Apologies for the poor lighting.
Pics illustrate the development of the short side, and the flattening of the turn....the floor becomes squarer with tigher radii on the corners, effectively 'D' shaping the ports. Final finishing is done once the guides and bosses and port floor is roughed out.







Development of the guides shape, profile, taper is very important. Most people grind them down, but they can be used quite effectively to direct, condition, energise and aid mixture condition. In this head the offset ports require the guide bosses to direct flow around different entry points and through the throat in different directions, so you can see quite easily that they blend and taper in different directions. Blending into the guide so the flow doesnt actually 'see' the guide or the boss is vital to making it work.



The OER ITB's flowed.

Point to consider is that at no point is a 'polished' finished ever used. Using correctly textured surfaces are better at supporting neat raw flow because the boundary layer thickness, or the actual layer of still air between mass flow and port wall, that flowing air floats on can be controlled to reduce losses, turbulance. Texture also aids mixturing and prevents fuel drop out as fuel never really comes into contact with the surface, and if ti does a shear state can be generated. Changing texture from near satin to rough can be used to energise the flow in directions.

More to come as it happens, all work and pics thanks to my Sponsor, Angel Works Technologies.. http://www.angel-works.co.uk