how do we what we havn't reached the limmits of flow yet?
every one seems to be stuck at around the 250 255 mark.

there aren't very many heads that can claim that sort of flow with such a small valve. anything i can find aftermarket that flows above 250 uses at least a 2 inch valve i'm proposing a 1.96 inch. also remember the swept volume of each cyl of this engine is quite high when compared to other common engines and becuase of this can tolerate a slightly larger port.

there is just no more physical room to have bigger valves , bigger doesnt always mean better , and beside you have to have pocket porting done behind the valve heads , not with a hand held grinder but a dedicated milling cutter making all the valve pockets identical

this is just scratching the surface of head work , and not to mention testing ports ( flow testing bench )

the exhaust and inlet nearly touch as it is now

one might consider either narrow or undercut stems and nicer profiled backs on the valve head and swirl polised valve heads to promote more airflow

one can spend $10 per valve upto $110 per valve




cheers

well how about i just leave the valves, that way if the engine makes some stupid figure like 98rwkw i can blame it all on the valves


na ill keep reading for a while an see what happens






but thanks to all who have given there opinion/suggestion/advice... its been a good read so far i think



EDIT: by the way, keep it all coming

The reason why I say this is because a 4.0 falcon with an unmodified tickford head ran a 13.8@99mph pass (in street trim). MPH are more consistent than dyno's and its fair to say that there are very few street falcons capable of 100mph passes. Also considering there is easily another 20-30cfm in that head with the right work (probably more like 40-50) its fair to say that street driven falcons are not being restricted by the heads.

Once again, Im not going to say that the valves/head wont become a restriction at some point, but if your not running over 100mph your head is probably doing just fine.

You mention power levels people get stuck at and in my mind there are lots of reasons for this. The two points that that I have notice people getting stuck at is 180rwkw on street cars and 250rwkw on methanol burning race cars. On those race cars Id put money on the fact that they are using the biggest valves they can machine into the head, but does that mean that going bigger on street cars will help. Im not so sure. I think the limit we see in street cars is imposed by the cams that are being used. Dev 5's for example do very well for themselves on the dyno, yet ask JMM and they will tell you it is made to work with a 9.6 static CR. These cams must be designed to keep the ecu happy and idle vaccum up and hence wants/needs a low CR. If you forget about trying to keep an unmodified factory ecu happy, open the duration, close the LSA, bump the compression ratio up and you are going to find more power. If you are clever about it, it might even be streetable.

Ok, im getting off topic here, but the point remains is that there isnt a lot to suggest that the head is much of a restriction. I haven't seen anybody post huge gains after fitting modified heads and there are some stock heads out there punching out some f**k impressive numbers. But of course the proof is in the results, and I am sure somebody will post here sooner or later either blowing my ideas out of the water or showing that it isnt a worthwhile mod.

This is something we looked at. First we considered AU valves but in the end went with undercut.

The AU valves would make a good little upgrade for earlier heads. The are the same size but have the thinner stems so will add a little extra flow.

hi

"one might consider either narrow or undercut stems and nicer profiled backs on the valve head and swirl polished valve heads to promote more airflow"

Like a member in this forum says " Keep it Tidy " yes just a few basics will increase cylinder fill and give you engine a few extra Kwatts from a few simple tidy mods.

Valve diameter is important in any engine to breathe well.

One has to ask himself or herself HOW MUCH POWER DO I WANT ??? and what RPM range , do you want you power levels to work at ????

Increasing valve diameter is one way of achieving more power out of a 4lt inline 6 cylinder falcon , but the biggest restriction is room. Valve shrouding in the cylinder head chamber and the engine cylinder walls are the biggest restriction .

3 , 5 and even 7 angle valve and seat cutting is employed to promote greater cylinder fill

Combustion chamber shape , inlet track , exhaust track ????????

Compression ratio ???? mmmm , is a very easy way of bumping up more horse power from a engine.

Most 4lt 6 cylinder engines live there life at a Static compression ratio in the lower 9:1 ratio(s). There is no reason one can not bump that up to 10.5:1 ratio and run on bowser fuel of a octane rating of 98 fuel quality.
Anything higher than a compression ratio of 10.5:1 ratio one has to start looking into racing fuels , or start adding octane boosters in there fuel tank.

modified engine ??but the down fall of this is how many people actually have a programmable ECU that can take full advantage of a properly tuned engine management system to take full advantage of a modified engine. ????? Incorrect ignition and fuel maps is the biggest killer of power.

Valve shrouding is a area no body touched on and like i said there are more factors needed to be discussed in cylinder head modifications.
Inlet track , inlet manifold , exhaust track , exhaust system , camshaft profiles , programmable ECU's

Also how many times have i seen people say im getting my head modified and nothing is mentioned of the bottom half of the engine that has traveled well over 100,000 km's plus . Bet your bottom dollar there is cylinder leakage ( Blow By ).

And lets face it yes we are talking every day drivers so most people just want a 20 to 30% increase of power from there engine.

Horse power costs money

cheers