Volume (mass) isn't the only thing you look for in a port job. Things such as velocity and the quality of the airflow are just as important...and probably more so on a street car. (lately, tumbling of the air flow is netting very good results) Is tumbling equally benificial for both traditional carburated and F/ I engines?
Just looking at something is a very poor way to judge a port job.
I was trying to say here that enlarging the throat was not aparent, it would take some very precise machining to get a t/plate to perfectly match the new throat diameter as it looks here, that's why I believed it was the stock plate. and radiusing definately has a benefit- it helps compress the air flowing through the tube, although not radicaly it has the same effect as slightly lowering the air temp.
That's why you use a flow bench...so you can measure your work and see your results. Sure a flow bench will give you the differences in air flow through the ported t/b, but my point was it's use in that situation wasn't going to change the results, however, using it on the heads to balance the flow through the ports is extremely useful in getting the most out of a porting job.
I can show you some very pretty port jobs that are absolutely worthless on a car. Removing metal in the wrong spot makes parts useless. For example, playing with the short side radius of a port may look nice, but in actuality, ruins the port in most applications. I agree that removing metal in the wrong places can do more harm than good, but the reason for radiusing the port opening to the gasket edges is again to compress the airflow, not just increase it. Also if the corresponding intake manifold is not matched to the head port, in some cases there will be no gain and possibly a loss of HP.
Most porters for street heads spend the majority of their time in the first inch of the port below the valve. Huge gains can be made there. That's because that's where the most inhibitions to the airflow are found, just smoothing the radius on corners here where they make the most radical bends greatly increases airflow more dramaticaly than anywhere else in the head.( this is also where Extrude Hone is the most effective, where it's most difficult to reach with hand porting tools).
Extrude honing can be nice...but does nothing more than smooth out an existing port design. That's not a true port job. But some gains can be had that way. Extrude Hone will do more than just smoothing out the port, they'll also do a gasket match hand port job, and I'd rather have someone who spends all his days just grinding ports working on my heads than someone in the local speed shop who knows how to do it but has far less experience.
You should never attempt a "home" port job unless you know what you're doing. As I mentioned, remove metal in the wrong spot and you've just made junk. You will hurt power. You also want to make the ports work in the rpm and valve lift of the engine you are running them on. It makes no sense to build a set of heads that are real screamers at 7000+ rpm and work best at valve lifts over .600" since you're engine will never see that. Remember, you can port a head to move a ton of air...but if it slows velocity at low rpm and low valve lifts, you have just built yourself a slug on the street from the loss of low end torque. No argument here-- If you're not watching what your'e doing and leave any of the job done half a**d, you'll pay the price. You need to be criticaly aware of the thickness of the port walls or you'll be creating coolant leaks that will junk the whole engine. Is velocity as important on a F/ I engine as it is on a carburated one? I don't know about the V8 on the LS, but on the V6 there is an electricaly controlled valve in the intake manifold that decreases airflow at lower RPM's to increase velocity. I would think that adjusting it's function through the pcm would help with problems here.
But hey...I only NHRA raced for 20 years and set four National Records...and built engines for four more record holders...so what do I know???
