Re: Its a new year Not to disagree with you tkmotion, but in a way I guess I do. Volumetric efficiency (VE) is achieved by a number of factors. It is the flow of the heads, not the size of the ports. To large of ports will decrease VE. Other factors include everything that moves air effect VE. Including valve size, exhaust system efficiency, intake system efficiency, throttle body efficiency, Mass Air Flow Sensor efficiency, and of course the heads. A stock engine does not have the efficiency in these other area's to fill and flow large ports and achieve VE. There for, large ports on a stock motor will actually drop VE and the power it produces.
Volumetric efficiency (VE) is used to describe the amount of fuel/air in the cylinder in relation to regular atmospheric pressure.
Just like with carb's, and cam's. Put a 1200 cfm carb on a stock motor and watch what happens. Or .700 lift cam on a stock motor. Sure they move more volume of air. But everything around it cannot move that much air fast enough to get it into the cylinder. Again, you lose VE and the power it produces.
Bigger is not always better. A more general example would be to put a 4'' diameter piston in a "4.50 size hole (cyl.). How much compression is that cylinder going to produce? Sure you have bigger hole moving more air, but all the pressure or compression which makes power leaks back down past the piston. The more packed air you can get into the cylinder, the more power your engine is going to make.
If none of this were true, you wouldn't need a flow bench, you would just hog out the ports on the heads as big as possible and be done with it. Engines are series of components that need to be matched.
I am sure you know these things, I explained it more for the visitors. I personally think that advising people to spend money on porting heads on a other wise stock motor is not helping them. Building race engines for more then 22 years, I have a pretty good idea what quality Head Porting costs and I can think of much wiser investments for a return on Horsepower for a stock.
Correct me if I'm wrong, but what I hear you saying is; take a well performing stock motor, like a 5.0, buy a set of aluminum heads, send them to you for porting, make no other mods, and they will be very happy with the results of the money they spent.
I too want to make things clear. No flaming intended. But I just want to get the facts out in the open. This is a big decission and investment many of the visitors here may consider. |