ok i know port velocity is a good thing. so whats the best way to get it in low rpm aplications...say no more the 4000rpm. i know i dont want huge ports. and my ports are polished. so is there anything else to do?

 

3 to 5 angle valve job

 

Long runner intake, long tube headers, port/gasket match everything, back cut valves.

 

how do i get longer runners? they dont make a spacer for the 5.8 that i know of

 

If the motor is fuel injected you already have what you need. If you are running a carb, stick to a dual plane manifold. For high velocities under 4000 RPM there is no need for aftermarket manifolds. Bigger is worse in this situation. Velocity is what continues to pack the intake charge into the cylinder as the piston rises toward TDC and the intake valve begins to close. Flow at the valve is critical to this. A smooth short side radius, bowl, and valve guide are essential. As mentioned earlier back cut valves and multi-angle valve job will help as well.

 

yes. it is efi and if it was worth it. i have access to a cnc mill and can make a spacer.

 

all valve jobs are 3 angle ifyou dont cut 3 it wont work i think it a crock when these guys run ads saying 3 angle valve jobs and you dont need 5 angle unless your close to clipping valves then you would backcut the valve face. moondogg

 

A multi angle valve job is the cutting or grinding of 2 or more angles on the seat and valve. The purpose of a multi angle valve job is to improve airflow. Five angle valve jobs are more applicable in the American iron heads. Older American iron heads may benefit from a five angle or radius valve job but only because the head is so bad to begin with. It has absolutely nothing to do with clipping valves. All valve jobs are not 3 angle either.

 

http://www.theoldone.com/articles/

This guy has been working on engines for a while and has some good info on his site. Much of the info is about Honda engines, but the principles are the same.

 

i dont want you touching my heads

 

sorry, dogg but steve is right...all valve jobs are not 3 angle, although 3-5 is much better.

 

LOL, yeah it depends on what you are counting as angles also. If you start at the chamber angle and count that and top cuts, seat cut, bottom cuts, bowl cuts and bowl angle and then back cuts on the valve you could have as many as 10 angles or even more!

But basically anytime you increase the overall airflow of your port with chamber and valvejob work you are increasing velocity, of course there is a cut off point for all things like this. Increase the efficiency of the valve job to a point where the short turn or another part of the port becomes the restriction and you will run into separation problems and the airflow will drop off. Typically building engines for optimized running in really low rpm ranges involves using relatively small cross section runners in the head and intake as well as long manifold runners. Short cam timing that closes the intake valve early will help build cylinder pressure as well as fairly narrow lobe sep that delays exh valve opening and can take advantage of some scavengine to help initiate the intake charge. Cams like this usually will boost low and middle rpm performance and because of the early intake valve action and late exh valve action but also run out quickly when the engine runs out of time to get the exh gasses out and the intake valve closes too early to take advantage of charge inertia in the upper rpm's also those ultra long tight runners tend to tune to much lower rpm's than larger shorter runners.

 

Installing the cam int centerlobe in relation to timing....

Also, shaping the port around the valve guide is important as is the port taper as you head towards the lower radius...port volume has to drop a bit to increase velocity as the charge makes its way to the back of the intake valve.

Yes I also agree that not all valvejobs are created equal....back cutting valves is also a good idea.

A K and N type filter will also help straighten air out before it hits the runners.

Headers help depending on the camshaft profile....this is where valve overlap helps pull the intake charge into the cyl...(at the cost of idle quality and emissions at the tailpipe.

For low end torque be sure to get a cam with good vacuum qualities and a slight increase in valve lift.(always check P/V clearances to be sure the valves don't hit the pistons.

www.camresearch.com makes good custom grind cams.