Let's say you got your hands on a extra set of plenum and manifold and being the DIY's you are, you decided to port using the porper high speed bit. How much much enlarging of the ports can you go before being too big.

How about the runners within the manifold, the manifold is short enough where you can get the high speed bit all the way thru. Know I realize the best way is with a flow test machine, but you're a DIY's and it's a extra set. A larger TB already taken care of, was just waiting to see what I was going to do with the plenum and manifold. Matching the manifold to head ports not going to be easy unless the heads are removed, which I'm hopefully planning soon for other reasons.

So lets say the plenum to manifold ports are X.XX will .05, .10, .20, or even .30 be too big. What's a fare guess to make these ports oversized? Remember no flow bench machine and trying to keep the cost to a minimum, basically my labor cost.

Same thing goes for the manifold to head ports, what size over is too much

Of course they can be adverse effects if the ports are too large, lost of lower end torque, etc.

One more thing, lets say the ports are kept OEM size but the runners enlarged will that provide any gains?

 

The plenum upper and the plenum lower are pretty close to being matched up. If you wanna match the lower plenum to the heads, you can gasket match, or make a template. Any more than an exact match is too much. The idea is a smooth flow, from intake, to TB, to upper, to lower, to heads, to exhaust manifold, to y-pipe, etc.

How big to open if you open it up? On the upper/lower manifold, smoothing it all out will be enough. If any of the ports are larger or smaller than the ones they are matching up to, you've defeated the purpose.

Don

 

Don pretty much summed it up, the only way to really see what good your doing is with a flow bench. For a DIYer cleaning up any casting flash and smoothing everything, and matching sizes is your best and probably only option. Be careful when increasing, sometimes it can be detrimental.

 

it's called "Port Matching"

 

Because I was going to drop you a pm since you are/were working on your N/A motor build up. Gasket matching sounds like a good and easy idea to do. I already bored out the plenum to TB port in order to match my oversized TB, and gasket matching the upper to lower plenums and lower to head ports sounds like a good idea. But answer me this, or maybe you already have. As I mentioned the runners within the lower plenum are pretty short, short enough where I can get the bit all the way thru.

Q---> Would enlarging the runners yeild any beneifts, while keeping the ports matched?

 

Don is right.

For porting ie..enlarging the entire port, there is absolutely no way you can determine if what you are doing is of any benefit w/o the use of a flow bench. It's probably much easier to screw up the flow than it is to increase it in a beneficial way. Even if you manage to increase the flow of one port, you must be able to duplicate it in the other 5 ports. Virtually impossible. And totally impossible for a beginner. It takes a skilled machinist years upon years to get this right. This is why most heads are cnc cut nowdays.

The one good thing about most Japanese heads/intake/exhausts is that they are generally really clean and "flash" free. And their designs are pretty good from the get go. It's how you can get V8 power from a 3.0 V6.

The idea that you could get lots of power from porting polishing etc.. came from the old muscle car guys modding their old inefficent V8 heads and manifolds. (this excludes the mightly Hemi heads of course!) Nowdays Mustang and Vette head design is pretty state of the art.