Chevy/GM Cylinder Heads - Breathing On A Budget

Today's technological advancements are great. We've got products rolling off assembly lines that can make more power and will last longer than even the most highly modified parts could a few years ago. With advancements in technology there may also come a reduction in cost. Cylinder heads have benefited tremendously from today's advancements, but there's still something that can be gained from a set of stock heads in the hands of an experienced head porter. Stock, in this case, means GM's iron Vortec small-block heads, and by experienced head porter, we mean Joe Mondello.

For those of you who might be unfamiliar with Mondello's work with Chevrolet, he was porting small-block heads long before he became famous for his Oldsmobile stuff. Back in the '60s Mondello worked closely with GM engineers on refining the cast-iron heads of the day, and many of his modifications were incorporated into the factory castings that made more power. Even the heart-shaped chamber of the Vortec heads was something Mondello worked on over 30 years ago, so we thought it'd be best if we asked him to show us how to make a set of Vortecs flow.

Why'd we choose the Vortec heads? Cost is the reason. A complete set of iron Vortecs (GMPP PN 12558060) will cost you just $477.50 plus freight from Scoggin-Dickey Chevrolet. These out-of-the-box castings are only good for cams with about 0.450 inch lift, which is okay for mild everyday street cars, but if you want something that can take more camshaft and breathe better, Scoggin-Dickey also sells modified sets of Vortec heads for a little more cash.

The stock valve job can be... 

   

  read full caption

The stock valve job can be improved on Vortec heads. Mondello got more cfm at high lift after performing his own 35/45/60-degree valve job and 75-degree throat cut, but this sacrificed some flow at lower lift (compare: Intake tests 1 and 3).

Experience Pays Off
As we mentioned before, Mondello's experience in porting Chevy heads has allowed him time to fine-tune the process. It's also given him the opportunity to test practically every modification in the book and determine what works on the Vortec heads. Of course, it also helps to have a flow bench handy when you're trying to find out which porting modifications work best. But, since most of us don't have one, we asked Mondello to show us all the details of what he thought would be the best porting modifications for Vortec heads, street or strip.

He took a set of Vortec right out of the box and clamped them down to his Superflow bench. With 230-cfm max flow, these heads are actually pretty good, except when you notice that peak flow is at .700 inch valve lift, and no street cams are that big. What Mondello tried to do was mainly concentrated around gaining more flow at lower lifts. And when you compare the flow figures below .500 inch lift from each test, you'll see that some things worked, while others didn't. That's the truth about porting.

Not all modifications work on all heads. And there's really no way to tell ahead of time if the mods you plan to make are going to help or hurt. Pay close attention to the test notes listed in the charts to see what mods Mondello tried for each step. Then, take a look at the photos to see details of some of the modifications he performed. Basically, if you compare tests 4 and 1, you'll see the first definite improvement at almost all lifts-after Mondello performed a valve job and then blended the bowls into the 75-degree throat cut above the seat.

Then, for later tests Mondello went all out and performed what would equate to about an $800 porting job on the heads to see how they would flow. Tests 8/4 and 10 reflect those results. It's plain to see that full porting has some advantages. But for the cost, you'd be better off buying a set of aluminum heads that'll flow those figures out of the box. All in all, for any stock small-block head to flow 262 cfm is outstanding, especially for a head that started out costing under $250 each!

Mondello scribes lines at...        read full caption Mondello scribes lines at the widest section of the ports. Look closely and you'll see the scribe mark on the top of the port (bottom of photo) is much higher. This is where Mondello raises the roof to a Fel-Pro (PN 1206) gasket's dimension.	The intake valve on the left...        read full caption The intake valve on the left has a 21-degree back cut to improve airflow at low lift. The exhaust gets a 22-degree back cut.	Getting the corner radius...        read full caption Getting the corner radius correct is one of the hardest parts of porting. Mondello uses a tube with a radius equal to the gasket (most gasket manufacturers can supply this info) to scribe and check the marks.
Mondello starts on the sides...        read full caption Mondello starts on the sides of the valve guide boss bringing them into the mark he's made using a special tool he developed and sells. Once the sides of the guide are done, Mondello begins to teardrop the guide, in the direction of the port to aid airflow around it.	Blend all high and low spots...        read full caption Blend all high and low spots in the chambers. Make sure to put some old valves in the pockets at all times when working the chambers, and always scribe the gasket opening onto the cylinder head so you don't go too far.	You'll need a set of stones...        read full caption You'll need a set of stones to finish your porting and a dressing tool to shape the stones. Mondello shapes a large stone to smooth the big radii in the chamber. This helps maintain the proper combustion chamber shape while still smoothing the casting. All flat surfaces on the chamber get smoothed with a sanding disc. The final polish can be done with a flapper.