Valve bowl porting is a smart way for shops to boost power and profits. A few new tools and a little knowledge can score big with performance heads
Many shops in the country are getting lots of calls and opportunities to do cylinder head porting work. Many shops are stock rebuild businesses that are afraid of taking on some porting work. Well, if you’re such a shop, you shouldn’t be afraid of this profitable performance niche opportunity; it really isn’t difficult if you purchase a few specialized tools to be used in addition to the tools and equipment you probably already own.
You can do valve bowl (pocket) porting fairly quickly using a minimal amount of abrasives and cutters. Your customer will be very satisfied with the extra 25-40 hp and the additional torque that you will be able to deliver. Just as importantly, you’ll be satisfied with the extra money your shop will be pulling in.
Most of you have cylinder head machining centers with steel, three-angle valve seat cutters and bowl hawgs. If you are going to do a valve job anyway, try to sell your customer some valve bowl porting. When you open up a valve bowl with a 70 degree cutter or a bowl hawg, the job is not complete unless you blend in all the sharp edges and reshape the short turn radius.
At Mondello Technical School we have created specialty tools for doing a lot of this type of work. These tools will do the job very easily, as do some of the equivalent products that are available in the aftermarket through your suppliers.
In the case of our own tooling, carbide cutters have special shapes, especially the one for the short turn radius. Our experience is that the use of these tools can save up to 50% in time; and as every shop owner knows, time is money, and you can take that savings to the bottom line.
You can run these cutters and abrasives with air or electric grinders. If you are going to increase the valve size in the heads, e.g., go from a 1.940" intake valve to a 2.02", and a 1.500" exhaust valve to a 1.600", I recommend you use a 45 degree, three-angle valve seat cutter with a 60 degree to 70 degree throat cut angle below the 45 degree primary cut. Or you could use a 70 degree to 75 degree bowl hawg to open up the valve bowl area before you start your valve bowl porting.
If you are going to run the same size valves, scribe a line below your 30 degree or 45 degree primary valve seat so you can have a margin line that you can port up to. Our scribing tool, #VST-400 (see photo above) is available in Sioux pilot size .385" or Kwik Way 7/16". This is a great tool for anyone’s shop. I have seen an equivalent tool out there, but I don’t know who offers it.
Our tool measures the valve seat width on the valve and transfers it to the valve pocket for maximum metal removal in the valve bowl area. Valve bowl porting is a lot like deburring; the grinder movement while removing metal is important and must be done cautiously in order not to grind away too much metal below the valve seat or nick the valve seats.
You have to remove a good amount of material (not just break the edges) to give your customer their money’s worth. I have seen some examples of horrible valve bowl porting jobs that should have been offered for free because they were so poorly done. You do not have to port the whole valve bowl area down to the top of the valve guide boss to be efficient. But you need to remove a sufficient amount of material below the seat, leaving a small radius roll under the primary valve seat for maximum air flow.
The photos within this article show you where the metal should be removed. The most important part of the valve bowl porting is the shape, roundness and smooth roll around the short turn radius blending into the floor of the intake and exhaust port runners. The amount of flow difference and horsepower increase due to the surface finish is not very much – about 2%.
If you do a good smooth job of opening up the bowls with carbide cutters and do not stone or cartridge roll the surfaces you have carbided, it will still run well. The stoning and polishing of the surfaces looks more like a finished job and will always be accepted better by the customer. It also provides 2% better flow and horsepower which couldn’t be achieved if you had only carbided the valve bowls.
The difference in time is only about one-half hour for a pair of heads to stone and polish the surfaces; consequently, I would opt to do this finishing procedure. A good valve bowl porting job with proper tools, techniques and grinder movement should take a person with some experience about two to three hours from beginning to finishing the job.
Most shops are getting from $200 to $250 per set of heads for porting the intake and exhaust valve bowls, including stoning and polishing. These prices are at and above the normal valve job prices, but do include machining for the oversized valves, if needed.
The job of valve bowl porting is a quick way to make some good money with a very small investment in additional tools which you may not already have. If you had to buy everything we used in this article, from the scribe tool, carbides, stones and abrasives, you would spend about $150, and this is enough material to do six to eight sets of heads. The carbide cutters can be resharpened many times leaving you a very low material cost per set of heads (about $5).
A quick review
Let’s recap procedures for valve bowl porting. You should always rough out the valve bowls first for oversized valves with fixed angle seat cutters and bowl hawgs. Stone-type valve seat grinding equipment can also be used. Using the correct tools for the job is the most important part of completing the job to your customer’s satisfaction and your expectations for profit.
You should use Dykem layout dye in the valve bowl area and then scribe a line below the valve seat with scribe tool VST-400 for maximum metal removal, leaving a small radius at the bottom of your primary 30 degree or 45 degree valve seat. You should run your carbide cutters between 20,000 and 25,000 rpm using medium pressure against the work surface.
For maximum results, always use sharp carbide cutters with the correct shape. The egg- or oval-shaped carbide cutter should be used for both intake and exhaust valve bowls as well as for part of the short turn radius directly below the valve seat. The reverse cut carbide (the one shaped like an ice cream cone shown in the photo at the bottom of page 24) is to be used only for the short turn radius so you can achieve a very smooth, gentle, rolling radius into the floor of the intake and exhaust ports.
Once you have completed the porting and shaping of the valve bowls the stoning and polishing should be done next. The shape of the stones is done with a Desmond "0" style steel wheel stone dresser and smoothed on the surfaces with a 1" x 1" x 3" resin stone dresser.
The cartridge rolls to use are ½" x 1-1/2" x 1/8" 60 grit. This is as smooth of a finish as you will need to complete the polishing job. After you have ported and polished the valve bowls, go ahead and do the final finished valve job and machine work to complete the heads.
This column begins a series of four articles we will be doing for Automotive Rebuilder magazine. The next article (June issue) will be on how to correctly perform a high performance valve job with either cutters or stones. I hope I have covered valve bowl porting in depth for you so you can start adding more profit to your shop income. We welcome your comments, and always remember, we make horsepower, not promises!
Joe Mondello teaches high performance cylinder head technology at his Mondello Technical School located in Paso Robles, CA. He is happy to answer your questions or comments regarding this and future column material. He can be reached by calling 805-237-9185, or FAX to 805-237-9154.