Port Authority
When the name Buick comes up in any bench-racing session, the conversation turns to 455 big-blocks, Stage 1s and the venerable GSX. What rarely gets mentioned is the small-block 350. Constantly overshadowed by the other GM small-blocks, the Buick 350 lacks the aftermarket support it truly deserves. This creates a problem for those who want to keep their 350 and not perform the common 455 swap. Sure, a basic small block rebuild can be had for fairly cheap, but what about making power? They are called muscle cars after all, and the stock 260-280 hp leaves a little to be desired. The small-block Buick has quite a bit of potential. Supercharged 1,000 hp Buick 350s have been built proving the block can handle serious power; the trick is getting it out.
Back in the late sixties, Buick’s engineers knew a thing or two about head design. The Buick 350 head features a tall, skinny intake runner, which yields excellent port velocity, unlike the SBC, which is big and fat. Higher port velocity allows the engine to breathe better, letting the builder run a larger carburetor, while maintaining big bottom-end torque.
In order to achieve real power, with bolt-on performance parts non-existent, real engine work must be brought into the mix. With such a well-designed, yet under-realized head, porting offers the quickest way to awaken a sleepy Buick. Beginning with the basic gasket port matching, a beginner can make some progress without risking too much. The next step requires the port to be completely ported and polished, bowls blended, and the guides are reshaped to really open up the heads.
Porting a cylinder head is a mix of art and science. Understanding the characteristics of airflow while maintaining the integrity of the head take time to learn. An intimidating task for the novice, the guidance of a seasoned engine builder can unlock the mysteries of head porting.
One such person is Jim Burek, of Performance Automotive Engines, a high-performance Buick specialist. PAE has been in business since 1988, specializing in building all things Buick, from v-6s to an all new aluminum 455, Jim has made a career of building the better Buick. Poston Enterprises, who specializes in supplying quality Buick engine parts, supplied a set of swirl-polished stainless steel valves, valve springs, keepers, seals and an aluminum S-Divider intake, which will be port matched to the iron heads for the Buick 350 project.
With the heads off the 1971 Buick GS 350, Jim took possession of the vintage iron and transformed them into what will become an integral part of the 400 hp small-block Buick that will surely turn some, uh, heads.
As with any performance modifications, the project isn’t finished until the numbers are in. After all was said and done, a 25” percent increase was found in both the intake and exhaust flow. Keep in mind, these heads are using the stock sized valves, even more increases can be found by enlarging the valves. By picking up 50 cfm over the stock head, these heads are capable of produces 480 hp. A key element to utilizing ported heads is selecting the right cam. The increased flow at .500” lift would require a cam capable of that much lift. For this engine, a Poston Enterprises GS350-112 cam with .510”in and .518” ex lift will be used to take advantage of the extensive port work.
VALVE LIFT STK IN. CFM STK EX CFM PORTED IN CFM PORTED EX
.100 66 44 74 55
.200 119 93 135 110
.300 169 124 187 145
.400 198 128 241 167
.500 198 130 243 176
.550 N/A N/A 251 178
.600 N/A N/A 254 181
1. The basic tools needed to port a head are air-powered die-grinders and an electric die grinder with a foot control for precise cutting.
2. An assortment of fine carbide burrs assist in getting the most out your iron. Head porting kits can be purchased from most mail order parts warehouses and include all the tips and sanding rolls needed. Do not use coarse tips on cast iron.
3. The stock bowls and valve guides can certainly use some work here, a lot of iron can be removed to open up the flow.
4. Use a sharpie to trace the outline of the intake gasket for use as a guide for port matching the intake runners.
5. After using trimming the walls of the intake port to the lines, the cone burr works well for removing the material in corners.
6. After completing the carbide work, a sanding roll finishes up the job of smoothing the walls.
7. The gasket is put on the head again to verify the porting. Each intake was widened by 0.100”.
8. In comparison to a stock head, the difference is quite amazing.
9. The exhaust bowl work begins by laying back the short turn in the bowl. This step is crucial for proper flow.
10. The valve guides are reshaped using the electric grinder, controlling the speed with the foot control. Clean up the guide until the iron is blended smooth to the opening. Use a 1\2” tip for the intake and 3\8” tip for the exhaust bowls.
11. A flap disc yields a smooth, round finish inside the bowl
12. When completed, the intake and exhaust bowls should look like this. Note the radical reshaping of the valve guides.
13. The exhaust throat was enlarged by .100”
14. A round ball stone is perfect for smoothing the short-turn radius on both the intake and exhaust bowls.
15. The stock exhaust runner before any work has been done
16. Here is the completed exhaust port. Notice the shape of the guide and the lack of flashing and pitting. This helps the exhaust flow and reduces turbulence.
17. Polishing the combustion chamber reduces detonation by eliminating the hot spots. A series of sanding rolls accomplishes this task.
18. The head is set up on the Sunnen machine to cut the competition 3-angle valve job.
19. The swirl polished stainless steel valves feature a 30-degree back cut. While the stock valve sizes (1.88” in, 1.55” ex) are used here, larger valves can be used to increase flow even more, for extreme high-performance engines.
20. Compare the completed head with the stock head. Fact: the high-nickel content of Buick heads eliminates the need for hardened valve seats.
21. Several times during the porting process, the flow bench is used to check the progress of the job. The final numbers are impressive, gaining 25% more flow than the stock head.
22. Along with the heads, a Poston Enterprises S-Divider Buick 350 aluminum intake gets port matched to the heads. Tip: repeatedly dip the coarse carbide tip in ATF fluid to keep the chips from clogging the bit. Only use a coarse tip on aluminum, not on cast iron.
23. Like the head, the gasket is placed on the intake and marked with a sharpie. Begin the work by creating a steep angle to the guidelines. The trick here is to be careful and use light pressure. DO NOT go beyond the lines, if the intake runners are larger than the head runners, flow will be decreased because of turbulence.
24. Keeping the tool parallel with the runner, blend the initial cuts to the rest of the port.
25. Finish up the intake runner with a sanding roll to smooth out the rough cuts, remove the bumps, and create a finished surface.
26. Compare the completed intake port with the uncut port. Fact: Jim Burek, who supplied his handiwork here on these heads, designed the Poston S-Divider in the late 1980’s.
I notice that this article is 3 years old, was PAE still in business 3 years ago or is this info from 20 years ago?
The S-divider intake was proven to be a horrible design and port matching hurts flow more than helps it! That’s probably why there wasn’t any before and after flow numbers, just a bogus percentage written?
The only material that should be taken off of the floor of the port is the irregularities from the casting process to make them uniformed so they’re all the same. In higher end porting work the floor of the port is actually raised with epoxy to straighten out the airflow path.
Porting to the gasket on the sides of the port is a waste of time because the air will only flow as much as the smallest point in the port, the pinch point.
Using inside calipers, measure the smallest pinch point of all the ports, then open the calipers .100″ and grind until the calipers fit all the way up and down through the pinch point on one side of all the ports. Then open the caliper another .100″ and do the other side of all the ports. Now all the ports are all opened up the same width without doing unnecessary grinding.
Most of the material that needs to be removed in the port is from the roof of the port. Slot the bolt holes in the gasket to align the bottom of it with the made uniform floor of the ports and THEN match the roof of the port to the gasket, angling it down blending to where the valve guides are and done with roof.
The short turn radius should be angled so it is aimed to the outer edge of the roof and re-radiused to transition the air down the bowl of the ports.
The bowl info in the article was the only thing any good about it!
Then in the chamber the valves can be un-shrouded from the sides of the chamber. Put the head on the block and use a scribe to mark the edge of the bores where the valves are the closest to the chamber wall. Remove heads from block and cut on an angle from the edge of the valve exit to the scribed line on both sides and done.
Doing it the above way will yield WAY better results then in the article!
Seen some dyno sheet from PAE before and the correction factors corrected the atmospheric conditions as if the engine was being dynoed in the eye of a typhoon! That being said, its no wonder that there were no before and after flow numbers in the article.
Derek,
I appreciate your comments, but disagree with your assertions. This article was written about 10 years ago, and yes, PAE has closed since then. The information is till quite valid, however. The porting results are noted in the flow bench numbers provided in the article. I am glad you commented because there had been a glitch in the posting, and the flow numbers were not showing up. I have fixed that, and as you can see, there is a great deal of improvement in the flow of the cylinder heads. There is certainly more than one way to skin a cat, thanks for commenting.