You did a tech answer around two years ago which was about adding a set of Vortec heads to a small-block Chevy. How much of a horsepower gain could you expect from porting these heads using the cam and everything? — R.B.
Jeff Smith: We wrote about Vortec heads in 2016, and that article spawned this question.
The original answer was related to modifying the heads to accept more valve lift.
Stock Vortec heads are limited to 0.425- to maybe 0.450-inch lift. The details on how to increase the retainer-to-seal clearance can be found in the article and comments here:
Our original answer combined the Chevrolet Hot cam with a set of these Vortec heads. Our estimate then and now is around 350-375 horsepower.
Your question relates to porting the Vortec heads to improve the flow, which is a great idea. The Vortec heads offer great intake port flow despite the rather small 1.94-inch valves.
Where you can gain substantially more power is by concentrating on the exhaust side of the head.
The Vortec heads are much like other stock small-block heads in that the intake port flows fairly well, but higher rpm power is limited by a weak exhaust port. Based on information from different cylinder head porters, they feel that you could pick up an easy 20-25 hp by modifying the exhaust side just in the area directly under the exhaust valve seat.
This is often called pocket porting and the area just below the 45-degree valve seat is where you can gain the greatest airflow improvement for the least amount of effort.
We pocket-ported a set of stock iron small-block Chevy heads a long time ago with direction from a good friend – Rod Sokoloski – who passed away in 2013. Rod worked for Edelbrock for a long time and was the company’s resident cylinder head guru. He showed me how to perform a simple pocket-porting effort on both the intake and exhaust side.
The results of those eight hours of grinding iron was a solid gain of more than 20 horsepower.
We flowed the heads before and after, and the improvements were mostly on the exhaust side.
Rod attributed the jump in horsepower to the flow increases we generated on the exhaust side. He said if the engine had gained more torque, that would have revealed an improvement on the intake side but since we saw only minimal gains in torque, he said the exhaust side improvements were mainly responsible for the horsepower increase.
So while we’re running your engine on our theoretical dyno, if you could find a cylinder head porter who is still willing to grind on cast iron (it’s nasty work and takes much longer than working on aluminum), we will venture a guesstimate that with a mildly pocket-ported set of Vortec heads and that GM Hot cam on a 355 cubic-inch small-block Chevy with 9:1 compression, an Edelbrock Performer RPM intake manifold, and a set of long-tube headers that combination could make 400 hp and maybe a touch more.
That may not sound like much compared to today’s big-power LS and Chrysler Hemi engines, but it’s pretty good power for a somewhat dated small-block Chevy with production iron heads!
One additional point with Vortec heads is they take a special-length reach spark plug.
The reach is defined as the length of the threaded portion of the spark plug. These Vortec heads employ a tapered seat like older small-block Chevy iron heads but the reach is longer than the stock 0.460-inch iron small-block. The Vortecs use a mid-length 0.708-inch reach with a tapered seat versus the more typical 0.750-inch gasketed plugs used in performance cylinder heads.
If you mistakenly use the typical 0.460-inch reach plugs that are commonly used in small-block Chevys, this buries the active end of the plug inside the threaded portion of the head. The engine will run poorly and not respond to tuning. So be sure to use the proper spark plug application. A stock heat range plug would be a set of Autolite 605 plugs or an ACDelco R44LTS6.