We go over all that in Chapter 10.ĭart has long been considered a racing or ultra-high-performance cylinder head company, especially given owner Dick Maskin’s extensive experience in drag racing, especially in NHRA Pro Stock. But the potential is certainly there if you do a good job of home porting. There are important procedures that must be followed if improved flow is to be obtained. We must also use this occasion to voice the obvious warnings that you cannot just go in and start hogging out exhaust ports in hopes of improving flow. The porting information is intended to show that even a relatively obscure, stock replacement head can show promise for a mild street engine if the engine builder is willing to invest a little effort into improving flow. This head has been around now for two decades and still serves a useful position as an inexpensive improvement over a used production head. This was done, again, as part of the head’s “stock replacement” origins. It’s also worth noting that the S/R retains its stock bathtub-shaped combustion chamber which is also a bit lazy when it comes to combustion efficiency. While not as good as the Vortec in stock trim, there are times when it’s not financially feasible to use the Vortec, which opens the door for the S/R. The ported S/R is up 30-plus cfm over the stock Vortec, which means that you might be able to get away with a mild dual pattern or even a single pattern cam with exhaust flow numbers of this kind. The ported S/R rocks the Vortec (which admittedly is exhaust limited), revealing a significant potential power gain.
However, on the exhaust side it’s a completely different story.
If we compare the ported version to a stock Vortec, the intake is still down slightly, while the S/R employs a larger intake valve. The average E/I improves to just over 70 percent, which means less camshaft exhaust duration is necessary to make power. Note at 0.300-inch lift, the port flow improves by an amazing 40 cfm, which computes out to a 30 percent gain in exhaust flow at that one data point alone. The intake improvements are minimal since most of the work is concentrated on the exhaust side. Granted, this head received more than mere bowl work, but it also shows the gain from a head that is generally considered a mere stock replacement piece. By opening the throat area, this percentage improves significantly.Īs an example, we’ve included a second flow sheet on a mildly ported version of the S/R. Production and the S/R heads generally have a weak exhaust port as evidenced by the drop in the exhaust-to-intake percentage from 82 to barely 60 percent at 0.600-inch lift. Merely increasing the throat diameter on the exhaust and doing nothing else significantly improves horsepower above 4,000 rpm while costing no power loss anywhere else. We get into more details in the porting chapter, but typically these heads are cast and machined using high-volume production techniques, which leave a restricted throat area that can use some tweaking. It’s a similar story on the exhaust side, and this head would certainly benefit from simple modifications to the pocket area, especially on the exhaust side. As you can see from the flow charts, compared to the Vortec production head, the S/R is down 12 to 20 cfm on the intake side across the board, so performance would be down slightly in comparison. The initial run of small-valve S/R heads was so successful that World introduced the S/R Torquer, which was the larger 2.02/1.60-inch valve version of the S/R. This was when World Products began casting iron stock replacement (S/R) cylinder heads for both the 305 and 350-ci small-block.
#Edelbrock thumper cam 350 small block crack#
Chevy began building lightweight castings that seemed to crack the moment you unbolted them from an engine and the core market looked in danger of drying up. In what seems almost like a time forgotten, there was a period in which, besides the iron Chevy Bow Tie, there was little to choose from for a mild small-block other than stock heads. These engines may not be number one on the horsepower hit parade, but they are the most popular street engines on the planet. This chapter focuses on mild aftermarket small-block heads that work well when combined with a performance dual-plane intake manifold, a smaller primary header pipe diameter, and a mild flat tappet hydraulic camshaft.
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