One interesting note is where the exhaust port saturates. It reaches max flow at 0.400 inch valve opening and is flat up to 0.600 inch. This is where adding a larger-lift camshaft has minimal affect on performance. A simple valve job and increasing the throat diameter and blending the short-side radius will correct this problem. This will unlock a ton of performance from these early heads.
For the best technical information on cast-iron Chevy heads, check out Brzezinski Racing Products, which offers complete porting services, legal and "cheater" heads for limited-rules racing classes, and a complete line of very trick flow bench tools.
El Cam OverdriveQ: I've been a subscriber for years and love the rag. I have a '74 El Camino SS 454 with a factory big-block and a TH400, a 10-bolt with a 3.73:1 Posi. The engine has a Performer RPM Air Gap, a 750 Holley double-pumper, headers, and a camshaft with approximately 230 duration at 0.050 inch tappet lift. The automatic is quick but boring. I want to swap in a five- or six-speed manual. What would fit the best? I don't want to cut up the tunnel more than I have to.
Paul Van Slyke
A: That's a very nice Elco you have there. Does it still have the factory SS bodywork on it? There were the Laguna Malibus, and some of the SS El Caminos had some of the different bolt-ons in the front. Lucky for you, the later, larger A-bodies had quite a bit of room under them. A five-speed swap should fit with no floorpan modifications if the model was originally equipped with a four-speed.
Classic Chevy 5 Speed and Keisler Engineering have a complete line of five- and six-speed swap systems for a number of applications. They have everything, and it's the easiest and most complete way to put a high-strength, modern overdrive Tremec TKO five-speed transmission in your GM A-body with automatic transmission.
As for your big-block car, we'd go with the TKO 600. This transmission is rated at 600 lb-ft of torque and features a 0.64 overdrive in Fifth, which will allow you to enjoy the performance of your big-block with some fuel economy. They have both factory mechanical clutch linkage and optional hydraulic clutch linkage. They can supply you with just what you're looking for.
Q: I have a problem with my '72 Nova rearend. I moved the leaf springs over and centered my rear up off the pinion. But when I measure off the rim with a tram gauge, the passenger side is off 1 inch. When I measure the perches they are fine. I thought the quarter-panel was messed up, but the body shop says it's not. I have to run two different backspacing rims-the driver side is 5 1/2 inches and the passenger side is 4 1/2. Hope you can tell me how to fix it.
A: Did you notice that the engine and transmission in your Nova are offset to the passenger side for steering box clearance and to fit the floorpan better? When you centered up the rearend off the pinion to the framerails, you offset the axle to the driver side! If you measure the crankshaft centerline between the front frame, you should find that the engine is offset about 1 inch, and then measure the output shaft of the trans and see where it falls. It should be slightly less offset at the rear of the trans.
Is this going to cause you a problem with your car except for the wheel offset? Not really. The U-joints are just going to work a little harder with the added inch of offset compared to the trans output shaft. Sorry about this, bud.