Take a closer look. A measuring caliper will show that the distance between the center of the piston wristpin bore and the piston deck, usually referred to as compression height, is shorter on the 350 slugs. The actual compression-height measurements of the factory pistons are listed as 1.675 inches for the 327 and 1.56 inches for the 350. As you undoubtedly know, both engines share a 4-inch bore, but the 350 has a longer stroke-3.48 inches compared to the 327's 3.25 inches. Since both engines use a 5.7-inch connecting rod and a block with the same deck height, the increased stroke of the 350 crank requires that the wristpin be located higher in the piston. Putting the 327 pistons and rods in the 350 would create a situation where, at top dead center, the pistons would protrude above the deck of the block.
Spare Parts, Mopar StyleI'm looking to replace the stock 318 in my '69 Coronet 500 with a larger small-block Mopar. I have a '71 360 block, as well as a set of '69 340 full-floating rods lying around, plus a set of 10.5:1 stock 340 aftermarket pistons. Is it possible to bore the 360 0.040-inch over and use the 340 pistons and rods in the 360?J.R. KorenCooperstown, NY
As you know, the 340, though smaller in displacement, actually has a larger bore than the 360 (4.040 inches versus the 360's 4.000 inches). The 340 has the same 3.31-inch stroke as the 273 and 318, so the 360 obviously gets its increased displacement from a significantly longer stroke (3.58 inches). Both the 340 and 360 share the same length connecting rod, so the problem with the combination you suggest lies with the compression height of the piston-the wristpin bore is closer to the piston deck on 360 pistons (see Spare Parts, Part One). Installing standard-bore 340 pistons into an overbored 360 will result in pistons traveling up beyond the top of their bores at top dead center.
We ran your proposal past contributor Steve Dulcich, who has assembled a number of Mopar small-blocks, and he noted that if you actually have a set of low-compression 340 pistons ('72-'73), you could assemble the engine your way. However, he points out that you'd still have to machine the tops of the pistons to shave off a little more compression height, and basically, that's not worth doing. The 340 rods are the same as those used in 360s, but they're bushed on the small end for full-floating pins. You could get a set of aftermarket 360 pistons set up for full-floating pins and retain your 340 rods, but there really isn't that much of an advantage to full-floating pins on a street motor. We mention this because it's likely that the wrist pin bushings in your 340 rods are worn out, and replacing them is somewhat costly-between the cost of the bushings and the labor to install and size them. If you want a 360, you're probably better off simply rebuilding one using 360 guts.
Environmentally Compatible?I've heard a lot of talk about which headers are emissions legal and which are not. I have several questions on the subject.
1. What kind of headers are compatible with a catalytic converter: short-tube or long-tube?
2. If long-tube headers are compatible, would they make more horsepower than short-tube headers?
3. Would catalytic converters be less restrictive if placed closer to the headers?Bob AdamsOcean City, NJ
First of all, the only headers that are truly 50-state smog-legal are those certified by the California Air Resources Board (CARB), and CARB's exemptions are only granted for specific applications on a case-by-case basis. Laws vary from state to state, and they're fairly stringent in New Jersey. Many states have adopted California standards, and simply installing a catalytic converter does not ensure smog compliance. Full-length headers generally allow too much heat to escape from the exhaust gasses before they reach the cats. This prevents the cats from "lighting off"-the term used to describe the point at which the exhaust-scrubbing chemical reaction begins.