Getting Down to the Short Strokes
If I wanted to build a Chevy 302, could I stroke a 283 block with a 327 crank? If so, which pistons and rods would I have to use? If not, was the Chevy 302 a specialty block produced during these years, and would I have to find one of these to start with (yeah right, good luck)?
Bolton, ON, Canada
Installing a 3.25-inch-stroke 327 crank in a 3.875-inch-bore 283 block builds a 307ci engine. Chevy built 307s from '68-'73; they were all plain-Jane two-barrel base V-8s. Technically, Chevy did not use a "283 block" for the 307 build because all 307s used large diameter 2.45-inch main and 2.10-inch rod journals, while production '57-'67 283 blocks all had small-diameter 2.30-inch main and 2.00-inch rod journals. There were both small- and large-journal 327 blocks and cranks, however (see table).
The high-perf Z/28 302 engines combine a 4.00-inch bore (the same as a 327 and 350) with the 283's 3.00-inch-stroke crank. Small-journal 302s were produced in '67; large-journal 302s were made in '68 and '69. Although the small-journal 302 cranks had the same stroke and the same main and rod journal sizes as the 283, they carried a unique part number because of a different balancing factor needed to match the 302's larger pistons (you can rebalance a 283 crank to work). Small-journal 302s are extremely rare.
It is possible to home-build a 302 by either destroking a 327 or 350 4-inch-bore block using the appropriate journal-size 3-inch stroke crank, or by boring certain "thick-wall" '62-and-later 283 blocks 0.125-inch oversize. The rare Chevy II block with a relocated oil filter boss (casting No. 3790721) is one such thick-wall casting; Chevy used it to build both 283 and small-journal 327 engines.
You can home-build a small-journal 307 by using a 283 block and small-journal 327 crank. The '62-and-up 283 blocks usually have the necessary crank-clearance reliefs machined in the bottom of the cylinder walls. But why would you want to?
All small-blocks except the 264 and 400 use 5.7-inch-long (center-to-center measurement) con rods. However, there are two different rod journal sizes to match the two different crank journal sizes available. Pistons must be correct for the bore size and crank stroke (for example, a 283 converted to a 307 would use 307 pistons).
I own a '72 Skylark GS Stage 1. The 455 big-block has been upgraded to '70 specs along with 1 7/8-inch headers and 3-inch collectors, and a B-4B Edelbrock intake. This car is mostly street-driven and wanders onto the strip very little. I have been told by some of my local Buick friends that a 2 1/4-inch exhaust system provides better low-end throttle response than 2 1/2-inch-or-larger pipes. Is this true? And which mufflers provide the best torque for the street?
Updated to '70 Stage 1 standards, huh? That would give you 370 hp at 4,600 rpm, and 510 lb-ft of torque at only 2,800! Just how much more low-end can you need (or use), anyway? Leave the 2 1/4-inch pipes for the wimpy small-blocks-large-displacement big-blocks need at least 2 1/2-inch pipes...or even larger! Borla, Flowmaster, and Walker DynoMax all have mufflers that'll do the job-it boils down to what tone you like and how much you have to spend. And by the way, 455 Buicks run pretty strong through the stock exhaust manifolds, especially if they've been ported.
Borla Performance Industries Inc.
5901 Edison Dr.
Oxnard, CA 93033-8720
DynoMax Performance Exhaust/Tenneco Automotive
111 Pfingsten Rd.
Deerfield, IL 60015-5616
800/767-DYNO (dealer locations) or 248/852-9347 (tech)
2975 Dutton Ave.
Santa Rosa, CA 95407-7800