Chevy Small Block V8: Getting Down to the Short Strokes
If I wanted to build a Chevy 302, could I stroke a 283 Chevy Small Block with a 327 crank? If so, which pistons and rods would I have to use? If not, was the Chevy Small Block 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 Chevy Small Block 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 Chevy Small Block 283 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
What is the difference between a standard 350 and a "Gen 2" LT1? Would it be possible to bolt a standard 350 into a '90s Caprice with the stock transmission? What about an LT1/TH350 combo? Are the engine mounts in the same location? Which engine parts are compatible, and which aren't?
Wood Ridge, NJ
Classic 350 complete assemblies physically bolt into the same space as Gen 2 engine complete assemblies (and vice versa). The following individual component parts interchange between Gen 2 (LT1/LT4) and "classic" 350ci small-blocks:
• Camshaft and lifters (with '87-and-later hydraulic roller cams and lifters when used with correct timing chain and gears; may need to change dowel pin)
• Cam, main, and rod bearings
• Classic 350 rear-mount distributor will fit Gen 2 (remove LT1/LT4 jackshaft, use GM Gen 2/LT1 carbureted intake manifold PN 24502592 and cover hole in front cover; front cover plug PN 12367600 works on '96 LT4 engines)
• Connecting rods
• Crankshaft (with '86-and-later one-piece- seal cranks only)
• Engine mounts
• Exhaust manifolds
• Flywheel or flexplate (with '86-and-later one-piece-seal cranks)
• Head bolts
• Main bearing cap bolts
• Oil filter (with correct adapter)
• Oil pan (with '86-and-later one-piece-seal pans)
• Oil pan windage tray (with correct trays designed for '86-and-later one-piece-seal oil pans)
• Pistons (compression ratio may be wrong)
• Rear block-face (bellhousing) bolt-pattern
• Rings (with late-model production pistons machined for metric ring grooves)
• Rocker covers (with '87-and-later center-bolt covers)
• Valvetrain components (except LT4, which uses a net-lash valvetrain with 10mm rocker studs)
The following parts do not interchange:
• Cylinder block (different water jacket and front-end)
• Cylinder head (different water jacket)
• Gen-2 front-mount ignition system won't fit classic small-block
• Harmonic damper (Gen 2 balancer bolts onto hub that slips onto crank; no keyway or timing marks on balancer)
• Head gasket (different coolant passages)
• Intake manifold (different bolt angle and coolant passages)
• Timing chain and gears (if retaining front-mount ignition system)
• Front timing cover (different shape and bolt-pattern)
• Water pump
As for bolting a standard 350 to a '90s Caprice trans, you did not address whether the engine would be computer-controlled. The 4L60-E transmissions, used '94-and-up, require a late-model computer or aftermarket stand-alone controller. The 4L60 and TH700-R4 can be made to work without a computer. Due to ignition system differences, an LT1 computer cannot be used to control a non-LT1 engine.
You can run an LT1 without a computer by defaulting to an old-style ignition and carburetor (see preceding list for parts compatibility). To remain fully emissions-compatible, a computerized LT1 requires a VSS (vehicle speed sensor), which installs in the tailshaft of late-model transmissions. Exact VSS configuration will vary according to the LT1's model year and original installation chassis, as well as the type of speedometer interface required for any nonstock installation.
The TH350 and similar vintage transmissions have no VSS provisions. Nonemissions LT1 applications may dispense with the VSS under certain circumstances provided the '96-and-later OBD-II computer is not used. For more information on VSS interface, including providing a VSS pulse-signal in applications where the trans has no provisions for a standard VSS pulse-generator, contact Howell Engine Developments or Street and Performance. Mike Knell's book, Chevrolet TPI and TBI Engine Swapping is a good guide to the intricacies of late-model EFI swaps, including solutions to the VSS problem (the book is available through Summit Racing).
Howell Engine Developments
6201 Industrial Way
Marine City, MI 48039-1326
Street and Performance Inc.
1 Hot Rod Ln.
Mena, AR 71953-1169
Summit Racing Equipment
P.O. Box 909
Akron, OH 44309-0909
330/630-0270 or 800/230-3030
IROC's Getting Ready to Roll
I need your expert opinion on the motor I'm building for my '86 IROC-Z. I plan to build a 350 bored 0.060-over with a torque plate. It'll have a balanced bottom-end with TRW forged pistons, LT1 rods, Air Flow Research 190cc heads, TPIS ZZ-9 cam, TPIS large-tube intake runners, TPIS baseplate, BBK throttle-body (58mm), and SLP headers (1 3/4 inch). My goal is to run in the 12s. The car weighs 3,350 pounds without a driver, has a 3.27:1-geared 9-bolt, and a 2,800 stall converter. I used forged pistons just in case I use (need) nitrous oxide, but I'm a little hesitant to use it.
Another question I have is, does anybody make ring-and-pinion sets for 9-bolts? I already shredded my 10-bolt with 3.45s, so I lost some launch with the 9-bolt.
According to TPIS (TPI Specialties), your well-planned combo should make about 430 lb-ft at 3,500 rpm, and 365 hp at about 5,000 rpm. With driver, the car should weigh just over 3,500 pounds. On street tires with a stock suspension, you're looking at 13.20s at around 108 mph. Hook it up and/or turn on the nitrous and you'll be well into the 12s. Invest in a set of 9-inch-wide slicks, and maybe a set of Air Lift's rear air-bags to preload the chassis. Fuel-injected, computerized engines are well-suited to mild nitrous oxide systems because the O2 sensor and the knock-sensor team up to act as a fail-safe.
The low-production Borg-Warner of Australia 9-bolt rearend uses a 7 3/4-inch ring-and-pinion compared to the 7 5/8-inch gears found in the more common GM F-car corporate 10-bolt. That makes the 9-bolt's potential tooth contact area only about 1/16-inch greater (diameter/2) than the 10-bolt. Both rearends' posi cases are weak, but if you need a new case for the 9-bolt, it's a $600 dealer-only item. I only know of one non-stock ring-and-pinion for the rare 9-bolt: U.S. Gear's 3.70:1 (PN 01878370BW). Assuming around a 26-inch-diameter tire is used, you'll turn better e.t.'s with the existing 3.27:1 gear (shift at 5,800 rpm).
P.O. Box 80167
Lansing, MI 48908-0167
800/248-0892 or 517/322-2144
9420 S. Stony Island Ave.
Chicago, IL 60617-3695
Mechanical Response Response
I thought I'd send a brief note on the installation of a mechanical fan on the LT1s (Ask Marlan, Sept. '98). This fan is a good setup; however, it will only work with B- and D-chassis engines. This is due to the longer crank hub on these vehicles compared to the F-bodies, as well as the accessory drives being different. This setup could possibly be used on an F-car accessory drive setup with attention to pulley-to-balancer spacing, and radiator hose and water pump clearances.
Al Hassenboehler Jr.
A C Engineering
Thanks for the additional information. For those readers unfamiliar with the modern LT1 balancer, instead of slipping directly onto the crank like the classic style balancer did, the LT1 balancer bolts to a separate crank hub that in turn presses onto the crank. Because there's no keyway on an LT1 balancer, when removing it you need to make appropriate reference marks so it can be correctly reinstalled.
The B/D (full-size) chassis LT1 crankshaft balancer hub referenced by Mr. Hassenboehler carries GM PN 10168570; the F-car (Camaro/Firebird) accessory drive bracket is PN 10186132.
As a "driveability tech" at the local Chevy dealer, Mr. Hassenboehler reprograms GM computers on the side as a hobby. For "off-road use only," he can "do anything from '86 to '95 chips," as well as reflash the chipless '94-'95 LT1 and LT4 computers. Those of you who need such work done in the New Orleans area might want to get in touch with him.
Crank's Got His Goat
I have a '69 400 Pontiac GTO with a four-speed. Recently, the crank I purchased and installed posed a problem. The boss for the new flywheel is only 2 1/2 inches in diameter. My old flywheel and crank used a 3-inch boss. What crank did I install? Is it a newer 400 or possibly incorrect? If I get the right flywheel, can I use it in my engine without any problems?
Saint Augustine, FL
There have been three different Pontiac V-8 crankshaft flywheel mounting-flange registers since 1961. A 2 1/2-inch-diameter boss was used on '61-'63 V-8 cranks, the '65-'75 had a 2 3/4-inch boss, and the '76-'79 boss measured 2 5/8-inches. Both 2 1/2- and 2 3/4-inch bosses were used in '64; the '76 455 retained the 2 3/4-inch boss while the other Pontiacs moved to the 2 5/8-inch boss. The Pontiac 326, 350, 389, and 400 share the same 3.75-inch stroke, so the smaller engines' cranks will fit the 400 subject to the following limitations.
The '66-and earlier 326 and 389 cranks require a corresponding harmonic balancer and front timing cover because the early crankshaft snout is about 1-inch shorter than later crank snouts. Very early cranks with the 2 1/2-inch flywheel boss are quite rare these days; using one in your '69 additionally requires either a corresponding original 2 1/2-inch crank-boss flywheel, a custom aftermarket flywheel, or the fabrication of a custom flywheel mounting flange spacer ring to interface with your existing '69 flywheel.
The '67 326 and '68-'75 350 cranks are a direct bolt-in (except for balance, see below), but you don't have one of these because of the flywheel flange differences. The crank definitely isn't from a 421, 428, or 455, either-regardless of any flywheel flange dimensional differences, these cranks had larger main journals, so they won't physically fit in the 400's main saddles.
Most likely you have a '76-'79 350 or 400 2 5/8-inch Boss crank. Using it in a '69 requires a corresponding late-model flywheel that is also compatible with your particular '69 clutch disc and pressure plate (Pontiac offered several different clutch options). Suitable components are available from GM or aftermarket sources.
Use of an early or late Pontiac crank, and/or a crank from a different displacement engine, usually requires rebalancing the crank because of varying stock piston weights. For example, a late Pontiac 350 crank is factory-balanced for 33-ounce heavier pistons than most '69 400 cranks were balanced for.