Good morning. I'm starting out on a stroked Pontiac 389 build for my '65 Convertible. I've been prowling the forums here for ideas and so on. So this thread is spot on for research. Thank you to the participants.
My objective was to retain my date code correct OEM block and maintain a period correct look of an engine which could have been assembled in the early 70's when these cars were easily obtainable and hot rodded, but add modern internal technology to improve output. Motivation to do this now comes from discovery that my stock crank is cracked on several rod journals and the otherwise well running engine had become contaminated with grit when doing a carburetor swap / valley pan PCV grommet oil leak repair. I took the engine apart for cleaning after it was removed to install reproduction cast iron headers which led to magniflux inspection of the crank.
Finding the crank cracked led me to toss my rods, pistons, rings, and main bearing caps in the trash. In my opinion all were components which might have sustained historic damage because the crank had apparently been overloaded to failure by years of racing, high speed touring, and substandard (modern) fuel; despite those parts passing magniflux and dye glow inspection now. Because of modern oil issues causing accelerated flat tappet cam wear I've led myself into wanting a roller cam conversion but feel a few of my tappet bores may be quite thin to stand increased side loading. I've been aware through conversations with Ed Iskenderian back in the early 70's of Micky Thompson's efforts to buttress Pontiac tappet bore areas with filler plates and epoxy since the late 1960's, so implementing this sort of modification path became indicated. As I added up the costs associated with reinforcement of my block with 4 bolt caps, hard block cylinder filler, tappet area buttress plates, and various "normal" race engine machine work of square decking, etc to withstand increased operating forces, an aftermarket block became a more cost effective solution.
However that contradicted my initial goal of maintaining vintage hot rod period correctness. This realization is leading me to build two stroker engines. First the period correct engine to run on the street messing around, then next an all aluminum light weight engine to run more aggressively, perhaps in track day events. This decision has made head and cam selection much easier. It has also simplified decisions about porting and piston design. So this post will slant towards the first engine, an engine which would have been possible to build in the early 70's with externally visible parts one could have had made or purchased back then.
This path led clearly to Butler and Ames and their subcontractor vendors, but also includes various other companies making specialized internal parts or providing specialized processes.
1
OEM Block Size (ie 326, 389, 400, 455. etc) - retain 1965 389 cid block but upgrade with Milodon 4 bolt caps, block filler, Mega Brace from Butler, bored, decked and so on.
2 Crank Size Used (ie 400, 455, etc) - I went to SCAT for an AERA engine conference and talked to Tom Leib about cranks for Pontiac engines. He said there is no downside to using the largest stroke he makes (and provides to Butler) with rods and so on. I ordered a lightweight Pro II 4.500 inch stroke crank.
3 Stroker Kit Used The "kit" is coming from SCAT. Pro II I-beam rods at 6.700 inches. Clevite H series bearings.
4 Final Bore Diameter - 4.120 = 480 CID
5 Final Deck Height - 10.222 inches
6 Piston (Type, Make & Model) - KB 4032 Pistons to suit combustion chamber of Pontiac "670" head. 38cc dish, Gold thermal coating, and a Teflon skirt coating will be applied. Rings are Total seal gapless.
7 Compression Ratio (Static) - 9.2 to 1
8 Compression Ratio (Dynamic) - cannot calculate exactly until the camshaft is designed and then installed.
9 Heads (Make & Model) OEM Pontiac "670" castings fully ported and air flow balanced. Heat riser bowls blocked.
10 Head Valve Size (Intake & Exhaust) - 2.11" intake, 1.77" + .100" longer stems. exhaust w/hard inserts for unleaded gas conversion and bronze guides. Stud upgrade for roller rockers, fully thermal barrier coated by CALICO COATINGS.
11 Head Chamber Size (Actual in cc's) - 73cc
12 Head gasket thickness - .040
13 Intake to Head Port Matched? - Yes.
14 Head to Exhaust Port Matched? - Yes
15 Intake (Make & Model) - Using '65 OEM tripower manifold EXTRUDE HONE process applied to maximize plenum area and port match to FEL PRO gasket size 1/4 " thermal blocks with gaskets under carbs. .
16 Exhaust Manifolds or Headers - Reproduction cast iron from RAM AIR Reproductions. 2 1/2 inch to 3 " head pipes with O2 bungs and back pressure measurement taps added.
17 Exhaust system - 3" oval pipe to X oval style crossover from SPINTECH to 15" x 10" x 5" box mufflers. Front style in/out to side discharge ahead of rear tires. Entire system is thermal barrier coated by SWAIN in their "White Lightening" compound. Head pipe to X = 44 inches.
18 Carburetor (Make & Model) - OEM correct tri power with OEM RAM AIR conversion added. Jetting reworked substantially.
19 Cam (Make & Model) - Custom cam ground by Dema ELGIN CAMS mutually designed from air flow and specific engine design parameters.
20 Cam Specs -
21 Rocker Ratio - 1.6 to one projected to be used.
22 Rocker Type steel roller
23 Rocker (Make & Model) - CROWER 73624 - 16
24 Push Rod Length - unknown until engine is trial assembled and fit. Will come custom from SMITH BROTHERS in Oregon.
25 Estimated Flywheel Horse Power - 500
26 Dyno'd Flywheel Horse Power -
27 Dyno'd Horse Power at the rear tires -
28 Lifter Type - Mechanical roller
29 Lifter (Make & Model) - ISKY RED ZONE with upgrade bushings.
30 Ignition: - OEM distributor with PETRONIX upgrade.( for now )
31 Fuel - proposed 91 Octane
32 - Availability of fuel I buy race gas at the track when I need anything higher than 91. Comments from Lake Speed jr a month ago mentioned +/- 3 octane points is typical for pump gas today and it is never on the high side. Verified by dyno testing on their calibration mule engines. Also modern gas degrades from sunlight exposure within a couple of days time. Use steel cans only. So the 91 you buy is likely 88ish and maybe causing issues....... like cracked cranks.....
- Custom made PCV system based off a photo of dealer installed RAM AIR option and trade practices of implemented conversions meeting California Air Resources board rules in early 70's.
- Belts and front pulleys are all OEM.
- 1965 GTO convertible.
Rear tire size is P275 x 60 R 15 by BF Goodrich on OEM Corvette 8 inch Rally rims. The car has been lowered slightly. I replaced the rear axle assembly with a unit from Currie narrowed 2 inches from stock to eliminate tire rubbing with OEM zero offset 8 inch Corvette Rally rims when running a GM 12 bolt Chevelle axle. I had Wheel Vintique make a set of look-a-like Rally wheels with 1-1/4 inch negative offset in the1990's that helped a lot to minimize rubbing when running L50 x 15 BFG tires (now long obsolete). But Wheel Vintique were unable to provide a 5th (spare tire) rim in the 2020's after a wait of over a year and a half for its production. I canceled that order after driving down there for a phyical plant inspection to confirm I'd been lied to about my rims being stuck in their powder coating department (for 8 months) when they had not even been welded up. I instead had an axle built so I could run the easily available Corvette zero offset 8" rim which also should solve a number of potential issues related to breaking GM 12 bolt axles vs the aluminum NASCAR Ford style center section with STRANGE ENGINEERING axles built for my Currie axle. I'm not a drag racer, and have no idea how this tire will hook up with a more powerful engine. The rear suspension is boxed and has a sway bar. OEM retrofit frame braces have been installed. My shock mounts are upgraded but have essentially OEM geometry. I'm open to comments about how others have set up rear suspensions for drag racing vs. road racing (which I am fully familiar with). Front tire size is P255 x 60 R 15 on OEM spindles with a 4 wheel power disc brake conversion.