Rocket Man
Don Wellford, Boulder, CO: I have a '72 Olds Cutlass S that I got from my grandmother, the original owner. It isn't the perfect little old lady car, but she kept it in her garage and had her mechanic on top of the maintenance. The body is in decent shape though the 350 two-barrel is a little tired. It would probably wake up a bit with a four-barrel swap, valve job, and new timing set and cam, but I think I'm going to put my effort and money into the 455 I recently scored. Trouble is, I don't know its origins. A friend who works in a garage got it from his boss, who said it had been sitting under a workbench since they pulled it in the '80s, and all he can remember about the car it came out of is that "it was big." I'm going to have it rebuilt, but I'd like to know what I'm dealing with first.
On the driver side of the front of the motor is a pad with the stamped numbers: 31M135022. Above the water pump the block has cast-in 396021F, and the bellhousing has an F cast into it. The cylinder heads show casting number 409100, and there is also a large letter G elsewhere on the heads. Can you tell what this engine is?
Terry McGean: The numbers stamped into the pad on your engine break down like this: 3=Oldsmobile division; 1= 1971; M=Lansing, Michigan plant. The other digits are the original vehicle's VIN. The numbers above the water pump indicate a '68-'71 455, as does the F in the bellhousing. The head number is for a '71-'72 non-W30 455, but the G indicates '71, while a '72 should have a Ga.
That's an 8.5:1 engine, but with a set of fresh pistons of your choice, getting the compression up won't be a problem; think 9.5:1 with iron heads, 10-10.5:1 if you opt to go with aluminum aftermarket castings from Edelbrock, Bulldog Performance, Rocket Racing & Performance, or Mondello (check our B.O.P. cylinder head guide, "Outfitting the Other Guys" in the Aug. '04 issue for the details). By the way, our number-crunching info comes from the book Oldsmobile Numbers Swap Meet Guide, by Dennis Mothershed, available from Dick Miller Racing.
More Info
Bulldog Performance; Indianapolis, IA;
317/786-9780; bulldogperformance.net
Dick Miller Racing; Hernando, MS; 662/233-
2301; dickmillerracing.com
Edelbrock; Torrance, CA; 310/781-2222;
edelbrock.com
Mondello Performance Products; Paso Robles, CA;
805/237-8808; mondellotwister.com
Rocket Racing & Performance; Waterford, WI;
262/895-3134; rocketracingperformance.com
Information Gap
Jim Rodgers, Sanford, MI: Ring endgap issues are leading me in circles. I'm rebuilding a '65 390 for my Galaxie. I've purchased Speed-Pro L2291F-30 pistons and the suggested E-180K 30 rings. Upon measuring a few rings in the cylinders I found 0.016-0.020-inch gap. I contacted both Summit and the Sealed Pro (Do you mean Sealed-Power or Speed-Pro?-Ed.) tech line and was informed that this is too large, and the machine shop messed up. My machine shop treated me rudely and said there is no problem, and that the gap can be as high as 0.035 inch.
Who is right? What is the max you suggest for this car? It is a cruiser, not a racer.
Terry McGean: As you're probably aware, piston rings need to have some gap to allow for thermal expansion. Too little gap and the ring ends could butt together during heavy loading, leading to a loss in power, rapid wear, and possibly broken pistons. Too much gap and precious compression and cylinder pressure leak past, costing power. There are a number of factors that determine what the proper ring gap should be in performance engines. Blown or nitrous engines tend to generate more combustion heat and therefore require larger gaps, but for pump-gas street engines like yours, there is a formula commonly used to calculate proper ring endgap based on cylinder-bore diameter: 0.00425 x bore diameter = ring end gap.