78cutlass

Thinking of putting this street/strip Olds 350 motor together:

'69 Olds 350 block

TRW forged BBO 425 pistons (.068 overbore/362 CI)

'65-'66 Olds 330 crankshaft (forged)

'69 Olds 350 rods, or 403 rods, or maybe even aftermarket forged SBO rods

'68-'69 BBO 455 "C" heads

(CR = "pump gas friendly")

-TELL ME WHAT YOU THINK-

AJCDFIN

Hey; Have you spec'd (blue-printed) everything out ? Also boring a 350 nearly .070'' is risky especially if it has not been sonic checked. What are your intentions/reasons for this combonation ?

380 Racer

TRW forged BBO 425 pistons (.068 overbore/362 CI)

Do they even make these pistons any more?

78cutlass

No, nothing's been sonic tested. All the components appear to be sound. I'm not sure if those pistons are still available, but I have a BNIB set. They're made by TRW (guess back in the days). I've heard from Olds gurus that early Olds 350 blocks can be bored that much safely (.068). Also, that putting BBO 425 pistons in early 350s was a past practice. None of this is engraved in stone. I'm just looking for feedback, that's all. Feel free to chime in. I know there's alot of Olds savy folks on this board. I value your input.

cutlassefi

Here's one of my most recent Olds builds;

69 350 block bored .068 to 4.125
SBC 400 piston (1.425 comp dist.) 12.5cc dish
Scat 6.200 I-Beam rods.
350 "N" Crank offset ground to 3.400 and SBC Large journal size
#5 Heads w/ 2.00/1.60 valves, 9.4/1 compression, very minor port work
Lunati Custom grind Hyd. flat tappet cam (223/231 @ .050) on a 108, .525/.550 lift with 1.72 Scorpion Roller Rockers
Edelbrock Performer
Holley Street Avenger 670

Runs awesome, he had it dynoed, said it made almost 350hp. I believe it, very responsive. You can use a flat top piston and use the C heads no problem. Many good, fairly inexpensive ways to go other than what you listed. Give it some thought.

78cutlass

Nice! Hey, can those early blocks be bored to .068 safely? Will punching it that much make the walls to thin? I've asked, but no one seems to know...

cutlassefi

On this one it was no problem, could've gone another .060 easy. Better to have it checked though like we did and others have suggested. Plus using a longer rod for a higher numerical rod to stroke ratio is easier on the cylinder walls as well. We had over .200 in some places after boring. The reciprocating assembly was much lighter than stock too. Balancing bobweights were about 200 grams lighter than the original cast piston/stock rod combo. That's a bunch.

If you use C heads you'll need a flat top piston and probably mill the head a bit to get to 9.25 or so comp. This one worked out to about 9.4/1 with the dished pistons, zero+ deck and about a 68cc chamber.