Engine Boring Question
 

I had to put a rebuilt 351W in my '70 Mach1. My original block was beyond rebuilding, not for the lack of trying. The new block is bored 60 over. Can someone please explain to me 30 over, 60 over? What does it do? What's the pro' and con's? Sorry, I am not mechanically inclined. Thanks for any assistance.

70' mach 1, nice car. and it means .30 and .60 over stock. sorry thats the limits of my knowledge.

Stock bore (diameter of cylinder) is 4.00" for 289/302/351. When rebuilding, the diameter of the cylinder is increased to make sure it is straight, because years of use can warp a block. .030 over means the bore was increased to 4.030" It is like re-drilling a hole larger to make sure it is the right shape.
Boring requires pistons for the new bore size.
Boring also increases displacement. Your 351W will now be 363 cubic inches.

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67 Fastback - Arctic White Pearl paint
351W ,Trick Flow Aluminum Heads, Edelbrock TorkerII, Carter 750 CFM, Comp. Cam 477/510 219/233@.050, Performance Automatic C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars.

My 351W Fastback

just one more thing....most small block fords can only be bored .030-.040 over....to go .060 over they probably had to sonic check the wall thickness before going that far. .060 is probably the absolute limit for a street engine.

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66 GT Fastback,fuel injected 5.0, 5-speed, cable clutch, JBA's and duals, 3.40 gears and handling mods...just call me "Doc"

.060 is the LIMIT. I have a 289 bored .060. It runs OK, but does have like to run alittle on the hot side. Not real overheating hot, just a tad more then most. But is livable, even here in FL.

i got my 302 bored .060 in my 69 and i havent had any trouble with it overheating, it actually runs on the cool side.

Thanks to all that replied. I have a better understanding of the boring. Just another question or two, will boring the engine that far shorten its life expectancy? Will the HP go up, if so, by how much. Thanks

Any hp increase from boring would come most likely from increased compression (larger displacement w/same size comb. chamber) or the unshrouding of the valves by moving the cylinder wall away from the valve, but it probably would not be enough difference to bore for hp if it is not otherwise needed. I would only bore the amount needed to insure a proper cylinder shape.

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67 Fastback - Arctic White Pearl paint
351W ,Trick Flow Aluminum Heads, Edelbrock TorkerII, Carter 750 CFM, Comp. Cam 477/510 219/233@.050, Performance Automatic C-4 Trans, 3.55 gears, Front Disc Brakes, 1-1/8" Fr. 3/4" rear sway bars.

My 351W Fastback

you will be able to notice the amount of torque gained from boring it .060 over. I sure did. can sit there and roast them now. You will like it alot better than stock. if you put some flat tops pistons in it you will gain horsepower b/c of the raised compression.