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Old 08-25-2007, 11:35 PM   #1
timmay334
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boring or stroking

ok so basically i think ive got the idea that stroking and engine is to make the cylinders, pistons and connecting rods longer and boring an engine is to make them larger. so whats better, to boreor to sttroke and engine? whats cheaper? whats more reliable? which one will give more power?

also what does a 12 bolt or 10bolt rear end mean? or a 4 bolt front? i cant find the answer to these questions anywhere!
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Old 08-27-2007, 07:22 PM   #2
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Re: boring or stroking

stroke = how far down the CYLINDER the crankshaft pulls the rod and piston. Its completely different than bore. Bore = how big around the CYLINDER is.

4.00 stroke means the crank pulls the piston down the hole 4 inches. If you "stroke" an engine than means you increase the distance the crank pulls the piston down the CYLINDER.

4.00 bore means the measurement from one side of a CYLINDER to the other equals 4 inches. if you "bore" an engine out, that means you have increased the measurement from one side of the CYLINDER to the other.

a 12 bolt has 12 bolts holding on the differential cover. a 10 bolt has 10.

The last question 4 bolt front, could you be meaning "4 bolt main". If so that means each bearing main cap is held in place with 4 bolts.



EDITED: Thanks Pbody... Where i kept saying "combustion chamber" i should have said cylinder (where i now capitalized above). Combustion chamber = in the head
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Old 09-06-2007, 09:18 AM   #3
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Re: boring or stroking

Hotrod's descriptions are pretty good, and "close". There are some things to clear up.

There are four "strokes" in a complete "cycle", which is why the engine is called a "4 stroke". By lengthening or shortening the stroke, the displacement (the amount of "air" moved in and out) is either increased or decreased. The length of the rod has no bearing on stroke (a common misconsception, the crankshaft is the ONLY FACTOR affecting stroke).

The "bore" is the diameter of the cylinder. It has little or no meaning to the combustion chamber, except for what does or does not "fit". "Boring" an engine will enlarge the diameter, increasing the displacement. For an average "rebuild", the bore is enlarged by .020 or .030". In olden times, it wasn't uncommon to hear "when in doubt, bore it out!". However, an overbore of only .030" is of little consequence regarding power output. It DOES provide a "fresh" bore surface for new pistons and rings to do their job as well as possible. One must usually go at least .060", and even .100" (like BBCs) to have a real effect on power output.

The displacement is fairly simple to compute. There are lots of "witch doctor" and "backyard" methods, but there's only one you would learn in a math class. Pai x R(squared) x H x no. of cylinders, where Pai = 3.14159 (3 1/7, rounded), R = 1/2 the bore and H (Height) = stroke.

For an average "production" engine, like 350 Chevy, increasing the stroke will yield more increase than overbore. Most production engines are limited in just how far you CAN bore them without getting the walls too thin. Fords aren't considered "safe" past .040". Later Olds and Chevy small blocks, same. Earlier small blocks are usually safe to .060" over, and some to .080".

These are not "hard/fast" rules. One must always measure to be sure. The cylinder wall thickness is measured by a professional machinist using a "sonic tester". $50-$75 for a V8 block, most places.

For the more popular engine families, there are many "stroker kits" available. Some are MUCH better than others. NEVER by a "kit" based on price, unless you don't plan to pound on it too hard, OR, you aren't planning to rev it higher than 5,000. The cheaper kits have cast crankshafts instead of forgings. Those Chinese-made castings are pretty weak. The one exception is the Pontiac stroker from Eagle. Because the Pontiac crank has such large main journals, they don't flex like the smaller ones. We've seen them as high as 800 horsepower without issues. (Chevy guys, doesn't that beat all? Wouldn't YOU GUYS like a crank that can take 800 HP for less than $300?)

You will, undoubtedly, hear of many "success" stories using the chap crap. Don't buy in. For every "success", you will hear of 20 failures... And usually, those promoting the cheap stuff, are rationalizing their own purchase, more than they are advising you!

We buld many a "stroker", Chevy, Ford, Dodge, and mostly Pontiacs. The small block Chevy "383" is probably the most popular, and among the better non-factory configurations. For maximum "street" power, it's hard to beat the 461 Pontiac. We routinely build 600-plus HP, 93 octane "friendly" monsters with more than 650 lb. ft. of torque, revving to about 6,200. While the horsepower numbers are not too difficult to attain with the small block, the torque numbers are nearly impossible at such engine speeds. The BBC fares a little better, but if rectangular port heads are used, drivability is in the toilet. With oval port heads, it's hard to get such efficiency on 93. It CAN be done.

We also have a few 499 Dodges out there (440-based) that are ANIMALS! One '68 Road Runner goes 10.80s all week long, on 93, with iron heads (906s, ported here) and a Comp solid roller. He can drive it to Richmond and back without worry (about 100 miles, round trip).

Jim
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Old 09-06-2007, 12:57 PM   #4
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Re: boring or stroking

Yeah, my description was off (so i edited it) . I dont know why i bother sometimes
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Old 09-10-2007, 08:47 AM   #5
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Re: boring or stroking

Hotrod,

Not to worry, dude. This isn't a "contest". I just try to make sure information is as accurate as possible. It can be very confusing to a newbe.

One other thing I did notice. A "12 bolt" rear has 12 bolts holding the ring gear to the carrier. There are some Olds and Pontiac rears from the late '60s/early '70s that had 12 bolts holding the cover on, but only 10 for the ring gear. Those aren't true "12 bolt" rears. the Chevy 12-bolt IS. At least, I've never seen a Chevy with 12 bolts holding the cover on, without 12 bolts holding the ring gear. My point here is to never assume it's a true 12-bolt unless you've actually removed the cover and counted the bolts.

FWIW

Jim
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