i have a block that is bored 60 over and my crank is 3.48 should come up to 360.4 cid correct?

 

You got it right there, 360 inches.

I just happen to have a set of Zollner 60-over flattops for you too!

 

rustydawg must be better than most of use here or know something we don't. there's no way to know what you have without knowing the bore diameter.

 

350 block bored 60 measured 4.060 inch bore w/3.48 inch crank stroke, i have another question with this also, if my math is right and is a 360 what is the downside of a 360 vs a 355, reason im asking is that i dont ever find much/hear much about anyone running a 360 but alot of 355's are going around

 

you don't bore oversize to increase displacement you do it to clean up and true the bore. reason you don't see +.060 is you go next size over and that's usually .030. also .060 is near or at the limit depending on the casting. the reality of it is it's a 350 +.060 and not a 360 or a 350+.030 and not a 355.

 

There seems to be some myth that boring a motor is a some sort of mystical horsepower gainer that will bring you lots of extremely easy, hot woman, and cold beer. PiR2xstrokex# of cylinders. Glad I payed attention to Geometry in tenth grade:lala:

 

i know that its used to clean up the walls when they bore it, and never thought that is was for a chic magnet, was just a curious question, that a fresh 355 sells for more than any fresh 350 ive seen, but i never hear of anyone haveing a 350 thats over 60, or a 360 but i hear enough of 355's. was wondering if anyone had the downside opinion on a 360 thats all

 

Most people feel as though a .060 over block is junk. They think the Cylinder walls will be to thin, and there weaker. Whether that is true or not, depends on the block. A .030 block can be bored 2 more times, while a .060 block is at the end of its boreable life...

 

The safe way to tell is if you have the engine sonic tested.

 

safe way to tell for what? the block and rotating assy are fine, the internals are new, and the block was just freshend

 

safe way to tell if the cylinder walls are too thin, or thick enough to bore another step. some blocks are safe to go +.060

 

yeah i understand that but it was just taken to +.060 so thats all fine, was just wondering what kinda power kicks a 360 produces vs. say a 350 or 355 and any upsides to the downsides if anyone knows of any that have been built and whats there personal oninion on them

 

The power increase is going to be next to nothing. Probably the difference of 5-10 horse. its not meant for a power gainer

 

'there's no replacement for displacement'

 

more diameter bore=move volume=more volume able to be compressed,
higher compression+more area(piston) to accept the combustion stroke=more power.

 

all else being equall larger bore = less compression

 

how though, you gain 1 cu in. + of space to fill per cylinder in the end adds up to one more cu in to the compressed stroke?, also
a little about the block if anyone cares, 3970010 casting, 010 behind the timing cover which mean 1% tin added to the block, large journal, and after being bored 60 out, the cylinder walls are .30" thick. and if you think of how a diesel gets its compression, bore+stroke

 

that last deisel thing makes no sense. a Deisel gets its compression teh same way a conventional motor does. BDC cylinder volume/TDC cylinder volume. Bore+ stroke is meaningless...

 

bore and stroke = area able to be filled, to in the end be compressed, now if you have more air to compress its gonna raise the compression ratio because evidently your compressing another inch of mass, may have a little effect on total power gain, but i guess thats what its all about in one way or another.

 

Ede is correct. Larger bore = lesser compression. While your thinking is correct trans_am_racing, keep in mind, its not the chamber or valves that determine how much air gets into the chamber, but rather the camshaft. The camshaft is what actually opens and closes the intake valves. and just because you increase the cubes of the motor, doesnt change the fact of how the camshaft is ground. Lets pretend you use the same camshaft in a 355 as a 383. the 355 has the shorter stroke which, as you mentioned, reduces the amount of total volume that can be filled. Now the cam will allow "X" amount of air into the engine. and since the 355 has less space to fill, that air gets squished into a smaller volume, hence higher compression. NOw take that exact same cam profile and place it into a 383. Now that same "X" amount of air gets placed into a larger volume so it has more space to inhibit. This means there is less air per cubic inch than in a 355. That factor of less air per cubic inch creates the drop in compression.

Of course you could always get domed pistons.

 

http://www.carcraft.com/techarticles/54258/

read this then tell me its not increased

 

Don't believe anything you read in those comic books. While I do subsribe to CarCraft, you have to keep in mind those guys are just your average backyard mechanics who write articles. most of the time, they don't even do the work...

 

heres a dyno of a 360 from http://www.geocities.com/MotorCity/7610/dyno.htm



360 Cubic inches

Hot Rod/Edelbrock 360 EFI motor

Four bolt main block, .060 over

Rebuilt 5.7" rods

TRW forged pistons, compression 9.5:1

Edelbrock hyraulic cam; 234/244 @ .050, .488/.510" lift, 112deg lobe sep

Crane Cams Gold aluminum roller rockers 1.5 ratio

Edelbrock Performer RPM aluminum heads, 165cc runners, 70cc chamber

Edelbrock Pro-Flo electronic fuel injection system

1-3/4" headers

RPM TQ HP
2500 323 154
3000 354 202
3500 344 229
4000 358 273
4500 407 349
5000 403 384
5500 393 412
6000 356 407
6500 343
402

This engine was a demo for Edelbrock's Pro-Flo electronic fuel injection conversions for small block chevys. It works well with the smallish heads, it proves to be as efficient as some EFI motors with tuned intake manifolds, which is very impressive for a basic carb intake plumbed for EFI.

 

Larger bore = higher compression ratio

 

ok i'm a dumbass and i can figure out the physics behind this one. lets say you have 10:1 copression ratio, that is basically the volumn at the bottom of the stroke compared to the volumn at the top of the stroke. when you increase the area the compressed matter has to fill the ratio decreases because the stroke stays the same at each end resulting in less compression. i'd subscribe to another hot rod magazine.

 

in the end your not adding the bored space to the compression area, that little area from the bore dosent = 1.3 cu in. more like maybe .5 of an cu inch extra space to fill, so if that were true to reason, 1.3 cu is obviously greater than .5 cu in that would leave around .8 cu in extra to be compressed regardless of the stroke because there is more mass(air) to be compressed in the end.

 

ede,

Your statements on this board are highly respected and valued...
But I don't get your statement that all things being equal... increasing the bore will decrease the compression ratio.

I used a compression ratio calculator I downloaded from Pat Kelly's website @ cochise.net IIRC, and tried the one on smokemup.com and prestage.com

They iterate I believe what CarCraft, CHP, etc. say

They all show increase in compression ratio when increasing the bore size and all other things remaining the same.

The increase in the amount of air being compressed... is more than the increase in the amount of space that the air is compressed into...therefore, higher compression.

Of course, I'm talking in terms of static compression...but I don't see how it would be any different with dynamic compression, either.

 

Just think about it this way. A 350 is just a bored out 305. All things being equal you really think the 305 will have the higher compression ratio?

 

ok lets compare :

motor A: a stock 350 standard bore of 4.0 in, a 3.48 in stroke, 4.03 headgasket bore compressed thickness of .021, a 58 cc 305 swirly head, +11 cc dome volume of the piston, with a .025 deck clearance = 13.67:1 CR..


motor B: 360.4 CID, 4.060 bore, same 3.48 in stroke, same 4.03 head gasket with same compression thickness of .021, same 58 cc head, same +11cc pistons, same deck clearance = 14.02:1 CR..

so in the end mix and match any junkyard parts you find and you'll be suprised what you might think/come up with, not what a magazine tells you, any way you slice it you compress more air into a larger bored engine any given sunday. simple physics

 

"Increasing the cylinder volume without making any other changes will increase the compression ratio because it enlarges the cylinder volume without increasing the combustion chamber volume. " (from the article)

Think about it like this... The volume of the combustion chambers with the piston at TDC on a 4.00" bore with 64 cc chambers is close to the same as a 4.030" bore with 64cc chambers... The difference is that the swept cylinder volume is higher with the bore increase (think of a slightly larger cylinder).. Then, you compress all of that larger cylinder (4.030 or 4.060 or whatever) into the same space that you used to when you had just the 4.000" bore...

Oh, and I realize that the volume of the combustion chamber with the piston at tdc will be slightly larger with a 4.030 bore as opposed to a 4.000 bore.. However, the volume of the swept cylinder is still much more than this small increase at TDC, hence yeilding higher compression..

 

it would, but they are not equal, different pistons, different cam, different heads, etc...

if u threw all the same components on both engines, the 305 would have bigger compression because its pushing the same ammount of air into a smaller space.

 

Are you really seroius? You're telling me that if you put 58 cc heads with a 6 cc dish pistons in a 350 and a 305 that the 305 would have higher compression?

 

If you took a weeoh5 that was zero decked, with flat tops,threw 64cc heads on it, with a .020 thick head gasket, compared to a zero-decked, flat topped 350, the 350 would have higher compression. Thats talking pure compression, not throwing the cam into the mix. Cranking pressure, thats a different story...

 

when was it compared to as a 305?

if you think of it this way a bigger bore allows more capacity, thus having more volume to compress as a whole into the same space at tdc, it has to raise the compression, the air dosen't dissapear. the 1.3 cu in has to be compressed, thus giving the factor that the 1.3 cu in when compressed equals itself out giving the whole compression stroke + .66 :1 ratio

 

No... Thats opposite of what we're telling you, the 350 would have bigger compression because its pushing more air into the same space...

 

The dynamic compression ratio on the 350 would still be higher compared to a 305.

 

We should clarify that pressures can be described in two different ways, Absolute and Gauge. In this case, we know that the air is at the natural pressure of 15 PSI, which is an Absolute pressure, so it is sometimes written PSIA. If you measured that pressure with an air pressure gauge, it would read 0 PSI, because there is no difference in pressure from natural. This is called gauge pressure, and would be written 0 PSIG. They mean the same thing, and absolute pressure is always 15 higher than gauge pressure.

 

Joshua, I think we're all agreeing here... Yeah, compressions gonna be higher on the 350 with equal chambers..

EDIT: I should have quoted the other guy in my first post (fixed).. Now I realize that you and I were on the same page, and it was him that I was actually correcting back through your counter-statement... Boy... confusing..

 

All else being equal, if the bore of the cylinder is increased, both static and dynamic compression will go up.

Just to keep this equal, I'm not going to include a gasket, nor deck height. Those aren't going to change anyway, so why include them?

Using 64 cc chambers.....

For a 4" bore.....

Radius of 2" squared x Pi = 12.566 square inches x 3.48" stroke 43.73 cid

43.73 cid = 716.6 cc's

716.6 cc's + 64 cc's = 780.6 cc's

780.6 / 64 = 12.2 compression ratio



Now using 4.060" bore......

Radius of 2.03" squared x Pi = 12.95 sq. inches x 3.48" stroke = 45.05 cid

45.05 cid = 738.24 cc's

738.24 cc's + 64 cc's = 802.24 cc's

802.24 / 64 = 12.535 compression ratio

Of course since the static compression goes up, so does dynamic. That would also mean cylinder pressure goes up. Kinda like what Stekman was saying about the cam being smaller, but the same thing happens with any engine; The shorter duration cam you use, the higher LOW RPM torque will be because of increased cylinder pressure at LOW RPM.

Putting the same cam in a 350 and a 383 will make it "appear" smaller in a 383, therefore increase cylinder pressure.