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360 stroker help

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Alliups View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alliups Quote  Post ReplyReply Direct Link To This Post Posted: Sep/25/2008 at 4:19pm
Originally posted by tyrodtom tyrodtom wrote:

I got the pistons from AMRACING about 4 years ago, I still haven't assembled the engine.
It took over 6 months, and several calls, for them to arrive.
They're hyperutechnic, not forged, and they are 4.125 bore,I'm pretty sure they're Chevy 396 pistons,  but the pin holes have been machined or honed out to AMC pin size, and the top looks like they've been machined to flat tops.
To tell you the truth, i'm a little unsure about them.


A trusted machinist could tell you if they are quality or not by how accurate the machining is. The next deal , I'm sure because you're a racer,  you know whether the pin compression height , etc. is what you're going to use the engine for.

Steve
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alliups Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2008 at 10:05am
Originally posted by amx39068 amx39068 wrote:

The overbore on the 360 alone will only minimally impact its power output.  It really depends on what else you are planning to do to the motor so if the answer is not much then your output will still be in the stock output range and will be more impacted by which compression pistons you put in the motor than the overbore.


An overbore alone or an overbore with a stroke increase would pump up your torque as well as make the engine more "flexible" in terms of 'lugging" it. You won't have to downshift as often.

Steve
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tyrodtom Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2008 at 11:57am
   You bore a engine out .030, how much added displacement do we have ? 5-6 cubic inches .
   You've got a engine that maybe, maybe, can make 1 hp per cu in, if it's really tuned. So at the best you're looking at a added 5-6 hp from the added displacement.
   How much do the pistons cost ? $500 maybe . Bore- $200+, if you do all the work yourself, and just farm out the machine work, you've just spent over $100 per added HP.
Boreing out a engine for added hp isn't very cost effective.
   You'll get more added hp from your old engine, if you bore it. from the improved ring seal on fresh, straight, cylinder walls than you'll get from the added displacement .
    Of course, if the engine needs a overhaul, by all means bore it, myself I don't like to bore to the max because of possible heat problems with thin cylinder walls. But it's your engine. 
   Then there's offset grinding a crank for added displacement. How much added displacement verses how much money spent ?


Edited by tyrodtom - Sep/26/2008 at 12:00pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alliups Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2008 at 12:40pm
I should have said "big bore". If someone were going to go 45 thou or above that'd be be a big bore. I was referring to the AM racing pistons and the original poster's interest in putting big pistons in. It's really only cost effective if the work is going to be done anyway. With an AMC offset grinding the crank would be more cost effective than switching everything over for a 390 or 401 crank.
    However, it is an interesting exercise and I think that after doing the engine math all AMC parts could be used. The piston doesn't know what rod or crank it's attached to. So-
9.208-3.57/2 +5.790 =1.633. That'd be a very tall topped piston. Unless you decked the engine and perhaps used 343 pistons. I'll check later when I have time. The point is you can up the size of the engine if that is your aim, without getting custom parts. The above example would require bushing the small end of the rod.
 Steve
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alliups Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2008 at 10:52pm
 Naturally, you are "only" getting a 374 C.I. engine unless you also ordered .040" over pistons which would be 378- 379 C.I. couple these changes to the right head and cam mods and you'd have a relative revver compared to a 390 with alot more torque than a 360- plus fairly cheap forged parts.
 Steve
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alliups Quote  Post ReplyReply Direct Link To This Post Posted: Sep/26/2008 at 11:17pm
Ok, here's an affordable combo:  9.208" deck height- 3.57/2 ( 390 crank stroke divide by 2 )+ 5.858" ( '70 390/401 rod length )= 1.565 CH ( compression height ). Egge apparently makes some 1.57" CH 343/360 pistons. That would leave you at .005" below deck height. Not sure what the compression would be but 10.7 to 1 would probably be on the low end- closer to 11 to 1 is my guess. Put in a cam that limits dynamic compression and you have a sweet running engine that is just shy of 380 cubes with some relatively light pistons as compared to a390 along with a smaller flame front area meaning it would be less prone to detonate. You are also using all AMC parts. Again the rod would have to be bushed for the smaller piston pin.

Steve


Edited by Alliups - Sep/26/2008 at 11:18pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote amx39068 Quote  Post ReplyReply Direct Link To This Post Posted: Sep/27/2008 at 12:22am

There is no way a simple .030, 040, or .060 overbore is going to have any measurable impact on torque, horsepower or anything else that an engine produces. And anyone who thinks that such a small overbore alone will impact an engine's output is ignoring a host of other factors that affect the output of power and torque on an internal combustion engine.  A piston swap with a shorter piston height on an otherwise stock setup will pretty much cancel out any gain that the nominal increase in bore might produce so there may not be any measurable gain at all other than what you would normally get from freshening up an engine.

On the other hand, stroking an engine or using a crank with a longer throw for bigger cubes or improving the intake flow and carb size, improving the valve train flow and/or increasing exhaust flow will indeed have a signficant impact on the engine's output .  The bore size alone, as mentioned above, will prodice 6-8 morre cubic inches than the stock bore, or around 2% of the total engine's displacemen so in the grand scheme of things that nominal increase in engine size is a very small factor in an engine's output.
 
As for specifcs, the above referenced:
"affordable combo" of  9.208" deck height- 3.57/2 [not sure where that comes from as the 390 is 5.74] ( 390 crank stroke divide by 2 )+ 5.858" ( '70 390/401 rod length )= 1.565 CH ( compression height ). Egge apparently makes some 1.57" CH 343/360 pistons. That would leave you at .005" below deck height.
 
will actually result in the pistons poking out of the block by .007 (with the 1.57 EGGE pistons), which is actually a -.007 deck height not .005 so the valve to piston clearance should be checked to make sure the valves do not come in contact with the top of the piston particularly when using a cam with a hefty lift. 
 
The compression ratio at .030 with the above combination will be of 11.1:1 with 50.6cc heads and 10.2:1 iwith 58cc heads and stock 18cc valve reliefs. The size of the valve reliefs will significantly impact the comrpession ratio if the valve reliefs are smaller that the stock 18cc's.  The cubic inches will be 379.33 at .030 over the strandard bore of 4.080.


Edited by amx39068 - Sep/27/2008 at 12:25am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Alliups Quote  Post ReplyReply Direct Link To This Post Posted: Sep/27/2008 at 10:42am
Originally posted by amx39068 amx39068 wrote:

There is no way a simple .030, 040, or .060 overbore is going to have any measurable impact on torque, horsepower or anything else that an engine produces. And anyone who thinks that such a small overbore alone will impact an engine's output is ignoring a host of other factors that affect the output of power and torque on an internal combustion engine.  A piston swap with a shorter piston height on an otherwise stock setup will pretty much cancel out any gain that the nominal increase in bore might produce so there may not be any measurable gain at all other than what you would normally get from freshening up an engine.

On the other hand, stroking an engine or using a crank with a longer throw for bigger cubes or improving the intake flow and carb size, improving the valve train flow and/or increasing exhaust flow will indeed have a signficant impact on the engine's output .  The bore size alone, as mentioned above, will prodice 6-8 morre cubic inches than the stock bore, or around 2% of the total engine's displacemen so in the grand scheme of things that nominal increase in engine size is a very small factor in an engine's output.
 
As for specifcs, the above referenced:
"affordable combo" of  9.208" deck height- 3.57/2 [not sure where that comes from as the 390 is 5.74] ( 390 crank stroke divide by 2 )+ 5.858" ( '70 390/401 rod length )= 1.565 CH ( compression height ). Egge apparently makes some 1.57" CH 343/360 pistons. That would leave you at .005" below deck height.
 
will actually result in the pistons poking out of the block by .007 (with the 1.57 EGGE pistons), which is actually a -.007 deck height not .005 so the valve to piston clearance should be checked to make sure the valves do not come in contact with the top of the piston particularly when using a cam with a hefty lift. 
 
The compression ratio at .030 with the above combination will be of 11.1:1 with 50.6cc heads and 10.2:1 iwith 58cc heads and stock 18cc valve reliefs. The size of the valve reliefs will significantly impact the compression ratio if the valve reliefs are smaller that the stock 18cc's.  The cubic inches will be 379.33 at .030 over the strandard bore of 4.080.


Well, I'm one of those that does feel that any overbore past .040"  AND maintaining the original piston height to deck clearance or BETTER will produce noticeable seat in the pants torque improvement as well as quantifiable improvement. Anyone that thinks otherwise ignores basic physics. A .060 overbore represents about a 3.9% displacement percentage. if one's aim was purely to bore out then the 6% threshold ( about .080" over) would be a rough thumbnail for going that route to increase displacement. The lower overbores were just free rides- if you are going to stroke and go with an overbore- then the combination makes a great wallop in the rear.
    Yes the Egge pistons have a lower than stock CH which is perfect for the exercise I chose. If overboring alone one would have to take into account the CH loss and either shave the head or find other pistons. The simple overbore was never my focus and certainly digresses from the original poster's aim. I hope this closes beating a dead horse on the overbore issue. Moving on.
  
 Actually you are correct, in part on the stroke- the 390 has a 3.574" stroke. And yes the piston would be 7 thou above the deck. The machinist could best determine if any shaving would be necessary. The point which seems to be lost in all the trips down overbore lane, is how to jump on a 360, or 343 for that matter, and do with it what has been done with the ubiquitous ( look it up- or look at the context and stretch your vocabulary a little if you are a reader that has a problem with "big" words- I use what I use ) Chevy smallblock in the 383 configuration. 400 crank in a 350 block- brilliant.
   If you have or are considering getting a 390 or 401- that's great- but were dealing with 360's which in AMC land are the Chevy smallblock of the litter- quantity wise. But more important is it stretches people's imaginations and ingenuity to play with the 343/360's and make them do different things. People take 401's out to 422 and 434 CID. So if you can score just a 390 or even 401 crank and rods- why not play with a 360 too? If you can't afford or find these then offset grind the 360 crank - use some SCAT or other forged rods or simply inspect ( magnaflux ), clean up ( removing sharp edges and casting flash ) and ARP bolt a set of stock rods and stroke the crank to a level that allows picking the most readily available pistons while having to do minimal machining.
Then.......
 HAVE FUN!Tongue

Steve
     


Edited by Alliups - Sep/27/2008 at 11:13am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kc eatman Quote  Post ReplyReply Direct Link To This Post Posted: Jan/30/2009 at 10:52pm
i have ran a 360 bored to 4.125 , 6" alu. rod with 3.910 stroke to make 418 cubes. it also has a 700" roller @ alu. indy heads & je pistons. it makes a little over 700 hp.  been running it for 8 years with no problems other than an ocasoinal rod change. i would think you could do what your wanting to with no problem.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Hurst390 Quote  Post ReplyReply Direct Link To This Post Posted: Jan/31/2009 at 7:15am
Originally posted by kc eatman kc eatman wrote:

i have ran a 360 bored to 4.125 , 6" alu. rod with 3.910 stroke to make 418 cubes. it also has a 700" roller @ alu. indy heads & je pistons. it makes a little over 700 hp.  been running it for 8 years with no problems other than an ocasoinal rod change. i would think you could do what your wanting to with no problem.
Finally some reality and not theory..or percieved theory...Clap
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