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#1
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360 Crank in a 318
Can a 360 crank be used in a 318? I know that the main journals need to be turned down to 318 size, but is there anything else that I need to do? I have 360 crank in the garage, and am doing just a slight build on my 318, and I was hoping that this would work fairly easily so I could get a longer stroke. Thanks.
Eric |
#2
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Oh, boy. This is a BIG can of worms. Most people will tell you that this is a bad idea. "Why are you so STUPID to build a 318/360 crank hybrid when you can just build a 360", they will say. And, in a large part, they are right. IF 360s are cheap and plentiful where you live (they aren't around here) and IF you want to build a 360 and be like everyone else you should just forget this idea. There is no doubt that a 360 makes the most sense to build under most circumstances.
However, if you want to know more about the poor little 349, as most call it, then read on. A 318 block bored .030 over with a stroke of 3.58" (360 crank) produces 349 cubic inches. You will need to have the crank turned to 318 main journal size and pistons can be somewhat of a problem. I got lucky and found two sets of Clevite TC1930 cast flat top pistons with a compression height of 1.678 for $60 per set. I can tell you that those pistons/crank set into a 318 block at zero deck with 60cc Magnum heads (10.77:1 static compression ratio) with a Strip Dominator and 750 mechanical secondary carb will run 11.30-11.50 in the quarter. This is in a 2850 lb Dart. The fun thing is all the guys you run the pants off of thinking you have a 318 in the car. Some will even crawl under to read the numbers on the side of the block. If I can answer any questions just ask. I also have a good combo in a .040 over with dual plane and milder cam that produces great torque. The cost of balancing can be pretty substantial ($225 - $250) but I have been told it is much less expensive to balance to 360 specs. Turning the crank runs $100 - $125 at most shops, mine was $75 each but I had three turned at once. |
#3
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The cylinders on my block are still good, so I don't want to bore it, just hone it , and was hoping to just re-ring it, but i don't know if that's possible. I'd like to have as little machine work done as possible. Was hoping to have the turning of the crank be the only machine work.
Eric |
#4
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Quote:
If you are looking to do this just to save money it is probably not your best route. Even around here I can find a good 360 core for $350- $450 and you will likely have that much in machine work. |
#5
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Yeah I can find 360 block all over the place, but they are bare blocks, so I start out with nothing. I don't want to pump a lot of money into my 318, but I do want to use it. I would like to use the 360 crank to get a longer stroke, and would probably go with a .010 overbore, but don't want to get too crazy with it. Just something to make my pullin truck go and go pretty hard. Also, you said you had 2 sets of those pistons? Where did you get them, and are you using both sets?
Eric |
#6
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Both sets have been used. They have been hard to find but look on Ebay. The key is to find pistons with a compression height around 1.687. This would be perfect for zero deck if your block is at factory spec, which it ususally isn't.
If you can measure your actual deck height then it is easy to determine the compression height needed in a piston. I am running the street engine at .007 below deck with a .028 head gasket with no problems yet. The race engine is at zero deck with .039 head gasket. Turn it 6700 RPMs (with cast pistons!) with no problems. |
#7
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You have any other ideas for a mild 318 build up for not a lot of money?
Eric |
#8
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How about this for the lower end. I found a set of those Clevite pistons you were talking about on ebay for $76 shipped. They are standard bore. I was thinking hone the cylinders for a cleanup, mill a 360 crank, to 318 on the mains, and .010 on the rods, and just use the stock rods. How does this sound? Based on if the deck height is exactly factory spec (doubt it), i should have the piston .007 in the hole. Now if this sounds good so far, what should I use for a head gasket? I am planning on using a set of 308 heads milled to up the compression a little bit, as long as I won't have valve clearance problems. Oh and the cam is an Erson 292 214 449 cam. Thanks.
Eric |
#9
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ewatts,see the current discussion in "360 crank in a 273" Among other points someone mentioned the loss of the hard surface on the main journals when they're cut to the smaller (273-318) dia. Another $$$ factor to consider?
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#10
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You may try calling speed-o-motive about the 349 setup if you're concerned about the loss of hard facing when turning down the journals to fit a 318. They seemed very knowledgable on the subject.
I asked them the same question when ordering my 349 kit, from what I remember they recommended nitriding the turned down journals for people who are going to beat on their engines (high rpm, heavy towing, etc)... I played it safe and just paid the extra $, think it was ~$125... just depends on how many miles you want it to last. |
#11
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With 318 pistons and a 360 stroke crank you need to pay close attention to piston skirt to crank counterweight distance. I know there are some pistons on the market with the correct CH, but will bang the counterweights at BDC.
As far as the grinding off the hardened surface goes.... what do you think happens when you have a crank turned 0.010" or 0.020" ? |
#12
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bbr, good question! I have to assume (bad word!!) that .010" won't get through the hardened surface. True, if the crank was induction hardened. Don't know about Tuff-triding or nitriding. Anyone care to give us a short description of these processes as to their effective depth?
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#13
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The factory cast cranks are not hardened and most of the forged cranks aren't hardened either. To get a hardened Mopar crank you have to find a -3 truck engine or buy one of the forged 8 bolt flange cranks. I wouldn't worry about the journal harness at all.
BTW, I have an 8 bolt 3.45" stroke LA crank that is going into a 318 with .040" oversize forged flat tops. This will push the pistons .070" higher in the bore. Valve reliefs will be cut in the pistons, but I still have to check piston skirt to counterweight clearance. Other than the extra stroke, head porting and an RPM Air-Gap intake this engine build will be very similar to Dulcich's 400hp 318. I already have my block, crank, resized rods with ARP bolts, Magnum heads, Rollmaster timing set, oil pump, pushrods, rings and bearings. I still need cam, lifters, valve springs, retainers, head bolts and machining. The current plan is to run it in a friend's '52 Packard 200. I have to see what headers will fit in the cavernous engine compartment. My only worry is the steering box. |
#14
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Quote:
But are you saying that all 8-bolt cranks are hardened? I thought only the truck ones were... And what, exactly, is a '-3 truck engine'? |
#15
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8 bolt LA cranks
Ray, there are several small block "8 bolt cranks" out there. The most modern are the after market or Mopar Performance cranks. I am sure the 3.45" crank mentioned above is a Mopar Performance crank and is an excellent choice to get 318 pistons up to the deck. I have a 3.38" 8 bolt crank in a 318 that got near zero deck height. I also have a 3.51" 8 bolt crank in a 273 block with custom pistons.
The early Poly cranks were also 8 bolt cranks. Pre 1962 cranks extended rearward about an inch longer than the post 1962 cranks. I don't recall which group the 1962 year fell into. |
#16
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'62 were short and 6-bolt...
So we're talking about a totally different 8-bolt setup here? The early Poly 8-bolt crank, as you say, about an inch longer, it had no threads in the 8 holes, the bolts fed through from the back and the extra inch of clearance was there to get a spanner in to tighten the bolts. Somehow I think the later 8-bolt setups were to give a better crank fixing at the regular distance from the block? And there are threads in the holes? |
#17
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Sorry I wasn't clear about the 8 bolt crank flanges. The one I speak of has the 426 hemi bolt pattern on a Mopar Performance forged (and surface hardened) small block crank. All you need to run this crank is an 8 bolt flex plate or flywheel, 2 extra attaching bolts and the appropriate pistons.
The -3 truck engines are the premium heavy duty truck engines used primarily in 1 ton and heavier trucks. There were 225-3s, 318-3s, 361-3s, 413-3s and probably others. There were also other slightly less heavy duty versions with the -2 designation. I can't say if the -2 engines got hardened cranks, but I'm reasonably certain the -3s did. |
#18
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We're told of... and have seen one example of... catastrophic breakages of cranks in trucks fitted with Polys.
Could it possibly be that cracking through the web is facilitated by a brittleness introduced to the journal (particularly in the undercut) by hardening? |
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