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Are 318 Magnum pistons different from 318 LA? #1071459
09/08/11 04:19 PM
09/08/11 04:19 PM
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69L78Nova Offline OP
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I'm in the middle of my little budget 318 build and I've hit a snag. The 95 Magnum 318 short block I picked up has a small crack in one of the cylinders. I already bought a new Mahle ring set for the Magnum pistons. I have a 75 318 in immaculate condition needing nothing more than rings, bearings and resealed. My question is, can I use the Magnum pistons in the LA block for a little compression bump, or are they basically the same except for the metric size rings. I was going to use the K6900 cam and Magnum heads from my current 360 in the 318 LA. I don't have the spare dough to have the Magnum block bored and buy new pistons, so I was looking to do it on the cheap. Or should I stick with the 75 318 pistons?


1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
Re: Are 318 Magnum pistons different from 318 LA? [Re: 69L78Nova] #1071460
09/08/11 05:15 PM
09/08/11 05:15 PM
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Two Harbors, MN
chrgr340 Offline
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I don't recall what the exact difference is, but I just read somewhere a day or two ago that LA and Magnum pistons are different. I'd probably stick with the LAs.


1972 Dodge Charger - F7, Rallye pkg, 340, A833
2007 Dodge Charger R/T R&T - 12sec daily beater
1999 Dodge Dakota R/T - M1, cam, heads, T56 swap
1997 Dodge Dakota - 318, NV3500, 3.92 Sure Grip
Re: Are 318 Magnum pistons different from 318 LA? [Re: chrgr340] #1071461
09/08/11 05:23 PM
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Moparnut426 Offline
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the width of the rod is it. the LA rod wont fit between the wrist pin bosses.

If you run a scat I beam they fit. Pluss will be full floating.

Kasey

Re: Are 318 Magnum pistons different from 318 LA? [Re: Moparnut426] #1071462
09/08/11 05:47 PM
09/08/11 05:47 PM
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Maryland
GO_Fish Offline
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If the Magnum bore is the same size as the LA's bore(both virgin, both +.020,etc), you should be able to swap the magnum crank, balancer, rods and pistons over to the LA block and keep moving. Use the Magnum head bolts to bolt the Magnum heads on the LA also.


Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph
Re: Are 318 Magnum pistons different from 318 LA? [Re: Moparnut426] #1071463
09/08/11 05:48 PM
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Glendale, AZ
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69L78Nova Offline OP
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Whoops, I'm sorry. I should have been more clear. I mean I was thinking of using the Magnum pistons AND rods in the LA engine. Would that work, or is the rod different on the crank end as well? The only reason I ask is because the magnum engines are rated as being 9 to 1, and the LA is 8.5 to 1. I don't know if the magnum heads on an LA block would boost compression, or if the magnum chambers are around the same size as the old 70s 318 LA heads.


1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
Re: Are 318 Magnum pistons different from 318 LA? [Re: 69L78Nova] #1071464
09/08/11 05:50 PM
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Moparnut426 Offline
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They will go in, I recomend balancing the whole shebang though. Also you shouldnt have any piston to valve clearance issues, still way shy on compression to be worried about that. The chambers on the LA heads are bigger than the nice chambers on a magnum head.

Kasey

Re: Are 318 Magnum pistons different from 318 LA? [Re: 69L78Nova] #1071465
09/08/11 05:53 PM
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RapidRobert Offline
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360 piston ~584 grams pin 154.6 rings 56.6 comp height 1.590". Mag piston 470, pin 134, rings 40 grams CH 1.662". As said th LA rod small end is 2 wide but can b narrowed but that'd b $$$ plus then you'd need to weigh all the pieces 4 the balance factor & you're doing a budget build. Not sure what I'd do but that's what I could come up w


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Re: Are 318 Magnum pistons different from 318 LA? [Re: RapidRobert] #1071466
09/08/11 06:02 PM
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69L78Nova Offline OP
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Could I use the whole 1995 rotating assembly in the 1975 block? Crank, rods, pistons, balanced and flexplate? I would just like to use the newer stuff if I can.

I wasn't aware the old 70s 318 two barrel heads were open chamber. I guess ya learn something new every day!


1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
Re: Are 318 Magnum pistons different from 318 LA? [Re: RapidRobert] #1071467
09/08/11 06:10 PM
09/08/11 06:10 PM
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Central TX
roe Offline
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wouldn't the magnum heads on his LA 318 give him a nice bump in compression, especially with a thinner head gasket. If the LA is in such nice condition why not re-ring, new bearings, magnum heads and go with the LA 318?



1971 Plymouth Satellite
408/904 8 3/4 3.23 SG
Re: Are 318 Magnum pistons different from 318 LA? [Re: roe] #1071468
09/08/11 06:13 PM
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69L78Nova Offline OP
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That's what I planned to do. I wasn't sure if the compression height of the Magnum pistons was the same as the LA pistons. If the difference is minimal or not worth it, ill just run the LA stuff


1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
Re: Are 318 Magnum pistons different from 318 LA? [Re: 69L78Nova] #1071469
09/08/11 06:28 PM
09/08/11 06:28 PM
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Central TX
roe Offline
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Im definately no expert on this. Somebody a few posts back said that you can swap over the entire rotating assembly. If that true what king of issues could he run into? Wouldn't that be like slightly stroking the 318 to about 349 or so? Would he have to start worrying about clearance issues with those pistons/heads in the 318?



1971 Plymouth Satellite
408/904 8 3/4 3.23 SG
Re: Are 318 Magnum pistons different from 318 LA? [Re: roe] #1071470
09/08/11 06:50 PM
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69L78Nova Offline OP
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No, both are 318s. One Magnum, one LA


1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
Re: Are 318 Magnum pistons different from 318 LA? [Re: 69L78Nova] #1071471
09/08/11 09:59 PM
09/08/11 09:59 PM
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Maryland
GO_Fish Offline
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Quote:

Could I use the whole 1995 rotating assembly in the 1975 block? Crank, rods, pistons, balanced and flexplate? I would just like to use the newer stuff if I can.




Yes, that is what I was saying in my earlier post. Use the whole 95 rotating assembly so you do not have to rebalance anything. You would still have a 318, but the compression should be the same as a Magnum. You would essentially have a magnum less the roller cam and lifters. You'd need hollow pushrods from Summit or other to finish the conversion.


Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph
Re: Are 318 Magnum pistons different from 318 LA? [Re: GO_Fish] #1071472
09/09/11 01:06 AM
09/09/11 01:06 AM
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69L78Nova Offline OP
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Ok, good to know. I already have the complete Magnum top end on my 78 360, I would just transfer the heads, manifold, carb, and K6900 cam/lifters into the 318. Looks like that's what ill do.


1969 Nova
454/M21/3.31
Mild mid-11 second weekend cruiser

1994 F150 XLT Super Cab 2WD
5.0/4R70W/3.55
(Daily driver)
Re: Are 318 Magnum pistons different from 318 LA? [Re: 69L78Nova] #1071473
09/09/11 10:01 AM
09/09/11 10:01 AM
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Grand Haven, MI
patrick Online content
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Quote:

Could I use the whole 1995 rotating assembly in the 1975 block? Crank, rods, pistons, balanced and flexplate? I would just like to use the newer stuff if I can.

I wasn't aware the old 70s 318 two barrel heads were open chamber. I guess ya learn something new every day!




yes, and is what I'd do.

compression height is marginally higher than the older pistons, and the metric ring packages are the big differences between LA and magnum 318.


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Re: Are 318 Magnum pistons different from 318 LA? [Re: patrick] #1071474
09/09/11 11:44 AM
09/09/11 11:44 AM
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You might already know this, but make sure you match the lifters to the lobes. If not, the cam and lifters are certain junk.

Kasey

Re: Are 318 Magnum pistons different from 318 LA? [Re: 69L78Nova] #1071475
09/09/11 05:13 PM
09/09/11 05:13 PM
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Central TX
roe Offline
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Quote:

No, both are 318s. One Magnum, one LA




Silly me, not paying attention



1971 Plymouth Satellite
408/904 8 3/4 3.23 SG
Re: Are 318 Magnum pistons different from 318 LA? [Re: roe] #1071476
09/09/11 08:57 PM
09/09/11 08:57 PM
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Sterling Heights, Michigan 483...
daniel_depetro Offline
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Supposedly the Magnum engines have a lighter rotating assembly weight too.


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1972 Plymouth Road Runner (400, 4-speed, 8.75" 3.23)

1974 Plymouth Duster 360 (360, 4-speed, 8.75" 3.23)
Re: Are 318 Magnum pistons different from 318 LA? [Re: daniel_depetro] #1071477
09/09/11 10:22 PM
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Maryland
GO_Fish Offline
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That is true (lighter Magnum rods and pistons). That is why the whole Magnum rotating assembly needs to move to the LA block to maintain correct balance without a trip to the machine shop for custom balancing.


Scott B. "I'm a self-made man... I started with nothing, and I still have most of it!" 68 360 rusty B'cuda 'vert (GO Fish)13.59@ 98.72 mph 69 340 GTS stock 14.18@ 95.60 mph 01 5.9L Ram 1500 Quad Cab 4x4 01 3.5L 300M 16.23@ 86.97 mph
Re: Are 318 Magnum pistons different from 318 LA? [Re: GO_Fish] #1071478
09/10/11 12:13 AM
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The differance in piston height is about .080 witch will make a nice bump in compression. However just swapping magnum heads onto a 318 LA with magnum heads will not yield you as much compression as a factory 318 magnum because the 318 magnum had a lower deck height also by about .015.


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