Magnum swap questions

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408Dartman

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Okay... I bought a 318 magnum from a mid 90's Dakota and I want to swap it in my Dart. Here is my plan tell me if it's not going to work... I was thinking a retro-fit cam, hydraulic roller of course, with the long snout and swap my LA timing cover on so I can still use my mechanical fuel pump. I also want to swap the LA alt., ps and water pump ( should work ). I have a 360 CAR oil pan for a mid 70's car... I also need to get a neutral balance 318 flex plate, magnum 318's I believe are neutral balance. Did I leave anything out other than intake and carb?
 
It will already have a roller cam so you don't need a retro-fit cam. Just purchase a replacement cam of your choice with the long snout.

If the engine has a serpentine belt the water pump will spin the opposite direction which will be OK if you use the same fan.

The 360 oil pan will not work on an LA 318 due to the different size pan end seals. I believe the Magnums are no different on this.


Chuck
 
I see, I guess one problem is I am having a hard time finding a Hyd, roller cam with a long snout, that or I don't know what I am looking for.... The oil pan thing, I thought the magnum 318 had a bigger seal than the LA did thus the reason for 360 LA pan with the center hump? I'll see if I can verify it later, I still got the magnum in the back of the truck....
 
Call comp for a custom. No problem. Or Crane, Huges...etc.......
 
Actually the LA360 pans have a smaller seal than the LA318 pans. It is the main bearings that are bigger.

I was looking thru the Comp Cams catalog and I see your dilema. You can't use the retro-fit and replacement LA roller cam because they are for 1.5 rockers and have oil holes in the #2 and #4 bearing journals. You can't use a Magnum roller because they have the short snout. You are going to either have to run an electric fuel pump or get a custom cam ground possibly.

Chuck
 
well electric fuel pump it is... can I still swap the LA timing cover over and water pump, then just block the mechanical fuel pump off?
 
OKay I did some research last night and I don't see the problem in running a LA hyd. roller... I know the oiling for the cylinder head in a LA motor is through the cam journals like 340 mopar said, but what does it matter on a magnum? A oil hole in the cam on a magnum block should not matter, it oils through the pushrods... IF it was a problem, magnum headed LA blocks would have to change cams, because they no longer oil through the cam journals. I think as long as I use the LA timing cover I wil have no problems ( I hope ) that way I don't have to deal with the Magnum reverse rotation water pump and use the LA water pump, alternator and power steering.
 
The LA cams are ground for 1.5 rockers and the magnum is 1.6. Sure you will gain more lift but that is not how the cam was designed to run and might not be advantagous but probably will be. I would call a cam company and get there views on it like Rumble said.I do not see why you couldn't put on the LA timing cover and just block off the fuel pump opening.

Chuck
 
340mopar said:
The LA cams are ground for 1.5 rockers and the magnum is 1.6. Sure you will gain more lift but that is not how the cam was designed to run and might not be advantagous but probably will be. I would call a cam company and get there views on it like Rumble said.I do not see why you couldn't put on the LA timing cover and just block off the fuel pump opening.

Chuck
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Cam doesn't know whether the rockers are 1.5 or 1.6 ratio so there is no issue there. The shape of the lobe is dependant on the type/size of lifter that it acts on not the rocker ratio. One of the more popular changes on a magnum motor is to use 1.7 ratio rockers for the added lift.

One of the advantages of swapping a set of magnum heads onto an LA is the 1.6 ratio rockers and the slight increase in lift at the valve. I am taking advantage of this on my LA/magnum hybred 360.

Off the shelf magnum cams are ground with emissions in mind so may not be the best choice. I would go with the LA retro fit cam or have a custom one ground and don't worry about the oiling holes. If you go this route then you can use the LA front cover an all the accessories including a mechanical fuel pump. Also, Mancini has an adapter that allows the fuel pump eccentric to mount to the short snout magnum cam.

Also, I believe that they standardized the rear main seal area on the magnum engine to the 360 size so your 360 LA pan should work on the 318 magnum.
 
dgc333 is the go to guy on the Magnum and hybrid engines, he answered all my questions a couple of years ago. I'm on my fourth Magnum head/LA build now, and they run great. Lots of torque, my '72 Swinger ( 10.5 cr 360) ran 13.80s with a 3.55 gear last fall. Also gets 19 mpg all day long.
Bob
 
Last time some one talked about me like that I was out riding my dirt bike, my head swelled up,the pressure from the helmet blurred my vision and I road into a ditch and spent three months in the hospital! ;/
 
dgc333 said:
Last time some one talked about me like that I was out riding my dirt bike, my head swelled up,the pressure from the helmet blurred my vision and I road into a ditch and spent three months in the hospital! ;/
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LOL dude that sucks....


Thanks for the help.
I do have have a 360 LA pan that I was going to try to use, so it is good to know it will work, I also bought the fuel eccentric extension for the stock cam for now in till I figure out what cam I want... I have the airgap knock-off on the 318 now, so I just need to stick the LA timing cover on and swap oil pans, then I will be ready to go.
 
dgc333 said:
Cam doesn't know whether the rockers are 1.5 or 1.6 ratio so there is no issue there. The shape of the lobe is dependant on the type/size of lifter that it acts on not the rocker ratio. One of the more popular changes on a magnum motor is to use 1.7 ratio rockers for the added lift.

One of the advantages of swapping a set of magnum heads onto an LA is the 1.6 ratio rockers and the slight increase in lift at the valve. I am taking advantage of this on my LA/magnum hybred 360.

Off the shelf magnum cams are ground with emissions in mind so may not be the best choice. I would go with the LA retro fit cam or have a custom one ground and don't worry about the oiling holes. If you go this route then you can use the LA front cover an all the accessories including a mechanical fuel pump. Also, Mancini has an adapter that allows the fuel pump eccentric to mount to the short snout magnum cam.

Also, I believe that they standardized the rear main seal area on the magnum engine to the 360 size so your 360 LA pan should work on the 318 magnum.
Click to expand...


Of course the cam doesn't know what rocker is on the heads but the engine will know and this could be good or bad if you re-read my post. Adding lift is not necessarily a performance gain, on stock cam, most likely, but if you are already at the limit of lift and duration on you engine package adding bigger ratio rockers could lessen your performance by adding to much lift and duration. If you purchased an aftermarket cam for your package with the lift and duration based on 1.5 and you put 1.6 rockers on it you can throw out the window the cam manufacturers recommendations on power range. That is the point I was trying to make.


Chuck
 
Duration is what will impact the rpm of the power range and duration is changed very little by going from 1.5 to 1.6 ratio. The total duration is not impacted at all and the duration at 0.050" is only a degree or so which is not significant. If the added lift is above the point at which the heads will flow more then whether you add the lift with a cam change or a rocker arm ratio change it's not going to help.

Other than getting into a mechanical interference issue (which you need to check any time you deviate from stock) there may be no upside to the ratio change but there will not be a down side.

A rocker change is likely going to be more costly than a cam change so from a dollars and sense standpoint changing the cam makes more sense.

For 408dartman he already has an engine with 1.6 ratio rockers. The LA roller cam will allow him to use the LA front cover and mechanical fuel. The short snout magnum cams will require an adapter or the use of a electric fuel pump.

FWIW, even the magnum specific cams in the Comp catalog have their lift based on a 1.5 ratio rocker even though the magnum engine as always used a 1.6 ratio.
 
Again go back and read my post, I say in it that it might not be advantagous but probably will be. I mention nothing about anything negative about going to 1.6 rockers from 1.5. The only reason on my second post I say that it could lessen performance was in rebuttal to you making an insinuation that I was saying the effect would be negative and was trying to give an example of how it could be negative. I didn't say it changed the duration I said that if you are at the limit of the duration the higher rocker ratio could effect the performance this is because of the added rocker ratio the opening and closing rates of the valves are faster which makes the engine think it has 2 to 4 degrees more duration. Again the gain might not be there but it probably will.

FWIW, Comp's catalog lists specs with the 1.6 rocker ratio on their Magnum specific cams not 1.5

Chuck
 
I stand corrected on the Comp catalog. Looked at the listing for "Computer controlled EFI" cams and blew right past the the 85-92 year designation.
 
I know this is a old thread, but I wanted to update the status so others will know.

I currently have the magnum 318 in with a LA timing cover and cam extension on the stock cam so I can run the mechanical fuel pump. I used LA front accessories and a LA 360 oil pan for a car ( center hump ). I have a edelbrock 600cfm ( 1405) carb and the Air gap knock-off intake ( cross wind). With the 4.56's from the previous owner ( don't ask LOL) I ran a 14.40 at 86mph running out of gear at the 1000ft.
The only other mods are MSD 6AL, full exhaust including long tube headers and a decent built 904 with a 2800rpm stall. I just installed 3.55's so I can actually drive the car on the highway :-D and I will be taking it to the track soon.
 
Question 408dartman. Did the 360 oil pan work? I've heard they will but never got into it myself. Would just like to know.

Thanks, Tracy
 
408Dartman said:
Yes it did, just swapped over the correct pick tube and put it all together.
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what did you mean by the correct tube do you have the use the la tube or the magnum tube and does it have to come from a certain engine 318, 360 thanks Justin
 
jjr426 said:
what did you mean by the correct tube do you have the use the la tube or the magnum tube and does it have to come from a certain engine 318, 360 thanks Justin
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Justin I believe what he meant was he had to switch to the center sump tube. The truck engines only came with a rear sump oil pan and that won't fit in a car so you have to switch the pan and pickup to a center sump pan style. There's no difference in tubes between a LA or Magnum or any engine size. The pickup tube will fit any engine.
 
ok thanks for clearing that up that is exactly what i needed to know thanks alot fishy. justin
 
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