Magnum heads

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RPMLegends18

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Hi guys,
I having been thinking about doing the Magnum head swap onto my 318, the block has a casting date of 12/27/1968 or maybe the 12/28/1968. Anyways its a 68 block. I have been reading tech archives and many things before I try and attempt this project but then I was reading one archive that states this," The lifter bosses in a roller block are approximately 0.40” taller than a non-roller block. Since the roller lifter is much taller than a standard hydraulic, the taller boss in necessary to keep the oil holes covered at max lift. Otherwise you will have little or no oil pressure. The lifter bores *could* be bushed taller, but that is getting a little more involved than most guys want. Retrofit roller lifters ARE available but are kind of expensive. CAT has listed retrofit rollers on their site, but are not yet available." And my guess would be that my block is not a "roller block" at least I dont think. I am not too familiar with all that. The cam that is in it is a MP P4120231 which is a hydraulic flat tappet cam. It also came with MP lifters.
I am pretty sure the block was decked, but not sure if it was zero decked. It was a 340 crank, stock rods, and flat top pistons. The tops of the pistons are pretty close to being flush if I remember correctly, I know that sounds pretty stupid... This wasnt a performance build, but I would like to get a little more HP out of it.
So my two questions are; one, will my block be able to support this without having the lifter bores bushed higher. And two, is my setup going to hold up...like the lower end and pistons? Its a street car, that after going to a couple drag races, I would like to take it down the track every now and then and get some decent passes. I read the 400 HP build with Magnum heads on a 318 and that got me really interested. So those my questions and thank you for reading and for the possible help.

Thanks,
Ryan

added** the block has also been cleaned up to .030
 
The roller blocks came out in the mid 80's so you don't have a roller block. The bottom end of a 318 is stout enough for 400 hp. with a cast crank. I would stay away from the nitrous though. No since in pushing your luck. I have a collection of parts necessary for the Magnum head conversion: heads with valves and seats ground with new Mopar Performance springs,retainers and keepers, Air Gap intake, Mopar Perf. black Magnum valve covers,Comp Cam,
(I'd have to look up the specs), MP lifters and special pushrods. Let me know if I can help. toolmanmike
 
Your block will not handle the roller lifters unless you have the roller cam ground on a smaller base circle, there is a thread on this somewhere here where a guy tried a retro fit roller cam and lifters and the lfters cam up to far which led to the above warning/problem of oil lose.
 
So if I were to install a flat tappet cam I wouldnt need to worry about that? In the build specs it says that they are using a Comp Cams 280H Magnum hydraulic flat-tappet cam. They also say that they are using the engine out of their 68 Barracuda fastback. Doesnt say if its a later year block but I am assuming its a 68 block. So with that cam would I still need to worry about low/no oil pressure? And I will defiantly keep you in mind toolmanmike. And if thats not the case of solving the low/no oil pressure what is the cure? Special lifters? Are those the ones you are referring to toolmanmike? The MP lifters? I guess I kinda need a list of what is needed, if I can please. Because I was looking through the MP catalog for the Magnum head conversion and it says to use Jeep tappets (P4529220AB). Now Im guessing the tappet is the "proper" name for lifters?

Thanks,
Ryan
 
I answered within the quote below;
RPMLegends18 said:
So if I were to install a flat tappet cam I wouldnt need to worry about that?
Click to expand...
Correct.

So with that cam would I still need to worry about low/no oil pressure?
Click to expand...

You mean the Comp Cam 280 H? No worries. Why would you worry? It's a Hyd. cam just like the factory used.

And if thats not the case of solving the low/no oil pressure what is the cure?
Click to expand...
You'll have no issue with oil pressure due to the cam, or it's tappets, however, if you have low oil pressure it could be alot of things. If you have low oil pressure now, don't swap the cam.

Special lifters?
Click to expand...
Oil through pushrod lifters
The MP lifters?
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Mp sells the lifters. Most aftermarket companys sell Mopar lifters that oil through the pushrods without telling the MoPar guys that they do.

I guess I kinda need a list of what is needed, if I can please.
Click to expand...
The Mopar books used to list all parts needed for the conversion.


Because I was looking through the MP catalog for the Magnum head conversion and it says to use Jeep tappets (P4529220AB). Now Im guessing the tappet is the "proper" name for lifters?
Click to expand...

Yep, alllways was,
 
Thank you for the reply Rumblefish, as of now the engine, once its fully warmed up is around 59-60 psi of oil pressure under normal driving conditions. I am assuming this is normal operating range. Its not a high volume oil pump. It is just a standard Melling oil pump, so I think that is all gravy there. So the Comp Cams 280H, pushrods, and lifters then I will be set, of course the heads, valve springs, retainers...all that and I should be good to go. Well also what about exhaust? I am running exhaust manifolds, I read the Magnum heads dont have the point at the bottom of the exhaust port. Will the manifold cover the exhaust port or will I be looking at getting a set of headers again?
 
There is a port mismatch between the small port magnum head and the large port 340 exhaust manifold, if that is what you have. When I did mine , I made a 16 gauge steel plate that had a magnum port hole with the large exhaust o.d.
 
Well we have a set of 340 manifolds but I am running 318 manifolds now. The 340 looked way to big for the exhaust port on the 318. But I have both sets so I will check the size and see if I need to do what you did Bob. So its a 16 gauge piece of steel thats sandwhiched between the manifold and head? Thats how I am picturing it in my head. And I will have to check the pushrod length as well, to make sure. I know I will need a new set that oils through the pushrods. Mine are the stockers.
 
I run that exact cam in my LA 360 with Magnum heads. I think it might be a little to much cam for a basicly stock 318 though. If you decide to stay with that cam I would recommend a set of headers to help get rid of exhaust gasses. As far as the oiling goes, a stock set of AMC lifters work fine and are cheap. The push rod problem can be solved by mocking up the heads on the block and using an adjustable pushrod to determine the length of the pushrod you need and then ordering pushrods of the correct length. Remember you will have to use a Magnum intake.

Jack
 
All the parts I pm'd you about are correct for the conversion. I got the part numbers from the "How to Build Big Inch Mopar Small Blocks" book. toolman
 
From what I have researched about the retrofit roller lifters the problem with the low oil pressure comes from the block itself. Hughes has a good example of the different lifter bores found on the LA smallblocks. I talked to hughes and they told me that all the blocks will work, you just have to run a smaller cam. here is a link to the issue with the LA blocks.


http://www.hughesengines.com/Index/...ZW5naW5lcw==&level1=TGlmdGVycw==&partid=11035
 
If the block has been decked the listed MP pushrods may not work. Ask me how I know after wiping out a cam. Go on the safe side and measure the length of pushrod you will require.

Jack
 
Coyote Jack said:
If the block has been decked the listed MP pushrods may not work. Ask me how I know after wiping out a cam. Go on the safe side and measure the length of pushrod you will require.

Jack
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Good point Jack. Anytime machine work is done that could change clearances
every part effected should be checked for proper fit. toolman
 
Also, the ratio of the stock Magnum rocker arms is 1.6; the LA motor is 1.5. Account for the difference in lift. I don't know the specs for the 280 cam but for example my cam has .480 lift--with the magnum rockers it is now .501. Just checked, we have the same cam.
 
RPMLegends18 said:
Well we have a set of 340 manifolds but I am running 318 manifolds now. The 340 looked way to big for the exhaust port on the 318. But I have both sets so I will check the size and see if I need to do what you did Bob. So its a 16 gauge piece of steel thats sandwhiched between the manifold and head? Thats how I am picturing it in my head. And I will have to check the pushrod length as well, to make sure. I know I will need a new set that oils through the pushrods. Mine are the stockers.
Click to expand...

Yep, you got it. I have no exhaust leaks.
 
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