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Discussion Starter · #1 ·
I have an '89 W100 w/ 318 TBI. I am planning on doing a conversion to the magnum top end. I want to use stock heads and intake. I'm not sure about the drivetrain though. I know I have hollow pushrods, but not sure about the lifters. I will have to get longer pushrods, the 7.625" length. I want to use the 1.7 rockers as well, but I would guess the rods that come with that kit are stock length. Everything I have read says that I have a hyd. roller cam which would mean hyd. roller lifters, but the recommended lifters are AMC type. To me it looks like those are not roller lifters. I think I will go with the HarlandSharp 1.7 roller rockers. Can anyone enlighten me on this project? Any and all help would be greatly appreciated. Thanks.
 

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I wouldn't do it, if anything i would get involved with the heads you already have, you do realize that you have to go with a different intake with those heads
 

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Well all im gonna say is i am no fan of those heads
 

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Well, the LA block isn't the same as a Magnum block. The bolts are in the wrong place. On the Mag they are vertical, and the LA they are slanted. Good luck, though
 

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Why not finda magnum block ? you do know Edelbrock came out with new Magnum heads that will not crack like the factory heads tend to do alot . So if you are wanting a magnum engine that is stout go this route .
 

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ramcharger_blue02 said:
Well, the LA block isn't the same as a Magnum block. The bolts are in the wrong place. On the Mag they are vertical, and the LA they are slanted. Good luck, though
The angle of the bolts has nothing to do with the block as the intake doesn't bolt to the block.
 

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The commando heads are good heads from MP with alittle porting there better than edels heads
 

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Discussion Starter · #12 ·
Just to clear up any confusion that may exist regarding my post. This is not just a Magnum cylinder head conversion. It is an entire top end Magnum conversion. I am changing engine computer, intake, heads, wiring harness, everything. I will be using a '89 LA block though.
 

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I don't know how your gonna use that roller lifter with that head, your gonna have to find out if it works if not i wouldn't use the mag set-up.
 

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Did you do a search in this board for this topic? It's been covered before. Here's one thread on Magnum/LA valve train issues. There's several more. You might get more info than "I don't like it."
 

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Just buy quality aftermarket hydraulic flat tappets and forget the roller lifters, all the companies make the pushrod oiling holes so they only have to stock one lifter that covers amc and mopar engines.
 

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txs said:
Just buy quality aftermarket hydraulic flat tappets and forget the roller lifters, all the companies make the pushrod oiling holes so they only have to stock one lifter that covers amc and mopar engines.
Don't do that, don't go backwards if anything forget that mag head and get a set of commando heads or something else, forget the stud mounted rockers and oiling thru the pushrods, forget heads altogether and just do alittle work in the heads you have now on your 89 and you will be happy.
Just out of curiosoty what gains do you think the mag head is gonna achieve as a bolt on, just so you know the mag flows worse than the x and j head in stock configuration and the RT mag head is good until .400 when it steadily drops off, the mag RT head is better only on the exhaust side, but then again were not talking about mag RT heads.
Do some work in the heads you have.
 

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Evildriver-3 said:
txs said:
Just buy quality aftermarket hydraulic flat tappets and forget the roller lifters, all the companies make the pushrod oiling holes so they only have to stock one lifter that covers amc and mopar engines.
Don't do that, don't go backwards if anything forget that mag head and get a set of commando heads or something else, forget the stud mounted rockers and oiling thru the pushrods, forget heads altogether and just do alittle work in the heads you have now on your 89 and you will be happy.
Just out of curiosoty what gains do you think the mag head is gonna achieve as a bolt on, just so you know the mag flows worse than the x and j head in stock configuration and the RT mag head is good until .400 when it steadily drops off, the mag RT head is better only on the exhaust side, but then again were not talking about mag RT heads.
Do some work in the heads you have.
Thats not true. Marty you are so against the magnum head but know little about them. I knew little about them till recently. THEY ARE NOT STUD MOUNTED! They have blocks that bolt to the head and the rocker moves on that. Its not a ball pivot like the chevy's. The pivot on the magnum is that block that mounts firmly to the head. The rocker arms on the magnum head are more firmly mounted then the chevy stud design and better then the previous shaft mount design. the magnum design dont alow any side movement like the rocker shaft design does so more high rpm stability. I didn't know any of this till recently. Next thing is they flow way better then the X and J heads. LA engines have poor exhaust flow and the magnum head cures that. Better flow balance between cylinders and and better ratio flow between intake and exhaust. This is all fact so no need to bring this all out in a long debated discussion. The problem with magnum heads are they crack.

As far as converting an older engine to magnum specs yoru better off geting a magnum engine. they made other changes such as adding a crank sensor which has a special provision on the back of the block for that. You need that for the computer. You should also change the front cover and go with the serpentine belt. cause the mounting holes on the magnum heads are different. So accesories on the older engines need some mods to bolt up right. You would need to use a magnum cam with and lifters with that if you want to keep rollar cam. Your fuel pump don't put out enough PSI either. TBI uses about 15 psi and magnums need 45 psi. The list goes on and on. Save yourself the hassle and just get a magnum engine.
 

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I said they flow better on the exhaust side, and this is all in stock form non ported heads but this is the RT head C300 not the run of the mill mag head, do some bench tests on them
lift .05 .10 .20 .30 .40 .50 .60
Stock 340X: 32 38 125 172 208 221 210 exh 22 45 95 122 135 140 142
915J Stock : N/A 66 123 170 206 220 216 exh N/A 63 110 135 145 148 148
137 Magnum 31 60 118 165 195 209 205 exh 23 54 99 131 167 138 138

This is an MP mag head not a factory head
140 Magnum R/T 34 70 137 181 209 211 211 exh 24 62 111 142 163 168 171
That is the mag head with the better exh flow.
 

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They all look pretty comparable on the intake side. I've seen two heads of teh same casting number vary by about 20 cfm in stock form. Things such as casting shift and and quality of the valve job can affect that. I know there is other numbers out there for magnum heads. I would have to dig them up. I do see that for some reason the stock magnum head spikes up to 167 at .400 lift. then drops back to 138. was that a typo?
 

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Ah sob im gonna have to wait till answering that maybe i copied it wrong.

On the rocker thing though ok you are right not exactly stud mounted but i don't think everyone is familar with a buick version rocker and olds rocker and it is closer to that with it's bolt and little trunion thing and it's need for guide plates, and when you start putting real cams in them there is a reason they go back to shafts, just like the gm motors do, but that is if your gonna want to get more than just some little gains, for a truck ok it's fine unless your gonna race the truck, but i don't like them for these reasons to me it's an added expense with just 2 more steps to being a useful head
 
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