Magnum heads on 360 LA

Posted By: Mapandjlp

Magnum heads on 360 LA - 04/28/10 02:46 AM

I've been trying to figure out the best way to build the 360 for my Challenger. I'm considering magnum heads but have a couple of questions.

First - are the holes for mounting the PS pump, A/C, and Alternator bracketry the same as the LA heads?

Second - any thoughts on what effect they'll have on compression ratio on my '75 360 if I stick with the stock pistons?

Thanks, Guys! If anyone can help, I know you all can.

Posted By: volaredon

Re: Magnum heads on 360 LA - 04/28/10 02:49 AM

it will improve the CR. and when I put the "EQ" Magnum heads onto my 83 318 truck engine everything bolted up fine.

Posted By: RapidRobert

Re: Magnum heads on 360 LA - 04/28/10 03:19 AM

my unmilled mags were 63 cc's

Posted By: Mapandjlp

Re: Magnum heads on 360 LA - 04/28/10 03:33 AM

Quote:

my unmilled mags were 63 cc's

Any idea what the standard '75 360 head cc'd at?

Posted By: Prince_Valiant

Re: Magnum heads on 360 LA - 04/28/10 03:36 AM

iirc b/w 68-72cc's.

Posted By: Evil_Ways

Re: Magnum heads on 360 LA - 04/28/10 04:12 AM

If your going to use Magnum heads, spend the cash and get the EQ ones that are always on E bay. You can even get them already drilled for LA intakes if you already have an LA intake.
The stock ones are prone to crack right between the intake and exhaust valves. I made the mistake of buying some freshly rebuilt stock ones and ended up with a pair of giant paper weights.

Posted By: 70AARcuda

Re: Magnum heads on 360 LA - 04/28/10 06:40 AM

http://www.hughesengines.com/Index/produ...mp;partid=25702

$699 ready to go with LA intake..or they are also available with magnum intake..

Posted By: Kern Dog

Re: Magnum heads on 360 LA - 04/28/10 07:15 AM

Regarding the "Large Paperweights" cracked heads....What caused you to remove them? Did you blow a head gasket or get leaks into the cooling system? I passed on several junkyard heads when I saw that they were cracked. My machinist said that in most cases, the cracks would pose no problem. I didn't want to risk it.

Posted By: gdonovan

Re: Magnum heads on 360 LA - 04/28/10 10:23 AM

Quote:

Regarding the "Large Paperweights" cracked heads....What caused you to remove them? Did you blow a head gasket or get leaks into the cooling system? I passed on several junkyard heads when I saw that they were cracked. My machinist said that in most cases, the cracks would pose no problem. I didn't want to risk it.

As a retired Chrysler line tech I can't recall a single magnum 5.2 or 5.9 that was in the shop for a problem caused by cracked heads.

Intakes plates sucking oil yes, cracks in the head causing a problem no.

Like anything in life I'm sure it caused someone a problem but working on thousands of Dodge rams at Linder Dodge we never ran across it.

IMHO

Gary

Posted By: patrick

Re: Magnum heads on 360 LA - 04/28/10 11:00 AM

Quote:

I've been trying to figure out the best way to build the 360 for my Challenger. I'm considering magnum heads but have a couple of questions.

First - are the holes for mounting the PS pump, A/C, and Alternator bracketry the same as the LA heads?

Second - any thoughts on what effect they'll have on compression ratio on my '75 360 if I stick with the stock pistons?

Thanks, Guys! If anyone can help, I know you all can.

with stock pistons and if you can find the thin (.028") head gaskets, you'll be about 8.75:1 with magnum heads. the hughes ones for $699/pr is the best deal around, as they have springs that'll handle a nice hydraulic roller or solid flat tappet up to about .540" lift.

the accessory holes are in the same location as the LA heads, but they are all on the same plane, wheras the LA's lower hole is rearward by like 3/4" or 1". I had to modify my alternator bracket to fit. also, the front shape of the head is slightly different, and interfered with the back of the alternator, and I had to space all my accessories out about 1/8".

Posted By: dmerc

Re: Magnum heads on 360 LA - 04/28/10 11:18 AM

I used Magnum heads, Weisco dished pistons to get tight quench and a 4 inch crank. I'm very happy with the results

Posted By: Mapandjlp

Re: Magnum heads on 360 LA - 04/28/10 08:41 PM

Quote:

I used Magnum heads, Weisco dished pistons to get tight quench and a 4 inch crank. I'm very happy with the results

Did you have to do any other work to the block to use the 4" crank? No clearancing? What rods did you use?

Posted By: radar

Re: Magnum heads on 360 LA - 04/28/10 09:23 PM

My 4" crank cleared with eagle sir rods- they have the ARP capscrews. I think nut and bolt setups or H-beams need notching.

Posted By: dmerc

Re: Magnum heads on 360 LA - 04/29/10 12:39 AM

Quote:

Quote:

I used Magnum heads, Weisco dished pistons to get tight quench and a 4 inch crank. I'm very happy with the results

Did you have to do any other work to the block to use the 4" crank? No clearancing? What rods did you use?

Nope, no grinding on anything. I too used the SIR rods and as a bonus I was able to neutral balance the crank without using any mallory metal.

Posted By: HEMIDOG 70

Re: Magnum heads on 360 LA - 04/29/10 01:01 AM

I guess I'm the odd case then. My 98 5.9 ram had cracks between the intake and exhaust valves on both heads. #1&7 also #2&8. The truck would miss and coolant bottle would drop slowly over time. I finally snapped a spark plug off in the head trying to remove it. Thats when I decieded to replace the heads. The truck only had around 35000 miles on it when this happened. It was out of warrenty by time not miles. Chrysler offered nothing to help

When I called them they said no problems they are aware of. I said thats funny the local rebuilder says most sets they see are all cracked between the valves. The truck now has about 86000 miles so far so good. The reman heads I put on were repaired in this same area.

Posted By: RapidRobert

Re: Magnum heads on 360 LA - 04/29/10 02:18 AM

Quote:

Nope, no grinding on anything. I too used the SIR rods and as a bonus I was able to neutral balance the crank without using any mallory metal.

Which 4" crank and do you remember the bobweight?

Posted By: Evil_Ways

Re: Magnum heads on 360 LA - 04/29/10 04:58 AM

Quote:

Regarding the "Large Paperweights" cracked heads....What caused you to remove them? Did you blow a head gasket or get leaks into the cooling system? I passed on several junkyard heads when I saw that they were cracked. My machinist said that in most cases, the cracks would pose no problem. I didn't want to risk it.

Actually I never even installed them. I bought them from someone who had them on a freshly rebuilt motor (maybe 1500 - 2000 miles on them) and then decided to go with some edelbrocks and a bigger motor. After reading about so many people getting magnum heads and then finding out they were cracked. I took mine to my usual machine shop just for some piece of mind.
They called me back and said they were BOTH cracked right between the intake and exhaust valves. They said they see alot of the magnum heads come in and that's the spot they always crack. Something about a thin spot in the castings.

Posted By: dmerc

Re: Magnum heads on 360 LA - 04/30/10 10:26 AM

Quote:

Quote:

Nope, no grinding on anything. I too used the SIR rods and as a bonus I was able to neutral balance the crank without using any mallory metal.

Which 4" crank and do you remember the bobweight?

Pretty sure it was an Eagle cast crank and the bob weight total was 1760 grams.

Posted By: RapidRobert

Re: Magnum heads on 360 LA - 04/30/10 01:44 PM

Quote:

Pretty sure it was an Eagle cast crank and the bob weight total was 1760 grams.

thank you Dmerc and I have an Eagle cast 4" crank.

Posted By: HotRodDave

Re: Magnum heads on 360 LA - 05/01/10 05:21 AM

the eagle cast cranks balance very easily because they leave out critical weight in important places on the rod journal side of the crank, particularly the front journal overlap area, seen quite a few break in extremely mild engines

Posted By: RapidRobert

Re: Magnum heads on 360 LA - 05/01/10 01:56 PM

Quote:

the eagle cast cranks balance very easily because they leave out critical weight in important places

alright, it's going into a 406 build for a daily driver torque eng in a 65 dart as I just ain't gettin enough respect w the stock 318. I'll show em

. thanks Dave for the heads up I will keep it mild (sort of)

Posted By: dmerc

Re: Magnum heads on 360 LA - 05/02/10 12:39 AM

Quote:

the eagle cast cranks balance very easily because they leave out critical weight in important places on the rod journal side of the crank, particularly the front journal overlap area, seen quite a few break in extremely mild engines

I noticed this very thing when I had my machinist balanced my crank. He didn't seem concerned though... But they are scary thin in spots. Hope mine doesnt grenade soon

So far so good though

I wonder what happens when a crank breaks like that. Maybe it's not as bad as a thrown rod

Posted By: HotRodDave

Re: Magnum heads on 360 LA - 05/02/10 02:26 AM

Quote:

Quote:

the eagle cast cranks balance very easily because they leave out critical weight in important places on the rod journal side of the crank, particularly the front journal overlap area, seen quite a few break in extremely mild engines

I noticed this very thing when I had my machinist balanced my crank. He didn't seem concerned though... But they are scary thin in spots. Hope mine doesnt grenade soon So far so good though I wonder what happens when a crank breaks like that. Maybe it's not as bad as a thrown rod

Just depends on the RPM it is running when it breaks and if you got the pedal to the medal or letting off and how fast you shut it off, same goes for rod break or crank break

FWIW the last time I saw one of those cranks break it was in a 408 with untouched magnum heads 21cc dished pistons stock cam and manifolds and all, he just wanted more tq but the eagle cast crank broke right there by the front at low speed, a few bent valves a new SCAT cast crank and he tossed the eagle rods in favor of SCATs this time and all is good. His motor could not have made more than 400 hp MAX and was not even doing that when it broke. On top of the thin spot common to them all, it also had a bubble in the casting that I suppose weakened it but no way of knowing it was there before hand.