Magnum heads on an LA enigine

-
B

Brian Hood

Well-Known Member
Joined
Jan 10, 2009
Messages
128
Reaction score
0
I am thinking about using 97 Magnum heads on an older 318 LA. I have read that they do give more power. Has any one done this? I wonder how much more power? 10 , 15 HP or is it good for 5 or less hp? Let me know if anyone has done this and if its worth the money it takes.
Thanks!
Brian
 
Hundreds, if not thousands of people have done this swap. I did it last summer on my '73 360. There is info all over this forum and all over the web about it. They are a little better in that they have closed chambers and the exhaust port flows much better than the old LA heads. The closed chambers will up your compression, which you will definitely feel. Do some searching around; "magnum head swap" .
 
You can't actually say how much hp you'd gain because there are too many other variables but they should make more power for the reasons wish4hemi said.
 
Here's a website with lots of info.

http://www.dippy.org/forum2/index.php/topic,295.0.html

I have the parts you may need listed in this post.

http://www.forabodiesonly.com/mopar/showthread.php?t=87995

I don't think anyone has done a dyno test on a stock engine and then installed the magnum parts for a comparison so how much horsepower does the conversion gain? A stock 318- 2 barrel usually puts out 230 horse and with the magnum heads and a 4 barrell , headers, and a good cam, you can get close to 400 hp. Mopar Muscle did a 400 hp 318 with magnum heads. Here's the link:

http://www.moparmusclemagazine.com/techarticles/mopp_0409_318_engine_build/index.html
 
According to comp cams desktop dyno my magnum headed LA 318 is making 320-330 hp and 350-360 lb tq. That is with a smallish 256 cam, but my bottom end is flat top pistons and it put my compression ratio about 9 to 1 using .026" head gaskets. Magnums also come stock with stamped 1.6 rockers so you can take advantage of a little more lift. Runs good for a 318.
 
There you go Brian, A 2 barrell stocker puts out 230 hp and a mild Magnum head motor puts out around 325 hp. Badart's desktop dyno tells the story.
 
Your not exactly comparing apples to apples there when comparing a stock 2 barrel LA 318 to a Magnum headed 318 with a (I'm guessing) 4 barrel carb, better intake, much more aggressive cam, headers and good flowing exhaust. Possibly higher compression also. Desktop dyno is only as good as the information input to it and even then it's not perfect. In other words a bunch of things can affect it's output and it's usually on the order of 5% higher than you'll actually get. To make the comparison apples to apples you'd need to use the same cam (except add a little more lift cause magnum rockers are 1.6 ratio), carb and intake, headers and exhaust but change just the heads and see what happens. You also need very reliable flow numbers for each head and input the correct valve sizes for each on not only the main screen but on the head flow file.
 
You're absolutely correct Fishy. No apples to compare here. The desktop dyno is just a guideline and the results aren't gospel but they are a general estimate. But, the results give you a good idea of what's going on. I don't remember anyone taking a stock engine and just installing the Magnum heads with dyno tests before and after for a true comparison. So Brians original question can't truthfully be answered until someone does a comparison. The reason why Mopar Muscle used
Magnums is because they were easy to come by, they have a small combustion chamber that will raise compression, they flow well and respond well to light porting, they have 1.6 rockers for more lift, small valve stems, through the pushrod oiling, and the list goes on and on. toolman
 
Thank you everyone for your suggestions and comments. I will process this and post my finding.
Brian
 
toolmanmike said:
You're absolutely correct Fishy. No apples to compare here. The desktop dyno is just a guideline and the results aren't gospel but they are a general estimate. But, the results give you a good idea of what's going on. I don't remember anyone taking a stock engine and just installing the Magnum heads with dyno tests before and after for a true comparison. So Brians original question can't truthfully be answered until someone does a comparison. The reason why Mopar Muscle used
Magnums is because they were easy to come by, they have a small combustion chamber that will raise compression, they flow well and respond well to light porting, they have 1.6 rockers for more lift, small valve stems, through the pushrod oiling, and the list goes on and on. toolman
Click to expand...

That's right Mike. Desktop dyno is a decent tool for comparisons if you have all your figures right.
 
And the more info you have, the closer the results would be. I entered the specs of my stock HP 273 and came up with 234 hp (it's supposed to have 235)
Thy must use the stock specs as a guideline and build from there. Mike
 
The number I hear most often is swapping magnum heads onto a 360 with no other changes is worth 20 HP. A 318 wouldn't be as much.

I am using magnum heads on an LA 360 but the engine was built with the heads in mind. The biggest advantage is the closed chambers, they allow you to run higher compression without the fear of detonation. My engine has zero decked flat top pistons and an 0.039" thick head gasket for a compresion ratio of 10.6:1 and it runs fine on 89 octane. I don't have a big cam either that bleeds off a lot of cylinder pressure. I just did a compression test last weekend and I have 190-205 psi of cranking pressure (compared to 185-195 when I first built the engine, maybe a little build up in the chambers or a better seal on the rings now).
 
You must log in or register to reply here.
-

Back
Top