Magnum heads on LA block H.p increase

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Slantsix64

Slantsix64

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So been thinking a about magnum head swap on my 318. I already have a roller camshaft in this pre magnum block. My carb will be a 600cfm Carter AFB intake will be an rpm air gap. The heads on there now are 302 casting. I was hoping the bigger valves better flow and lift increase due to 1.6 ratio rockers would gain me at least 30-40 H.p what are your guys experiences!


Magnum heads.
Better flow.
1.92 1.65 valves.
62cc.
1.6 rocker ratio.
Closed Chamber



302 heads
Stock valves 1.78 1.50
64cc
1.5 ratio
Close chamber
 
A 300hp crate engine is a stock cammed 5.9l truck longblock and dynos 320 hp with 4bbl and headers 300 hp without headers can't see a 318 being too far behind that.
 
300 hp crate engine dyno results (the mod is like eddy heads and a comp 275 roller on the stock shortblock), 318 might be a few hp shy and peaking a few hundred rpm higher.


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My question would be...... do you have a set of serviceable uncracked Magnum heads already in your possession?
 
I have a pair. I sure don't see any cracks
Some headbolts and pushrods too.
 
I’m guessing it would even be better than 30-40 hp, they seem to give that over 1.88 360 heads never mind 1.78 318.
 
273 said:
I’m guessing it would even be better than 30-40 hp, they seem to give that over 1.88 360 heads never mind 1.78 318.
Click to expand...
Im getting ready to do this swap, should i take the roller lifters and push rods off the magnum block as well,

or just use my roller lifters in my 89 318 block?

i was thinking of just swaping everything over along with the heads
 
Slantsix64 said:
So been thinking a about magnum head swap on my 318. I already have a roller camshaft in this pre magnum block. My carb will be a 600cfm Carter AFB intake will be an rpm air gap. The heads on there now are 302 casting. I was hoping the bigger valves better flow and lift increase due to 1.6 ratio rockers would gain me at least 30-40 H.p what are your guys experiences!


Magnum heads.
Better flow.
1.92 1.65 valves.
62cc.
1.6 rocker ratio.
Closed Chamber



302 heads
Stock valves 1.78 1.50
64cc
1.5 ratio
Close chamber
Click to expand...
All i can say is buy new.
Mag'ems will out perform ootb 302 heads no problem.
 
273 said:
I’m guessing it would even be better than 30-40 hp, they seem to give that over 1.88 360 heads never mind 1.78 318.
Click to expand...
You saying you think magnum heads will make 30-40hp more than a 1.88 j head on a 360?
I think maybe 20hp.

How much hp increase in your opinion by putting ported 1.92/1.94 eq heads in place of stock mag'ems?
 
From what is written, the valve stems are a little smaller, they flow a little better, and the chamber is smaller and more efficient. But is it worth the extra parts you need to make the conversion work?
 
toolmanmike said:
From what is written, the valve stems are a little smaller, they flow a little better, and the chamber is smaller and more efficient. But is it worth the extra parts you need to make the conversion work?
Click to expand...

i think so, pretty much got a rebuilt magnum block for 150.00 bucks off my buddy
30-40 H.p for 150.00 bucks and some effort im down for that lol
 
I was going to just run the whole motor but my 89 318 roller already has a sweet camshaft in it, probably a day or two and im back on the road swapping heads, i can sell my old intake and 302 heads as well
 
MOPAROFFICIAL said:
You saying you think magnum heads will make 30-40hp more than a 1.88 j head on a 360?
I think maybe 20hp.

How much hp increase in your opinion by putting ported 1.92/1.94 eq heads in place of stock mag'ems?
Click to expand...
i think he meant 30-40 h.p over the 302 heads with 1.78 valves
 
MOPAROFFICIAL said:
You saying you think magnum heads will make 30-40hp more than a 1.88 j head on a 360?
I think maybe 20hp.

How much hp increase in your opinion by putting ported 1.92/1.94 eq heads in place of stock mag'ems?
Click to expand...
if you got eq heads you gonna rock
 
MOPAROFFICIAL said:
You saying you think magnum heads will make 30-40hp more than a 1.88 j head on a 360?
I think maybe 20hp.

How much hp increase in your opinion by putting ported 1.92/1.94 eq heads in place of stock mag'ems?
Click to expand...

I did mean stock there worth 30-40 hp
The main power increase from LA 360 to Magnum were from the heads and the little bump in CR the cam is pretty similar between the two. We know the magnums can do over 400 hp stock, I haven't seen stock 1.88 heads do that maybe 380 hp, ported Ive always heard LA does better but stock seems the Magnums respond well to basic cam 4bbl headers, Not saying I'm right but that's how I've heard and seen it so far. Would be nice to see a basic shootout same cam intake on La 360vs roller 360vs magnum.
 
273 said:
I did mean stock there worth 30-40 hp
The main power increase from LA 360 to Magnum were from the heads and the little bump in CR the cam is pretty similar between the two. We know the magnums can do over 400 hp stock, I haven't seen stock 1.88 heads do that maybe 380 hp, ported Ive always heard LA does better but stock seems the Magnums respond well to basic cam 4bbl headers, Not saying I'm right but that's how I've heard and seen it so far. Would be nice to see a basic shootout same cam intake on La 360vs roller 360vs magnum.
Click to expand...
Yeah and I'd like to see a j head fitted with 8mm 1.92 valves and see it's not most of why they make more ...To believe the chamber 'that varies in size from the factory' is worth that much power..eh.
Consider this
Almost every advertised chamber volume , like 99% have been misleading.
The only heads to hold true are the 302 @64cc in all of the cores I've checked.
Mags vary 3 cc and usually to the big.
In fact almost all are to the big side.
906 late castings and others can be huuuuge. The x heads I have held onto have had 5 valve jobs since I've owned them with a light mill and are still 68cc from printed 69cc...lol total bullshit. 273 heads 66cc, 318 heads 675 68cc stock, 163 and all other smog open chamber.. 72, as big as a 360. The head they sell as aftermarket are 62cc and really are...till you open the chamber for the 2.02 and bore size, cut the top angle ,chamber blend the wall side and short turn side as well the exhaust... then they hit 65-66cc... and you have to mill them near .025 to get to 60-61 cc.
That's a good idea to cast small for that alone. Sure bigger valves actually fill the chamber and eat up volume..but when it comes to a closed chamber head ..making them work for you means opening up the chamber around those valves. Open is a drop in and eat up around 3cc's instantly going from 72 to 69..then the basic mill of an old crust head.. .004 or .005 ...67.8-68 'accounting for loose factory average chamber size'.
All I know is that stock magnum isn't very dependable. These were cracked for a long time. I added water every month to the overflow tank. ..about 6 yrs. End exh seats were sunk .060.. football field seats..geometry was bad from the factory valve tips all worn .030 in from the exh side off the edge of the inside..and only got worse with wear... no valves were spinning ..burnt exhaust valves.
Oh yeah... what were we talking about again? :D

20210813_190639.jpg


20210813_190626.jpg


20210813_190653.jpg
 
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Best I remember from the magazine articles is that the big difference between the LA and Mag heads was the exhaust port and the balance between the intake and exhaust flow. Maybe it was a trumpted up reason they spoon fed to less than knowledgeable magazine readers (like me), but it's what I remember.

I will have to go back and look, seems like I remember having an article where they dyno'ed a 318 with LA heads and then swapped to Mag heads. Seems like 30-40 hp was the result.
 
DionR said:
Best I remember from the magazine articles is that the big difference between the LA and Mag heads was the exhaust port and the balance between the intake and exhaust flow. Maybe it was a trumpted up reason they spoon fed to less than knowledgeable magazine readers (like me), but it's what I remember.

I will have to go back and look, seems like I remember having an article where they dyno'ed a 318 with LA heads and then swapped to Mag heads. Seems like 30-40 hp was the result.
Click to expand...
Mag'em heads perform better than LA 318 heads.
Mag'em heads perform better than 1.88 valve 360 LA heads.
Mag'em heads do not perform better than "all" LA heads. 340 X, 2.02 J 915 head, J 974 even has killer exh ports and with a serdi will make the numbers a mag will and survive doing it. 308 head is another serdi candidate with great exhaust ports and int port.
But aside from those limited year pieces...the mag'em is a better performer.
They 'magems' are a great idea or design , in ways, but somewhat cheaply/poorly executed by the factory...however the aftermarket got it right...and that's where I would source them... but imo they need to offer a shaft mount version again with a multi intake pattern or choice of.
I like the vertical bolt design.. its just that some of my favorite intake manifolds can't play with them.
 
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MOPAROFFICIAL said:
Mag'em heads perform better than LA 318 heads.
Mag'em heads perform better than 1.88 valve 360 LA heads.
Mag'em heads do not perform better than "all" LA heads. 340 X, 2.02 J 915 head, J 974 even has killer exh ports and with a serdi will make the numbers a mag will and survive doing it. 308 head is another serdi candidate with great exhaust ports and int port.
But aside from those limited year pieces...the mag'em is a better performer.
They 'magems' are a great idea or design , in ways, but somewhat cheaply/poorly executed by the factory...however the aftermarket got it right...and that's where I would source them... but imo they need to offer a shaft mount version again with a multi intake pattern or choice of.
I like the vertical bolt design.. its just that some of my favorite intake manifolds can't play with them.
Click to expand...


<<shrug>> Don't know.

I did look for the article and either I found a different one or I am remember wrong they didn't do a back to back test.
 
MOPAROFFICIAL said:
Yeah and I'd like to see a j head fitted with 8mm 1.92 valves and see it's not most of why they make more ...To believe the chamber 'that varies in size from the factory' is worth that much power..eh.
Consider this
Almost every advertised chamber volume , like 99% have been misleading.
The only heads to hold true are the 302 @64cc in all of the cores I've checked.
Mags vary 3 cc and usually to the big.
In fact almost all are to the big side.
906 late castings and others can be huuuuge. The x heads I have held onto have had 5 valve jobs since I've owned them with a light mill and are still 68cc from printed 69cc...lol total bullshit. 273 heads 66cc, 318 heads 675 68cc stock, 163 and all other smog open chamber.. 72, as big as a 360. The head they sell as aftermarket are 62cc and really are...till you open the chamber for the 2.02 and bore size, cut the top angle ,chamber blend the wall side and short turn side as well the exhaust... then they hit 65-66cc... and you have to mill them near .025 to get to 60-61 cc.
That's a good idea to cast small for that alone. Sure bigger valves actually fill the chamber and eat up volume..but when it comes to a closed chamber head ..making them work for you means opening up the chamber around those valves. Open is a drop in and eat up around 3cc's instantly going from 72 to 69..then the basic mill of an old crust head.. .004 or .005 ...67.8-68 'accounting for loose factory average chamber size'.
All I know is that stock magnum isn't very dependable. These were cracked for a long time. I added water every month to the overflow tank. ..about 6 yrs. End exh seats were sunk .060.. football field seats..geometry was bad from the factory valve tips all worn .030 in from the exh side off the edge of the inside..and only got worse with wear... no valves were spinning ..burnt exhaust valves.
Oh yeah... what were we talking about again? :D

View attachment 1715782643

View attachment 1715782644

View attachment 1715782645
Click to expand...
How many miles were on the magnum engine your heads came off of?

What is the stock intake port volume on a magnum head? What is the stock intake port volume of a X or J head? If memory serves correct the magnum has very good port efficiency?

The Crack between the seats doesn't hurt performance but it does short the valve job life. I never seen any of the magnum heads leak antifreeze through the cracks between the seats. That motor must have been over heated a time or 2 for them to be leaking antifreeze into the cylinder bore. Might be why the valve stems are burned also.

The story is usually that some one bought a good running magnum to do a swap then decided to freshen the engine and then all of a sudden they find the heads cracked between the seats and think they are junk
 
jammied said:
How many miles were on the magnum engine your heads came off of?

What is the stock intake port volume on a magnum head? What is the stock intake port volume of a X or J head? If memory serves correct the magnum has very good port efficiency?

The Crack between the seats doesn't hurt performance but it does short the valve job life. I never seen any of the magnum heads leak antifreeze through the cracks between the seats. That motor must have been over heated a time or 2 for them to be leaking antifreeze into the cylinder bore. Might be why the valve stems are burned also.

The story is usually that some one bought a good running magnum to do a swap then decided to freshen the engine and then all of a sudden they find the heads cracked between the seats and think they are junk
Click to expand...
Cracks between the seat hurt performance because they leak shortly after forming and that's lost pressure and a burnt valve...because they grow.
Head gasket was fine, No I never overheated it. Cracks in the seat can slowly siphon out coolant..head gaskets that loose fire ring and combustion leak are what puts pressure into the cooling system.
150cc vs LA 2.02 155cc and 1.88 160cc
That easy, the pushrod pinch is near closed compared to the LA , that's 5 cc right there.
 
Hmmmm I thought X and J heads had 175cc intake runner?

Don't get me wrong. It's been awhile since I had one in front of me but is there a coolant passage between the valves?.

So unported la heads will flow 200cfm just by installing larger valves? Other than big valve X And J heads that do flow 200cfm but through alot larger port.

I did have alot of la 360 heads that were cracked and running coolant into the cylinder.
Guess I would have to see dyno and track numbers cracked vs non cracked. Of course this is if they are cracked between the seats. I have seen Utah awesome on there website dynoed a truck with cracked heads. Still never seen a magnum head leak coolant from the Crack between the seats
 
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