Cheap Magnum Heads and some porting

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JGC403

JGC403

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I want to try my hand at porting a set of Magnum heads I have. I would like to port them and put new valve seals on then slap them on my Duster and have a little fun for as cheap as possible.

I know that the magnum heads are prone to cracks in the combustion. So I don't want to dump a lot of money into these heads. I just want to use them to see what I can do.

The heads are out of my 1995 Jeep GC with the 5.2. The engine had about a 160,000 miles on it when I pulled it.

How do you tell if the heads need a valve job? I have a set of valve seals laying around somewhere so I might as well put them on. As soon as I'm done typing this I'm gunna finish disassembling the heads. So what should I look for as I'm doing it?


I pulled an intake and exhaust valve. The intake valve seat is shinny all the way around. The exhaust valve seat is wide compared to the intake. If you look close, i guess the best way to describe it is that its dimpled all the way around the seat.

O I also put the valves in a drill chuck, to check to make sure they weren't bent. So far they look straight.

Can I get away with just using some valve lapping compound on the seats?
 
If the exh seats are pitted they will need attention ie valve job. Have the valves faced, and back cut the intake valves. Don't be surprised if the exh valves wont clean all the way up on the face. I'm doing the same thing with a set of Magnum heads. Just some mild port work and a good valve job. Gonna use some Chevy LS retainers and Beehive springs.
 
I see people say they crack all the time but I just saw like my 6th pair not cracked. I have yet to find some cracked magnums. Now 302s are another story. lol
 
Yeah and I been jumped all over for sayin I aint seen any that were cracked. Like they thought it could only happen in my world or something. I'm sure it's simple coincidence.
 
Well maybe its worth getting them at least magnafluxed then. The shop that just finished building my 408 charges $96 to cook and mag a set of heads.
 
With 160K on the heads, I would suspect they'll need guides at a minimum. So long as the seating surface is concentric, lapping can improve sealing somewhat at the expense of widening the contact area. Guide clearance is typically the killer with high mileage heads.

But, if you want to experiment, port away, lap the valves and bolt them back on. It'll only cost you a gasket set and time. At the end of the day you'll just go from high mile heads to ported high mile heads
 
C130 Chief said:
At the end of the day you'll just go from high mile heads to ported high mile heads
Click to expand...

Lol, true.

I think that is what I'll do. If they turn out good. Then maybe someday I'll pull them off and have a valve job with larger valves and new guides.

Anyone know what the max lift is on a set of stock magnum heads? I thought I read it somewhere in one of my books but i can't find it now.

Also does anyone have a picture of a ported set of mag heads. Been trying to do a little research on where to clean them up. I have some ideas, but would like to know what other people have done.
 
JGC403 said:
Well maybe its worth getting them at least magnafluxed then. The shop that just finished building my 408 charges $96 to cook and mag a set of heads.
Click to expand...

Highway robbery I say.
 
JGC403 said:
Another shop wanted $155 to cook and mag a set of heads. Anyone know of a place that will do it cheaper in the Reading, PA area?
Click to expand...

Might call around,ask some of the local circle track/drag race guys.
 
Well this is what I have doe so far. I'm hesitant to take out to much metal. This is my first porting attempt and I'm not sure how much metal to remove.


This is what I started with:





I started with blending the valve throat into the as cast intake port. I know I don't want to open the valve throat itself. I'm using a dremel tool and a tapered grinding stone. I think I can go a little farther than what I did in these pictures. I know I want to leave the intake port surface rough though this helps keep fuel in suspension.





Then I moved into the combustion chamber. I radiused all of the sharp edges, to reduce the chance of any hot spots. I figured I will polish the combustion chamber to help reduce carbon build up.


 
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