Magnum replacement heads

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The Mopar magnum valve stem size isn’t really “correct” for 5/16” or 8mm.

For “stock replacement” valves, the stems are listed as .3115.
8mm is .3150.
So if the guide were exactly 8mm the clearance would be .0035”. Too loose.
5/16” is .3125”...... which would yield .0010” clearance. Too tight.

By comparison, a stock replacement LS valve, which are also 8mm, has a stem diameter of .3136.
The guide bore is listed as .3154...... clearance is .0018”....... perfect.

So, it seems the aftermarket magnum heads are using “standard” 8mm sizing...... which isn’t what the factory used.

Someone wasn’t paying attention when they specified the guide sizing on the new heads.
Ideally the guides would be .3125-.3130, so that the final sizing could be set by the shop finishing the heads with a simple honing.

Fortunately(?) installing liners will allow you to set the guide clearance to what you want.

As for the flow, I can’t help you with that without having one here to test.

As a side note, I had a set of lightly used EQ’s in the shop here a couple years ago(I rarely ever see any magnum stuff).
The guide clearance was pretty loose, and the guide bores were very rough and poorly finished. They got a set of 16 liners installed.
 
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So I think my plan is to put in guide liners, for a 8mm valve, and put a 2.0 intake valve in, hopefully have a little more room to get the seat and top cut shaped a little better. Its cut for a 1.920 as is. And leave exhaust at 1.620
 
I guess the other question is, how much power are you trying to make, out of how many cubes, and how mild/wild is the overall combo going to be?
How much flow do you think you’ll need to get there?
 
replicaracer43 said:
So I think my plan is to put in guide liners, for a 8mm valve, and put a 2.0 intake valve in, hopefully have a little more room to get the seat and top cut shaped a little better. Its cut for a 1.920 as is. And leave exhaust at 1.620
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If you’re planning on using LS valves, I’m not sure how close the OAL is, but the tip length is different and they use different locks.

Might create a bit of a valve spring “situation”.
 
PRH said:
I guess the other question is, how much power are you trying to make, out of how many cubes, and how mild/wild is the overall combo going to be?
How much flow do you think you’ll need to get there?
Click to expand...
Customer would like to make 400 flywheel hp, with a stock short block, (360) a 214/218 @.050/ .532/.539 lift hyd roller cam. These heads and a edelbrock air gap. Not sure this can get there
 
Well...... you put it together..... and iiwii

Seems like the 360hp crate engine had quite a bit more duration than that.
 
The whole guide sizing thing was a eye opener. No way a guy could buy these heads and just swap his parts in, as people think. I'm not a expert like some of yall, but I do what I can.
 
replicaracer43 said:
The whole guide sizing thing was a eye opener. No way a guy could buy these heads and just swap his parts in, as people think. I'm not a expert like some of yall, but I do what I can.
Click to expand...


Oh don’t you worry...... plenty of people will do just that.
 
replicaracer43 said:
Customer would like to make 400 flywheel hp, with a stock short block, (360) a 214/218 @.050/ .532/.539 lift hyd roller cam. These heads and a edelbrock air gap. Not sure this can get there
Click to expand...

I suspect these are the same heads as these. I order them from a company called CCCN and yes the guy that runs it is Chinese and the name he goes by is "Chinese George". The heads take a metric F@#$ ton of work to equal an EQ casting. J.Rob

360 TrueStreet Magnum Build
 
RAMM said:
I suspect these are the same heads as these. I order them from a company called CCCN and yes the guy that runs it is Chinese and the name he goes by is "Chinese George". The heads take a metric F@#$ ton of work to equal an EQ casting. J.Rob

360 TrueStreet Magnum Build
Click to expand...
Thanks! I just read that whole thread, and being a non-professional head porter, I still feel like I wont be able to get him to his 400 hp goal with these heads. Especially after what you went through. And we cant find a new set of EQs around here anymore. His low mile magnum heads are cracked between the seats, I dont see a economical way to fix those either.... Not many options left
 
I have 1 cast iron speedmaster head that i confiscated from my machinist that were leaking from the deck face. It has 2 welsh plugs 1 at each end.

Has anyone flowed 1 to see what it is capable of?
 
Hysteric said:
I have 1 cast iron speedmaster head that i confiscated from my machinist that were leaking from the deck face. It has 2 welsh plugs 1 at each end.

Has anyone flowed 1 to see what it is capable of?
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Read the link ramm posted, he has flow numbers in the thread.
 
Hysteric said:
I have 1 cast iron speedmaster head that i confiscated from my machinist that were leaking from the deck face. It has 2 welsh plugs 1 at each end.

Has anyone flowed 1 to see what it is capable of?
Click to expand...


My Nein was Welsh. Lol J.Rob
 
close up of valve seat on speedmaster cast iron head.

20200415_155855_resized.jpg
 
I short cutted the whole metric ton of work by telling him to send those pos heads back and find a better set. He is bringing me a set of magnum R/Ts and a set of indy lax heads. Hopefully we can put something together out of that pile.
 
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