360 Commando head dilemma

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soaringcowman

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Hey everyone, i've got a little bit of a dilemma for you all. I'm currently running a 92 360 commando in my 70 duster and i'm wanting to upgrade the heads with something that will flow a little better without dropping alot of cash and something that will work on a 408 build down the road. The 360 commando has a set of MP308 heads on it now which are the 1.88/1.60 heads, which i've been told are suppose to out flow a X and J head if opened up to a 2.02 intake. But i have stumbled across a set of big valved J heads for $200 that are in good condition to bolt on right away. Which set of heads would be better in the end on the performance side for flow and cam lift? Because cam swap is in the near future....

thanks

adam
 
my buddies engine builder who's been building his chevy big blocks for him will, we call him "frank heads" cuz his speciality is porting heads, and he himself is a big block mopar guy, he's got a big blocked dodge cornet
 
Neither head will properly support a 408 so to me it's a wash. If the done heads have a flow test sheet with them they may be better than what you have. But stil not enough for a 408. A decently done set of ported 308s will work ok on a 4" engine and better than similar prepped set fo Xs or Js. But that's "just barely good enough". Not "good". If it was me I'd tell you to stick with what you have and continue saving for the right parts.
 
moper said:
Neither head will properly support a 408 so to me it's a wash. If the done heads have a flow test sheet with them they may be better than what you have. But stil not enough for a 408. A decently done set of ported 308s will work ok on a 4" engine and better than similar prepped set fo Xs or Js. But that's "just barely good enough". Not "good". If it was me I'd tell you to stick with what you have and continue saving for the right parts.
Click to expand...

And you are only guessing that?
Whats similar?
you mean you wanna compare tomatoes to apples??
how prep the heads the same, then what?

You can get a heck of a lot more port volume out of an old J/X etc than you think.

IMO,Until you know what each set of heads flow...you should stay where your at with heads.
It's about what you have to work with, not what we wish you had.
...so if you have 'time & money' to work with.. buy heads that are better than both the 308/J 's.

IMO-I tell you this though, If I knew that one set of heads flowed better than the other by 15-20cfm, I would swap in a heart beat cause cfm=power, the port volume issue/cross sectional issue only/mostly limits the rpm where you make the power.
you'd definitely have velocity.lol
[The pats will swap between headsfwiw.]
I have J's heads on my 410 sb, it pulls to 6500rpm no problem, but also has a small carburetor and un port matched LD340 dual plane intake w/small tube headers ...so figure that.
 
not much info to go on, your not going to have to change springs on the J's? i would just keep what you have for now, when you build your 408 and you want to make big power then get a set of indy's, 308's and x/j's can be made to flow in the 280 cfm range but its big $$$.
 
"And you are only guessing that?"
Not sure what you think I'm guessing... I'm not guessing in regard to the comments about the X/J/O/"915"/"308" heads. The fact that an individual could make them work is irrelevant unless that individual is building this engine. i.e. - Mullen & Co and Bob Glidden could do crazy things to make iron LA hads scream. Paper thin, relocated stands and pushrod holes, epoxy... But unless this was their build, their ability to get the performance is not relevant.

"Whats similar?"
The intake port cores are similar. Most exh ports until the 308 are similar too. And they all are similarly worn marginal factory quality machining and parts. As I said unless they are really worked to get the performance the 4" engines like it's better to replace them with a better set than spend cash on creating iron dust after you replace the guides, the seats, and the valves too.

"you mean you wanna compare tomatoes to apples??" No, I mean there is little to compare between apples and tomatoes other than they won't properly support (albeit by my own standards) a 4" arm engine.

"how prep the heads the same, then what?" Not sure what you meant by that... Assuming sets of X and "308" heads were identically prepared and tested, we can have identical resulting flow numbers, with identical port volumes, with identical minimum cross sectional areas, in different casting numbers, and one will still perform better on an engine than the other because it's not about flow numbers, volumes, shapes, or casting identity alone. It's about how it all works together. I like factory heads and I make plenty of power with them. But at some point it becomes an exercise in ambition to stay with something just because of personal choice. It's like a guy who is brand loyal will walk past the water and the Coke to get to Pepsi. They guy who is just thirsty will stop and grab the water.

"You can get a heck of a lot more port volume out of an old J/X etc than you think." No, I agree they can be made big. Except port volume is one of the last things I worry about. I've never maxed out a set of iron heads. Because I believe it's better and cheaper for the average Joe to simply get a better head than pay me or anyone else to try to make a the best diamond we can out of sandstone.

It's not about what you can do. Or I can do. Or Glidden or Curtiss Boggs can do with iron heads. It's about the best choice for the OP. I think we agree on that part. "Stick with what you got."
 
I agree. I started porting 21 years ago and I'm to the point that I dont have the time or interest much any more. Over the years I've destoyed heads I couldnt afford to replace and used up a bunch of tools to get to where I am. Everyone I know that's good spent $$ to get to the place they are at. If I was going to port I'd rather spend time on aluminum. Probably getting lazy there... So maybe that's it...lol
I'm sure 8 out of ten have different opinions on cheap and affordable too. And thats all good too.
 
so whats a good set of heads that would be a step for the 360 now and when the 408 comes along will kick a$% on it after some good porting? Edelbrock? Indy RHS?......
 
In terms of budget and ease I go with LA RPMs. I like the RHS heads but they are iron which is weight and more $$ (time) to port later. In out of the box stock form RPMs are just adequate for a 408. But with a little work they are a pretty good head and with a CNC or pro porting they will make some serious power. In terms of cost I think the RHS might be a little cheaper after all is said and done. We're talking a couple hundred bucks or so. For the RPMs expect to drop extra money on correcting the valve job and having them checked before you run them, and you need the right head gaskets (they need the pre-flattened fire ring type) and bolts for them. For the RHS I'd go with the LA rocker design/manifold holes, in bare castings and I'd have my shop do the valve work and assembly.
 
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