596 casting or 308 casting for mild 360 4bbl

[Cudafever]

You do realize that Until the secondaries open, your new top end will not make a hill of beans difference right? So if she can't spin the tires now, both of them,then the new set up won't be but a tad quicker to 30/40 mph, depending on your current rear gears and TC stall.While the duals and freeflow exhaust will help some below 3500rpm(maybe lots depending on how restrictive your current single? pipe is; the secondaries may not open until 3000plus rpm.With 2.76s, that would be about 35mph.See what I'm getting at?
-If you put a bigger cam in it, all other things remaining, it may actually be slower to 35mph.This is because without a compression increase to keep the Dcr up, a bigger cam invariably trades away low rpm torque for high rpm power.
If you really need some giddy-up, the biggest bang for the buck will be a slightly higher stall TC. Then gears if you can afford to give up some hiway comfort; and you can never lose with a free-flowing exhaust.
-Since you already said gears, then that is the very first thing to do;before you spend a bunch of money on the engine. By itself a 20% increase in gearage will be dynomite, and absolutely none of your planned mods will make it any quicker below 25/30mph or so,than it now is, and it will not be felt until the car is really moving, and then you will be speeding;cuz 5400 with 2.76s in first gear is about 65 mph.
I'm not trying to ruin your day, but gears should be #1 for you;not last.
-Going from 2.73s to 3.55s is a 3.55/2.76 =plus 28.6%. This is huge. Your engine will feel like it grew by that same 28.6% or over 100 cubes. No other mod to a NA streeter will touch this mod for grin-factor.
-BTW, with a stock compression ratio, I would leave the cam swap for dead last. I mean it.It's really hard to beat that stocker for off-the-line giddy-up.And if after the gears are in, and the exhaust is hung, you still feel the need for more, a 4bbl set-up might kick in another 15 hp; but you might not feel it, until she gets wound up. You'll hear it,all right, but it will be awhile before it gets going.Worse if you stick that 268cam in there.
-I suppose I'd be remiss if I didn't take budget into account.If you already have the money earmarked for your plan, there's not much wrong with your plan, just so long as you have money to finish the combo.
-But if the cam is for sure going in, then at least cut the heads to get back some Dcr.
Whatever you decide;All the best to you

THIS IS THE BEST ADVICE YOU CAN GET!

Here are some DIY porting results on a set of 596 castings. This was about a 3rd set of heads I ported, pleased with the results. Your are probably not going to go that extreme in terns of the port work though.

LIFT I E

0.100 67 57
0.150 99 79
0.200 130 104
0.250 162 125
0.300 189 140
0.350 215 152
0.400 235 160
0.450 253 167
0.500 262 172
0.550 261 175
0.600 248 177

The finished chambers/ports looked as follows:

I would assess the situation from the perspective of how much $$$ are you going to sink into either stock casting to make it perform? These days, that type of money will buy you a decent aftermarket iron head.

At the very least, consider optimizing your static CR to work with the heads and camshaft in particular. That will be the key to making good torque.

I WOULD NOT GOT THIS FAR with the cam you're using. Velocity is every bit at important as flow ###.

With a 2.02 valve installed and a 3 angle valve job. The 65-70 degree bottom cut will take a lot of metal out of the bowl!!!
all you need to do is clean up the last cut. Just a mild blend into the as cast of the bowl.

Remember a good valve job is the largest cfm JUMP! After that you have to work at it, with less gains.

Just like using too large of a cam will kill that bottom end, so will using too big of a head, aka port.

 

[M_Body_Coupe]

...I WOULD NOT GOT THIS FAR with the cam you're using. Velocity is every bit at important as flow ###....

To clarify, my comment was not a recommendation regarding how much porting the OP do, it was merely an illustration of the potential of 596 castings if one were to CHOSE to port for max flow gain.

Now, consider that these flow numbers are for a 180 cc intake runner...that's stil a pretty good amount of velocity.

 

[rumblefish360]

My '79 Magnum is listed at (IIRC) 3675.
318/904, ac/ps/pb bench, full spare tire.
I did add weight to it with a '78 "P" code Cordoba's XHD trans cooler, XHD A/C condenser, 727 & (3.55's) 9-1/4 rear. Buckets seats and center console.
I did go back to a small block (5.9) and retained a SB 727 for use.

Only weight savings items are a new aluminum radiator, rpm intake, headers.

The car move well. (Nothing the right cam wouldn't fix! And a good set of heads to allow some more power! )

 

[rumblefish360]

Double post

 

[Infecteddog]

It might be moot, but I think Chrysler SAID they made 245 with <8.4.
They also SAID they made 275 with 10.5.
They Said a lot of things.
Like 425 out of a hemified 426,

They also said their 3800lb low 15 second trucks had 225hp. If the results aren't worse from the '70s than in the '90s from themselves and other makes...

Raising the compression alone will not just make more power all around on the same gas in the same powerband- it's not gonna happen with everything else staying the same. Whole lot better having 30 less HP than not being able to run pump gas. Those E58 and E55 cars and Lil Red Expresses had larger cams with the same low (actually calls out less) compression as the other 360s and those were not slower. Not to 60, not to the end of a quarter, nor in top speed.

 

[AJ/FormS]

Ultimately what I am looking for is power under the curve and a nice fat powerband. Now I learned years ago that horsepower is for race cars; torque is what is what rules the street. Horsepower, after all, is just a mathematical derivative of torque.

I don't wish to start anything here.So, um Firstly, I agree.
However, when looking at dyno charts, it is useful to look at the torque curve from the torque peak down, and it is useful to look at the power peak, from there on up to about 800/1000 rpm after the power peak. This is because the torque curve amplifies the step by step low rpm numbers, so you can get a good idea of what to expect in that rpm range. And the power curve amplifies the step by step numbers up top, so you get a better idea of what to expect up there.You can better match the rest of your powertrain to take advantage of whichever characteristics your chasing.Sure you can work off either curve, cuz they both represent the same engine.It's just easier when looking at the magnified numbers.
As a ferinstance, consider the lowly stock slanty. Looking at the powercurve is almost a waste of time. But looking at the torque curve, gives you a lot of useful information, as to transmission and rear gear-ratio selection.
Then consider a 340 with a big cam. Looking at that torque curve you can clearly see what you will need to do for a starter gear; and looking at the power curve, you can also see what tranny you will want to run.
Now we come to the 360. This engine is kindof fun, cuz you can build it either way. It has enough cubes that it can be tuned for high rpm power, and still have a generous bottom-end torque curve. It can be tuned for almost any tranny,and almost any rear gear.

 

[popinsmoke]

I don't see anybody as starting anything, I appreciate the advice good, bad or otherwise.

There is no perfect combo and even more to the point, no one will ever agree what the perfect combo would be.

I like to hear opinion and options and then make up my own mind, bench racing is half the fun.

I just want make it clear to all the posters that I appreciate the time and effort it takes to comment. I may not agree with everyone every time but I always try to learn.

BTW just to keep things moving along anybody ever run the RHS LA-X heads I know where I can score some virgin unassembled for a reasonable price.

 

[m880]

440's are hard to come buy now. Back in the 70's I could pick 440 super commandos out a junkyard easily, now I haven't seen one in years. Anybody that has one thinks it worth a fortune. Stick with the 360.

 

[RustyRatRod]

Say what you will but I have driven a Magnum both before and after a big block swap. I will just say there's no substitute for cubic inches.

 

[AJ/FormS]

Amen to that
Even a stock, 68 Chrysler RB pulls hard right from idle. That Surge from tip-in is so surprising.Especially when you consider the weight of the beast.
But not only surprising, also deceptive; when you look down at the speedometer and see the needle climbing at such an alarming rate. It's like riding a turbine; smooth,quiet,powerful,and then the 4bbl opens....................

 

[496 polara]

Maybe consider the comp 262 or equivalent to keep cylinder pressure up and generate more low speed torque.I t will work well with the stock converter and won't be dependent on lower gears to help it get moving.

 

[CordobaDart]

A friend of mine since childhood got his parents 79 Cordoba with a 2bbl 360. Had 170k miles on the bottom end and a burnt exhaust valve. They bought it in 1980 or 1981. After his mother quit driving it in 2003, he started working on it as a 14 year old. Had the heads repaired with new guides a new seat, and new exhaust valves with a little cut from the head to make it straight. He then put a .484 purple shaft cam in @104 and an rpm air gap with a holley 750 vac secondary. It performed okay for a big car with 2.45 rear gears. By the time he was 17 he went to an 8 3/4 rear with a 3.23 sure grip and the car got noticeably quicker. The original lockup 904 trans died and he put in a built 727 with a 3500 stall converter, now the car was impressive for a low compression high mileage 360! Last month he pulled the old tired 360 and it is getting turned into a 408 now, so it will be fun to feel the difference that will make! Just an experience I thought I would share.

 

[318willrun]

All of what weight? There's a 150 pound difference in the two engines. I can throw that across the yard.

LOL....

 

[CordobaDart]

That old engine was still working well but dripping an burning oil pretty bad.

 

[MOPAROFFICIAL]

Get the 308 heads, there is as much "swirl" tech in them as a j head, only diff between the 2 is the better exhaust port and tighter pushrod pinch. Last set i ported went 267 @.500 3/8 stem 2.o2. Throw some 11/32 stem 2.o2 valves in either head and they'll flow close or about the same intake wise, 308 heads will trump the 596 on the exhaust side however.
Ultimately the heavy car with the aforementioned 360 will move well....but if you want tire ripping muscle, stroke it and use either heads and you wont leave potential for disappointment.

 

[leblanc]

If you 0 the deck and end up with a 9 to 1 compression ratio your combo would be close to what I have. About 350 HP in an A-Body. Just enough power to have fun with and not too much so the cops search for you all the time.

 

[moper]

Gentlemen,

I am building a mild 360 4bbl in my 78 Magnum, The short block is the stock low compression 360 2bbl that Ma Mopar made millions of.
Now I am in the process of installing a Comp Cams XE268H complete kit as well as an airgap intake and street demon 625 4bbl carb.
The lean burn system has been ditched in favor of the MP electronic conversion with the orange box.
Plans are at this time to run the big outlet dakota exhaust manifolds in to a 2.5 inch true dual with an X pipe.
So my question is the car has 596 casting heads currently sitting in boxes that came off the car and 103k miles, I have access to a pair of 308 castings at the local bone yard as not allot of Mopar guys frequent my yard.
Everything that I have read says that the 596 castings are the best of the smogger heads but the 308's are the best pre magnum head, my question is how much better?
If I am having 2.02 valves and bowl work performed anyway is there that much of an advantage to the 308 "swirl port" design $ for $?
Also looking for the MP head porting templates anyone know a good source to find them?
Thank you in advance for any advice.

IMO not worth the big block swap unless you have the donor car with it for the mounts and oil pan at minimum, the transmission, the kickdown, thtrans crossmember, and driveshaft at most.
The heads on the engine will be fine if you go through them and add performance valves and get a real valve job in them. IMO the added expense of 308s is not worth it. Take your heads, have the shop fit them with performance 2.02/1.65 valves, and have them do a modern 5 angle performance valve job. That valve job and valves will get you to very close to the template porting work and for what you're doing they will be more than fine.
You don't want a DCR of 9:1. You want a DCR of less than 8.25:1 and a static ratio of no more than 9:1, and you won;t reach that without pistons or a ton of milling. Milling is not the means to that end - cost wise you will spend a lot more beyond the milling to make it all work right and the jump in compression will not provide much additional power in and of itself.

 

[IQ52]

I don't see anybody as starting anything, I appreciate the advice good, bad or otherwise.

There is no perfect combo and even more to the point, no one will ever agree what the perfect combo would be.

I like to hear opinion and options and then make up my own mind, bench racing is half the fun.

I just want make it clear to all the posters that I appreciate the time and effort it takes to comment. I may not agree with everyone every time but I always try to learn.

BTW just to keep things moving along anybody ever run the RHS LA-X heads I know where I can score some virgin unassembled for a reasonable price.

Now this is a set of RHS LA-X heads.........1.94/1.625 valves 280 cfm intake/236 cfm exhaust @ .600" lift.

Photo by heyoldguy

We used them to get 468 HP from that ol' 273.............