Replacing 302 heads with magnum heads

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turtleheadjoe

turtleheadjoe

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I know the 302 heads are supposed to be pretty good but the magnums appear to be much better in every respect. I know I need to change lifters, pushrods, intake, etc but I'm ok with that. I'm aware of the cracking issues on the magnums as well.

Any reason not to go ahead with this? I already have the magnum heads ready to go onto my pretty healthy 318.

Are the 302s rare/valuable enough to mess around with selling or are they dime a dozen stuff?
 
I was able to find a couple sets of 302's in the pull-a-part yard near me, but they were all cracked (after being magnafluxed) and eventually was able to find a set that had been rebuilt. In hindsight, I could have gone the magnum route after I had went through all the trouble to find the 302's. So the rarity factor may be something to consider, but, they do not flow like magnums.
 
There not a dime a dozen, but are still out there available. sell them. If you got the entire magnum package ready to go, they flow better and you get 1.6 rockers so the cam gets a boost too. 302's are nice to drop onto an old 273/318 with no other changes, thats what makes them good as well as the compression bump.
 
What are you putting them on? If it's a 273/or318, I would stick with the 302s. Anything bigger, go with the magnums. Try to find the EQ magnums- less prone to cracking than OEM magnums, and can be worked over to flow up some really good numbers.
 
I put a set of magnums on my LA360 and really like them. You need to get new pushrods and lifters, they oil through the rockers through them. The push rods will need to be measured to get the preload correct. The chambers are smaller, mine came in at 68cc's.
 
You should be able to get a few hundred million for the 302s, retire to the Caymans with a Swiss account drawing at least 18%.
 
I'd go the magnum route if you already have all the parts...they're a better head and the compression difference between them is negligible (58cc nominal 302 vs 62cc nominal magnum), so any power difference due to compression would be offset by flow in the magnum's advantage.

Ex: Assuming a 4-5cc difference between the two, the static CR would be a max of about 0.5:1 in the 302's favor, but that difference is worth about 2% at best...so if your making 400hp, hypothetically, it might be worth 8-10 peak difference, which again would be overcome by the better flow coming from the magnums.

Food for thought...
 
Ok, another question.

Is it worth the trouble to make the switch, meaning is it going to be worth more than a few horsepower?

The car is a 318 with flat tops, mild cam, performer intake and 600 edelbrock, hooker headers. It runs good now. If the magnums are worth ~10% I'd say it's worth it, if they're worth 5 peak hp I won't waste my time because, after all, it's just my weekend beater not a track car.
 
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What kind of heads are on it now?

Do you have any real desire to increase power output?

Realistically you're looking at a decent chunk of change...

Heads, assembled with rockers and valve covers, gaskets...
Intake, gaskets, thermostat housing, bypass fitting, and hardware; fortunately, pretty much anything you buy for it would be an improvement over a stock small port performer
head bolts-I would strongly recommend you buy new ones (about $35)...I know there are people on here who'll fire up the flame thrower here against me, but the stock head bolts on magnums are torque to yield (TTY), which means the bolts plastically deform when torqued to spec, therefore when loosened will not provide the same clamping force again
exhaust gaskets
oil through lifters
pushrods
RTV
coolant (unless you're really thrifty and capture/reuse)
Carb gasket
 
turtleheadjoe said:
Ok, another question.

Is it worth the trouble to make the switch, meaning is it going to be worth more than a few horsepower?

The car is a 318 with flat tops, mild cam, performer intake and 600 edelbrock, hooked headers. It runs good now. If the magnums are worth ~10% I'd say it's worth it, if they're worth 5 peak hp I won't waste my time because, after all, it's just my weekend beater not a track car.
Click to expand...

I'd have to vote that it isn't worth it for the 318.
For 360 or a 5.9 OH HELL YES! :D
The big advantage of the EQ Magnums is that they don't have the cracking problems, have 1.92 valves right out of the box and flow about 230 untouched.
I don't think a 318 could make good use of that.

I might be wrong, but it doesn't seem worth doing to an already decent running 318.
 
txstang84 said:
What kind of heads are on it now?

Do you have any real desire to increase power output?

Realistically you're looking at a decent chunk of change...

Heads, assembled with rockers and valve covers, gaskets...
Intake, gaskets, thermostat housing, bypass fitting, and hardware; fortunately, pretty much anything you buy for it would be an improvement over a stock small port performer
head bolts-I would strongly recommend you buy new ones (about $35)...I know there are people on here who'll fire up the flame thrower here against me, but the stock head bolts on magnums are torque to yield (TTY), which means the bolts plastically deform when torqued to spec, therefore when loosened will not provide the same clamping force again
exhaust gaskets
oil through lifters
pushrods
RTV
coolant (unless you're really thrifty and capture/reuse)
Carb gasket
Click to expand...


I've got almost everything to do it, and I agree on head bolts. Now I'm trying to decide if the labor is going to be worth it.

It has 302 casting heads on it now.
 
...and pretty much any stocker 318 small port head flows how much compared to a magnum? Like 200cfm at .500" lift? To saying nothing of the probably 30 cfm or so improvement at mid lift levels.

To say that the engine can't take advantage of the greater flow would be like saying a sail couldn't take advantage of stronger wind. There's this apparent perception that increasing the flow numbers by only a marginal amount, it'll kill whatever bottom end you do have. I could see that rationale playing out if you dropped on a set of ported W2s to a stock 318 with a mild cam, but we're talking about stock parts for stock parts...his swap would be more akin to putting on a set of stock J heads, but the chambers were magically shrunk to 62cc and had the advent of way better velocity into the chamber.
 
turtleheadjoe said:
I've got almost everything to do it, and I agree on head bolts. Now I'm trying to decide if the labor is going to be worth it.

It has 302 casting heads on it now.
Click to expand...

The labor output once you get all the parts is gonna be about a whole day's worth of work, or a more measured weekend...

EDIT: You have to be the one to determine if it's worth your trouble...I can only provide some info...
 
Exactly, that's what I'm trying to decide now, is it worth all the work? If we're talking <10 peak horse I don't see any real value, but if it's a good number throughout the range it would be.
 
We're talkin hypothetically here, but I'd guess you'd feel more torque and drivability difference than you would peak hp, or RPM...especially depending on the cam profile

probably 15-25hp difference if all you're changing are the heads and intake...
 
I didn't bear much thought to this one until now--what cam are you running? pishta mentioned more lift from the cam, and that's accurate. You will have a limitation to how much lift you can run before running the spring retainer into the guide...
 
I know it's "just a 318" but it's what I've got to work with. I'd like to make it as good as I can but if the magnums don't make sense I can get what I've got invested back out of them.

I'm running 3.55s if that matters. The car really runs good now but I've read so much about magnum engines that I thought it'd be a nice improvement on my engine, I'm just really on the fence now because I can't find any numbers on how they work on a 318.
 
You ever see this article?

Mopar 318 Engine - Car Craft Magazine

Might not be your build, but it's worth a look for perspective...also google "junkyard jewel 318"

If you're 318 has good ring seal and compression, I personally would recommend the swap as long as you make sure the cam doesn't cause issues with the extra lift...but that is ONLY my opinion. 318 owners have been doing this swap for years, and as far as I know, happy with the results. I know my stock 5.2 with a 4bbl makes me happy...
 
txstang84 said:
I didn't bear much thought to this one until now--what cam are you running? pishta mentioned more lift from the cam, and that's accurate. You will have a limitation to how much lift you can run before running the spring retainer into the guide...
Click to expand...

This one from summit

image.png
 
I personally don't think the swap would be worth the effort. You might see a little difference, but not much. If you were going to do a cam, intake, and heads, then maybe, but not with what you've got. I had a 302 headed 318 in my Duster before I built my stroker, and it was a good little motor. I just sold it to a guy at work, and the only reason I sold it is because I'm going to be moving soon and needed to downsize.
 
I just read both articles. It might be more cost effective and practical to get my 302s worked over this winter? I dunno.
 
64physhy said:
I personally don't think the swap would be worth the effort. You might see a little difference, but not much. If you were going to do a cam, intake, and heads, then maybe, but not with what you've got. I had a 302 headed 318 in my Duster before I built my stroker, and it was a good little motor. I just sold it to a guy at work, and the only reason I sold it is because I'm going to be moving soon and needed to downsize.
Click to expand...

Yeah I've already done the cam, intake, header basics. I'm not against changing cams again, it ain't that pricey.

I really can't believe I'm putting so much effort into this decision, it shouldn't be this difficult.
 
If you really want to put the magnums on, and are willing to swap the cam, go with a cam with a little more duration and lift with a 110 LSA. Comp Cams HE268H or XE268H are both good 318 cams. If you want more of a lope, go with the Magnum 270H. The HE268H worked well in mine with the 302 heads.
 
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