Which 360 Block to use: LA or Magnum?

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lgjhn

lgjhn

"The faster you go, the faster you go..."
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I haven't been on FABO for quite a while now, and I don't believe I've ever started a thread on here before. Being a pretty old fart, I've found it fascinating how engine tech has kinda left me "in the dust" so to speak over the past few years. What was once considered "gospel" in some areas now has newer tech to make it "not so much" anymore. With all that said, here's my situation/question:
The 318 in my '73 Dart Sport was more than tired when I pulled it out. I still ran ok with all the miles on her, but way down on power and started to use some oil. It's time for a serious upgrade on the engine/tranny/rear. I've already completely rebuilt a salvage yard A-body 8.25" with a new set of 3:55s and now have it installed in the car. I've built up a SB 904 tranny and it's ready to go once the engine is completed. I'm wanting to build a good street/strip stroker motor with the emphasis on the "street" side. There are a couple of good, clean blocks available at my disposal. I have an early ('71) LA std. bore 360 as well as a late model std. bore 360 Magnum. As stated, both are in pretty decent shape albeit a lot of miles....they're well-seasoned blocks. Whichever one is used will get a set of the EQ heads on the top side.
I'm wondering what other members feel about which version of block to select: the LA or the Mag? Is there any distinct advantage to the Mag block over the LA when all things else considered would be the same in the build? Maybe oiling? Thanks.
 
magnum. better castings,typically less bore wear and roller cam provisions.
 
Magnums have a better oil pan..... and a roller spider boss. and a wacky reverse rotation water pump and a serpentine belt system, and maybe no provisions for a mechanical fuel pump on the cam (?) and of course the different flex plate and balance provisions...and a limited intake manifold selection, but has 1.6 rockers...on studs. plus ugly valve covers but they seal better due to a machined gasket surface. and the heads do seem to flow a little better with smaller valve stems...Hmm what else. Hows the motor mount provisions on a Magnum? Any inexpensive after market SFI dampers? Heck, I never owned a Magnum, what do I know.....except the rod little ends are thinner.
 
Magnum without question. Especially if your gonna use eq heads, you can get them with LA intake pattern and have more intake choices.
 
replicaracer43 said:
Magnum without question. Especially if your gonna use eq heads, you can get them with LA intake pattern and have more intake choices.
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Yes, the EQ heads I'm using have the LA intake pattern as I have nothing but LA intakes at my disposal.
 
replicaracer43 said:
Magnum provides roller cam, plus metric lower tension rings
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Plus the stock rotating assembly is lighter in the Magnum than in the LA.
You can Bolt the LA water pump on the front of the Magnum get rid of that reverse rotating crap that way. Buy the little adapter piece that goes on the front of the camshaft and you can run a mechanical fuel pump then you put old style valve covers on it and nobody knows it's a magnum.
 
The Magnum heads have small, closed chambers for quench and 1.6 rocker ratio. Magnum blocks have a shorter deck height for better compression. They also have roller camshafts. Their only down side, if it is one, is that they have pedestal mount rockers. Although Hughes Engines makes some REAL nice roller rockers for them.

I don't think I would ever build another LA. Not because the Magnums are necessarily better, but because of the excellent wear characteristics. I've torn down a lot of them and so far, I've not seen one without cross hatch still in the cylinders.
 
RustyRatRod said:
The Magnum heads have small, closed chambers for quench and 1.6 rocker ratio. Magnum blocks have a shorter deck height for better compression. They also have roller camshafts. Their only down side, if it is one, is that they have pedestal mount rockers. Although Hughes Engines makes some REAL nice roller rockers for them.

I don't think I would ever build another LA. Not because the Magnums are necessarily better, but because of the excellent wear characteristics. I've torn down a lot of them and so far, I've not seen one without cross hatch still in the cylinders.
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All the above reasons tilt the field to the Magnum. But the LA has a certain appeal, being older.

I suspect much of the reduced bore wear is due to fuel injection.
 
There are two choices that need to be made to determine which block suits your build best.
1. What type of camshaft are you thinking about? Hydraulic rollers are nice for mild builds and the Magnum has all the stuff for that. Any "Magnum specific" stuff will be changed anyway, but you can reuse the lifters and spider/dog bones for the new build if you go hyd roller in the Magnum block.
2. Which heads? You already answered EQ Magnums - but there are some restriction on using them... Meaning things need to be kept fairly mild due to the valve spring/rocker arrangement Magnums use. So the output level of the build needs to be mentioned. If the cam limits set by the head choice are not enough, you need to reconsider the heads.
Personally I like the LA block. More head choices, more rocker and intake choices, and equal in terms of most anything else. But at this point the world is your oyster...
 
nm9stheham said:
All the above reasons tilt the field to the Magnum. But the LA has a certain appeal, being older.

I suspect much of the reduced bore wear is due to fuel injection.
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I agree......plus newer reformulated oils. Remember, those old LA engines, slants and big blocks never got the benefit from the ultra light 5w whatever for good oil dispersion on startup. Not to mention the modern additive packages!
 
nm9stheham said:
But the LA has a certain appeal, being older.

I suspect much of the reduced bore wear is due to fuel injection.
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Being older to me has no appeal, to be 25. and know everything I do now that is appealling. LOL

Low tension Rings is more the reason for less cylinder wear.
 
Thanks guys for all the great input. FWIW, I've not been messing with my cars for quite awhile now even though I do go to Carlisle every year just to drool all over myself...LOL. Now, I got a little time & money (retired), I want to get back into em....besides, I got this little ***** of a Camaro down the road that I want to smoke in the 1/4 mile....LOL. He refuses to run against my 392 SRT8 Challenger, but never missed an opportunity to punish my poor, old '73 318 Dart Sport. That's fixing to change...big time. :)
So, I had to do a little inventory-taking out there in the shop over the weekend. I have a couple good 360 LA short blocks, 1 340 short block, 4 complete 318s, 2 complete 440s and that one 360 Mag block that I can't even remember where it came from. I know its not something I would have bought. Maybe got in a trade or something.
Moper, I agree with all your comments for sure. I'll be running a roller cam which I haven't yet spec'd out and looking for 450-500 horse which should be plenty in that Sport. The combo needs to work with my built 904 and the 3:55 gears in the back. It has to remain reasonably streetable whatever that means...LOL From what I've read, those EQs flow better than any of the stock heads ever made thus the reason for that choice. I do have a decent set of early 340 "X" heads and an early 340 non-EGR intake, but was saving those pieces for another project that needs to be geared more towards an "original" so to speak. I've got 2-3 sets of various 360 LA heads as well, but I don't believe they would flow enough for that amount of power without a lot of porting expense.
One other question for you guys running these strokers. I notice that the kits can be had balanced or unbalanced. Are you guys buying them unbalanced and using a 360 external balancer? Or buying them balanced and using something differ for a balancer?
EDIT: I remember I did all the oil modifications to one of my 360LA blocks a good while back, and I think this is the block that will get the green light for the build.
 
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I never trust a kit to be balanced. I will always have my shop do it. I also always internally balance. In addition to being the best for the crank and block longevity, that allows use of any neutral dampener and neutral convertor.
 
Pretty darn good advice and I fully agree with it all. Thanks much!
 
Check out my thread. " another 408 build". It made 504 hp with a medium sized Thumpr hydraulic roller and a dual plane Airgap intake, at 5700 rpm. Cost about $6,000.
 
This is simple, really. Look at the Ford and Chevy guys. They are not using old 302 or 350 blocks. They are using LS and Coyote motors. Since the new Hemi hit the scene, even the Magnums are prehistoric by comparison.

It's a shame Chrysler won't wake up and make something that really competes with the all aluminum LS engines. And before you think I'm a Mopar hater.......that couldn't be further from the truth. I cannot STAND the LS stuff, cause it's everywhere.......but it works.
 
gregsdart said:
Check out my thread. " another 408 build". It made 504 hp with a medium sized Thumpr hydraulic roller and a dual plane Airgap intake, at 5700 rpm. Cost about $6,000.
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Thanks, Greg. Much appreciated.
Yep. Just read it. BTW, love your early A cars.
Jeez, based on your build, I could probably get close to 450 hp without even stroking it. Just go with those EQ heads, cam, intake & a decent set of pistons with a .030 overbore to clean it up. I'm thinking that would be very similar to the $4000 engine that IMM built that's in the recent issue of Mopar Muscle.
 
RustyRatRod said:
This is simple, really. Look at the Ford and Chevy guys. They are not using old 302 or 350 blocks. They are using LS and Coyote motors. Since the new Hemi hit the scene, even the Magnums are prehistoric by comparison.

It's a shame Chrysler won't wake up and make something that really competes with the all aluminum LS engines. And before you think I'm a Mopar hater.......that couldn't be further from the truth. I cannot STAND the LS stuff, cause it's everywhere.......but it works.
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I can't disagree, but gotta work with what's available. But yeah, I was at the U.S. Nationals in Indy last month. That particular NHRA race is mainly sponsored by Chevrolet so they had a big display on the vendor-side of the track. I was looking at their parts, engines, etc. they had laid out there. Without a doubt, they provide their "gear heads" with a lot of fine, high-tech stuff for sure.
 
I'm thinking that would be very similar to the $4000 engine that IMM built that's in the recent issue of Mopar Muscle.[/QUOTE
That is the same motor you discribe
 
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