Calling Mopar guys: Magnum Heads on an LA block

So I'm finally getting all of the extra parts delivered from my dad's shop to start building my 66 Barracuda motor. We have a 1973 340 short block but the heads are cracked at the air injection ports. I think that they are probably usable but they are J heads and nothing special.

I was looking at an upgrade to the more modern magnum heads since they are so much more efficient and I like the added quench area on them.

So I'm going to be yard diving in a couple of weeks to grab a complete engine so I know I have most of the factory parts for them.

Anything to look for? Is there a specific year/car that I should hunt down? Anything extra I should grab while there?

Mike

For some reason the 90-92? 360 truck heads stick in my mind. Rob Mopar will confirm/deny this.

Magnum engines started in 92 and went up to the early 2000s. Pretty common to put them on earlier engines, just can't remember offhand what all is required. Rob Mopar will help us out.

I might be temped to get a 360 Magnum and just use it with its roller cam and all (minus the EFI stuff) and sell the 340.

81cpcamaro wrote: Magnum engines started in 92 and went up to the early 2000s. Pretty common to put them on earlier engines, just can't remember offhand what all is required. Rob Mopar will help us out. I might be temped to get a 360 Magnum and just use it with its roller cam and all (minus the EFI stuff) and sell the 340.

Valvetrain is the biggest boondoggle, I think. I, too would sell the 340 to somebody who cares about that sort of thing, and install a gently used magnum 360...maybe with a bit more cam, just to liven up the top end a bit.

I've already got the 340 short block rebuilt and it's a 73 which is not really all that desirable.(cast crank and not forged) We got to the heads and my dad found the cracks and he just ran out of money.

So now that the car is mine, It's time to pick up the torch and finish what he started. I know I'll have to change the lifters and pushrods.

Just get a whole magnum engine and trans. Better power and mpg. Can also use a newer trans if u want.

Any info on Allpar.com?

You need special pushrods for oiling. Beyond that I can't recall.

Jaxmadine wrote: Just get a whole magnum engine and trans. Better power and mpg. Can also use a newer trans if u want.

I think this would be your best bet.

The Magnum 5.2 and 5.9 (fuel-injected versions of the old 318 and 360, respectively) will run forever.

The other thing to think of is the fact that 340s have different Chambers because the piston protrudes from the block.

Sorry, just saw the post. It's been busy in the shop.

All of the production Magnum heads are the same. All Magnum heads are a closed chamber design. The 318 Maggie started in '92, the 360 in '93. They ran through 2003.

The '73 340 is a low compression 340. Those should be flat top pistons in there, but over 40 years other parts could have found their way in. Confirm they are flat top, not the earlier domed pistons that gave the '68-71 340 higher compression. The domed pistons will not work with closed chambered heads.

The Magnum heads use pedestal mount rockers that oil through the pushrods, not shaft mounted rockers the LA motors had. To run the Maggie heads the lifters need to be replaced with ones that will oil through the pushrods. Most aftermarket Mopar lifters are setup to do this. They are shared with AMC.

The head conversion requires different pushrods. Mopar Performance sells a kit for the conversion, but they are a little on the short side. You are better off mocking it up, measuring the correct length, and ordering a custom set from somebody like Smith Brothers.

The Magnum intake bolt pattern is different from the LA heads. You can either redrill the Maggies (make a jig off your old J heads) or go to something like a Mopar M1 or Edelbrock RPM Air Gap intake for the Magnum heads.

The Magnum heads have a tendency to crack between the valves. They don't tend to go through to water, but some do. When 'yarding, grab the lowest mileage one you can find.

As several other people have posted, if you are grabbing a complete Maggie out of the yard, I would strongly consider using it instead of the 340. Some restorers will pay top dollar for a 340 block (usually the '68-71's though). If your 340 needs any other machine work, I'd be building up a Maggie 360 to go in there.

We've built a few for friends and customers. With a mild cam (268 adv duration) and street gears they run 13's in the quarter all day without breaking a sweat.

Most of the Magnums I've opened up are very clean inside. Only the neglected ones were ugly. Even on some of the ugly ones the cross hatching was still visible in the bores.

Jaxmadine wrote: Just get a whole magnum engine and trans. Better power and mpg. Can also use a newer trans if u want.

The overdrive trans won't fit his A-body tunnel without surgery. The trans crossmember does double duty as the torsion bar anchor. The area needs to be re-enforced if cut for trans clearance.

Always get a 5 speed. Powa!

In reply to Jaxmadine:

The NV3500 is a pretty big 5-speed. Still requires the floor surgery. And its geared for a truck. Plus they aren't all that common in yards.

The earlier NV2500/NP535 isn't quite up to snuff behind a V8. AX5 & AX15 were available in some Daks, and that opens the door to the Turbo Supra swap, but then that gets away from the whole junkyard single donor deal.

Jaxmadine wrote: Always get a 5 speed. Powa!

You have to do some major hackery to the floor or the trans to get a 5-speed in a Mopar.

Every Keisler I've seen leaked where they modified the case.

Thanks Rob. You confirmed what I thought.

I'm staying with the 340. It was the last motor from my dad's circle track car back in the day and it's going into the last classic car my dad owned. That motor has been in the family for over 35 years now.

The 904 is staying put too. This chassis is way too nice to chop up.

The pistons are 9.0 to 1 keith black pistons. I should be about 9.5-9.7 to 1 if I did the math right so I'm cool there. I assembled the bottom end and bagged it last year when I was home for Christmas.

I was looking at selling the classic LD340 intake and the Weiand stealth I have for the edelbrock air gap magnum to go on there.

I've already got the 401 AMC lifters sitting in a box from my old cherokee. The cancer bug got to it before I ever got to rebuilding the motor.

BTW Rob, Where is your shop? Just wondering.

Why not pony up for some x heads or some eddys? Other than cost.

Another way to go is the casting # 308 head from a fuel injected LA 360. They have a combustion chamber very close to the Magnum head as well as good ports. The exhaust ports are as close to W-2 ports as production LA small block pushrod angles will allow according to Larry Sheppard. Going this route you don't have to source different lifters and pushrods, all the rocker gear and intake manifold. I used this head on my 360 oval track engines and they worked very well.

Because it's a cruiser and I'm only looking at 325-350 HP range. I don't want it to be too crazy. I really just want the closed chamber heads. For my application, the eddys really are a waste. Worse case there is a place local that has 30 of them for $60 a piece.

It a 66 barracuda that I'm not going to chop so 245's are the max tire I can fit i there. Anything much more than that will just be tire smoke.

In reply to bmw88rider:

My shop is in PA. About an hour south-west from Philly. When it comes time for headers & exhaust, keep me in mind. I'm a TTI dealer.

I completely respect keeping that 340 in the family and the Barracuda too.

The LD340 is a very nice manifold. I have one here for my wife's Challenger. The used Stealth I had is going on my buddy's '65 Valiant now.

The 308 heads Mtownneon mentioned are good ones if you can find them. They were on the TBI 360's from around '88 through '91. I'm not sure the 360 got TBI in '88, might have been '89. Look for flat nose B-vans in the yard. They came with 1.88/1.60 valves but can be opened up to 2.02's. Just need to check for the cracking like the Maggies.

If you go with the 308's, you can use that LD340. And if you find the 308's in the yard, snag the block for future use.

Some guys go nuts looking for the 318 #302 castings. There was an article about 10 years ago showing them making great power after being hogged out. They are fine for a 318, but by the time you get done porting them to work on a 340, the walls in the ports are too thin along the cooling passages. They will crack and flood.

Depending on what you find (or don't find) in the yards, some of the iron Indy LA-X heads might be a good deal for your build, or the Ed aluminum ones if you have the budget. I'm running the Ed's on my '68.

Your last post came in while I was writing another thesis.

The 308 heads are open chamber. The 302's are closed, but don't waste your money.

The Maggie heads use 1.6:1 rocker arms. Keep that in mind when going to select your cam. The LA's used 1.5's, so all the flat tappet advertised specs are for 1.5's.

The 380 horse 360 Magnum crate motors ran production heads. With minor carb and ignition tuning Dulich got 410 horses out of it. Hitting your 325-350 target should be like walking in the park.

Cool. I'm originally from the other corner of the state. Erie area. My dad use to race up at the Erie county speedway. I still have the 70's style Kendall GT-1 racing jacket and 2 Kendall trash cans in the garage.

This car was originally from there as well. It was restored by a family friend up there before my dad bought it. He has owned it now for 24 years.

I'm in Texas now.

I'll be hitting you up come exhaust time. That will be probably early next year. I'll need a set of headers at least to let this puppy breath.

Cool. One of my best customers has a '71 Duster that came from Erie. I haven't made a trip to that part of PA yet, but I want to.

My '87 Daytona came from a buddy in Fort Worth. So I guess we kept the PA-TX Mopars in balance.

I'm also a dealer for Kendall & Brad Penn. When you order the headers I'll see if I can get some Kendall swag from my distributor. We were guests of Kendall at the NHRA Nationals at Maple Grove a couple weekends ago.

That's me in the black shirt, V.Gaines in the red, and his Pro Stock Avenger behind us.