M-body engine swap

[Mac108]

I own an '86 Fifth Avenue and I looking into swapping to something with more power and potential. It currently has a 318 with an automatic transmission. I'm new to Mopars and just trying to figure out which direction I need to go. I've been looking at junkyard 5.9L Magnum engines, but I don't know much about them.

What would be the best performance engine for the money? I'm on a budget and if I do swap the engine, it's going to need all kinds of other parts so I need to keep things as economical as possible. Someone please get me started in the right direction.

[dodger1]

Cheapest bang for the buck would be the last of the 360's. Trucks from 89-92 used them with throttle body injection. (I may be off with these dates but someone will correct me) They have good heads, and will bolt right into your 5th without hassle. You'll need to order a 360 style left side mount (or shim with a stack of washers) and find a left-side pass. car exhaust, or go with headers. You could adapt the TBI, but swapping to a carb (my choice) is a bolt-on as well. Tranny will bolt up. Be sure you get a 360 external balance converter and harmonic balancer. The Magnum 5.9 would be a nicer but costlier set-up, providing you get the entire efi computer, sensors, and wiring harnesses with it. You'll also want to get the complete front accessory package as they are different from your LA motor and won't interchange, and adapt the bell-housing to use the crank position sensor. Converters and balancers are specific to 5.9 Magnums as well. I did my Mirada in 98, when 360LA's were plentiful. Easy swap. Have fun - it'll really wake up the 5th. One more thing - you'll need to lose the ridiculous rear end ratio these cars came with. Mine had a 7 1/4, 2.24 gear. Now has a 8 1/4 2.94 Auburn LSD from an 84 Caravelle copcar. Big difference and still decent gas mileage.

[nhdriver]

Does your 5th ave. have the infamous "lean Burn" system on it? If you want to perk up the cars performance before the going the engine swap route, try removing the lean burn. It was a crappy set up which made the 318 perform like a slant 6 pulling a heavy trailer. I had a '84 5th ave which ran like crap. I yanked the system out and it was a different car! You need to get a mopar performance ignition kit (the one to retro fit an early point ignition car) remove the lean burn distributer install the one in the kit. You also need to change the carb. A carb from an early '80's Pick up or van works well.
Another problem w/ these cars was the awfull rear end ratio they came with.
Check to see what ratio the rear end has (there usually is a tag on one of the bolts on the rear cover)
The combination of the lean burn & the lousy gear ratio made these cars a very "lazy" performer.

[dodger1]

Not to start an argument, but the ESC (Electronic Spark Control) these cars came with does not necessarily affect the overall performance if it's working correctly. The biggest issue with it is that you cannot tune it, nor diagnose a problem without the factory tester. These low-compression, small-cammed, smogger 318's are only rated at 130 HP or so, and an ignition system change won't do much about that. I agree that a carb swap might release a few ponies, but you aren't working with much of a base here. (Ask me how I know )

[Mac108]

I was looking to the 5.9L Magnum with the EFI. I know I'd need headers, exhaust, electric rad fan, EFI fuel pump, rear end, and a bunch more.

What about transmissions? Is it possible to run one of the later model hydraulic 4 speed autos in place of the A904? Would the 46RH fit the same space? I know it may need a different driveshaft and/or crossmember, but as long as it fit in the same space, it wouldn't be a big deal.

[dodger1]

If the 5.9 Magnum is in the budget, I'd go with that. Obviously if the engine donor happens to have a 46RH bolted on, I'd grab that too. Our cars don't have a torsion bar X-member to deal with so it's a bit easier to modify the stocker. Shorter driveshaft of course, and I believe a BFH may need to be applied to the floor pan.

[Mac108]

I am on a budget, but I want EFI and it seems the Magnum is the way to go for that. I don't want to have to modify anything like the floorpan. OD would be nice, but if a 4 speed won't fit, I'll go with a 727.

What kind of options do I have for the rear axle? Would that need to be swapped or could I get axles and a diff for the stock housing?

[valiant64]

Maybe check out the Mopar Muscle magazine website. I seem to remember that they did a 360 swap into a car similar to what you have & came out with a pretty good cruiser.

[Mac108]

Looks like if I want to do this swap right, it's going to need a lot of suspension work. It's not too big of a surprise given the car's age and mileage which is about 147k. However, I was surprised to learn about the weak K-members. I'm going to do some research on suspension stuff before I go any further.

[dodger1]

Mac108, I hadn't heard anything about weak K-members on these cars. I do know that swapping the rubber K-member mounts for solid ones is recommended from a handling viewpoint. The only other (easy) change I would suggest would be to upgrade to the 1 1/8" front anti-roll bar and add the rear bar from any M-body cop car. I have done this on my Mirada and there's quite an improvement. The fat bar stiffens the suspension only when cornering, same as a thicker torsion bar does.

[Mac108]

The K-members used prior to '88 are prone to cracking or warping. They cause the front suspension to sag. Firm Feel offers worked over K-member and other suspension parts, but they are expensive. Just Suspensions, Energy Suspensions, and Performance Suspension Technology all offer high performance suspension parts as well.

My goals for the project are to have a sleeper good for straight line performance, but also some decent handling. Because of the police use, there is enough to aftermarket support to make these cars handle well considering their age and aerodynamics.

So far I need or would like to have the following parts:

Engine
5.9L Magnum engine with EFI and full accessories including A/C
Aftermarket aluminum heads with roller rockers
Aftermarket camshaft
Headers with dual exhaust with cut outs
Engine oil cooler
Shim or engine mount for 5.9L proper fitment
Nitrous system

Transmission
46RH Transmission or a 727 if the OD unit won't fit
Shift kit
High stall converter
Deep sump transmission fluid pan with cooling fins
Transmission oil cooler

Drivetrain
Driveshaft if needed
2.94 Cop rear differential with sway bar
Upgraded rear axles
Upgraded LSD

Steering
Upgraded steering box and components
Power steering oil cooler

Suspension
Cop grade leaf springs
Heavy duty shocks
Firm Feel K-member
Solid K-member mounts
Full front suspension rebuild with urethane bushings
Larger front sway bar
Welded subframe connectors
Wider rear wheels
High performance tires

Misc.
Electric radiator fan
Electric fuel pump for EFI

I'm sure I probably left a few things out, but that's a good start. Some of those things are overkill, but that would be my ideal mod list for the car. Of course I could hold off on many of the mods to keep costs down.

The problem would be that the best time to do all of the suspension work would be when the engine and transmission are out of the car. That means spending a lot of money at the same time. I know all of that stuff throws a budget out a window, but if I am going to do a swap, I'm going to do it the right way the first time.

Ultimately my goal would be to have a 12 second sleeper Fifth Avenue that could also turn a corner.

[rb77413]

I would hunt the yards and grab the k-member and suspension from an AHB equipped M-body. "AHB" being fleet/police service. I'm working on an 88 Gran Fury, and keeping the stock 318 4bbl but ditching the lean burn and if I can find my old Thermoquad, I'm putting that on it on the stock intake as well. For exhaust I'm am looking into using magnum exhaust manifolds off of the EFI 5.2/5.9L vans as that is all I can find in the yards with a 3" single exhaust. No pickups, of when there is one it is completely stripped by trime I get there. Eventually a 408 stroked 360 magnum will make it in there, with maybe the Mopar EFI kit, or I always wanted to try the megasquirt.

[nhdriver]

Originally Posted by Mac108

I am on a budget, but I want EFI and it seems the Magnum is the way to go for that. I don't want to have to modify anything like the floorpan. OD would be nice, but if a 4 speed won't fit, I'll go with a 727.

What kind of options do I have for the rear axle? Would that need to be swapped or could I get axles and a diff for the stock housing?

You have to see what rear end is in the car, some of them had the dinky 7.25 rear. If it has one of those you will need to upgrade to the 8.25 rear. They came in the same basic car ( Diplomat & Gran Fury) w/ police package . They are great choice for the M body . Somewhere here on Moparchat is a chart to I.D. the type of rear axel you have.

[dodger1]

Axle ID is easy - the 7 1/4 axle tubes neck down where they enter the center section, 8 1/4 tubes are 3" for the full length. Diff covers are different but you'd need to see a picture of each - I couldn't describe the differences properly. I agree that the time to do the front end, at least, is when the engine is out of the car. Drop the K and everything bolted to it for easy access. Shop around for a running M-body copcar - the cheapest way to get the bits and pieces. I bought mine for $500 and drove it home! Ex R.C.M.P. car, still in the weird purple/blue paint with the white doors. Got lots of respect on that drive

[dwc43]

Originally Posted by Bob'armchair'Diamond

I wana puta 440in akcar anyoen fone that.

Too many on here have made that swap, including me. I have a A body with a 440 plus in it along with a dually with a built 440.

[kick_the_reverb]

It was a little hard to see what he was asking about, as the spelling is not great, but I think he was asking about a 440 in a K car...

[thatwasfunny]

That guy was a turdburger and is gone...k car....440..... gimmie a break
Sorry guys, but this just in.. k cars suk.lol

[5thAve]

If you want a bit more power a cheap way is to put a 4 barrel on it and change to a vacum distributor. 1 good thing about that is the parts are the same for a 360 so if you do change the engine later you can keep the same parts. 360 is the easiest engine swap but it will kill your gas mileage so that better not be the only car you drive. Dont worry about the K frame most of them never have problems. You dont have to do anything with the exhaust for the 360 but youll probably wreck the 7 1/4 with it and might have transmission problems too.

[namvet67a1f]

Hey 5th .. you had probs with the 904 ? ... and how well does that cast-crank stroker package work?