High Performance Big Block Cadillacs
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Author Topic: G-Body Swap Guide  (Read 9610 times)
~JM~
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Posts: 1853


« on: December 04, 2007, 11:32:16 AM »

I've had this information in my files for several years now. Unfortunately I do not know who the original author was.


GM G-Body Cadillac Engine Swap Guide

('78-'88 Monte Carlo, Malibu, El Camino, Grand Prix, Le Mans,
Cutlass, Regal, etc.)

You can use a Cadillac radiator. Use the radiator saddles and top brackets from the Cadillac. The Cadillac radiator has a heater hose fitting at the top of the passenger-side tank. Strap the hose to the battery tray to keep it away from the fan.

If your Cad engine has a heater hose fitting on the rear of the passenger-side head, remove and/or plug it and put a new fitting in the boss on the outside, below the thermostat housing. Pre-'71 engines came with this configuration from the factory. This will give you more firewall clearance.

In order to fit the Cad radiator in the G-body chassis, you'll need to trim the core supports to clear the tanks. Reinforce the bottom of the support with 3/16" x 1 " flat stock after trimming it. Make sure the radiator only makes contact with rubber all the way around.

A pair of Chevy Citation electric fans will work. If you use an engine-mounted fan, use a shroud modified for clearance.

A stock Cadillac upper hose will work, but you may have to use a universal ribbed hose on the bottom. Make sure the idler arm bolts don't rub against the lower hose. You can cut the bolts flush with the nuts and grind them smooth to make additional clearance.

If you use factory iron exhaust manifolds, on the passenger side you'll have to eliminate the heat riser valve, if any, and weld the header pipe to the exhaust flange at an angle in order to clear the frame. Maintain a minimum 3/8" clearance. On the driver's side, you'll need to grind the bottom outside edge of the flange to within 1/8" of the bottom stud in order to clear the cross member.

The most common rear end ratios are 2.41 or 2.73:1. The stock rear will survive behind a mild motor if you stick with street tires and it's in decent shape to begin with. You can use the Cadillac transmission yoke on the G-body drive shaft. The U-joint bearing sizes are the same, but you'll have to cut out the ball that's there to center the Cadillac's constant-velocity joint assembly. Shorten the drive shaft to
42 15/16" (measure your installation to be absolutely sure), measured between the U-joint centerline, to accommodate the Cadillac long-shaft transmission. You can use a short-shaft transmission, but it provides no functional advantage, and the drive shaft will have to be shortened anyway. If the stock drive shaft is too small for your application, you can start with the 2 3/4" unit from a '78-'82 Camaro or Firebird.

Use the Cadillac power steering pump. If you're eliminating the air conditioning, you can run a belt straight from the pump to the crank. A Gates 11A1195 should be close. The stock Cadillac power steering hoses will usually work. If your steering box has metric fittings, you can use 3" sections of the hard lines from the steering box as adapters. The low-pressure return hose can be clamped to the stub of tubing from the box. Trim the fitting off the high-pressure hose and join it to the cut line from the box with a 3/8" compression fitting.

To delete the AIR pump, if you can't locate a pulley set from a '70 engine, use a complete pulley set from a '77-'80 425 engine. These used no AIR pump either. You can seal the air tube fittings on the front of the heads with cup plugs, or tap them for pipe plugs that you KNOW won't blow out.

Air conditioning can be retained with minor modifications to the heater/AC box, with reduced access to the #7 spark plug. You'll have to cut a clearance well in the outside of the housing to clear the valve cover. Make sure you don't cut into the A/C gear inside. This is better done with the top half of the housing removed. Heater-only cars will require a smaller clearance hole in the housing. Thin sheet aluminum or fiberglass can be used to create a clearance pocket in the housing, making sure that you don't run into the squirrel cage fan.

Maintain a half inch clearance between the driver's side exhaust manifold and the steering column. You can shift over the lower end of the column by re-drilling the holes that attach the lower column bracket to the firewall inside the car. If your steering coupling has a grease fitting, you'll need to cut or remove it, or replace the coupling with one without the fitting.

If you want to run headers, your best bet is to start with big block Chevy shorty headers designed for a Chevelle (A body) and add Caddyflanges, available from MTS, Sanderson, or Headers by Ed. The Sanderson headers require tucking up the #1 cylinder tube and flattening the bottom of others on the passenger side, and extensive mods to the driver's side to clear the steering shaft. Other brands might provide better or worse clearance. An alternative here would be to use street-rod-technology U-joints and a swivel shaft support to move the shaft away from the engine. You will need a U-joint at the steering box, another close to where the steering shaft comes through the firewall, and a third in the middle next to the swiveling shaft support (looks like a heim joint) bracketed to the frame.

Create additional exhaust clearance at the firewall by cutting flush the five sheet-metal screws protruding from the firewall next to the steering shaft. Flatten the passenger side of the lip around the
steering shaft hole in the firewall and dimple the rest of the firewall in this area approximately 1/8".

The column shift linkage won't fit. Remove it, being sure to fix the lever on the column in a "steering unlocked" position. Use a floor shifter instead.

The Cadillac valve cover will reportedly clear a factory power booster.

You may need to cross the fuel line over from the passenger to the driver's side of the chassis. If so, use a 4' section of hard line attached to the existing line with a compression fitting. Route the line in the depression on the back of the cross member, securing it with insulated clamps screwed to the frame. Maintain the hard line to within 8" of the pump, and add a section of rubber hose to allow for engine movement.

Use a '68-'76 Eldorado oil pan, pickup tube, dipstick and dipstick tube. The rear-sump pan requires a different dipstick, and the dipstick tube needs to be inserted in the rear hole in the block. Knock out the ball bearing plugging this hole and transfer it to the front hole. After tapping the dipstick tube into its hole, gently bend the section of the tube inside the pan down toward the sump, keeping it away from moving parts. If you don't do this, the oil will read too low on the stick. The front oil pan drain plug should be cut out and replaced with a flat plate. This plug interferes with the cross member and it will be inaccessible anyway. The notch in front of the sump that's used for front-drive half-shaft clearance prevents the oil in the small front sump from draining back, so either remove it or fabricate a drain back channel through it. Heli-arc or TIGwelding is best, but in any case be careful to avoid cracking or warping from excess heat.

The oil pump from the '77-'84 368 and 425 engines (Melling part # M58G) tucks the filter much closer to the block for clearance. You can use a remote filter setup, but the consensus is that this is to be avoided because it reduces flow and takes longer to build oil pressure on startup. You can also reportedly space the sway bar down 2" and retain the 472/500 oil pump.

You will need an aftermarket transmission cross member, such as the one offered by MTS, or you can fabricate one. When placing the transmission mount, make sure the engine centerline is parallel with the vehicle centerline. The engine may end up shifted slightly to the passenger side of the vehicle depending on how you fabricate the engine mounts. That's fine as long as the trans mount is shifted a like amount to keep the engine's centerline parallel with the car's. If the engine is angled in the frame, you will get serious drive line vibration due to improper alignment of the U-joint(s).
« Last Edit: December 04, 2007, 02:42:31 PM by ~JM~ » Logged

PS. You don't have enough cam. Grin

...Summit has a kit for $99.... Shocked
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