Some Comparisons of a Chevrolet Iron Head L98 VS L31 350

I picked up a L98 out of a 89 Firebird last summer during a Pic-A-Part outing. I bought the long block with the intention of rebuilding it for Pepe. Upon tearing it down, I discovered the short block had a broken piston skirt. The previous owner had replaced the L98 camshaft with a Crane Power Max 2032 and had also done some amateur port work on the intake side of the heads. During another outing a few weeks back. I pulled a 140K mile L31 Vortec from a 1996 Tahoe.

There are some expected differences between the 2 engines and a few unexpected.

OIL PAN

I expected the truck pan to be totally different from the Firebird. They were actually almost the same shape. The L98 is in front or to the left.

The most surprising difference is that the L31 pan had a separate windage tray like a L98 Y body. If you look at the L31 pan on the right, it has two holes drilled in the pan tray for clearance of the main bolts that hold the windage tray.

HARMONIC BALANCER

The two are completely different diameters. L98 on the left, L31 on the right.

I don't know if this information is interesting, but here is a picture of the L31 camshaft with a code on the end.

#8Chevrolet 4.3 G Body Serpentine - Videos

#2 Chevrolet 4.3 G Body Serpentine - Air Conditioning

Living in Nevada, having working A/C is mandatory. This part of the swap was a bit complicated due to a larger distance from the condenser to the compressor due to the V6. The serpentine conversion relocates the compressor from the drivers to passengers side of the engine.


The first complication is that the high side port can be placed in a number of differing spots depending on whether it's a B body, F body or BOP G body. On the Chevrolet G body the port is on the line coming into the evaporator. On the B body it is in the manifold that connects to the compressor. On the BOP G body it is just aft of the manifold going into the condenser.


Below is a B Body a\c manifold with the high side port.

The evaporator outlet on a G body points to the side where the F body comes straight up. Below is a F body outlet.

On the Chevrolet G body, the condenser is on the top left side. On the BOP G body it is on the right top side. The F body that is late 80's has a high efficiency parallel condenser where the connections are middle right. I went the F body route. The condenser was a direct fit that didn't inter with anything on the El Camino.


Another snag is the accumulator. The Chevrolet G body has the low side line hooking up at the top. On some B bodies and BOP G bodies, the accumulator line is on the bottom and is not removable.


The setup I cobbled together were the late 80's F body manifold and a G body BOP high side line from the condenser to the evaporator. There were three issues with this setup. 1) The high side line of the manifold was too short as it came off of a V8 Camaro. 2) There was no high side port on this setup. 3) The low side line was kind of long and hit the overflow tank off the radiator.


The high side fixes were to first cut off enough of the 1/2 line with the condenser male fitting from a junkyard unit. Second, cut out the high pressure port from the old G body piece leaving the male end. Lastly using a 1/2 - 3/8 compression adapter fitting from Home Depot, make a new piece. To say it another way, take the Home Depot fitting and mate the 1/2 inch condenser outlet piece to the 3/8 inch end of the high pressure fitting from the old G body line. What you now have is the manifold line screwing into the new piece which screws into the condensor.

The BOP G body condenser to evaporator line fit without any modifications.


The low side fixes involved removing the radiator overflow tank and judiciously working the line with a tube bender and doing the same coming off the manifold. It wasn't pretty but it worked!


Changing the compressor from V belt to serpentine wasn't too hard with the correct tools. Before I went to the junkyard I stopped at Autozone and rented the clutch tool, a clutch hold tool and a 2 tong puller. You'll also need a pair of snap ring plyers that can spread at least an inch. The crummy Harbor Freight tool doesn't spread far enough apart. With the proper tools, it was fairly easy to change the pulleys. There are some good you tube videos that I am glad I watched beforehand.

#5 Chevrolet 4.3 G Body Serpentine - AIR pump

The smog pump is ugly and takes up valuable room on the left side of the engine. It also can effect the functioning of the TBI injection if it doesn't work. If the O2 sensor can't tell the pump is sending air, the computer will compensate the mixture. The pump has to stay and be operational!


The 4.3 TBI pump is hooked to the double solenoids by various pieces of formed hose. The pump outlet points the wrong direction when positioned in the serpentine bracket.


The fix was to remove the G body outlet and replace it with a F body outlet. The F body piece is solid rather than a bunch of angled hoses. The F body piece puts the solenoid right next to the heater case, so it had to be bent upwards a bit. In a V8 configuration, the whole thing would sit a few inches forward. I have a 4.3 V6. The hard plastic outlet where the solenoid bolts to the F body piece has to be cut flush. Otherwise, the existing solenoid leads are long enough to plug in. The rubber tubes off the downstream pipe and the cylinder head pipe will hookup with a bit of bending.


The really ugly part of this is that with the a/c compressor, the F body smog pump bracket and solenoids, best of luck getting to the passenger side spark plugs!!

 

#7 Chevrolet 4.3 G Body Serpentine - Costs-not including cores or parts not used

Fan Blade	5.50
Water Pump	11.00
Bracket	5.50
Belt Tensioner \ Bracket	11.00
3 Pulley's	16.50
PS Pump	22.00
A/C Condenser	38.50
Belt	1.10
Alternator Pigtail (SI)	2.75
A\C High Hose	12.00
A\C Manifold	23.00
Fan Clutch	5.50
Alternator	22.00
Battery Cable	2.75
EC82 Adapter	19.99
Crank Pulley	11.00
Compression Adapter	5.32
Water pump gasket	1.99
Tax	20.01
Environmental Fee	6.26
Total	249.93

 

#6 Chevrolet 4.3 G Body Serpentine - Power Steering

The Saginaw pump used on the serpentine belt cars is supposed to be a superior unit to the G body model. A bonus that the F body has is a line that acts like a PS cooler. I used the F body outlet lines and the G body return line.

 
 

The cooler section bolted right to the G body lower radiator support.

 
 

Here's my you tube video concerning this part and the final assembly of the entire conversion

 
 

 
 

#4 Chevrolet 4.3 G Body Serpentine - Cooling system

The serpentine belt runs the water pump backwards of a V belt setup. This was pretty uncomplicated but required a few pieces to work correctly.

 
 

I used pieces off of a 1993 305 TBI Caprice for the parts forward of the water pump. The fan and the FAN CLUTCH go together. GM designed the fan so that it can't be used with a V belt fan clutch. The parts don't fit together.

 
 

The water pump donor was from a 1989 TBI Camaro. This is a water pump with a provision for a heater outlet. I pulled the outlet off the original 4.3 water pump and transferred it to the Camaro one. The Caprice pump may have worked but the Camaro one looked fairly new. The Camaro pump didn't use a mechanical fan, so I had to steal the studs off the Caprice water pump.

 
 

The parts matched up fine with the 4.3 fan shroud!