HOW TO Convert your BMW 325 / 318 Drive train to a Small Block Chevy Power
I have received numerous emails wanting more details about HOW-TO perform the conversion. I have plenty of notes and need to get them on the web before I forget all the details. I built the car in a few months. There are many ways to attack a conversion project. I performed research and took many ideas from the JTR s-10 Conversion Manual. This conversion requires fabrication skills. A sawzall, welder, drill, grinder, and common sense are required to perform this conversion. I hoisted the motor into the engine compartment and studied the engine, engine compartment, and thought of how to attach all the necessary components. I don’t claim to have all the answers. This is how I performed my conversion.
I installed a B&M Pro Stick in the factory 5-speed console. I put the backup lights on a switch. The neutral safety switch works. I had the dash apart several times. Everything works except the trip-o-meter. The speedometer is electronic and gets its signal from the rear differential. The factory gauges were manufactured by VDO. I installed VDO Tachometer and Voltmeter. I converted from 5-speed to automatic gas and brake pedals.
I used a hammer on the firewall where the trans. tunnel starts. Since I used a 700R4 instead of a TH350 I had to trim a small section (about an inch-inch and a half by 12inch long) of the tunnel on the passenger side where the tunnel flattens out to floorboard. I used a factory transmission crossmember. I turned it around and moved it back (in the floorboard slots). My Father welded a plate on it to bolt the transmission mount to it. There is another crossmember under the car. I used it under the rear of the transmission. I bolted a rubber snubber from a traction bar to it to help support the rear of the transmission. We had to tweak the Transmission Dipstick Tube to face toward the front of the car a little more.
BRAKES
The original brake booster would not
clear the valve cover. There were many options..BMW motor sports offer a very expensive manual
brake kit. There are also many aftermarket master cylinders (Summit/Jegs). I chose a part I had on the shelf a master cylinder
from my 70 Chevelle. The unit is cast iron, heavy,
but functional. I installed it but
the brakes didn't work as well without a stiff push. I changed the relationship
of the brake pedal, push rod and master cylinder to achieve a better ratio
(more brake pressure with less foot pressure). I can't remember the ratio but
do remember that I came up with a ratio slightly more aggressive than what WILWOOD
brake manufacturing suggests (probably 6.5-7 to 1).
POWER STEERING
I haven't hooked up the power
steering yet. I just hooked the 2 rack hoses to the factory reservoir. The car
steers remarkably well so I haven't been in a rush to add the power steering
pump.
CROSSMEMBER AND OIL PAN
I clearanced the front crossmember for oil pan clearance and then welded a few strengthening pieces to it. My motor is a 70’s vintage 350 with 99 Vortec Heads. The OIL PAN that I used is the same used for S10 4X4 V8 conversions. An oil pump pickup from a 4x4 V6 S-10 was installed.
I originally tried to use the factory BMW motor mount locations. It wasn't working out that well. I took a faster, easier route. I ended up using a front motor plate. The motor plate spacing the water pump out 3/8 of an inch, which created pulley alignment problems. I cut and welded a pulley that I used for a while. I came across a SBC pulley from a mid 80's Monte Carlo SS that lines up pretty well. I'll find out how it works come spring.
I installed a HOWE aluminum radiator with a front
mounted fan..very
unfortunate that there is not as much room between the water pump and radiator.
The front mount
electric fan pretty much rules out an air conditioning install.
SUSPENSION
I haven't changed the factory suspension (Yet). So far the car drives well. It is a little more front heavy than before. The car has a little bit of a front end down rake. I figure the front came down about an inch and the rear came up about the same.
My drive shaft is
actually 3 shafts welded into one. Chevy trans. yoke welded to a junkyard
(Chrysler I believe) shaft that is welded to the BMW rear "yoke". The
BMW drive shaft is NON-serviceable. I found this out after taking the u-joint
off. We found a u-joint that fit at a local auto store. My father put
everything together and hit it with a couple tack welds to hold the u-joint
caps in place. I used epoxy to completely secure the u-joint in place.
STOCK REAREND.
Both axles had a bad cvc boot when I bought the car. It made a little noise when putting the car in drive or reverse. I made it a few thousand miles before one of the CV Joints pretty much came apart. I replaced the axle shafts with 90,000-mile axles and haven't had any problems since. I do have a 3.73 rear end to replace the 2.93 but haven't felt the need. I know the acceleration would be better but I really enjoy cruising in 4th gear below 2,000rpm on the freeway.
Some Extra Thoughts.
I put the Chevy motor in because I had it and I'm a Chevy guy. The HEI played a big part in engine location. I didn't want to get rid of the heater. The blower motor is at the top of the firewall and is pretty large. A crank trigger ignition would allow the motor to be set back further. If air conditioning was a must I would install a 4.3 V6. 200HP is easily obtainable with basic modifications. I would install this motor with the factory Fuel Injection and computer. The car would get over 25MPG with this setup. A small block Ford might fit easier than the SBC. A small block ford could be tucked further back in the car, possibly as much as 2 inches.
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