Welcome to the second installment of our build series on the Project Unfair Camaro. The first article in Super Chevy last month focused on raising the floor, reducing weight, and lowering the center of gravity (COG). This month we will focus on moving weight to get a better weight balance. The typical iron small-block first-generation Camaro from the factory is about 56/44 percent front-to-rear. The total weight of a '67-69 Camaro is usually between 3,400-3,600 pounds depending on body style (coupe or convertible), engine type and options.
The biggest influence on front to rear weight balance is the engine/transmission combination, which makes up about 20 percent of the car's weight, all in front of the vehicle center point. The typical iron small-block and transmission package can easily weigh 800 pounds. We are using a lightweight all-aluminum LS engine and accessories. When you add up the weights of the original small-block fully dressed and the weight of the LS motor fully dressed, the LS engine is almost 150 pounds lighter. However, we are adding 75 pounds to our engine with a huge Kenne Bell supercharger so our net weight reduction is 75 pounds or so.
Still, 75 pounds is a lot of weight and that weight is all at the front of the car. However, moving that reduced weight 8 inches towards the rear makes a big difference in weight bias. We would like a weight balance of 50/50 or even a tiny bit of bias towards the rear. The sidebar provides all the engineering math and formulas for how much weight we moved and how much the F-to-R weight bias changed. To summarize, we moved about 60 pounds from the front of the Camaro to the rear by moving the engine and transmission 8 inches from the stock location. We also moved another 40 pounds (with us in the car) from the front to the rear by moving the seats back 4 inches. Thus, we moved 100 pounds from the front to the rear. As you'll see in the sidebar, the effect on weight bias is significant.
Also in this article, we set the engine and transmission height based on the subframe being installed with no body bushings. We already lowered the body over the floor 1.5 inches. Installing the Art Morrison subframe with no subframe bushings will lower the front an additional inch, giving the car a total of 2.5-inch front body drop and 1.5-inch rear body drop. This will give us a nice minimal rake without compromising suspension geometry.
Raising the subframe does create a couple issues, though, which need to be addressed. The first is the engine and blower are pushed 1 inch closer to the hood, and our engine package with the massive Kenne Bell 3.6-liter blower is pretty tall. Second, the transmission tunnel has to be raised to make room for the T56 transmission.
Moving the engine has some great benefits, and in our case was a necessity because of our tall engine package and compressed subframe to body relationship.
If this were a naturally aspirated LS engine with no blower on top, we could have moved the engine back a couple inches and tucked the engine transmission package under the hood easily, even if we compressed the subframe and body by using no bushings. For us, we wanted to move the engine a lot anyway for the weight balance effect. But we also have to say that cars can still handle wonderfully without changing the weight balance. We do not want anyone to feel they have to move the engine to get a great handling car. Remember, we are being Unfair!
The above paragraph is a disclaimer of sorts because the firewall and tunnel modifications are by far the biggest scratch fabrication projects we will do on Project Unfair Advantage. There are no reproduction replacement parts for what we are doing. So we simplified the process so someone else could do this possibly at home, or at least trim labor hours at your shop building your car. A $40 wheelbarrow from our local hardware store saved dozens of hours trying to form a recess for the engine which is moved 5.5 inches under the firewall. In our case, we have to also notch the upper firewall for blower clearance. Our supercharger now is going to be even with the edge of the cowl filler between the windshield and hood.
Follow along, and next month we will put our super-trick Art Morrison suspension in. I promise you have never seen anything like it.
Calculating The Effect Of Moving The Engine
Moving the engine back is an old trick for hot rodders. On our front engine/rear drive muscle cars, moving the engine back solves several problems (but creates new ones-see below).
On Project Unfair, we not only had to move the engine back, but down as well. The massive Kenne Bell supercharger sits high on top of the engine and we want to keep our hood to a 2-inch cowl. No 4- or 6-inch cowl hoods for us, thank you.
Before going into the calculation of what moving the engine 8 inches will do to the weight bias of Unfair, let's quickly recap where we are with the car's weight:
Stock: 1,900 front/1,500 rear/3,400 total
56/44 front-to-rear weight bias
With a weight loss of 75 pounds for the engine and 90 pounds for aluminum sheetmetal before we move any weight (assuming 80 percent of the weight savings comes off the front, and 20 percent from the back)
1,900-0.8*165 pounds front, 1,500-0.2*165 pounds rear
1,768 front/1,467 rear/3,235 total
Putting us now at 54.5/45.5
In order to drop the engine, we have to go back 8 inches before going down because we have to get the engine behind the Tony Woodward rack in order to lower it. Making these changes was a last resort solution: We didn't want to have to do this.
Hopefully the use of a hardware store wheelbarrow is a trick you can apply to your own projects should you decide to grab your torch and welder and make a similar fix.
The math shows a significant gain in the weight bias front to rear. The mass of the engine/transmission is now completely between the axle centerlines (a factory Camaro has the number one spark plug even with the front axle). Let's assume that the car started out as 54.5 percent of the weight on the front tires, the engine/clutch/tranny combination weighs 800 pounds, and that the car will weigh about 3,000 pounds empty and 3,200 pounds with driver. We are moving the engine 8 inches and our wheelbase is 108 inches.
The approximate effect per axle can be calculated using the following equation:
Wb = (Mm/WB)*(M/TW)
Wb = change in weight bias
Mm = movement of mass (the engine/transmission) in inches
WB = wheelbase
M = weight of mass
TW = total mass of car
Plugging in, we get Wb = (8/108)*(800/3000) = 0.0197, then multiplying by 100 to get percentage gives us 2 percent.
In plain English, moving the engine back 8 inches moves 2 percent of the weight from the front tires, and puts 2 percent more weight on the back tires, for a total swing of 4 percent.
Since we are probably around 54.5/45.5 already with the aluminum panels, the engine movement results in us being around 52.5/47.5 now.
We are also moving the driver and seats 4 inches backwards since the firewall moved. Let's figure 200 pounds for the driver and 50 pounds apiece for the seats. That gets us another half percent (1 percent overall), putting the car around 52/48, or around 1,682 front/1,553 rear.
We'll be moving more weight rearward in the coming months: battery, wiring, and electronics, along with additional front of car weight reduction to get to our goal of 50/50 weight distribution. We still need to move about 65 pounds from the front to the rear, or take another 130 pounds out of the front. The battery movement alone will get us a long way towards our goal.
We also moved the engine down 1.5 inches, lowering the COGH (center of gravity height) a like amount (the best approximation of a car's COGH is the camshaft height). Now we can use that awesome Auto Metal Direct 2-inch cowl aluminum hood!
All this movement from stock locations isn't free. We've compromised our A/C evaporator position, complicated the driver's ergonomics, pedals, steering wheel, and shifter), made the header fabrication more difficult, and we'll have to make custom motor and transmission mounts. We should be able to return to more standard parts and fabrication sequences now. - John Parsons