In my last write-up, I mentioned the ongoing tuning difficulties encountered after Tim's GA16 engine was rebuilt and modified for more power. Things are pretty much back to normal now after installing a new set of GAl 6 injectors and seals in lieu of the SR20 injectors that we had put in place. It seems that the standard injectors and computer are more than capable of compensating for the additional airflow and compression that had been built into the new engine. Not only does the engine run substantially better than before and make more power, it also increased the fuel economy by about 50%.
Another part of this whole equation that is important to consider in this day and age is emissions legality. With the catalytic converter in place, this engine flew right through emissions testing without a glitch. Gotta love it. Another problem encountered however, is apparently a big problem on other Nissan engines as well. Only on this engine, it's exaggerated by the Total Seal rings. The engine started consuming oil at an alarming rate. On a 2 1/2 hour trip almost 1 1/2 quarts of oil were consumed. Apparently the increased vacuum created by the Total Seal rings and the higher compression were drawing oil vapor into the intake manifold via the valve cover breather hoses. The simple cure was to route those hoses into a tee fitting and run that into a remote overflow/breather tank. Oil consumption was now normal, and there was no need to worry about fuel octane dilution in the combustion chamber due to the presence of oil.
On an entirely different note, I found a novel way to remove some weight off the front of the car. Naturally, the air conditioning components on this car were removed a while ago once its racing career began. This takes a lot of weight off the very front of the car, so handling is affected positively. But the bracket that bolts to the block which holds the air conditioning compressor is made of cast iron and weighs somewhere around 11.5 lbs. That may not seem like a lot, but it still is up front in the car and is unnecessary weight. Of course the simple thing to do is to remove it, right? Not so easy I'm afraid. It (the bracket) also serves as the lower alternator bracket. I simply cut the upper part of the bracket off from the lower section, retaining the two upper bolt holes. I also spent some time with the cut-off bracket and drilled a bunch of holes in it. The end result was a 2 lb. bracket, so I saved 9.5 lbs., which is a fair amount to say the least. Find that much weight on 10 other parts of your car and you've lost 100 lbs. You'll get better acceleration, better cornering (especially off the front of your car) and better braking.
O.K., so on to the track we go. At a recent early spring Lime Rock time trial, the Sentra was flying. The new roll cage was doing its job keeping the car flat through the turns, letting the 450 lb. front and 275 lb. rear coil-over springs do their jobs. This combo has no understeer whatsoever, and was turning some kick-butt times at the track. Of course, everyone was saying "Wow, your SE-R was flying out there!". And of course no one believed it was a 1.6 liter. It doesn't even sound like a 1.6 anymore. It was screaming down the straights, but this would prove to be its' undoing. The combination of a pretty constant 6500 rpm's plus, and the higher horsepower and g-forces were taking their toll. Oil pressure began dropping significantly enough to warrant pulling into the pits. In fact the warning light flickered a few times mid-way through some of the turns. The Red Line synthetic oil was water thin and seemed very hot. So the rest of the day Tim took it easy on the car while I planned the next course of action.
An oil cooler was definitely a needed addition, so that was taken care of the week after Lime Rock. But I was also concerned with the oil volume left in the oil pan at 6500 rpm's in the middle of a turn. I doubt if there's even two quarts in the pan at that point. The next oil fix was a bigger oil pan. So I fabricated up a custom pan from a spare stocker we had. The depth was kept stock to keep ground clearance, but I added kick-outs front and rear for an extra two quarts of oil capacity. In conjunction with the oil cooler and the oil lines, there's now about 7 quarts of oil in the system. I also skid-plated the bottom and front leading edge of the new pan with 12 ga. steel for protection, and added a rear-facing oil temperature fitting for a VDO gauge that was added to the dash. Now the oil temp stays below 220 degrees pretty much no matter how hard the car is thrashed on. It got tested hard at the Apple Hill Rallycross event in Middleburgh, NY. Tim drove the hell out of the car and came in third overall, destroying all the other 2-wheel drive cars and only getting beat (barely) by two turbocharged all-wheel drive Mitsubishi Eclipses. And those were both putting out over 300 h.p. Not too bad for only a 1.6.
Most recently, the intake tract was cleaned up a little more by replacing the fluted plastic intake duct from the SE-R that we had installed with a smooth piece of 3" aluminum tube. It's a little larger inside but a lot smoother. We used neoprene connectors between the throttle body and tube, and between the airflow meter and tube on the other end. The tubing was made longer since the battery was being relocated to the trunk anyway. Surprisingly, the length of the tubing made the biggest difference. It was tried with both a short aluminum tube and a longer aluminum tube, and the longer tube had better torque and throttle response. Bonus.
By the way, getting rid of the battery from under the hood and putting a slightly heavier Optima battery in the trunk made a 3.5% difference in front to rear weight distribution. The car used to have a 62/38 % front to rear ratio. After the battery was installed, just behind the right rear wheelwell, it changed to 58.5/41.5% front to rear. It almost drives like a rear wheel drive car now.
The one item that I was really looking forward to installing on the car is the header. Well, I hate to admit it, but I still haven't had the time to build a new custom header. Judging by the torque improvement that the longer intake duct made, I think the longer 4 into 1 header will make a drastic improvement over the current shorty header. And it'll be head and shoulders above any off the shelf tri-y headers I've seen. Until the next time.
last modified November 15, 1999