69427
The Artist formerly known as Turbo84
Did a test and tune session at Mid-America Motorplex in SW Iowa today. Had a few changes to the car that I wanted to evaluate (lower front roll center, different brake pad compound, additional bellypan area, CAI box). Beautiful day, 77* and clear skies.
The first session was reasonable uneventful. Just went out to re-familiarize myself with the track (my second time there), and slowly build up some speed to bed-in the new pads. Lotsa bite with the new pads, but I found a couple times under hard braking that the rear got a bit loose. I'd like to think that the reduced camber gain in the front allowed the front tires to be more effective, causing weight transfer off the rears and causing them to unload, but I'm realistic enough to admit I don't have the exact reason figured out yet. Because I had limited time at the track to figure everything out, I pulled out the new compound pads in the rear and put the older (lower Cf) compound back in. The brakes were very comfortable and predictable after that.
The second session was fun, for a while. The engine ran great, the brakes held up without overheating (I've got some tabs on the bellypan to divert air from under the car out to the four wheels), and the car was pretty predictable, with a hint of oversteer at the limit. (I'm curious at times if I have too much camber gain in the rear, which might also be a factor in the loose while braking issue. I need to figure out an answer to that.) The cold air box was working, as evidenced by a couple pieces of tape hanging on the scoop entrance bending inward towards the air filter at speed.
A problem arose halfway into the second session. The engine suddenly felt soft going through a couple corners, but felt crisp at the exits. I recalled that my '84 always does that when it's low on fuel, as the fuel sloshes away from the pickup in the corners. I looked at the fuel gauge and it was on E, and I cussed at myself that I forgot to add fuel between sessions. But then I thought, this engine is carb'd, it shouldn't be that sensitive to fuel pickup during cornering as the mechanical pump can just keep pumping all the fuel in the eight foot of tubing between the tank and the pump. While I was trying to process what the problem was (and trying to keep the car between the green stuff) the engine died and I couldn't get it to refire by periodically letting out the clutch. I was trying to get the engine to restart, but I was also trying to coast the remaining mile back to the pits, and I couldn't afford to slow the car down unnecessarily. I finally ran out of momentum and pulled off the track. I got out of the car to check the fuel level in the tank (and got my ass chewed for getting out of the car a bit later when the tow guy showed up) and saw that I had about 2-3 inches of fuel in the tank. Why wouldn't it start? Did I have an ignition failure, or ??? I popped the hood and pulled the air cleaner lid off and the fuel was pouring out of the carb and down into the manifold. If I had a stuck float needle I would expect some flooding while running, but once the engine/pump stopped, the fuel flow should stop reasonably soon afterward, shouldn't it? But the fuel was still pouring in after a minute or two (the time it took for me to check the tank and remove the air cleaner top). So I thought, did I just get a good case of vapor lock, and I'm boiling the fuel in the line somewhere? Possible, but crap, it's 77*, the coolest track day I've run in the past two summers. The engine ran fine on those previous 95-101* days, so WTH?
So, I got towed back to the pits, and winched the car into the trailer, as I didn't want to try to start the engine in the pits with gasoline-diluted 3 weight oil in the pan.
I want to get car back into the garage and get the oil drained & replaced, but I don't want to lose another pan of oil if the carb pukes again while I'm debugging it. Maybe I'll rig up something to put a few psi of fuel pressure on the carb before I change the oil.
The first session was reasonable uneventful. Just went out to re-familiarize myself with the track (my second time there), and slowly build up some speed to bed-in the new pads. Lotsa bite with the new pads, but I found a couple times under hard braking that the rear got a bit loose. I'd like to think that the reduced camber gain in the front allowed the front tires to be more effective, causing weight transfer off the rears and causing them to unload, but I'm realistic enough to admit I don't have the exact reason figured out yet. Because I had limited time at the track to figure everything out, I pulled out the new compound pads in the rear and put the older (lower Cf) compound back in. The brakes were very comfortable and predictable after that.
The second session was fun, for a while. The engine ran great, the brakes held up without overheating (I've got some tabs on the bellypan to divert air from under the car out to the four wheels), and the car was pretty predictable, with a hint of oversteer at the limit. (I'm curious at times if I have too much camber gain in the rear, which might also be a factor in the loose while braking issue. I need to figure out an answer to that.) The cold air box was working, as evidenced by a couple pieces of tape hanging on the scoop entrance bending inward towards the air filter at speed.
A problem arose halfway into the second session. The engine suddenly felt soft going through a couple corners, but felt crisp at the exits. I recalled that my '84 always does that when it's low on fuel, as the fuel sloshes away from the pickup in the corners. I looked at the fuel gauge and it was on E, and I cussed at myself that I forgot to add fuel between sessions. But then I thought, this engine is carb'd, it shouldn't be that sensitive to fuel pickup during cornering as the mechanical pump can just keep pumping all the fuel in the eight foot of tubing between the tank and the pump. While I was trying to process what the problem was (and trying to keep the car between the green stuff) the engine died and I couldn't get it to refire by periodically letting out the clutch. I was trying to get the engine to restart, but I was also trying to coast the remaining mile back to the pits, and I couldn't afford to slow the car down unnecessarily. I finally ran out of momentum and pulled off the track. I got out of the car to check the fuel level in the tank (and got my ass chewed for getting out of the car a bit later when the tow guy showed up) and saw that I had about 2-3 inches of fuel in the tank. Why wouldn't it start? Did I have an ignition failure, or ??? I popped the hood and pulled the air cleaner lid off and the fuel was pouring out of the carb and down into the manifold. If I had a stuck float needle I would expect some flooding while running, but once the engine/pump stopped, the fuel flow should stop reasonably soon afterward, shouldn't it? But the fuel was still pouring in after a minute or two (the time it took for me to check the tank and remove the air cleaner top). So I thought, did I just get a good case of vapor lock, and I'm boiling the fuel in the line somewhere? Possible, but crap, it's 77*, the coolest track day I've run in the past two summers. The engine ran fine on those previous 95-101* days, so WTH?
So, I got towed back to the pits, and winched the car into the trailer, as I didn't want to try to start the engine in the pits with gasoline-diluted 3 weight oil in the pan.
I want to get car back into the garage and get the oil drained & replaced, but I don't want to lose another pan of oil if the carb pukes again while I'm debugging it. Maybe I'll rig up something to put a few psi of fuel pressure on the carb before I change the oil.
