Analyze My 1/4 mile Time and New Problem

[StreetSnake]

I thought I would again come to the vast knowledge bank on this site. I took the Cobra to the drag strip for the 1st time this evening. This is the first time I've been to the track in over 12 years and that time I was 18 driving a 5.0 mustang with an automatic. So I knew I was going to be rusty. I was only able to make one pass.

Car spec:
427W w/ TWM stack EFI (Perform. engineering built motor)
FAST Engine management system (450 +/- rwhp)
335/17s PS2 on rear
TKO 600
No fancy suspension work (AFCO streetrod rear coilovers)

First to the problem. After making the pass I pulled back into line and shut the car down. It was shut off for about 20min. When are lanes were flagged to stage, I fired the car up and couldn't keep it running. It didn't seem to be hot at all (80 degrees C). After about 10 minutes or so of starting it and trying to keep it running (holding at 2500rpms, it seemed to be ok. I pulled back around to get in line again and it died again. This time I just parked it and it sat for about 25minutes. After that, I decided to call it a day and head home. I did not notice any problems with it missing or anything of consequence. Thoughts???? (voltage, fuel dump issue)

Now to the results of my 1st pass in 12 years
I spun through first, hit the rev limiter, spun a little in 2nd, hit the rev limiter, and 3rd and 4th? seemed fine.

reaction: .5571
60 ft. 1.92
330ft. 5.47
1/8 ml 8.19 @ 94.34 mph
1/4 ml 12.37 @ 117.55

Although I was only able to make one pass, I remember why I love the drag strip and why I could spend all my time there. Thanks for all your thoughts.

[undy]

My first thought would be fuel system heat soak (vapor lock), all other things in proper working order. After you make a 1/4 mile run with an already warm motor you build up a lot of heat. After the pass there's a lot of stored energy (heat) still remaining in the engine, coolant system and surrounding under hood areas. With the hood closed (you didn't mention you opened it so I'll assume you didn't) your under hood temps go through the roof, causing the fuel to boil in the lines. Your injectors are set for a certain pulse duration. That pulse duration assumes that the fuel is in liquid form. If your fuel is a gas/liquid combo you could be starving the injectors, hence the extreme stumble and inability to keep it running. Try insulating your fuel lines better with the reflective foil coated insulation sleeving available through any performance parts outlets. Or .... try opening your hood always between runs..

Other things it could be are. leaking injector(s), ignition failing under heat (MSD?), heat related F/I control module problems etc..

Dave

[StreetSnake]

Thanks for the information. That makes sense.

[undy]

Originally Posted by StreetSnake

Thanks for the information. That makes sense.

Another thing Street.. Most of the US is still on "winter blend" fuel. That fuel has a much higher "vapor density" than the "summer blend" stuff. That means the fuel is much more prone to flashing off at lower temperatures. Under cold weather conditions that's a good thing... but ... when it warms up outside it can be a real pain in the arse. Now you have fuel that wants to "vaporize" in your fuel lines, as well as you intake tract/combustion chamber. You can check with your local gasoline suppliers to find out if you're still on the winter blend stuff. Believe, me, that can make a SIGNIFICANT difference.

Dave

[StreetSnake]

No S**t! I didn't know that the gas stations had different blends of fuel. Interesting. I learn something new everyday. Thanks for the info, I'll check with the local gas station.

[RACERAL]

I think that car with that HP should run low 11' maybe into the 10 once you get the rust off
Here you go for some compairsons
http://www.ffcobra.com/forums/showthread.php?t=196696

My stock 302 with TA radials and havent been on the strip since 78 was this
rt.574
60 ft. 1.900
330 ft. 5.510
1/8 8.482
mph 84.47

[RICK LAKE]

Streetsnake There are a couple of things you should do between rounds of running, First off open the hood to help remove the hot air from the run. After running the quarter mile on the return road run about 10-15 mph and turn on the coolant fans to help cool off the motor. If you are going to hot lap the car leave the fans on. Check and may sure that your charging system is up to the power needed to keep the motor, ignition, coolant fans, and battery charging at idle. If you are in the neg side of the amp meter, you are killing the battery. MSD needs 10.4-10.5v while cranking to start the car, anything less and the car may not want to start hot. Fuel system is another BIG issue if racing. As others here have said, If you are running small lines, it is very possible you are boiling the gas in the fuel rails. IMO a 3/8" supply line is not enough for a good supply to the injectors. I run 1/2" line to the injectors and 3/8" return. It is possible that your FI system is not tuned to run a little rich when racing, you could be running lean, the computor see the AIR temp readings high and the motor is not getting enough fuel too start. You need to race the car a couple of times and check the fuel maps, timing, and injector pulse rates. The motor coolant temp drops, the AIR sensor reading drops, and the car starts. This may not be caught on dyno runs. Start with a laptop and check the basic numbers. In the future make sure you open the hood between rounds for cooling off. Rick L. Without slicks, your numbers are good for Sp2 tires. The 60' times will kill you everytime. Mine are about the same as yours. You should end up in the mid 11's at 123-125 mph with slicks, if you don't start breaking things