Making the car more consistent
 

Just looking for a few idea's to start somewhere as to why my car runs off so much out of no where. Saturday it was in the 13.69's 2 time trials and first round, 2nd round came along and it goes a 13.637. Also when the car picks up it seems to be all the way down the track not just at the 1/8 mile or 1000" .Tire pressure is the same front and back stage the same shift at 5k 2nd and 3rd. I'm stumped on what to look for at this point. It's a 73 challenger 340/727 650 holley carb, edelbrock performer rpm intake other than that it's a stock motor (#'s matching actually) Any idea's would be much appreciated.

Re: Making the car more consistent
 

Does it usually pick up like that after 3 or 4 runs? or did the air change a bit? What does it have for stall? How old is the trans? 727 or 904? I assume this is a street car?

Re: Making the car more consistent
 

Usually it will just throw an odd ball run in there sometimes it could do it on the 2nd time pass. The Air did get a little better. That 2nd round I ran an 18 second SUV and he went .02 under his dial. Converter is a turbo action 4200 Stall converter. The Trans is a 727 it's the original that came with the car. I have had it looked at and also adjusted by Danny Crawley local racer that does Transmissions. He also put reverse manual valve body in the transmission as well. Yes I do drive it to the track but that is about it.

Re: Making the car more consistent
 

consistency starts and ends with the knucklehead wearing the brain bucket;)

That said, if the car goes from A to B pulling from the hit of the throttle to the stripe without a hint of an issue that's half the battle if not, you need to fix the mechanical issues first.

The other half is up to you. Start by leaving the hood closed between rounds, meaning don't change, adjust or screw with anything.

Make sure water temp is exactly the same every pass, burnout duration is exactly the same every pass, launch RPM is exactly the same every pass, shift points are exactly the same every pass and you are putting the car into the beams at exactly the same spot every time.

Are you observing and recording weather before every run and observing the flag?

Re: Making the car more consistent
 

I don't adjust or change anything at the track. All the other stuff i do exactly that. I have been making note of the weather but not the flag, But that wouldn't cause it to pick up that much, at least i don't think?

Re: Making the car more consistent
 

Post all 3 time slips, both time trials and first round

Re: Making the car more consistent
 

Re: Making the car more consistent
 

Looks like the second time slip should have been the fastest/quickest to me. Does the direction of the wind change much? Is the carb a vacuum secondary or a double pumper?

Re: Making the car more consistent
 

it's a double pumper and no i don't notice it changing much. I'm starting to think it's just me in the car. Maybe i am letting it bother me too much.

Re: Making the car more consistent
 

The carb is smaller than I would use, If the weather changes it will affect the small carb more. Does it have a hydraulic cam?

Re: Making the car more consistent
 

Just a suggestion.....Make sure you stage the car the same every run and the pedal to the left of the throttle is your friend! What viscosity oil are you running?

Re: Making the car more consistent
 

The cam is a old hemi grind cam. It was part of Dad's old small block stuff he put in the motor, but i don't know anything about it. Oil is 10W 30. I have a 2 day race this weekend i'm going to do some more testing hopefully it's just me flipping out.

Re: Making the car more consistent
 

is there a metter that i can buy for air temp and denisty

Re: Making the car more consistent
 

The carb size is fine. You do not need a larger one.
What's the list number on the carb?
What track are you running at?
Do you have any idea what the DA was on any of those passes?

Re: Making the car more consistent
 

Are you running slicks? If not, I'd suggest you try them.
What's the camshaft duration @ .050? If it's got any kind of performance camshaft, you should be turning it more than 5000 rpm. It won't be consistent if it isn't revved.

Re: Making the car more consistent
 

Racer 1320 makes a good point"Make sure water temp is exactly the same every pass, burnout duration is exactly the same every pass, launch RPM is exactly the same every pass, shift points are exactly the same every pass and you are putting the car into the beams at exactly the same spot every time."
It's possible that the motor was a littler colder on the last pass which would reduce it's tendency to detonate at the top of each gear and at the traps (You can't always hear when they are detonating) which would make the motor run better and pick up all the way down the track.
If you don't have a weather station to calculate density altitude I would recommend that you track and log the air temperature. It's a reasonably good indicator. If the temp drops 10 degrees, depending on your jeting, you could pick up as much as 0.1

Re: Making the car more consistent
 

Thanks all for the help, I finally got my issue taken care of. That electric water pump motor and 2 electric fans took care of it. For driving on the road though i'd say i would need an 8blade water pump to drop the temp even more. Since Lucas Oil Raceway is only 20 min from my house I don't have far to drive and it barely hits 190 on the temp gauge now. I was bracket racing at the Fall Classic this weekend first pass was the slowest all day then it got faster. 8.57 /8.554 /8.544 and i broke out 3rd round it went a 8.508 this was at 8pm saturday and it was cooler. I have to say i didn't expect it to pick up that much.