Tuning issues with hoter weather

Guys I have one car that is giving me fits as most if you know we throttle stop race and one of our car seem to be slowing down a lot. The weather adjusted altitude is 9400 fr today and is slowing done one car a lot and not affecting the other near as bad. This thing had a box stock Holley 8896 and its 90 square no power valves. I'm not with a shit in reading spark plugs but just trying to figure out what's going on



Ace

is it running good off the start then starts slowing or has a slight bog?if yes it is going lean try 2 sizes bigger main jets to see if that helps.show us the plugs you will need to have as less as possible idle time on them.

Larry this is a throttle stop car. .100 seconds into the run it kills (close's a set of throttle blades under the carb) the rpm's to 4200 then coms back on after a determined amount of time.

Ace

Fuel cell material?? Fuel Line? Length of line, pump location? Pump type? Bowl level setting? Thermal insulation of carb from engine heat?

Not only the atmosphere's temperature has changed. The temp of the gasoline has also gone up ALOT> Gasoline behaves different at both temperature and pressure. That is one of the characteristic differences of Aviation gas over conventional auto gas. As the atmospheric pressure drops and temps come up, bigger issue with fuel flashing to vapor, (boiling). Back in the stone age, lots of guys would run a coil of fuel line through a 3lb coffee can and fill it with ice.

Fuel cell is just behind the seat. 12" of line to pump then out to the regulator and then under 3' to the carbs. All MagnaFuel 300 and this set up has been on the car since it was built in 2000. Checked fuel pressure and flow. No filter and there nothing in the float bowls as far as dirt or junk. Float level is at the bottom of the inspection hole. This car has been falling off since last year and we have lost 1.0 or a full second in out timer. My kids pretty up set and has been hinting a new car from Phillip! We have changed converters and had no changes as both converted are pretty close. The one in the car has slightly better MPH but the same ET's when the car was ran all out.
Please remember I have a second dragster and it repeats all the time and we have never lost more .20 over the season from spring to fall. What littler changes we make we have no idea how or which way it affects the car and the as part is we do not have any time to test outside or our scheduled races. This really sucks as this is the 3rd year in a row my kid has entered the mile highs and I feel he's a sitting duck!
I'm going to leak the motor down and see if that points me any where. Things I have checked
Converter
Ohm'd all ignition wires
Swapped out all the pills in the ignition box
Checked and cleaned the carb. Fuel lines , fuel pressure and fuel flow
This weekend we tried a new set of rear tires as the goodyears were old and we lost more than a full tenth in the 60ft times. No luck the M/t did do anything and we lost more MPH

Ace

How old are the valve springs?

Good question? But it has a very very small cam


Ace

powerstrokeace wrote:Good question? But it has a very very small cam


Ace

Cycle time is everything on a spring.

Are the rpm's down also?

The last time we struggled with a car gradually slowing (from 60' times through e.t.'s) we tried every tuning trick we could think of...and finally discovered that the Powerglide was giving up the ghost.    Freshened the trans and all was right. Just a thought.

So if you start out lean and the air goes up your engine should get happier/closer to ideal air fuel ratio...

If you start out rich and the air goes up your engine will get less happy/ further from ideal air fuel ratio/richer than it was before..

So if you are already pig rich the bad air will just make that worse.

That being said I agree with the above post.. Maybe something else outside the engine is causing your grief...  Tight brake rotor?

What is your line pressure? How many high gear plates do you run?? Super Comp Dragster?  MPH???

Oh and how much RPM are you losing on Stall? both dead stall and full throttle stall?

Only takes a couple hundred rpm dead stall change to affect timer settings a ton.

I check/set my dead stall every race.

dkp

Ok heres a normal run. once the tran brake is released the car launches, .100 seconds in the run it shuts down for the throttle stop (roughly 4500 rpm's). .500 seconds in to the run it shifts in to high gear. depending on the timer settings. (lets say 2.0 seconds) then when the time is done the throttle takes about 1.0 seconds to open fully which is slow to not brake the tires loose.
now we do not chip the launch and never have. it goes to 5800 rpms. this was running 9.50's (colorado super comp adjusted) at 158-160 mph. this was with 3.00 in the throttle stop. we just raced last weekend and we are now down to 1.9 in the timer and now we are down to 155-157 mph.
I think since it's some what cheap i will pull the trans tuesday night and pull the 2 gear pack out and inspect it. 2 reasons. wear are in 2nd for 9.45 seconds in the run and we did brake a trans fitting at the May race and lose the fluid right before the turn off at the end of the track. didn't think it hurt anything since our problem has started before then

ace

Do you monitor the actual rpm while the car is on the stop?

heres a run when the car ran right. last years divisional in june

https://www.youtube.com/watch?v=2lkkUUJ1A80

this is the 2nd test run at last years mile highs. you can see how far behind he is

https://www.youtube.com/watch?v=QZ1p-7xm0lo

Ace

here's second round we lost 9.48 at 158.88 mph

https://www.youtube.com/watch?v=-Wj7Jlci_PU

Ace

sad thing is I do not have any thing from this year as the guy that edits our stuff has not been able to get thing done

Ok those runs all look pretty similar... I did see at least one run where the rpm on the stop never dropped below 4500... the usual seems to be that it initially dropped to 42 or 43 and kinda crawled back up to 45 before kicking off.

What I have seen with my car before is sometimes air changes will affect the dead stall rpm much more than the overall horsepower.. maybe a 1000 -2000 foot altitude change has sometimes made 300 rpm difference on the stop... and that will kill et big time..

With the small cam maybe your deal is affected more at the lower rpm's..

Does your playback tach work?

The tack in not a play back. It has a shift light.

Ace

Well we went through the Trans and found no problems. So next I did a leak down and valve spring check and found #1 was 60-65% leakage! Wow pulled the heads dropped them off and will know more in the morning. Somethingl ooks a miss. The tip of the valve is not much higher than the retainer. These are out of the box 10 bolt TFS A460 heads with the 2.35 /1.88 valves. Any body know if this right? I did get this used last year


Ace

Sounds like you were very close to having one of those catastrophic   events!!!

Was there a lot of lash on that valve?....as in....had it moved since it was last adjusted? Broken locks in the retainer?

No lash problems.

Pop the retainer off yet?

The heads are at my cylinder guy. Ill know more before noon today


Ace

Update

None yet he is working in them as we speak. He is dedicating today to get these done before he leaves tomorrow for a weekend camping trip. I do know the heads have been worked on before with less than 25 passes for the same thing. Installed spring height was altered .050 to 2.050 for some reason. The installed spring pressure has been bench tested and are 190-204. Sad thing is my only choice for springs today is PSI. That's all he has in stock. I would rather have he PAC's


Ace