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Need tuning advise

5K views 86 replies 18 participants last post by  GTAShief 
#1 · (Edited)
Having issues with the car this yr that i havent seen before. When its nice weather out my car repeats and prints tickets all weekend. 1st weekend out this yr i made 27 passes in 3 days in 2 class and didnt move more then .009 in .60ft
Every weekend after that its been hot as hell and i have done nothing but chase the car. I have never raced with this much heat out for a whole race season. For example.. Yesturday i went 6.514 in my time run. Dialed a 6.52 as it got about 10 degrees hotter and we went up 500ft in DA. lost 11 thousand in .60ft and 3 hundreds in the 1/8th. Lucky i got the win. Car stayed on that same et into round 4 where it slowed another hundred and lost another 13 thousands in .60ft
So basically im round 4 i was almost 3 hundred slower in .60ft and 6 hundred slower on the big end then my time run. That round 4 pass was the slowest pass of the season. Others was not chasing there dial like i was and its been like this in the heat all yr. But yesturday was by far the worse. Heck on friday night when it was cool out i made 6 passes and it went 6.473-6.481
Im on alcohol and possibly just to rich? Or do u need to be making shock adjustments on these hot days? Im honesty lost. We have 4 races left and im 4 rounds out of 1st place so i need to do something. At least a place to start would be helpful. Sorry for the long read.
Sbc 383 13:1
Alky carb 160 jets
29.5/ 10.5 stiff tire
Strand doubles on back 6 on compression and 4 on rebound.
Qa1 singles on front.
 
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#3 ·
What do you want to know Besides what i put in original post? Its a leaf spring car. Weighs 2850 with driver. I stage at 160 and it is about 165 at the other end. Powerglide with transbrake. 4:56 rear gear
From what i always notice is that vapor pressure kills this car. When vapor pressure gets into mid 60 and up then it really slows.[/QUOTE]
 
#24 · (Edited)
What do you want to know Besides what i put in original post? Its a leaf spring car. Weighs 2850 with driver. I stage at 160 and it is about 165 at the other end. Powerglide with transbrake. 4:56 rear gear
From what i always notice is that vapor pressure kills this car. When vapor pressure gets into mid 60 and up then it really slows.
[/QUOTE]
There's ^^^^^ a contributor.

DO NOT TOUCH YOUR SUSPENSION !!!!!

IMHO -- the water temp isn't hot enough when you stage and if you're only seeing a 5* temp increase at the end of the run, the main jetting is too fat. You need to shoot for a 10-15* water temp increase.

Up the water temp to 170-180* when staging. Then start pulling out main jetting to get the 10-15* water temp increase.

The water pump should be running all the time the engine is. Use your fan to regulate the water temp.

HUMIDITY slows an alky burner.
 
#4 ·
At the risk of coming across like a complete smart ass, which is honestly not my intention... It sounds like it is predictable and consistent with the moves based on the changes. Why not just change the dial accordingly? Seems much easier than chasing a mythical tuneup that doesn't move with the changes... If you told me my car was ONLY going to move 4 numbers over the course of the weather swings we see here, I'd be tickled. Just cloud cover and/or wind changes can be worth up to 5 numbers for me (when everything else is fairly constant - although clouds do also typically affect the ambient air temp).
 
#7 ·
All cars change when the weather changes. You have to keep accurate records of what your car does in similar conditions. You need a good weather station and run prediction software to be able to accurately predict your dial. Typically a car will be more consistent when it is run on the lean side. Also if you have scoop on the hood plug it and pull air from around the engine bay. That will stay a bit more consistent than the air coming in an open scoop. Barometer and humidity are what will change the car more than temp. Keep a close eye on humidity. you cant burn water. My car will change 2-3 tenths from good to bad air.
 
#8 ·
Im well aware of weather moving the car around. I have a good weather station and log every run. Moving 5 hundreds in a few hrs on alcohol is alot. I dont see it from any other person i race around. So i just thought i may be off on my tune up.
 
#9 ·
I only raced sat. but I had a phantom slow 60' out there. Went 5.99 with a 6, 5.99 with a 6, then a 601 with a 8 (so I lost). Bought back and went 5.99 with a 2. So it could have been the track.
 
#15 ·
Try q16, i had few friends who went to alky and said it moved too much , went back to the q16,myself after the last refresh i went away from the q16, it worked great but just not worth it for bracket car running low 10s, plus the price and issues with corrosion makes the down side.
 
#16 ·
I've held 3 to 4 numbers before depending on who I'm racing. It's not uncommon for a dead on bracket car to move some. Track conditions and air temp have alot to do with it. I was dialed a .52 last weekend and in time trials never moved. Went into first round was a .006 to his .10 and ran it out and went a .56. Little more humidity in the air and track felt like it wasnt getting grip off the line like it was during time trials. Just adjust accordingly and dont sweat it.
 
#19 · (Edited)
One thing to keep in mind, and you might already know this, but "moving around" 4 or 5 numbers in a 1/4 mile is very normal, especially in summertime air. 1/8 mile maybe not so much. And whenever I have heads up runs with shitty weather, I always look to see if my opponent has a bigger cubic inch motor than mine. The 400 Pontiac is a combo that falls right into my class but at Bristol he has an advantage. Big cubic inch motors don't slow down ( in bad air) as much as smaller ones. And although outlawed in our classes, if they are running oxygenated fuels same thing applies. So watch who you are comparing yourselves too.
 
#20 ·
I'd start out by taking it down 8 numbers on the jetting and go from there. 4 numbers on most of the alcohol cars I have seen doesn't make much of a change. Try 8 and make a couple of passes, you should be picking up more temp in the run too, but cooling off back to the pit if you're running alky all the way. And since no one else is moving around, how many runs are on the slicks and the trans? How often you checking the band adjustment and how much temp are you carrying in the trans?
 
#21 ·
Slicks are new this season and trans is 2 yrs old. I do need to adjust the band though im sure. Trans temp is usually around 150 unless its late rounds and im doubled. Then it gets pretty hot. Im gonna hit a tnt next thursday and make a couple passes. Then drop jets down. I have a set of 154s to try. See if mph picks up or not.
 
#26 ·
So what is the difference between running slower with elevated humidity levels Vs running "great" in humidity?

Thanks for proving my point --- that not every drag racer has the water pump running when the engine is.
 
#27 ·
A local bracket racer, not the best in the country but definitely right up there, runs a 572-inch alcohol doorslammer - 2800 pounds, glide, that footbrakes (never uses a t-brake) to a 5.50 in 2500DA air. Bump that up to 4500, such as it was yesterday, and it's a 5.65 car. That's a tenth and a half. He doesn't waste 5 seconds leaning it out or fattening it up - he knows from experience and documentation what the car is going to run based on the DA and dials accordingly. But we're talking a man who has made probably 2000 passes down a drag strip and that experience is what wins him races.

Point being, I personally don't believe losing "3 or 4 numbers" as the day warms up is a big deal. You try chasing it with jetting, timing, tire pressure, etc and you may wind up just chasing your tail. Keep records of what your car runs as the air gets better or worse and change the dial, not the car.
 
#30 ·
Exactly..my car at any track in the south or around here runs a dead 52. Now, put it at Bristol in that mountain air high 60s. I dont go around changing timing, jets, I adjust accordingly.
 
#28 ·
.

Isn't that a huge drop for an alcohol car???
The entire reason I wanted to switch was watching a guy at the team finals, running 2 classes and never changing his dial in.
65* in the morning, 85* in the afternoon and back to 65* in the evening and he never changed his dial in!!!


.
 
#31 ·
Yeah it was and I doubt it was all due to DA. Most of the time his car doesn't vary nearly that much. The ambient temp was nearly 110; the track temp had to be pushing 150 and I'd imagine some slippage was at play. He just dialed it to match and went 4 rounds.

Once the evening air (still hot in the upper 90s) cooled things down a bit the car picked up .05. Anticipating the change he dialed 'er down and went a couple more rounds.
 
#32 · (Edited)
I think mine is very consistent & will repeat enough for me to be looking at thousandths to determine my dial. If it went a low thou & it starts cooling off I MIGHT dial it down a number or just leave it knowing I’m carrying a little extra. It doesn’t matter till you get down towards the stripe anyway.

That being said I have run early in the am at 800ft & gone a 65 & run at 2 pm at 2300ft & dialed it 69.... other guy red lights & I went a high 67 out the back door.

Track temp was way up at 2 compared to 8am.

I think a 4 number swing on alky is a BUNCH but your mileage can vary.
 
#34 ·
I do know my car will run about 5 hundreds quicker staging at 170. It is more consistent staging at 160 though. Usually when the humidity goes up my car picks up a little. When vapor pressure goes up then it tanks my car. So i generally watch vapor pressure. DA has very little effect on it. I talked to my carb builder today about the issues. He told me to lean it out 6 sizes and try. He also said it could be converter related as well. Here shortly i will post pics of runs and weather during them.
 
#42 ·
Mine printed tickets every weekend. Dialed off the trailer numerous times.
 
#43 ·
And yet you won how many races...mine prints em too. Been to several final rounds this year. I'm not concerned with who's done what or who hasn't. This is the OP's thread and I'm giving my experiences and what has helped me.
 
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