Tail wind?

quote:

Originally posted by Eman:
Time between runs,
First run 1:39 PM second 3:34 third 4:57 all runs in the same lane.
Trans temp between 125 and 150. Don't have an engine oil temp gauge yet.

Top 38, what other info? Tell me why 2nd should have picked up?, is it because of GPP of water? Is this an indication I'm too lean?
I went back and added MPH to original post

Assuming there were no other things impacting your second run other than weather, no wind, track etc, for some reason you slowed up and should have run faster than the first due to water in the air, a few degrees of temp is meaningless. And you saw this with your third run when it did what it should have based on the weather info you listed. As for jetting, you can try more fuel and see and go from there. Maybe a data logger would give you more info such as did it shift earlier for some reason which would also slow it up. You need to look deepier to find the answers.

Oil temperature.

Using a sampling of runs from my alcohol carbureted door car, there are a lot of weather factors that have a strong correlation to ET changes.

Dew Point is strongest, but many are close. You don’t have that but grains is extremely similar. My analysis shows a change of .01 in ET for roughly every 9 grains.

Density Altitude does still have a strong tie to ET and that will change .01 with every 175 feet or so.

I’d agree that your second run should have been quicker than the first although there are plenty of variables that are unknown here. Wind is absolutely top of that list and is really impossible to nail down. What you should have gained in grains, you lose about half of that from the increase in temp and decrease in barometer. Should have at least been a few thou quicker than run #1, all else being equal. The low mph could point to wind.

Fluid temperatures could also be in play but I don’t monitor those, and never do any warmup in that area. I just use high idle in the pits but don’t notice a change from run 1 to run 2 when things would be warm.

This has been a great discussion.
It was a weekend of a big weather swing. It had been very warm all week and Friday the rain was coming in which it did and rained us out Friday night. Car was slower on Friday with the high humidity. It rained all night Friday and the temps dropped. The Sat. it took a little time but the front moved through and conditions improved a lot. One factor could have been the wind as it was gusty as the front moved through. If anything it would have been a headwind which might have caused the slower pass that should have picked up. Hadn't thought about that until brought up here.
Car is good just always looking to be better if possible. Mostly to make up for the poor skills of the driver.

I try to do a decent warmup by just driving around the pits and a few powerbrakes. On this day they wanted some heal drying the shutdown area so I got to warm it up more and I put it on the transbrake a couple of times.

quote:

Originally posted by Woody B:
Oil temperature.

I'll explain more. Everyone who runs alcohol needs an oil temperature gauge. From what I've read it may have been a little cooler weather than previous races. You attempted a good warm up, but basically just putted around more. Even with a perfect fuel system you're going to get some alky in the oil. This alky in the oil affects oil level. In most situations if you raise the oil level any, even 1/2 pint it will lower horsepower due to windage. Methanol boils at 151 degrees F. Once you get the oil temperature above 151 degrees the methanol in it will start to boil out. This will lower the oil level, as well as lowering ET's. Get an oil temperature gauge, as well as some type of oil pan heater. Get the oil temperature at least 170 degrees and keep it that hot.

Assuming you were running in E TN on Saturday 10/16/21, there was a huge shift in the barometer and dewpoint due to a front that came through. It was very windy. It was almost impossible to dial due to the wind and the drastic changes in dewpoint.
We experienced it at Atlanta. I was totally unprepared and made terrible decisions with the juniors and my car and they all react differently to the weather.
It's a learning opportunity, but I wouldn't get too concerned about it. The dewpoint dropped from 68 to 45 degrees and barometer went up over .1 from noon to 6 pm. The temperature dropped about 10 degrees from noon to 6 pm.
Almost everyone was breaking out.
And..ditch the thermostat.

I’d give George Rupert a call and ask his opinion.

quote:

Originally posted by B.C.Malibu:
I’d give George Rupert a call and ask his opinion.

The next chance I get that I want to spend an hour on the phone I might. That's not a knock on George, just the way it is.

All good suggestions. Yes the weather changed drastically from early Sat. morning to the time the passes were run. Here in the mountains the weather can have big swings.
I do have an oil pan heat pad on the motor in the car. I do also have another motor that will go in the car son and the oil pan on it has a temperature sensor in it. The thermostat is an experiment and honestly it seems to work fine but as I said it's a $4 experiment that I had a previous discussion about on this board. I also use a moving blanket over the hood and blocking off the grill and cowl to help retain heat now that it's cooler and breezy.

This message has been edited. Last edited by: Eman,