Humidity & Water Grains

[Rat]

A little late I know but Happy New Year to everyone.
Looking for some guidance from our seasoned racers with regards to performance drop when the humidity and water grains are high. We did some testing yesterday and were way off our previous runs. Initially we tuned for the conditions but for the last pass everything was back to what we ran last time which is still very rich. So the 2 runs weather condition were
1. Temp 74.92 f, Humidity 25%, Uncorrected Barometric Pressure 30.04, Water Grains 32, Air Density with H2O 97% and Altitude 1074'
2. T 78.80, H 92%, UBP 29.80, WG 129, AD 94% and Alt 2230
Stack injected methanol 392 Hemi.
Thanks Neil

[Rat]

Using some figures from the Biondo Bros I calculated we should have run about an 8.79 to 8.10, but we ended up with a 9.48.

[wideopen231]

That much Alt. change would have required about .010 jet change on my stuff anyway . Look at fuel   flow to motor and will see thats good amount richer than should be and would knock it in the dirt.. I don't know about your expected numbers because that big span. Non adjusted tune and rich to start I could see cpl tenths because it went from rich to plain FAT. JMO

[Rat]

Thanks Wideopen, My calculations for a 4.8 AFR on that last run was a 134 MBP so yes with a 120 real fat. As that last run was only the 14th full run data is a little limited hence my question about how far the performance should have fallen away. We were off by over 1sec and 15 mph on the first run, tried a few thing and then for the last pass just went back to our base tune. I have a feeling the pump may have gone away. Anyway will investigate further this weekend.

[wideopen231]

if pump is gone and you are any where near original tune it should show lean,especially on top end. Unless pump has been bad for a while. Rich and lean can act the same if way off. Check vent to make sure clear have had issues with that before,but normally it runs great till it burns something if thats case.Also any poppet that might not open? Only one jet in main,it has happened.

[Rat]

We checked the poppets before and after, seemed ok. Will definitely check the breather as it had been months since we last ran. We are currently running the 2 bypasses, Main & Idle. Sneaking up on the tune before maybe adding a high speed. Thanks again.

[Curly1]

That far off I would say check for clogged nozzles.

[msundstrom]

What do the plugs look like?

[Rat]

We checked all the nozzles beforehand and during.
The plugs are rich as expected and were brand new.
Thanks for your thoughts, we will be rechecking everything tomorrow (Saturday here in Aust).

[Rat]

After checking everything else in the fuel system we had the pump flowed, all good.
We rechecked the balancer mark just incase. So far nothing is jumping out as the cause of our power loss.

[Rat]

We ran the Nostalgia event at Willowbank on Saturday and with just a barrel valve tweak it ran slightly off (0.2 & 4 mph slower) our best. The conditions compared to on our PB (8.585) were not that different other than humidity & water grains being double. This combination seems to not like high humidity & water grains.

[masracingtd1167]

Alcohol loves heat hates humidity !

[gregm784]

Humidity is Latin for more lead in mag.