Alright guys here's the story. I went to Brainerd (BIR) a couple weeks back for the first time with my car.
Car specs: 350 HO with XE268 cam, performer rpm intake, 1 5/8 ceramic shorty headers, Demon 650 vac sec carb, TCI 700r4 with fairly tight converter, 3.42 gears, street tires.
On the chassis dyno ran 260hp @5400, 290 tq @ 3800.
It was the hottest day of the summer so far, 85 degrees. The problem I had is once I would get to the end of second gear and all through third I would start to lose power, to the point where i would just let off the gas halfway down the track 'cause it really didn't make any difference. After a few seconds- through the traps- it would progressively start to make power again. It seemed like the bowls were running out of fuel but I had never had this problem on the street. And for how much I've tested it I would of thought I would have had this problem before. 11 runs and almost all had the same problem. I had never ran it with this carb on that hot of a day yet so that is the only factor I can think of. Man I was getting frustrated. If I could break 100mph trap speed I would win a T-shirt. I got close a couple times but the loss of power was killing me! I knew it would do it if it would just run like any other day! Well, towards the end of the day, I let it cool for 20 mins and raised my float levels a little- to the top line on the windows. That run which is what the video is, was the best, which seemed like only a little sputtering in third. The stock jets in there at the time were 70 primary, 78 secondary. Now of course once I got home it hasn't been that hot of a day yet where I could try to duplicate my problem. I have since leaned it out to 67 secondaries, 74 primaries, which seems decent. I'm not sure on the secondaries yet but I got the primaries where I want them. Could running on this hot of a day make much difference from a 70 degree day? I guess what I'm wondering is if it was really rich, is is possible it could load up going down the track? Any ideas? I ran the **** out of it on the dyno (65 degree day)with no problems whatso ever. Sorry for the annoying sound of rice and clutch burning on the video.

Time slip for the run on video:
60ft 2.336
1/8 9.132 @ 80.49
1/4 14.002 @101.01

http://s116.photobucket.com/albums/o...nt=Bestrun.flv

 

looks like its time to get some new rubber in the back. What do you have for an exhaust. For my car I have a 3 inch exhaust and as I go down the track, the car feels like its just not pulling anymore. I then opened the cutout on the next run and dropped .60 seconds and noticed a huge difference. So I don't know if your still running the stock exhaust and y, but if you are that could be a reason also. Your times for your power level are about where they should be. Around mid to high 13's

 

For exhaust I have 2 1/2" headpipes, they Y at the stock cat location to a single 3" all the way back to a Magnaflow crossflow muffler with 3" inlet , two 2 1/2" outlets. I don't think I have a major restriction there. The tires I have are 275/40/17 BF Goodrich G-Force Sports. So yeah- nothing sticky at all. Another idea for my loss of power- when my car sits for a while hot, either shut off or idling, I think the fuel in the carb gets hot or something 'cause if I take off pretty hard after the motor has been off for 20 mins, it sputters and will almost kill until it gets fresh cool gas back into the bowls it seems. Does anyone have this problem? I have a 1/2" heat spacer on there too.

 

It sounds like you're not getting enough fuel at the top end. The fuel pump isn't pushing enough fuel or the needle and seats in the carb are too small and won't let enough fuel into the bowl. Any number of things can restrict the fuel flow from a plugged or dirty filter to a pinched or too small of a fuel line.

Raising the float level won't change how fast the fuel enters the bowl.

Those hot, humid days also raise the density altitude. You were not making anywhere near what your dyno HP was. Higher altitude air means there is less air to mix with the fuel. Less air/fuel to burn means less HP. If jetting stayed the same but less air was available then the engine would be running fat (too much fuel for the air available). Brainerd has an official altitude of 1200'

 

You need some better tires for traction to get that 60' time lower. Your camshaft needs a converter that stalls in the 2300-2500 range for best performance.

 

Thanks for the advice. I realize I will need some tires for a decent launch. Well I'll be going back up there on the 17th so I'll see what happens then. My converter is a B&M Holeshot 2400 but is way tighter than advertised. My friend has basically the exact same car/engine but with a XE274 cam, 3.73's, TH350, and 3000 stall. With street E.T.'s he was doing 13.1 @ 104. His engine made 390hp at the crank. Do you have a good link or explanation with more about float levels and what they affect? I'm new to the Holley style carb, and can't stand not knowing what is going on in there.
Here's a video of our first run.
http://s116.photobucket.com/albums/o...t=MevsJosh.flv

 

http://www.barrygrant.com/demon/default.aspx?page=28

 

these are the very issues i'd address before changing much else...other than making sure you have plenty of fuel supply. 101mph at 14.00 does not indicate lack of power up top, but rather a lack of ability to get out of the hole.