AFR curve

AFR curve

Postby Ron Gusack » Tue Oct 03, 2023 5:17 pm

433 BBC drag only ho-hum Nova bracket car. 3k lbs. with me and has been 6.0's. My best set-up is an old C454 dual plane with a lean 3 circuit 9375 on gas. I don't get much tnt time so I'm asking for advice to correct the carb tune. My biggest issue is trying to stage for footbraking, under 2600 rpm. It's not clean down low, like it surges a couple hundred R's.
Floats are at 7/16, maybe a little high?
Fuel pressure is at 6 and I think it stays there for the entire run.
HP blocks with 4 holes and inconsistently drilled from Holley. Timing is 35 to 39, isn't locked but all in at 2300.
28/29
blocked
30-32
30-32
IAB-43
IJ-30
Inter AB-70
Inter Jet-39
MAB-30
MJ-94
TSR-73
MW exit-160
Banjo pin-160
Squirter-62 I know this seems extreme but I've been bit with a lean bog when air changed and I didn't catch it.
Bypass Air-140
1st gear AFR @
1200-22
1700-18
2100-17.7
2300-15.6
2600-10.7
5700-15.2
5900-14-13
6450-14.5
2nd gear
6450-13.89
3rd gear
6660-12.69
I'm thinking a smaller TSR might get it leaner and cleaner just off idle but will it stay clean at 2200 and up? In 1st, against the converter, it gets fat and then shoots lean during launch. Any advice is greatly appreciated.
Ron Gusack
 
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Re: AFR curve

Postby whammy » Sun Oct 08, 2023 10:56 pm

Are you sure those AFR numbers below 2200 aren't just lean misfire leaving unburnt fuel in the chamber that's burning when you load it against the brake at 2600, then showing up as rich?
whammy
 
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Re: AFR curve

Postby Ron Gusack » Tue Oct 10, 2023 8:16 pm

I'm not sure, but I thought pre launch weird afr's were from 2steps and would be way lean from the misfiring. I have neither of those conditions. What I'm trying to solve is not being able to get the r's to easily adjust against the converter. Holding the pedal in one spot has the R's moving around as much as 60 rpm. I thought someone here might see something obvious. I'm thinking about trying more timing and maybe a little more bypass air.
Ron Gusack
 
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Re: AFR curve

Postby jmarkaudio » Mon Nov 13, 2023 4:44 am

Try pulling the intermediate bleeds out.
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