AFR help

[Ron Gusack]

I bought a used HP 80511 (830 cfm), replaced the base plate with a BLP 1.75 throttle and opened the main well exit channel to .151. This is a drag only, 12:1,433BBC, 400 trans, 488 rear, footbrake car on gas.
IFR 037
IAB 073
MAB 033
MJ 92
Squirter 040
Emulsion
031
B
031
B
031
021 kill
Went to test and only got 1 run because of a trans fluid leak. Launched at 2900 with a tiny stumble and ran clean the rest of the way. AFR was 11.90 at the 1-2 shift, rose to 14.46 at the 2-3 shift, leaned out to a little over 15 and crossed the stripe at 14.11. The ET was 6.337 @ 107 which I thought wasn't too bad for a first pass, but I'd like to get the fuel curve a little flatter. There's no TSR and I don't remember what it measured, but I'm not used to seeing an unrestricted t-slot main body. I used the stock blocks just to see what it would do. I have some BLP billets so changing the stack will be easy.

Any thoughts are greatly appreciated.

[Right hand drive]

What is stoich of fuel?

Do plugs agree with AFR?

I have used a same sized annular carb before that delivered a good fuel curve with emulsion .025” x .020” x x with .025” mab. This only needed 76 and 85 main jets for my 383ci with pv. It does need more squirter though. I’d look to establish if the data is correct first though. Using gasoline AFR scale for fuel not 14.7:1 stoichiometric is one thing that can throw things off. Having the O2 sensor in the collector and dropping the exhaust could be another, not saying you are doing that though.

I’m a bit vague on it but I have recollection of Shrinker saying something to the effect of on up shift and demand dropping with revs there can be a situation of some main well fuel back filling the empty emulsion air well reducing what fuel reaches the booster. Would need the confirmation of the likes of Mark or Mike on that though.

[Ron Gusack]

[Ron Gusack]

The Racepak fuel AFR says "Raw data value B: 1 will become 14.7"
Raw data value A is 0 and will become 0, whatever that means.

[Right hand drive]

[Ron Gusack]

[Right hand drive]

[Ron Gusack]

I'm going with 028 x 025 x x and 028 mab... I've got some #4 brass set screws left over from the BLP blocks parts. Looks like 2 per block but I don't see where they go, any ideas?

[Right hand drive]

[Ron Gusack]

The BLP description calls the 4-40's E system jets. It looks like they might plug the top of the well, but these blocks came with them already installed. I looked at my other BLP billets and they have the same allen plug at the top of the well.

My goal is to try to get the car more consistent without going to alcohol. It does pretty well but it will pick up or slow down for no obvious reason. The restrictor plate system is also too unpredictable in my opinion. Ballast also differs from race to race. My nephew is an engineer that has worked with engine airflow and when I described my plate system he said that system is my problem for sure. I'm hoping that changing from 2" throttle bores to 1.75 will help some.