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Motor made 615hp at 5,600rpm's and 639ftlb torque at 4,600rpm's
Ok so the 509 I rebuilt made it to the dyno today.
Motor is a 502 gen6 MPI based motor that is .030 over (flat top JE piston 9.25 to 1 comp), stock bottom end (steel crank, dimpled 7/16 rods) that has new rod, main bearings, rings and oil pump. Top end has World Merlin 320cc iron heads (2.25in 1.94exh valves) Gellner Engineering custom hyd roller cam, morel lifters, comp cam roller rockers, Dart intake, BG 850cfm carb (89jets in primary, 96jets in sec) with 1in HVH carb spacer.

Had issues with lean A/F ratio at low rpm's (3,800rpm's -14.7A/F ratio then from 4,900-5800rpm's A/F ratio came down to 13.0) Tried to jet carb to 92jets primary, 99jets sec..not much diffrence in A/F ratio change.

Found the 1in HVH carb spacer was the issues! Removed HVH carb spacer and now A/F ratio mantains between 12.8 to 12.4

One issues which myself, the dyno guy and Dean Gellner can't understand is we did a pull with the flame arrestor on and the A/F ratio when up 1 full point of 14 to 1 A/F ratio. We removed it and the A/F ratio came back down to 13 to 1 A/F ratio. We figured by installing the flame arrestor that would riching the A/F numbers not lean the motor out? Its a HP500 style flame arrestor. Any ideas why it leaned the motor out when installing the flame arrestor?

Dyno pull, crappy video camera

changed the airflow entering the carb..slowed down the air which slowed down the fuel as well

The 1 in. Super Sucker did the same thing to my engines. Maybe you need a larger flame arrestor or just jet to suit.

So what is needed? A larger Flame Arrestor?

The BG 850 is already jetted to 91 primary and 99 sec. Can't go any more jet in the sec.

Why not ? Holley makes lots of jet's bigger than 99's

I had the same problem and went from 850's to demom 1050's we made 635 hp @ 6K RPMS with my 509's basiclly the same set up as your engines. My flame arrestors are big oval 5" tall

Is it the annular booster Barry Grant?
RMbuilder hooked me up with a guy at BG to help with mine. I was running lean with 104s in the sec. The carb just wouldn't draw the fuel. Sent it back to BG and they made some changes that helped. Pretty sure they changed the boosters.

Its the 5563010GM carb
The A/F ratio is good now, iam just worried about the flame arrestor. Iam going to try out the same one as Velocity Vector. Just need to figure out what type and where can I find something like that.

I always thought any jet size up from 100 is an alcohol jet and if the carb needs to be jetted that much and you are not running alcohol then there is just not enought carb on the motor. As of now the A/F ratio is good, iam just worried about the flame arrestor.
Erik