i have a stock 850dp on my 428,i changed from cj heads,pi intake to bbm heads,rpm intake.normally would you have to change jets after the head,intake swap
Jet size fore a specific carburetor ( 850 dp is around 80 ) is mostly related to venturi size, air speed/velocity making a depression in the booster/main fuel well. If you have to goo more than 2-4 numbers from Holley std jetting you have the wrong size carb fore your engine ore a really
screwed up combo of parts.
If you get a secondhand carb, a good ting to do is look at" Holley's numerical list" to identify your carb and std jetting.
Holley sometimes changed jetting over the years on there versions of the same carb but mostly on the PRI side and then often related to power valve channel restriction.
If you"over carb" your engine you have to go way up in jetting because the to big venturi in the to big carb for the combo, the engine has a harder time getting the air velocity going in the venturi. " Mr moor's LAW. If bigger is better to big must be best" Bigger jets in a combo like that gets the boosters going but with very poor atomization big droplets of fuel entering the intake tract and a very sluggish lazy performance and down in Torque/ power.
850 DPs are normally pretty lazy Falcon67
I learned the" Mr moor's LAW"lesson as a kid in mid 70is switching a 2300 Holley 500cfm back an forte between a std. 68 Fairlane 302 and a Volvo 4cyl 110 ci.
The Volvo needed over 10 numbers bigger jets just to accept throttle movements. By the way the 500 cfm carb was to big even fore the std 2brl
302. No response on seat of the pants power just taking a lot of gas.
Fore a hotted street driver big block, i really like the the "old style" calibrated Holley 750 with a choke its hard to go wrong with them.
The idle/ transfer calibrations is often very close to optimal, and preferably with vacuum sec. The old style 715-735-750-780 VS "loved baby has meany names" carbs with a signal tube into the right side PRI venturi can be sett up so the SEC throttles is following the PRI throttles like if it was a 1:1 linkage mechanical carb when "pedaling " super crisp on gas response and with the same power attribute as the DP.
One might say "the 850 and larger carbs make moor power". Shore does, but i will gladly give up " high rpm pump losses" those extra horses on the street,for a better manner/crisper engine easier on gas, usually your tires are up in smoke any way before you reach them extra horses.
Look at Barry R dyno carb test he did fore a customer prompting on a Holley 3brl VS carb.
The 850 better suits 550+ HP engines.I just calibrated ( 84 different single moments drilling and treading to get fully adjustable ) an old Speed Demon 850dp on a 572"/620hp C-brand crate engine in a 65 Impala great carb fore that combo.
Talking about carbs there is definitely certain carbs to stay away from, that have design issues, and i am not talking about prettiness.
The Edy 1407 750 cfm performance carbs that i have com a cross, hade the shorter PRI booster clusters from the smaller venturi 1406 carb.so that the booster didnt reach down ( about 3/8 to short ) in the smallest/narrowest part of the venturi and by that not getting a proper "signal to the boosters. The situation becomes like a "over carbing problem" the manufactures solution to this problem is drilling out the emulsion tube like a Swiss cheese. And moor,the throttle hight position in relation to tranferslot and ported vacuum hole in the boore is off.
Like that you get a super overly rich part throttle situation fouling plugs and on. Then one goose and by the "eminent" Jet, rod and spring assortment tuneup kit, and starts following the instructions but nothing you find in that box will sort out your problem, then people think they are stupid that cant follow a instruction properly
There are others to like som of the old Holle/summit copy ford 4100carbs.It could have been a great carb, with annulars, holley pump membrane, PW and no gas spilling working on them, some of them are not right in hight wear the cluster goes to the main body and if you raise the float level enough fore compensate, you get a driving ,corner, brake "spillover situation.
There are others to but getting way of topic and my bad English spelling takes to darn much time i better end this now.