Going from Bigs 950hp to a Quick fuel 850. Jetting???

So i've been running a Bigs 950hp ported body with 1.42" venturi's my best results were with 76 pri jet 86 sec jet with 4.5 PV resulted in 11.50 et @ 115mph. So I got a smoking buy on a Quick fuel Q series 850hp & now trying to get it setup but was thinking if now I have 1.56" venturi shouldn't I need to increase jet size a bit more?

You should always start tuning with the carb as delivered. Only exception is if you at a high elevation or something like that. The carb mfg should have their standard tune in the carb when it ships so start there.

And if you're handy w/a drill and a tap I can walk ya through some additional stuff.............

You may not have bought what you think you did. A Q series 850 (no choke horn, right?) has a 1.40 venturi, not a 1.56". The Q series 950 is still only 1.45. Their 1050 is 1.59 from what I read.

What does the Bigs 950 1.42 venturi look like? Pics?

Exactly.

Forget the "rated" flow numbers for carbs...... They tell you basically nothing anymore.

Look at the Venturi and throttle bore diameters for comparisons.

For example.....
Mighty Demon 850
Race Demon 1000
Race Demon RS 1025

All are 1.56 x 1.75....... Think there is a big(any??)flow difference there?

Holley-
0-9381 "850" = 1.56 x 1.75
Original HP "950" = 1.375 x 1.75
XP "950" = 1.600 x 1.75
Original HP "1000" 1.56 x 1.75

It's all marketing BS.

Between the Bigs 950 and a Q-850, I wouldn't really expect to see any on trac performance difference, unless one of them is doing a significantly better job of metering and atomizing the fuel, or gets the main circuit activated quicker so the car leaves harder.
For practical purposes, they are basically the same "size".

You may not have bought what you think you did. A Q series 850 (no choke horn, right?) has a 1.40 venturi, not a 1.56". The Q series 950 is still only 1.45. Their 1050 is 1.59 from what I read.

Porky you are correct on 1.40" venturi! The Marketing confusion & BS has got to my brain I guess. Yes its a Q series race carb with no choke horn.



Yes Thumper I am handy at that! Let me know

So I ran the QF 850 at the track back to back swap out from old Bigs 950, air was terrible & hot humid temps plus track prep sucked. I left the 850 alone out of box other than 4 corner adjustments & setting floats. Carb idled & ran pretty well, I didnt expect anything great ET wise car ran 11.70 @ 114 with QF850 & 11.81 @ 113.5 w/ Bigs 950 but it spun a lil & 60 was off it should have ran a .76 going by my old log of timeslips. I think this new carb is going to work pretty good if I get a chance to change plugs & get to mess around with jets & air bleeds with better conditions.

I feel dumb thinking it had 1.56 venturi's, I was going by old holley dimensions & having a hard time find data on the QF