Holly (Model 4150) 850 cfm vs. Holly Street Avenger 870 cfm

[SanDiego70RTSE]

Could someone please tell me the difference between these two carburators? I'm trying to decide which one to buy. Both of these come up as the recommendations for my engine when I use the Holly carburator selection program on their website. Which one do you prefer?

http://www.holley.com/

0-80531 850 CFM Four Barrel Street Carburetor    850 CFM Four Barrel Street Carburetor
Electric Choke; Vacuum Secondary; Model 4150; Calibrated for 502 Crate Motors or other High Performance Big Block Engines


(Street Avenger Series)
0-80870 870 CFM Four Barrel Carburetor    870 CFM Four Barrel Carburetor
Electric Choke; Vacuum Secondary Street Ready out of the box; Two adjustments and go

Thanks,
Mat

[firefighter3931]

What is the engine combo Mat ? 



Ron

[SanDiego70RTSE]

I may put 3.55's on it in the future. For now I'm going to keep the 3.23.

Here's what's in the engine (note all after market parts were brand new):
440 block bored 0.060 over
I have a factory crankshaft, balanced and polished, not the stroker crankshaft.
CP custom racing pistons all balanced to within +/- 1/2 gram
Edelbrock aluminum heads 78 cc combustion chambers
Cometic gaskets and moly rings came from Cometic
Edelbrock RPM performer aluminum intake matched to heads by West Coast Racing Cylinder heads
Manley H-beam rods
Comp Cams mechanical roller cam (streetable) RPM power between 2000-6000
Note the cam is grind XR274R-10. Specs on the cam are as follows:

gross valve lift intake: 0.564
gross valve lift  exhaust: 0.570
duration@0.15 tappet lift: intake 274, exhaust 280
lobe separation - 110 degrees

I have 2 inch ceramic coated headers from TTI with 3 inch collectors. All of my exhaust stuff such as the Xpipe and the dynoflow mufflers came from TTI.

All of the valve trains stuff is comp cams and there are heavy duty springs on the heads. There was a very very light port and polish on the heads by West Coast Racing Cylinder Heads in Reseda CA.

I'm surprised at how low the idle is on the car - it's 800.

I have the 727 torque flight with suregrip and 3.23 from the factory. I have the hemi 18 inche spline and the torque converter is set for 2400 rpms. The transmission was rebuilt with all heavy duty parts and a shift kit by a top mechanic in town who has a solid reputation.  I'm thinking of putting in 3.55, even though the car doesn't need it, I want to feel what these gears are like.

[firefighter3931]

Ok, now i remember.... you sent me that info in a PM. 

Proform 750 race series double pumper is what i would use on that combo. 

The PF 750 flows over 800 cfm and has smaller venturies than an 850 so it will be much more responsive off idle while not holding it back on the top end. 



http://store.summitracing.com/partdetail.asp?autofilter=1&part=PRO%2D67200&N=700+4294925239+4294839063+4294919007+400405+1051506943+4294902704+115&autoview=sku



Ron