Tuning Holley Carb- Engineering A Street Rod.mp4

Tuning the Holley 850 Carb that comes with the Chevy 502/502 Crate Engine was a fun but often frustrating task. Ultimately had to replace with an 850 Double Pumper. Even the Double Pumper needed modifications to meet our goal of 0 to 60 mph in under 3.5 seconds-which was accomplished. Details of what was done and why are outlined. Full details covered on our web site at www.netWelding.com/Holley_Carb.htm.

Category:

Autos & Vehicles

Tags:

• Tuning Holley Carb
• 850 Holley Carb
• Chevy 502 engine
• Chevy 502/502

[NetWelding]

Like the idea of wires reducing area of the air bleeds. Anything that reduces the area will work. The 850 double pumper does not have replicable air bleeds.

To get 0 to 60 times in the 3.3-second area a double pumper was needed. The fuel/air ratio meter proved that! Now starting at 1900 rpm the car is floored and the Double Pumper opens wide-No hesitation or bog! Need two 50 CC pumps and big squinters and the right accelerator pump cams on primary and secondary. Doesn't go lean now!.

[NetWelding]

My racing friends said the vacuum secondary carb wouldn't work; they were right! Here's why. A light car you can accelerate at 1 g or better off the line.. In a heavier car you won't fell the lag while the secondary’s wait to open. But if you’re going to accelerate to reach 0 to 60 in under 3.5 seconds even the slightest hesitation is not acceptable. Sure with a heavy spring it didn’t bog it just hesitated! That is not what I built this car to do! There was no "right" sping!

Jerry

[NetWelding]

Good comment. The 850 does not have adjustable air bleeds. However the issue was not coming off idle. Typically best 0 to 60 times start at1900 RPM (any higher and even the 16.5 section width Mickey Thompson's loose traction.) If I was setting up for racing, a carb with adjustable air bleeds would be useful. The air/fuel meter shows the extra pump shot did the job. Also the car accelerates fine from cruise.

[NetWelding]

@NetWelding The Vacuum Secondary Holley 850 that came with the 502/502 Big Block crate motor may work in a heavy mussel car but for a light street rod with good traction a Double Pumper was needed.

[NetWelding]

@177SCmaro Been so long, your comment made me wonder! Still have the Vacuum Secondary that came with the 502/502-anyone what to make an offer?? Just took off both front and rear bowls! The power valve on the secondary looks just like the one on the primary. Maybe smaller size carbs don't but 850 CFM does. On a 502/502 if your going to achive 0 to 60 in 3.3 to 3.4 seconds get a double pumper and open it wide ASAP. As Larry the Cable Guy would say- "Geter Done!" Jerry

[177SCmaro]

@NetWelding Right around 2:30 you talk about power valves in a vac secondary carb.

But hold on a second. On a vac secondary Holley, I'm assuming its a 4150, they don't have a power valve in the secondaries.

Generally when there is a hesitation in the transition from 2 to 4 barrels in a vac secondary carb it's because the secondarys are opening too fast, and because they lack an accelerator pump and power valve, there is momentary lean condition until fuel can be drawn from the secondary mains.

[wafrederick]

Easy fix,replace the Holley with an Edelbrock.Holley carbs are only good for racing applications

[kamphwagon1]

@505197 A 650 would work good but get over rich on the high end like a restrictor carb on a bush series NASCAR engine unless you invest in a HP series with changeable air bleeds and elmusion clannel tuneable metering blocks.. a 650 cfm is just to small for a 500cid engine..understanding the carb isn't black magic if it's undersized for the engine it will get to rich on the high end, unless your willing to invest the better part of a grand on the after mentioned stuff your better off with the 850

[bishdogg20]

this would cure ur problems. a holley double pumper. its machanical secondary so when u floor it, all barrels are wide open, as with all four barrels, but the air flap (idk the tech term) is wide open as well. and with the DP u get more gas. a like street rod is the perfect opertunity to us a mechanical secondary. vaccum is better for stock-somewhat modified stock motors. if u got a 502, got with a double pumper

[505197]

@RicerSchnitzzle I've used wire to block bleeds and fuel jets as well, it works suprisingly well. In fact I've eliminated bleeds altogeather on 2 bbls I modify for roundy racing, they have bored venturis and fueling them can be a struggle. I seem to have lost the patience for carb work anymore, I sold the race car and have lost intrest. One thing I've noticed is if you can find one carb man in the pits that's one more then usual. I ran a 2 in a 4 bbl class and did very well, it's hard to beat

[505197]

When someone says a carb won't work in a given application it get's me stubborn. If the secondary didn't open at all the car should run correctly on the primarys, any bogs would most likely be due to it opening too soon, causing it to go lean. I'd be looking at air bleeds, sometimes I'll block them with fine wire, it changes the timing of the fuel circuits from low speed to high transisions. Carbs are a black art, and sometimes it's just better to swap like you did. Wonder what a 650 woulda done