Small Block Chevy Holley Carb Tests - Danger Mouse Part 8

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We Tested 12 Different Holley Carbs For Power
This month, we took Danger Mouse (DM) in a completely different direction. In the past seven months, we've used DM to tackle various ideas on the dyno and see just how much power we really could make with a genuine street small-block. For the most part, the results have been fantastic, and DM has usually surpassed all power expectations. For our eighth installment on DM's testing schedule, we wanted to see if there really was power to be gained or lost by running the right or wrong carburetor.

Now, this type of testing can open up a whole, big can of worms, so to keep testing simple and fair, we chose to only run carbs from the same manufacturer, Holley. And we also chose to test only 4160- and 4150-style carbs, and not the giant 4500-series Dominator lineup. We gathered up 12 different size/style carbs, ranging from Holley's smallest four-barrel, the 390-cfm vacuum secondary unit, up to the big HP950 double pumper, and bolted each one of them onto DM to see if one stood out from the rest.

We established a baseline... 

   

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We established a baseline using Holley's old-faithful 0-4779 750-cfm double-pumper. We tried to sway the fuel curve into making more power by changing jets, but Holley's stock settings worked best.

We expected the smaller carbs to make good bottom-end torque but sacrifice peak power, which they did. But the thing that really threw us for a loop was that the biggest carb we tested-the HP950-made the most power of any carb! Does this mean that big carbs are best? Probably not, but it does mean that Danger Mouse liked the bigger carb. However, DM also liked the HP 750, and we think these tests really show that Holley's engineers have done their homework and dialed in the HP carbs to work best on just about any engine. It also means that all of those carburetor modifiers out there probably do have something good going, because most of them can take an old, abused Holley and make it work as good as a new HP, but the cost is about the same as if you just bought a new one, so which choice you make is up to you. From what we learned in this test vs. what we'd already known is that not all carbs are created equal, and if you're building a daily-driven street car, you should still go with something smaller than 800 cfm. But, you certainly can't judge a carb by its size alone. Check out the dyno charts to see what we found.

This month was the first time we bolted DM onto the Vrbancic Brothers Racing DTS dyno in Ontario, California. Shop owners George and Bob Vrbancic both supervised the test sessions with George at the dyno controls. Yours truly performed all the jet changes and kept a running tab of the results.

To establish a baseline we first ran Holley's old standard, the 750-cfm double-pumper (List 0-4779-8). After the baseline was done, we tested from smallest to largest, trying every different size Holley carb we could get our hands on. And in order to ensure accurate results we tried tuning fuel curves for the best peak power. It turned out, however, that the stock fuel curves worked best, and any time we strayed from Holley's settings for each carb, we usually sacrificed some power.

The Holley carb flow ratings (cfm= cubic feet per minute) and List numbers (also known as part numbers) are shown for each carb tested.

When compared side-by-side,...        read full caption When compared side-by-side, you can really see the difference in throttle blade size between the 390-cfm carb (left) and the 750 double-pumper. It's the small throttle and venturi size that kills top-end power with the little carb.

After the baseline, we bolted...        read full caption After the baseline, we bolted on Holley's smallest of the line, the 390-cfm vacuum secondary (List number 0-8007). It made good low-end torque, but not the most of all carbs tested. Top-end power really fell off with the little carb.

The 570-cfm carb was part...        read full caption The 570-cfm carb was part of Holley's new Street Avenger line and has quite a different appearance from the other carbs.