Simple Solution

As the race season moves along, tire compounds change, track surfaces change, and the task of getting power to the ground changes.  Your VDL carburetor is designed to get the most torque and horsepower out of your engine, but that can be too much of a good thing in some situations.  A good tuning device for reducing “too much power” is a carburetor spacer with interchangeable inserts.  Simply drop an insert into each spacer bore to reduce the bore size thus reducing air flow which in turn knocks down torque and horsepower numbers.  Several years ago, Jeff Hamner dynoed his 600 hp Hamner sealed SLM engine with our 750HP carburetor to find some guidelines to assist in the choice of inserts, and it has become a more common concern nowadays with the increase in performance of engines and carburetors.

So, the baseline was our gauge legal VDL 750 HP carburetor with the standard 1.6875 baseplate bore and Jeff found peak horsepower to be 599.7 at 7000 rpm.  He then made consecutive pulls with 5 different inserts under it, moving from largest to smallest inner diameter.  He also ran our 650 HP and 390 HP carburetors, unrestricted and with 1.200 inserts under them, comparing numbers to the same baseline 750 HP carburetor.

When placing a restrictor under the carburetor (no matter which size),

it is not necessary to make any changes to the carburetor because it will self-adjust to the new vacuum signal.

FYI – The 1/2″ spacer pictured here is from AllStar Performance, part number ALL26180.  It is also available in 1″, part number ALL26060.

Inserts are sold separately.

                                                                                         ~~ Our thanks to Jeff Hamner for his time and expertise.