Carburetor #3: Holley

when it comes to all out performance and making horsepower, i really am a firm believer you have to run a holley carburetor. Back when i was drag racing i make the switch from an AFB style carb to a beat to shit-second hand holley 4160 vacuum secondary and literally gained damn near a full second in elapsed time in the 1/4 mile using the same cfm rated carburetor. that was all the proof  i needed to know.

 there are literally hundreds of different style holley or holley based style carbs in the world like the stuff from Barry Grant.  in my opinion though if you ever watch one of their training video’s, you will realize rather quickly the guys at pro- systems have their shit together also. i was going to spend a big chunk of money with them just before i got out of drag racing. www.prosystemsracing.com. i am no expert when it comes to carbs, but i know enough to hold my own. so instead of trying to dictate a bible on the holley i will just share some of my experiences with you guys. there are great tutorial books available through a lot of sources like summitracing. com

like i said above, the first carb i got into was a 4160 holley 4 barrel. i got it second hand off a big block chevy that came out of a 69 camaro my friend and i were restoring for an older lady years ago. the first kit i got was from quickfuel through the summit catalog. what a piece a shit that was and a complete waste of money. the power valve was WAY too big, the non-stick gaskets were about worthless, and it was missing some parts. i like to use the holley brand jet assortment kits, holley brand power valves and/or power valve block off plugs, and the moroso rubber gaskets for the metering blocks and float bowls. i have used the clear plastic plugs before in the floatbowls so you do not have to remove the plugs to set float level, but after a year or so they tend to yellow.

the 4160 is like night and day over the q-jet. basically it is a modular design consisting of float bowls, metering block(s), main body, and baseplate. with the removal of 8 screws the whole damn thing will fall apart. it is a 4 barrel carb, with dual float bowls but only one metering block.  the front half of the carb being your primary side, it will house the metering block and have the accelerator pump. the back side however is a vacuum secondary with no accelerator pump or metering block. instead they use a metering plate within the float bowl. you can get different caliber metering plates by the way if necessary. the back barrels are controlled completely off  the vacuum signal off the front booster venturi’s not the engine vacuum signal like the q-jet. this means that when you bury the throttle into the floorboard, you engine is drawing full flow through the front barrels. if the demand signal is strong enough it will begin to open the back two barrels as needed by your engine. that may or may not mean they have to open all the way. by doing this, once calibrated,  the carburetor cannot overfuel the engine like a 4150 double pumper can be known to do on the street. 

i ran my 4160 street strip. the front half is basically identical in construction to a 4412 or 4150 and is calibrated in much the same mannor. on the rear barrels i installed an aftermarket adjustable secondary so i could change spring tensions on the rear barrels. this allowed me to set the back barrels to open fully either lower or higher in the rpm range. 

for drag racing or anything else you run full throttle all the time, i found that removing the block off valve and increasing the size of the jets 4 or 5 sizes to make up for it is the way to go. the power valve on the holley is contained in the metering block. if you want to drive on the street at all i have found it is necessary not only for mileage but when i tried running without one i would get random detonation at different rpm AND the engine would overheat. at the drag strip it is pretty much the opposite. the power valve is an extra variable that will throw off your E.T.’s enough to take you our of the racing when your running brackets. this is why i know a lot of guys that will bring their jet kits with a power valve block off to the track with them and change it around for racing-then change it back to drive home.  at the derby, i believe the power valve is also a liability as it will hang up and blow out when the engine gets hot and/or backfires. so i chose to run a block off plug for derby aplication on holleys as well. that is no necessarily the case with a 2G for derby though. what works for one brand may not work on another. never assume!

the 4150 carbs are really the workhorse of the performance industry in my book. often referred to as the double pumper, it is basically two-2 barrel carbs that are joined like siamese twins at the center. the double pumper features both front and rear metering blocks and accelerator pumps. the 4150 can also come with a rear vacuum secondary in place of the rear accelerator pump. however, unlike the 4160 it has a metering block and may or may not have an extra set of idle mixture screws. you can get a 4150 in numerous performance configurations with both annular and downleg boosters, larger accelerator pumps, both front and rear idle mixture screws(referred to as 4 corner idling), as well as a performance main body with a nice contoured intake omitting the choke horn all together.

most of the time on the 4150’s for racing, you will run the front jets slightly larger then the rear jets as the velocity of forward acceleration will have a tendency to make the front cylinders lean out and the rear ones run rich. on a dominator set up for instance like pro stock, guys will run as many as 8 different size jets from the front of the engine to the rear just because of this. jet sizing is not quite that critical on a double pumper but it was a myth for years that the back jets had to be larger than the front, and that simply is not the case. the front barrels are always the workhorse. treat the carb with that referrence.

the 4412 2 barrel that pops up in both circle track and derby on occassion is basically the front half of a 4150 double pumper. usually 500cfm, i have dealt with a few of these and found that they are a good straight forward simple carb. however, i have a tendency to avoid them for derby myself as usually it will overfuel the engine. but i also know guys that make em work time and again. here again remove the power valve to control you fuel AND on these the accelerator pumps were like 50cc’s and can flood the engine when hot so don’t be afraid of playing with the eccentric cam on the throttle shaft.

worth mentioning, i run across old 3310 carbs. i have made these work well for derby by disabling the rear barrels entirely, installing a power valve block off plug, and rely’n solely on front jet caklibration and the front barrels to run. omit the choke. you end up with around 300 cfm or a bit less and works fairly well on a SBC for derby. a fuel filter is a definite must as the needle n seat stick pretty easy on these.

other than jet sizes and power valve, there are 3 other adjustments you really got to worry about. the float levels are set by an adjustment screw and nut at the top of the float bowl. while the engine is idling, take the sight plug out of the side of the bowl and adjust the screw up or down to set your fuel level at the bottom of the sight plug but you running out of the hole.  your idle mixture screws are located on either side of the carb and are usually gold at about 1/4 to 1/2 a turn out in most cases. so don’t start at 2 turns out.

one of the most critical  (and overlooked) though is after you set idle and timing, adjust your accelerator pump linkage(s). at idle position it shoul just kiss the pump cam lever and acc. pump lever below the float bowl. too lose and you will have a lag before you pump goes- too tight and you lose motion and not a full squirt into the engine also causing problems.

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