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Holley Frequently Asked Questions

QUESTION What is the supercharger to manifold bolt torque?
ANSWER All of our blowers from the smaller 140 series to the 8-71 torque 10-12 ft lbs. You do not want to exceed this torque or damage to the supercharger may occur.
QUESTION Can I run a supercharger on a stock engine?
ANSWER In most cases you can depending on the size of the blower. If you use a smaller blower you can get away with 5-6 psi of boost on a stock engine on premium pump gas. If you are looking to utilize a larger blower, 6-71 or bigger, you NEED a specifically built engine for the blower. In most cases with a bigger blower you can't get the boost level down low enough to run pump gas.
QUESTION My engine has 9.5-1 compression. Can I run a blower and still use pump gas?
ANSWER We do not recommend it. The higher the static compression ratio of the engine the less boost you can run and still use 93-94 octane pump fuel. Usually on a 9.5-1 engine the most boost you can run is about 2 psi before you get above the octane rating of pump gas. That level of boost will usually not make enough additional horsepower increase to offset the cost of the blower kit. Remember, it takes horsepower to make horsepower with a roots type blower. The car will run slower if you do not make enough horsepower to run the blower!
QUESTION My supercharger uses a serpentine style drive belt. Do I need a “pop” off plate if it backfires?
ANSWER No. The serpentine style drives do not require a “pop” off plate. If the engine backfires it will slip the belt on the pulleys. If the blower is running a Gilmer (tooth) style drive setup then it does require a “pop” off plate. If a backfire occurs on a Gilmer drive setup the belt will NOT slip and it may lift the blower off of the intake manifold.
QUESTION I have installed one of your superchargers and my engine seems to run hot and my headers glow at idle. What could cause this?
ANSWER Usually an issue with glowing headers and a hot running engine are caused by two basic things. Either incorrect timing or the engine is extremely lean. There are others, but these two are the main cause. Blower engines like timing advance. If the initial timing advance is not enough it will cause these issues. Most blower engines will run between 12-20 degrees of intial timing and a total of 30-32 degrees. You do want a fairly fast timing curve. All the timing should be in by 2500-2800RPM.This is just a guideline. All engines are different. The other main cause is a lean running engine. Make sure the carbs are tuned correctly for the setup and that there are no vacuum leaks. Remember the blower moves a lot more air through the engine so it needs more fuel as well!
QUESTION Do I need to run a blower calibrated carb with a supercharger?
ANSWER A lot is going to depend on what the setup is and what you are going to do with it. If it is strictly a race setup with no street use then usually you can get away with a standard carb with the power valves plugged and the carb jetted up to compensate. This does not work well on an application that will get mostly street time. For those applications we do offer out of the box Holley carbs with Manifold Referenced Power Valves which will work correctly on the blower. These carbs will allow the use of the power valves which will give better idle quality and street driveability with a blower.
QUESTION What is a Manifold Referenced Power Valve?
ANSWER Nothing will kill a blower or Nitrous engine quicker that a lean condition. You want plenty of fuel available for the engine to use .There is a thing you need to know about the power valves on a roots style blower engine. The power valve is installed to keep the engine from loading up and running rich at an idle. On a normally aspirated engine the engine vacuum at idle will hold the power valve closed. When you step on the gas the throttle plates open and the engine vacuum drops as you accelerate. When the vacuum drops below the rating of the power valve, it snaps open and richens up the main system. On a blower with the carb mounted above the rotors there is constant vacuum all the time even under wide open throttle. The power valve will never open and you will have a lean condition. To remedy this there is a modification you can have done that is called manifold referencing the power valve. You plug the vacuum feed hole in the baseplate for the power valve. Then you drill a hole in the side of the main body into the hollowed out vacuum chamber for the power valve. You then insert a vacuum nipple in this hole. You will run a vacuum line to the lower intake manifold from the new vacuum nipple. Now you will have vacuum on the power valve at an idle, and when you hit the gas as the boost builds, it will force the power valve to open and richen up the main system. This can be done by most carb modifiers or even yourself. We offer quite a few different size blower carbs with this already done. Consult you local Holley dealer or our Techline for the correct application.
QUESTION I have a serpentine drive system for all of my accessories on my car. Can I use one of your supercharger kits?
ANSWER At this time all of our supercharger kits are designed to be run with “V” type belts and will not work on most serpentine style accessory drives without modifications. Usually our “long” nosed blowers will work with both short and long water pumps with up to 3”V” belts. The “short” nose blower kits along with the 250 Powercharger and larger (6-71&8-71) blower kits will only work with a short water pump and 2”V” belts max.
QUESTION I have a 6-71 blower on a small block Chevy and keep having trouble breaking the harmonic balancer. What can I do to keep this from happening again?
ANSWER When you go to a large blower like a 6-71 or larger it is a MUST to have the crankshaft cut with a double keyway and run a steel SFI double keyed harmonic balancer (not a fluid filled balancer).The stock cast balancer with the combination of the small single key in the crank will not hold up to the torsional load applied to the nose of the crankshaft from the superchager. The engine should be built for a blower this large any way and should already have a steel crankshaft.
QUESTION I have installed one of your supercharger kits and it does not feel like I have gained much horsepower. What should I look for?
ANSWER We recommend using a boost gauge. This will tell you what the blower is doing on your combination. There are a lot of variables that will determine boost output on one combination to the next. Carburetor size, air cleaner flow, camshaft size and lobe separation, engine load, exhaust size, and blower drive ratio are just a few. If the carbs are too small or you are running a restrictive air cleaner this can cause a lower boost. If enough air can’t pass through the blower it will not make boost. If the camshaft has less than a 110 lobe separation it can cause the boost pressure to bleed out of the exhaust instead of building cylinder pressure. If you do not have the correct drive ratio for the blower it may also build less boost. The blower WILL NOT make any boost on a free engine rev. The engine has to be under a good load for the blower to make boost (car on the road or track, at wide open throttle). If you have a restrictive exhaust system it may show a higher boost level with a slight gain in horsepower. The blower moves quite a bit more air through the engine and if the exhaust is restrictive it will back up the pressure into the cylinders and show a higher boost reading with no gain. There are other reasons as well so feel free to contact our Technical Service department for further help.

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