Vacuum Pump Application Guide and Technical Notes
If you're new to the use of a vacuum pumps for racing applications, this guide and technical notes will give you a good overview of what you need to know in order setup your vacuum pump system. We discuss just about everything you can think of on this page, and have another page dedicated to Vacuum Pump Troubleshooting that has even more information. Please remember you can also call us at 209-296-3793 or email firstname.lastname@example.org if you have any questions.
Vacuum Pump Sizing
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Click the chart and take a look at the air flow test results for our pumps against several of the leading competitors...
Vacuum pumps can be rated by their ability to flow air, the more air a vacuum pump flows the more vacuum it will make on a given engine. A "small" vacuum pump would indicate a less airflow capacity than a "big" vacuum pump. Airflow is measured in CFM (cubic feet per minute), vacuum is measured in "inches of Mercury"
All engines create a certain amount of blow by (leakage of compressed fuel and air past the rings into the pan area). This blow by airflow creates a positive pressure in the crankcase, the vacuum pump "sucks" air out of the crankcase with its negative airflow. The net difference between the air being sucked out by the pump and the air generated by the engine with blow by yields the effective vacuum. If the pump is not sized, plumbed and geared correctly, it may not be able to move enough air to create a negative pressure in the crankcase.
Typically smaller engines generate less blow by and don't require as big of a vacuum pump as large displacement engines. However the addition of low tension ring packages, power adders such as Nitrous Oxide, Alcohol, Blowers or Turbochargers (and the ring and piston types, clearances and modifications that go with those power adders) will increase crankcase pressures requiring either a larger pump or to spin a smaller pump slightly faster.
A small vacuum pump that is not quite making enough vacuum can benefit by increasing the rotational speed, or RPM, of the pump. Of course maximum engine RPM needs to be considered as well, as vacuum pump RPM should be considered. Although we have vacuum pumps being successfully operated at a maximum RPM of 7000 or so, we highly recommend keeping the vacuum pump RPM below 5000 RPM. Alternatively, a larger vacuum pump could be used instead. However, our experience has shown that using a vacuum pump that is to big may eliminate horse power gains altogether because of the parasitic horsepower it takes to run the pump. Keep in mind that it takes horsepower to pump air, running too big of a pump for your application will cost some horsepower.
How much vacuum should you use?
You should check with your engine builder as there may be some special issues or firm opinions that they may have. In general GZMS recommends no more than 15" of vacuum in a drag race wet sump application without pressure feeding oil to the wrist pins. In our own in house testing, anything over 12" seemed to offer relatively nominal increases in horsepower (Typically 3-10 more HP between 10" and 15").
Why limit vacuum?
Engine builders appear to believe that the lack of oil to wrist pins caused by removal of too much oil mist from the crankcase causes wrist pin damage. Some engine builders report fluctuations in oil pressure above 12", we have not noticed that on engines we have observed during testing. However in a recent article, it was suggested that the air velocity passing through the block to heads at the oil return locations causes resistance to oil flowing back to the pan, which could indeed reduce oil pressure. An air line from the fuel block off on a Chevrolet to the valve cover helps mitigate this problem as well as possibly helping to balance the vacuum in the crankcase to that in the valve cover.
Why use a Vacuum Control Valve?
Naturally to limit the maximum vacuum. Also, it is more advantageous to achieve maximum vacuum early in the power band, so if you wish to do that it makes sense to use a vacuum pump with enough air flow to require the use of a vacuum control valve. If you do not want to install a vacuum control valve use a smaller pump than recommended, check your vacuum and determine if you really need one.
Vacuum Pump Horsepower Ratings
GZ Pumps are rated by approximate horsepower, not by cubic inches as a small displacement engine with a power adder may make just as much HP as a large N/A engine. Our goal is to get the pump to run 6000 rpm or less for best longevity. To calculate the pulley sizes you need to meet the Pump RPMs desired, use this handy calculator.
400 to 600 HP
For smaller engines and low power adder ouputs we recommend our VP101 or VP102 Sportsman pump driven at 54% of crankshaft speed with a single input line.
For large cubic inch small blocks with power adders moving towards the 600 hp range, we we advise using our VP101 Sportsman Pump running at 64% of crankshaft speed and #12 inlet line.
600 to 750 HP
For engines around the 600 hp range, we advise using our VP101 Sportsman Pump running at 64% of crankshaft speed and #12 inlet line. Pump speed will need to be increased to 75% in most cases for best results as your power levels near 750 HP for the VP101/VP102 Pumps. The 75% pump speed should not be used for engines turning over 8000 rpm to avoid overspeeding the pump.
If it's likely you'll be making more power down the road, you might want to use our VP104 Super Pro Pump with single #10 intake line running at 54% of crank speed for a 750 HP Engine. This larger pump can be spun faster if needed, and you can increase the inlet line size to flow even more air. #12 line is a good upgrade to more air at lesser drag to the pump, however it is more expensive option.
750 to 1000 HP
On the low end of this range we suggest using our VP104 Super Pro Pump with single #10 intake line running at 54% of engine speed for optimum results. At the upper range of 900 hp, we recommend increasing the pulley ratio to 64% of crank speed and increasing the inlet line size to #12 to one valve cover, or two #10 lines to both valve covers.
For large cubic inch engines with power adders the VP104 Super Pro Pump is needed at 64% on the lower HP end of this range to 75% of crank speed at approximately 1500 HP and above, we also recommend #12 inlet line to one valve cover, or #10 lines to two valve covers for maximum air flow.
Adjust pump size to desired net crankcase vacuum desired. The following chart shows the net vacuum you can expect in a naturally aspirated motor with standard or low tension rings and no vacuum control valve. These values assume the rings are in good shape (leak down is not excessive) and there are no vacuum leaks in the engine. Note that net vacuum measured will tend to increase with RPM unless "blow by" into the crankcase increases enough to reduce the negative net airflow out of the crank case, thus reducing vacuum at higher RPM. It is common to see the vacuum increase to a maximum and then reduce some at max RPM if the vacuum pump is not rated for enough airflow to maintain a net vacuum throughout the RPM range.
|Engine Size||VP101 Pump||
w/single #10 line
w/dual #10 lines
|400ci and smaller||15-20"||20"+||20"+|
|400ci - 468ci||12-16"||14-20"+||16-20"+|
|468ci – 522ci||10-14"||12-20"+||14-20"+|
|522ci – 555ci||8-12"||10-17"||15-20"|
|555ci and larger||6-10"+||10-15"+||14-20"|
The larger the pump you use, the sooner the vacuum will be generated, and the quicker you will reach the limit of a vacuum control valve.
The larger the pump, the more horsepower required to turn it. For example, a VP104 Super Pro vacuum pump may not generate a horsepower gain on a small, naturally aspirated engine with standard rings that inherently will not create much "blow by".
Vacuum Pump Technical Guidelines
- GZMS vacuum pumps are designed to have oil pass thru them, and require oil for lubrication of the wipers at the vanes. Experience has shown that synthetic oil yields a longer pump life. A dry pump will wear out prematurely due to friction between the Rulon wipers and the carbon fiber vanes. GZMS vacuum pumps are warranted for one year with proper use. If a pump is returned that has been run dry, any warranty is void.
- GZMS products are installed and used by others, no warranty is made as to use of products as regards performance or safety. Motorsports are inherently dangerous, the user of GZMS products assumes all potential or risk of using those products.
- Pulley ratio is typically 64% of crankshaft speed, this is generated by using a 3.5" Crankshaft Pulley and a 5.5" Pump Pulley unless noted otherwise with a maximum pump rpm of 6000. GZMS Sportsman vacuum pumps are successfully run at higher RPMs, however, this is not recommended.
- GZ Motorsports pumps may pull in excess of 20 in. hg. of vacuum, therefore a vacuum relief valve is likely necessary. Please consult your engine builder for the proper vacuum level for your engine. If you're not sure how much to run, it is generally considered safe to limit total vacuum to 10 - 12 in. hg. but there are varying opinions on running more than that depending on engine setup, possible oil pressure drop, etc. Many competition engine builders will run up to or over 20" when the engine is designed for those levels.
- For high output power adder engines we highly recommend the use of a data logger to monitor vacuum levels downtrack. In general, vacuum should increase the longer the engine runs, and as the engine RPM climbs. If piston rings start to have problems, such as if engine timing is excessive, a loss of vacuum tends to occur due to the increased blowby when ring seal is compromised. You may find a benefit to not running a vacuum relief valve at low levels in this situation if you want to observe this occuring, as a relief valve may mask this early warning signal that may be caught by a data logger of ring seal issues. In all out competition where engines are ran on the edge, closely setting pump RPM to limit vacuum to the level desired may be preferable to limiting vacuum with a relief valve in order to help observe ring seal problems. This is something that should be discussed with your engine builder and or tuner.
- GZMS pumps are manufactured in our shop. After assembly each pump is tested on our pump dyno at 3500 rpm (Sportsman pumps), 2500 rpm Pro pumps and 1900 rpm Super Pro pumps. During testing Red Line racing oil is run thru them so when you get your pump you will see "blackened" oil at the inlet and outlet ports. This is normal and due to break in process. GZMS vacuum pumps all show the test vacuum and date tested on the part sticker on the pump. This is the test value at the test rpm noted above.
- The vacuum your engine will make is dependent on the amount of blow by it generates and any air leaks it may have. No two engines are identical.
- Ring Packages such as low tension rings typically generate an increase in ring blowby requiring a larger, or faster spinning pump.
- Power Adders such as Nitrous Oxide, Superchargers, Turbochargers all increase cylinder pressure generating increased ring blowby requiring a larger or faster spinning pump. The amount of Nitrous you are spraying, or the amount of boost you are generating increases the needs for a larger or faster spinning pump. Large Displacement engines typically generate proportionately larger amounts of blowby.
- The use of alcohol, especially in a "rich" condition generally reduces net vacuum and could require a slightly larger pump than a gasoline engine.
- Vacuum leaks in the crankcase, valve covers, distributor base, timing chain cover, oil dipstick, etc. reduce the amount of vacuum you will generate. You can easily check your engine by pressurizing it with air, be careful though, you don’t need much to find leaks and you could damage gaskets and seals.
- If you are going to continue to use a dipstick, consider removing the dipstick while running the car and covering the dipstick tube opening with a rubber vacuum plug to seal the tube off. That way you can eliminate leakage, but still pull the plug and check your oil level when need be.
- All engines are different depending on how fresh they are, how much ring end gap is used, cylinder prep and ring design. This is a general guide based on typical engines GZMS has fitted over the years as well as customer reports, some situations may be different, if in doubt email or call our tech support line.