RPMs and belt drive


I have a 18 hp vanguard engine on my current 5.5 gpm set up. The powerband chart shows it starting from 11 hp at 2000 rpm, and going up to 18 hp at 3600 rpm.
Mine is belt drive. What effect does the belt drive have on rpm’s? I’m looking at options moving up with a larger gpm pump.
Example general pump tsf2021 says 7.0 gpm @ 1450 rpm. I would be pretty low on the hp end to achieve the correct rpm. How would this effect the performance?
I appreciate any information on hp and rpm for choosing a pump. I’m completely lost now.


Rpm of the engine vs rpm the pump has to spin. The pulleys are a gear reduction


I understand the reduction. But the change in hp would bring it pretty low. Would it be enough to power 7.0 gpm?


If you have the engine running at 3600 rpms and you get the correct pulley to reduce the pump rpms to 1450 then it will be at peak hp.


With the calculator you need 19 almost 20 hp to run 7 gpm at 3000 psi. I think the 18hp vanguard can be converted to a 20 hp but don’t quote me on that.


Thank you!
I understand the hp calculations. How do I find the correct pulleys etc. to make a conversion? This is just an example. Also, what is the rule of thumb for max hp usage? Ex. Don’t exceed 75% of 18 hp.


Here. Read this. It will give you a starting point. You can search for “small engine pulley reduction” to find more choices.



Thanks @Power.Wash.It


A few things that may help steer you away from going to a larger pump frame with your engine size. When companies pair engines with pumps they most always tax the hell of the engine to deliver everything they can get out of the pump. What this means is your pump is spinning at max and your engine is dying holding it there at that psi. Short life for both. Now here you come along wanting MORE gpm from the same engine. That’s fine and all but you can’t have the same psi you had before as you need more hp for that and you started out with less that you needed t begin with. I run many 18hp Vanguards at 2550 and detune TS2021’s to 4.8 and get thousands and thousands of hours out them.

And also in your example you wouldn’t run the same EXACT pulley on your pump AND your engine so why would your engine be running 1450 making low hp???