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When I replaced the VP on my truck I bought from Oregon Injection and they asked me for the serial number of my truck and wanted to know if I was planning to run a chip on my truck.I was planning to put a chip on the truck and told them that. I asked why would that make a difference and they told me that they would give me a beefed up pump. I don't know if that meant HO or SO but they were emphatic about knowing whether I planned to run a chip.

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HO = High Output (6 Speed Cummins)SO = Standard Output (5 Speed or Automatic)As for the beefed up comment. Most likely internal parts are beefed up for the the use of chips. But so far I've not seen any heavy duty VP44 last any longer than the typical re-man'ed pumps.

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I beg to differ with my knowledgeable friends... I think that the VP44 varients for HO and HotRod Pumps have increased fuel flow. If you add a chip or programer or devise which adds more fuel it might be too much & work against you. My impression is that the add on fuel devises are based on a SO pump. That said, if I had a HO motor, I'd use a HO pump. All the electronics are calibrated around which motor is in the truck. Maybe the people who build pumps might shed more light on this.

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Just go with an SO pump, There are no "Beefed" up parts in a hot rod pump. The SO delivers more fuel than an HO pump the HO pump had different timing and less fuel delivery at a higher pressure.The HR pumps just have a combination of genuine Bosch SO and HO parts in the same pump, The gain you will get from an HR pump is minimal compared to other mods that can be made plus you will get a lope or erratic idle most times with an HR pump depending on what other mods you have.The SO is the best bang for the buck and will work on original HO rigs as well.

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Using an SO VP on an HO engine is true. Reasons are, the SO VP has larger fueling pistons but a milder fueling cam resulting in the capability of more fuel but at less pressure. When the HO motor was introduced the VP was equipped with smaller fueling pistons but a more aggressive fueling cam which actually ran at higher pressures along with injectors that have higher pop off pressures. The HO has the same fueling as the SO but without the same level of increased capability of fueling as the SO. This is why SO motors respond much better to electronic fueling devices than the HO motors and why the HO motors respond much better to larger injectors than SO motors. The Hotrod VP simply utilizes the SO fueling pistons along with the HO timing cam. Now there are other performance VP's than that but I'm not completely sure what they entail. Guys can replace their HO VP with a SO VP to achieve more fueling if so desired but I dont think there's much of a difference under stock situations. And I understand from many replies on this very topic that there is zero problems when performing this swap.

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