t8dyi,
The engine can be the reason for your issue, but not solely because of the engine itself.
The Volvo engine does rev lower than the Scania's by a considerable margin, which will lower your top speed. With certain configurations, I do recall that it's tough to go over 120 km/h with that engine.
Your transmission and tires also play a role.
For instance, even with a Scania engine with the higher rev limit, you won't be able to effortesly go over 150~160 km/h with an Allison transmission, but you would be able to go over that a bit more easily with select 12-speed transmissions (that is, before the server's speed limit kicks in). In terms of outright gear ratios, I remember that one of the Ivecos has a 12-speed transmission that lets you easily go over 160 km/h or even over 180 km/h, depending on your engine.
And also, your rear tires can affect your top speed slightly, because there are different size tires you can get, especially with the Michelin (and, I believe also Goodyear) DLCs. Basically, a bigger tire will give you a bit higher top speed.
przm83
TruckersMP Support