If you live in an area of the country where you have particularly hot summer weather, you may see your operating temperatures get too high. This will only happen if you are sitting in traffic with the engine idling. While the engine is running at a decent rpm you will not have any problems. However, you do loose some engine cooling power at lower rpm. This could be solved by a new radiator also. The underdrive pulleys do give a noticable power increase. I have successfully run mine for about two years and have never overheated so it can be done. I do not live in a large city, so I don't have to deal with hours of traffic on end either. You just have to be aware of the possibility.