Few weeks back, I started to hear tiny little bird from under the hood on cold start, getting progresively louder. So I decided it is time to change both accesory drive belts, idlers and tensioners. And while at it, I thought it would be a pefect opportunity to upgrade the upper pulley, or better said downsize it. I was thinking about ordering Powerhouse's 6% upper pulley + ECU remap, hoping to get anywhere near 470-ish Hp.
My question is to those who had done this mod on their cars, was it worth it, are you satisfied, how do your cars behave, did it in any way harm the engine/SC, what are the downsides if any? How about fuel consumption, did it affect it? And so on...

 

I guess it depends on the trust you put in the ECU remap. I haven't done it to my Jag, but I have two other experiences at each end of the continuum.

My Cadillac CTS-V has a smaller pulley, better intake duct, and is professionally remapped from new by geigercars.de. +100 HP, and now 118k km without any problems.
My former boat with a 502" engine and Weiand supercharger, I just kept adding power by putting on smaller upper pulley. And despite reading the plugs etc., it ended in a ruined engine, had to buy a new longblock

Do you really need that power? If so, do it, and face the consequences. Speed is just a question of money... If not, spare yourself the potentially massive cost.

tberg has done it I believe, with good experience.

 

Huh? Tons of ppl here run with added power on these cars including myself over 500hp on my 08 Xkr iv done tons of dyno and hundreds might be closer to thousand of full throttle runs for testing, lots of drag racing runs in the last 4 years and now car close to 100k mi. . There are others like Jahummer that push the car at the track with tune and mods and I have one customer with 07 Xkr that pushes his car to the limit on hyper rallies where they drive for hours with speed of over 120mph, his car is also tuned , has pulley and pushes a lot more power than stock. Later 4.2 cars especially are very reliable been said by many so just adding a 6% pulley which adds 10-15 hp by itself is nothing....
So to original poster, definitely go for it The difference in power is well worth it and it still will be safe and reliable
You can just skip the pulley altogether if you want as majority of the gains will be in proper ECU tune anyway

 

You also may consider your location. The ecu tune and such can be done remotely but it may be more convenient for Eurotoys if you are in the Midwest.

 

I just put a Velocity AP tune on my car but it seems to run the same speed or slower than stock (stg1). Does it take time for the ECU to adapt? How long?

Thanks