any down sides to changing the crank pulley and how much increase in hp can be obtained with significant risk to the engine

 

Very subjective and open-ended question there. There are MANY people on the forum (me included), that have been running lower pulley's with tunes, and a host of other mods with no issues.

Any time you modify any car, you increase the likelihood of something going wrong, and you should enhance all of the maintenance schedules when you increase power (oil/fluid/plug changes, etc..).

So technically, it does have a downside, in that it is increased to a power level not designed by the manufacturer. Up side...Fun as hell, and these cars have been modded quite a bit, with few issues so far.

DC

 

Downsides that most people consider prior to doing a modification such as this, include:
- The cost involved for parts and labor*
-*If doing the labor by yourself, then understand the lower crank pulley install, while not hard, is very tedious and time consuming (there are many posts on the process).
- As mentioned, the extra strain on the car and requirement to increase service intervals and monitor closer things like fluids, etc.
-You will require a tune for the car, so if still under factory warranty, you will ultimately be voiding many covered items assuming JLR detects the modified ECU (which most likely they would) and you cannot run the lower pulley without a tune file, or run the risk at WOT of damaging something and putting the car in limp mode, but what's the point if you don't plan to drive it that way.
-Upper pulley is also a challenging install, once again requiring an updated tune file if you only ever did the lower to begin with.
-There are other performance modifications that can make significant difference in power, such free flowing cats, different exhaust backs, lower and upper pulleys, betting overall cooling for the heat exchangers or adding larger/additional heat exchangers, transmission tune, etc.
- I think on these forums you will find many fans of @VelocityAP_Chris and their tune upgrades that can be found here: www.velocityap.com
-As far as power gains, that is relative to which year and model you are starting with? V6, V8S, V8 (R model), P300, R-Dynamic, etc. - Can't really comment without knowing what you are starting with.

 

I drive stage 2 with TCU update and will switch to stage 3. Why I go from stage 1 to 2 and now to 3 is quickly explained! At every stage of expansion, I never had the feeling that it could damage the car. Of course, you also have to consider the mileage per year and your own driving style. I only drive 2,000-3,000km a year. My engine is always warm before I hit the gas. I also drive normally 90% of the time, and rarely up to 6,800 rpm. So I don't think this will damage the engine. For example, if you drive 30,000 km a year and often go full throttle in OEM condition, you damage your car more. My opinion. Likewise, Stage 2 and TCU update feels mega. You never feel like you're driving a completely over the top, highly tuned car. Everything is buttery soft and feels like series. The difference is simple, Stage2 and 3 are worlds compared to OEM setting. I drive 100-200 km/h in 7.05 seconds, 0-100 km/h in 3.5 seconds. I'll probably do around 6.7-6.8 seconds with Stage 3, which I think is a great time. So I don't regret a single step so far. Engine oil is changed every year. Installed new spark plugs at 40,000km. Likewise, all oils from the differential, change gear, and also a complete gear oil flushing can be done. I think my car is healthy and will last a long time with my mileage per year :-)