This is from my tuning guide:
Adding parts – I don’t build very many maxed out tunes. Most of the racing that I do has a set PP level and tire selection so this is how I decide what to add.
Weight
I start with considering the car’s weight. I will admit that I have not done extensive testing in GT6 yet around weight, but so far the theories from GT5 seem to be working. I do not have definitive rules on when to drop weight vs. add power. I would say that my method has much gray area. I try to get into a weight range and then move to power. Weight is always thought about first. When I can get a car into the weight ranges listed below, my lap times are always faster than going only with power. This is what I look for:
- Heavy cars need weight reduction to get them between 1400 and 1450kg
- I prefer average cars that are between 1200 and 1250kg
- Lighter cars in stock form do not always need weight reductions, but 1000kg seems to be the magic number
Power
There are some significant changes to the PP and HP gains in GT6 that are making parts selection much more complicated. In GT5 there were some clear winners (low PP gain vs. high HP gain). In GT5 on almost every car, the first power part that I would add is the racing exhaust. Next were exhaust manifold, intake manifold, air filters and ECU, all being really equal on PP/HP efficiency. The least efficient items in GT5 were the catalytic converter, turbo and supercharger. On almost every car that I tested in GT5, this order was really consistent. Not so in GT6. For comparison, I built ten different cars from FF Ford Focus ST to FR BRZ S’12 to MR NSX R to Honda S2000 to Ford GT to Ferrari FXX to Mustang Boss 302, etc. and every single one had a different list of parts that were most efficient PP/HP. In GT6, racing exhaust no longer won hands down and catalytic converter moves from the junk pile to the most efficient part on most cars.
So how do I choose? Below are two examples of popular cars in the GT series. I have listed all of the weight and power parts and their effect on PP and weight/HP. Note that these are done without oil change for the reasons mentioned earlier in this tuning guide. Most of the columns are self-explanatory. The one that may be confusing is “Gain/PP.” For weight reduction parts I have listed weight loss divided by pp gain. All three stages of weight reduction seem to have the same efficiency value per car (18kg per 1pp for the M3). When you scroll down to the power parts under “Gain/PP,” it gets much more interesting. This formula is horsepower gained divided by PP gained. A higher number is more desirable, more efficient. In the column next to the power part gain/pp I have listed a rank based on this efficiency. Below are results for the M3 Coupe '07 @ 525PP and Ford GT ’06 @600PP.
Choosing Parts and Why - M3 Coupe '07 @ 525PP
1. Window weight reduction and carbon hood. It only cost 1PP for both. I will be adding this to every car I tune in GT6 from here forward.
2. Weight reduction stage 3. This car is just too heavy. Stage 3 takes it down to 1340kg and combined with window and carbon hood the car will now be all the way down to 1325. I will probably add ballast and run this car at 1400kg. Ballast will allow me to play with the front/rear balance during tuning.
3. Sports Catalytic Converter. The winning power part, hands down with 3.25 hp per 1 pp.
4. Engine Tuning Stage 3.
5. Semi-Racing Exhaust.
6. Power Limiter 98.2%.
Build is now at 525PP and 491HP.
Choosing Parts and Why – Ford GT ’06 @ 600PP
1. Window weight reduction and carbon hood. It only cost 1PP for both. I will be adding this to every car I tune in GT6 from here forward.
2. Weight reduction stage 3. This car likes around 1200kg. Stage 3 takes it down to 1204kg and combined with window and carbon hood the car will now be all the way down to 1189. I will add ballast instead of using the power limiter. I want to run this car somewhere between 1200 and 1250kg. Ballast will allow me to play with the front/rear balance during tuning.
3. Sports Catalytic Converter. The winning power part, hands down with 4.25 hp per 1pp.
4. Racing Exhaust at 4.0 hp per 1 pp.
5. Isometric Exhaust Manifold at 4.0 hp per 1 pp.
6. Ballast at 24kg.
Build is now at 600pp and 628hp.
The rest of my guide can be found in the links in my signature below. Hope this helps some.