So I did a true 9R build with the Carl's 900 boost top end on my 24 boost, and also put a BoonDocker intercooler kit with the TRS intake valve. I purchased the Carl's kit from BBA, and Chris flashed it fall of 23 with what I believe was a Polaris development map. Which ran okay that first season i had it, but untimely wasn't substantially stronger than my previous and other friends boosts. However the lightweight crank and the factory 9R fly wheel were awesome upgrades for the low end response improvement. Side note, the stock 9R flywheel is lighter than the ZRP lightened 850 Boost fly-wheel, I have both and weighted them and 9R is like 18 grams lighter (So not much, but it is the lightest).
So this season it branched out on the tunning aspect and have tried the 24 Carl's 50/50 mapping, and all the different Bikeman 900 maps. Then just this week I got the new updated 25 Carl's pump gas a and 50/50 mapping. I have also taken the time to learn how to use tuner pro to make my own changes to mapping to adjust things how I like them. So to keep it high level I will say in my humble opinion the Bikeman tunning the 24 mulit-map 900 flash, and all the 25 single map flashes are all by far the least favorable for me and what i like. Bikeman feels to pull a bunch of timing out of the top end of the mapping which makes the sled feel very lazy to me. I will not spend any more money on Bikeman tunes. The best of them so far for what i like, is the Carl's developed tunes. With this years Carl's 50/50 map being by far the best. It is based of the stock 25 base mapping from Polaris, which has noticeable improvements to the mid-range power valve strategy.
To further answer the original question, for my 2025 sled I did the 9R crank, and 9R fly-wheel with the stock 850 top end, also with the BoonDocker intercooler & TRS valve. Which to answer which is better, the 900 Carl's boost top end or the stock 850, both with 9R crank and 9R fly-wheel. My answer is they are both very close, the 900 Carl's has better mid-range grunt and very slightly better top end. Between the two to get the same rpm on the same clutching with the same target boost level, the 900 Carl's is pulling like 2 grams more primary weight. So the ultimate is the 900, but the best bang for the buck in my humble opinion is the 9R crank & 9R fly wheel, with the 850 saving the money of the keeping the stock 850 top end. Last year I ran the 900 with the SLP head that came wit the kit. This year I'm running the Speedwerx high compression heads on both of the sleds. Which both sleds are 165x3.25 Khaos Boosts, so very similar comparisons.
Right now what I'm playing with is turning the target boost level up on the 25 Carl's 900 tune. This weekend Ill by trying 1psi and 2psi above the Carl's 50/50 map target boost level. Which, I'm very confident will make me want to do anther 900 Carl's Boost on next years Boost.
