I hope it is in good condition. 120hr on it.

It will be 2” deeper with the XR lower so I hope it will be good!

+10mph gain would be great to get..

My 1:1.35 ratio on my drive, is that the upper XR only that is 1:1.35 or is it the upper + lower that is 1:1.35 ratio combined?

how will it affect my drive to add a lower that has been on a 1:1.5 ratio drive to my 1:1.35 ratio?

If the upper is an XR then the ratio is changed by the gears in the lower.
If the upper is an X then the ratio is changed by the upper gears.

Sorry, but you lost me there..

Let’s say my upper is a XR (Im like 99% sure it is) and with the Sportmaster lower it is 1:1.35 ratio.

Is the upper (XR) still 1:1.35 without the Sportmaster or is it the Sportmaster that is making the ratio 1:1.35?

And if I put the XR lower (that is 1:1.5 I think) with my upper, will it make it to a 1:1.5 then?

Actually I dont know if my drive is a XR or a X upper. The only thing I know is the gear ratio I have now with the Sportmaster lower - 1:1.35

Is it still possible to put a XR lower if my upper is a X?

In your first post (#1) you stated the boat as pulling 4800RPM @ 50mph/ 26p 4 blade... and the Whipple stage 1 kit was red line at 5450 rpm... that is at least down to a 24P to get the rpm up to 5200(ish rpm)... sometimes you have to go smaller (and proper) pitch to go faster as the engine and drive are lugging to turn the prop with its excessive bite. 2" pitch is +/-400RPM

A few posts back you said you ran 52mph at 4600rpm trimmed up = you are not turning enough rpm ideally with the prop dimension (diameter, # blades & Pitch) bolted to the drive. To me, it seems like you are fixated on identifying / justifying the drive ratio but haven't addressed the excessive pitch for what you have in your set-up.

My suggestion is to beg borrow or steal a proper spec prop in pitch and diameter and see what how the boat is performing mph wise in the proper RPM. You may find planing and top end are improved... then play with the drive height (as you have spacers) to fine tune the max rpm vs handling you can get out of the boat.....strictly my $0.02

XR uppers ALL have the same gear sets and the ratio gets changed with different gear sets in the XR (or SM) lower.
Your SM lower is what is changing the ratio IF you have an XR upper.

X uppers are available with 3 different gear sets which change the ratio. The lowers all use the same gear set.
IF you actually have an X upper that is a 1.36 and you put on the XR 1.5 ratio lower, your final ratio will remain at 1.36.

Both the XR 1.5 lower and the X universal lower use 15/19 count teeth gears.

Sorry, but the numbers in my #1 post wasnt 100% correct.
The post with 48 mph @ ~4500 rpm is more correct.

Then after that I installed the .5” spacer and trimmed down the water pickup.

After that I saw 52,7 mph @~4650 rpm.

And if I trim the drive out more the speed was falling down to like 49 mph and rpm go up to like ~4950-5000 rpm.

So to me it seems that the numbers changed to the positive way when I installed the spacer and got the drive lower.. ?

Thank you, now I understand better.

So if my upper is a X it doesnt matter, it will fit anyway with the XR lower?
Dont want to brake something

Have any friends that you could use their bravo drive for testing? My opinion with 26p at 5000rpm boat should run 70 or more. Going to 24p will raise rpm but I don't think MPH would increase much? How much does boat weight... because that engine power in my 270 Checkmate I'm sure would run mid 70's

No I havent, not that much boat people here..
I think the boat weights about 5500 lbs / 2500kg with engine and everyting

Sounds like you need a 2 inch spacer. Or a 1 inch if that is made.