1.36 drive to a 1.5 drive What props to try??
 

I have a 93 24 Outlaw with a 1.36 drive and have done some upgrades to the new engine. I now have a gen VI short block with the stock MPI setup, I pulled the cam and put an HP 500 cam in it from Precision marine, roller rockers, springs, new fuel system, flowed injectors, hardin marine headers, and ECU upgrades.
We are estimating around 500HP.
With the 1.36 drive I spin a 23p mirage thats had some lab work at 5100 RPMS at 72 - 73 MPH.
Im going to put on a 1.5 drive and was wondering were i should start with props.
Also im i going get a MPH increase by going to the 1.5 drive?
Thanks.

the 1:50 will decrease speed. but increase acceleration.
maybe try a 25

You're going to get a mph increase by a hp increase, not a drive ratio increase / decrease.

Hp to hp ratio changes give low end and mid range throttle response changes. If the hp is the same, figure almost 2 inches of pitch increase going down in g.r. (bigger #) and needing to up in propeller pitch.

Now factor in your hp increase.

so should i just leave the 1.36 on the boat, I was only interested beacause there is a spare dive in our group, but with no change whats the point.

Also Im getting mixed ideas.
Throttle Up claimes that in a past thread I "Quote"

"Thats why some boats will gain speed with a gear ratio change while other lose speed."

gear ratio change i the same as changeing gears in a car with a stick shift.

if your engines tachs out at 5200.your runing a 1:36 gear turning a 28. if you put a 1:50 ratio drive on with the same 28 you will still tach out at 5200 rpm and go slower. your acceleration will increase though.

on our boat we run a 1:50 gear and we turn a 36 6 bld herring. with this set up we have mad acceleration but sacrifice some top end. but around a course with turns you should use acceleration.
for long runs we use same ratio and turn a 6 bld 39 herring . same rpm and pick up about 15.
when we want to go for big numbers we swap to a 1:35 ratio and turn the same 6 bld 39 the same r.p.m . we loose acceleration, but we pick up about 20++ because we are runing higher speed , the water changes, lift changes , drag changes.
there is more than just ratio and prop to consider.

this pic is at 125 or 130 and this thing is just hangin. mad acceleration.small prop low ratio.

So as not to confuse people.

Your not really comparing apples to apples. You say if you tach out at 5200 you will hit the limiter with 1.5 gr if you are using a 1.36:1 and hitting the limiter. Of course you will, and of course you'll accelerate faster and go slower on the top. But, the full explanation is, if the rev limiter is 5800 instead of 5200, the R's will climb higher with the 1.5:1 ratio and the speed will likely be a wash but the throttle response will be stronger. I hope this makes sense to most people.

The reason going to taller gears gives more top end, in certain situations is, because you may run out of rpm room with the 1.5: ratio and need to go to the 1.36: ratio to absorb the HP the engine has to offer and to get off the limiter.

In general boating application, poker runs, family cruising etc., it is best to go to the lowest gear ratio that allows good propeller selection within the propeller family. Don't gear for a 22 or 36 Bravo 1 propeller but rather some where in between. Most applications today can use 1.5:1 ratios with 1.36:1 running a close 2nd.

The main concern is use the propeller as the last cog in the drive trains control of rpm. Stay off the rev limiter by 100-300 rpm and your propped correctly for the gear ratio you have.

Montaa, is explaining ways to change the boats acceleration and speed for various situations they may be in such as racing in todays short circle style tracks.

i would think your looking to prop to your power band. if your making peak power at say 5200 and typicly the limiter is factory set there about 5250 then when you put the 1:50 gear you ll probably need to go up in pitch to a 25 . im not sure what the smallest four bld is but that may be a possibility.

if you had some remaping then maybe they raised the limiter due to engine mods and you may not need to change props.

only testing will tell.

Im going to put on a 1.5 drive and was wondering were i should start with props.
Also im i going get a MPH increase by going to the 1.5 drive?
Thanks.


So as not to confuse people.

Your not really comparing apples to apples. You say if you tach out at 5200 you will hit the limiter with 1.5 gr if you are using a 1.36:1 and hitting the limiter. Of course you will, and of course you'll accelerate faster and go slower on the top.


i allready said that.

this all makes sence now. I sort of thought that way the hole but all me friends say one thing and reallity is another.
As in the beginning of this thread I basically have HP 500 setup And am running the HP 500 cam and so on, what is the max RPM's I should be at? I'm only spinning this 23 labbed 3 bld at about 5100.
should i try spinning more r's????????
also thanks for all the great info.

MONSTAAA
Nice pic of your boat
I think i may have wet myself a little.
WOW

hi i have 1988 240 136 gears 21 mirage lab 70 mph at 5200rpm my buddy has same boat has150 gears 25 mirage68mph same power i run 3000rpm 40mph i crus 3600 rpm doing 55running on 2 barrell good on gas

You will get better fuel economy and throttle response with a 1.50 ratio drive IMHO. Give your manufacturer a call, they can probably best tell you what will work....

Al boats are different..... some boats tend to gain speed with a lower gear ratio (Cats, lighter V's etc.) because they can overcome the torque load while others actually loose speed.

Here's a few boats I set up in the past along with my results.....

My own boat - 36' Apache: 1.50 ratio with 32" Bravo I's ran 83 @ 5100 rpms (GPS). Switched to 1.30 (Bmax - larger gears - more recipricating mass) and 26" Bravo I's and the speed was 81mph GPS. Also, with 1.50 RPMS went straight up to 5100, with the 1.30 RPMS would go to 49-5000, then creep up to 5100.

42' Fountain, flat bottom, triples. 1.50 gears, 27" Mirage Plus to 5600 rpms boat ran 88 mph. 1.36 gears and 25" Mirage Plus' boat ran 83 mph, boat was a dog.

29 Velocity. (don't remember prop sizes but they were Hydromotive's)... 1.50 gear ratio boat ran 72 mph. 1.36 boat ran 76 mph.

there are numerous combinations available so that the boat can actually run very similarly with either 1.5 or 1.36...prop selection would be the key...each boat is different, so the combination of gears and props is a trial by error equation......figure out the rpm range you mostly run in, (not everyone runs at WOT all the time), what type water you mostly run (flat or rough), then decide what prop/gear combination you can maximize........not an easy answer to your question