Jump to content

Welcome to TheMalibuCrew!

As a guest, you are welcome to poke around and view the majority of the content that we have to offer, but in order to post, search, contact members, and get full use out of the website you will need to Register for an Account. It's free and it's easy, so don't hesitate to join the TheMalibuCrew Family today!

Sign in to follow this  
DarkSide

Engine/tranny prop theory question

Recommended Posts

DarkSide

Someone please help educate the ignorant.  If I understand this correctly, and that is a BIG if. (Ratios rounded slightly for easier math)

Given:  2015 450 HP on 1.5:1 running at 3600 RPM. So effectively 675 HP (450x1.5), prop completes 2400 rotations.

In 2016 450 HP tranny 1.75  engine will have to run 4200 RPM to achieve same 2400 rotations.  450 will also produce effectively 788 HP (450x1.75)due to lower gear ratio.

2017 450 HP tranny 2:1.  Engine will have to run 4800 RPM to spin prop 2400 rotations.  HP also effectively 900 (450x2) due to even lower gearing.

This is assuming same prop, same boat, etc.  However as tranny ratios increase prop pitch (and sometimes diameter) can be changed to lower RPM, now that you have enough power to turn it.

Obviously this is very simplified and HP/TQ curves are not factored but is this essentially correct?  If not would one of the many who are smarter than me please correct me. 

 

 

 

Share this post


Link to post
SoulSurfer

Well, the transmission ratio multiplies torque, not horsepower.  That said - yes, I think you are generally on track, not accounting for the actual torque curve of the engine and the losses in the drivetrain.  Lower ratio (numerically higher) put more torque to the prop and result in fewer rotations at the prop for any given rpm at the crankshaft.  It would seem that the additional torque at the prop should hypothetically allow you to run a prop with greater resistance to turning (i.e. higher pitch number and/or larger diameter).

Share this post


Link to post
MadMan

SoulSurfer is right.  Gear reduction only increases torque.  Horsepower is torque x rpm x constant.  So as the torque is increased by the gear ratio, the rpm is lowered proportionally and the horsepower remains the same.

Share this post


Link to post
twitchee2

Yup, HP stays the same, torque increase as speed decreases.  

Share this post


Link to post
DarkSide

Torque is really the important factor though correct?  I used HP as those numbers are more readily available.  We as tow sports enthusiasts want the twisting force (torque) to be increased, thus increasing the ability to turn prop.  Yes???

As I start the search for a new ride.  The 572 was required in the 2015, I had 450 in 2014 and it didn't work well.  But as ratios change, the $10,000 may be better spent elsewhere.  That is the basis for the question

Share this post


Link to post
SoulSurfer

Note that the numbers being assigned to the Indmar Ford 6.2 engines aren't HP numbers.  They're torque numbers.  The reality is that you need both torque and hp.  HP is a measurement of the engine's capacity to perform work.  Pushing a loaded down boat through the water at 11 mph requires work. Practically speaking, any V8 engine with the torque you want will probably have the hp you need.  Lots of torque at lower rpm will let you turn a big/tall prop at a slower rpm (and coincidentally will also correlate to higher HP at that lower rpm). Or, if you're willing to run at a higher RPM, you can have a lower nominal torque engine and multiply what it offers through a larger numerical transmission ratio.  Since HP isn't multiplied, though, you'll not gain (and will probably lose) top speed and the ability to cruise at lower rpms. 

Share this post


Link to post
The Hulk

agree with all above, my 555hp 2013 LSA 23lsv was a beast from basically idle speed, jumped like crazy and was only on a 1.25:1, with a 14.5x16 prop, and it could of probably handled 14.5x17+ easily. i ran 3000-3100rpms surfing slammed, 3200 if it was crazy day and wedge position but normally about 3050rpms was the norm. (never ran any bow weight) i felt no matter the bow rise the engine could overcome it, effectively pushing my boat straight up to the sky if i wanted.

2016 25lsv with 450(torque) and 1.76:1, i'm near 4200rpms with a 15x14.25, and it needs to be a 15x16 or 15x16.50 range to lower that. On another note i did put 800-900lbs in the bow and dropped all the way down to 3600-3700rpms (500rpm savings at a minimum for same settings)  while if i were to build from scratch i'd probably do the SC 572, but it just didnt happen too many other goodies on the one and the deal i got so i sacrificed from what i said i would never do but ONLY due to the newer 1.76:1 gear ratio. Yea i loose top end speed but its a surf boat after all, and i should have more torque at the prop than before or similar given how you calculate it. now with increasing pitch and some bow weight i should be able to get down in the 3200-3500rpm range and im pushing a lot more weight than my previous boat and got a better wave. I may not get quite as good as GPH with the smaller 450 vs 572 but its probably minimal difference over the 5yr warranty period i plan on owning it and being able to get 90/91 e-free on the lake (if i have to is huge) before i had no option needing prem gas (off the lake) - hassle 

there is NO substitute for the SC engines that generate such huge torque/hp at the lower rpm range and it is very noticeable, however as mentioned above is it worth the upgrade cost? kind of up to you depending on the options you want, personally i would go G4, stereo and other upgrades.

Now with steeper prop/shaft angle on the 2017 and a 2:1 im anxious to get those folks feedback on rpms, yea bigger prop and possibly higher pitch but do they come out the same? or do they actually need more bow weight to overcome the loss of shaft angle? im guessing its going to come out nearly the same, less slip, but more angular loss, i'm guessing it will be close but with the expense of at least "guessing" 4"+ more draft depth. and much more expensive props.

i'm plenty happy with the 450 for what i do, but i surely do miss the SC engines.. but shopping for a new boat it would be a harder sell than in previous years with the new gear ratios.

anyhow my .02

Share this post


Link to post
tjklein

This is depressing to read as I'm in the process of working a deal on a 22MXZ and trading in a '14 23LSV with the LSA.  

The LSA combo with 1.25 ratio is amazing.  Top end speed, low RPMs and power to burn.  :-(  I hope the new boat and the 410 with a 1.76 ratio work well....

Edited by tjklein

Share this post


Link to post
teamerickson
9 minutes ago, tjklein said:

This is depressing to read as I'm in the process of working a deal on a 22MXZ and trading in a '14 23LSV with the LSA.  

The LSA combo with 1.25 ratio is amazing.  Top end speed, low RPMs and power to burn.  :-(  I hope the new boat and the 410 with a 1.76 ratio work well....

What is your setup going to be?

I just demoed a 23 with the 410 and 2249 prop. All hard tanks and 750 PNP it was around 3500 surfing. 100 elevation. I think it was around 3900 wakeboarding with that weight. I plan to ad some bow weight and switch to the 2277 prop. Getting the 2249 for a spare. 

Share this post


Link to post
tjklein

2017 22mxz with the 410 and the standard 1.76 gear ratio.  The upgrade to the 450 is a waste.  They're so close...so close I couldn't tell a difference.  The 575 just isn't worth it.  I'm taking a bath on my 555hp.  You pick up $2000-2500k on trade.  It's nice, but it doesn't change the surf experience.

Share this post


Link to post
The Hulk
2 hours ago, tjklein said:

This is depressing to read as I'm in the process of working a deal on a 22MXZ and trading in a '14 23LSV with the LSA.  

The LSA combo with 1.25 ratio is amazing.  Top end speed, low RPMs and power to burn.  :-(  I hope the new boat and the 410 with a 1.76 ratio work well....

Yes I would love the LSA on a 1.5:1 in the 25 with a 16x18 prop. Not sure if the 1.25 would work but maybe very well if keeping it at a 15" prop.. best of both worlds..

Share this post


Link to post
teamerickson
32 minutes ago, tjklein said:

2017 22mxz with the 410 and the standard 1.76 gear ratio.  The upgrade to the 450 is a waste.  They're so close...so close I couldn't tell a difference.  The 575 just isn't worth it.  I'm taking a bath on my 555hp.  You pick up $2000-2500k on trade.  It's nice, but it doesn't change the surf experience.

Sorry, what are you doing behind the boat? Weight setups?

Share this post


Link to post
The Hulk
28 minutes ago, tjklein said:

2017 22mxz with the 410 and the standard 1.76 gear ratio.  The upgrade to the 450 is a waste.  They're so close...so close I couldn't tell a difference.  The 575 just isn't worth it.  I'm taking a bath on my 555hp.  You pick up $2000-2500k on trade.  It's nice, but it doesn't change the surf experience.

Yes I checked around 3 dealers and was told about +$500-2k max for my LSA on trade in and one dealer said no difference.. buzz kill when considering a new boat ...better know it's a bigger hit than u think.. but pure awesomeness..

 

Asked why... general responses were.. it's waste to most people, premium gas hassle,.... harder to sell..whaaawhaaat?? Dealer basically said people don't slam their boats so why would they ever need it? 

Man if I wanted a SC again I'd be shopping USED for sure nearly a free upgrade when buying used!! Depending on warranty though..

 

Share this post


Link to post
tjklein
5 hours ago, teamerickson said:

Sorry, what are you doing behind the boat? Weight setups?

90% surfing and 10% wake boarding.  We find ourselves surfing more and more.  

 

I ran my 23 with Ronix 800s in the rear, 350 in the coffin, and a bow bag.  Usually had somewhere between 3-6 people in the boat.  LSA moved it with no sweat with 1.25:1 and 2247 prop.  Even the 1589, which netted 50mph moved all that just fine.  I demoed the 450 and with 2 people in the boat, factory setup and no PNP it felt about the same.  As 2 people slammed in my 23.

 

That being said I plan on running the 22mxz with the PNP 550s (that's as big as possible with the new bigger tanks) and some extra weight up front.  I surfed the 22mxz with stock tanks and it actually wasn't bad.  Better than the stock 23 for sure, that was almost unrideable to me.  (205lbs)  Note that the 22mxz is 300lbs heavier and the stock tanks are bigger, although it carries 140lbs less in fuel.  

 

I think the 22mxz will do fine even with the 2277 prop...it's just not going to race to get there.  At the end of the day I've decided on having a new boat, with the new features over the excess power plant.  I hope I'm right, but either way I learned my lesson on the big engine.  If I want to go fast I'll hop on the jetski...which I'd have enough money to buy another one instead of upgrading motors.  :-)

5 hours ago, The Hulk said:

Based off the 260 engine I think it's safe to say the reliability will be less than awesome.  :-)  

Fun toy as long as you don't wipe out at 80mph.

Share this post


Link to post
The Hulk

How much more stock is in the new 22 vs your 23? Is the new 22 stock same or more than a new 23?

 

Share this post


Link to post
The Hulk
3 hours ago, tjklein said:

Hope I'm right, but either way I learned my lesson on the big engine.  If I want to go fast I'll hop on the jetski...which I'd have enough money to buy another one instead of upgrading motors.  :-)

This is a great point I need to explain to the wifey that I "saved" enough to buy a jetski!! It's totally justified now!

Share this post


Link to post
tjklein

Looks like 481lbs more than the new 23LSV.  Max Ballast is 4431 to 3950lbs (w/wedge).  The rear tanks and front tank are certainly bigger.  On the new MXZs the tank is slightly deeper and goes up the side of the hull.  

 

Add in the difference in dry weight and you can see why the stock wave is better. 

Share this post


Link to post
teamerickson

I think 2017 22MXZ hard tanks are 1800.

Share this post


Link to post
tjklein
Just now, teamerickson said:

I think 2017 22MXZ hard tanks are 1800.

You're close.  It's something like that.  I thought the LSV was 1350, but I don't remember.

Share this post


Link to post
teamerickson
Just now, tjklein said:

You're close.  It's something like that.  I thought the LSV was 1350, but I don't remember.

I think so. I don't think the standard ballast figures on Malibu's website includes the bow? Looks like the MXZ's max is about 500 more then 23. Looks like the new tanks on the MXZ ad about 500.

Share this post


Link to post
The Hulk

So roughly 800lbs more in a 1ft shorter boat. Seems about right to make it noticeably better at stock..

Share this post


Link to post
The Hulk
6 hours ago, oldjeep said:

Wonder what the top speed is on that?  My folks supercharged RXP with 215HP goes 71

 

1f1fc44407191e9f71f28986e35be94f.jpg

Share this post


Link to post

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...