RPM Limitations of Outdrives w/ LS based Engine?

[evantwheeler]

If a guy wanted to utilize an LS based engine that spun up to ~6000 rpm in a small boat, what would be the best outdrive? Lets say about 600hp/500tq at the crank (i'm basing this off what my stroked LS3 in my sand car makes). Any of the mercruiser options work? I saw recently that Tahiti had a 6.2 supercharged LSA in a 242 skier with a B1 outdrive. Boat was said to do 70, and I find it hard to believe that the LSA wouldn't push it much much faster than that. I've got a similar hull with a 6.2 MPI and I can get 62. That LSA has to have an easy 200hp over my setup. I'm assuming RPM or power / prop selection vs. outdrive strength kept it limited? I've searched and there has been lots of chat about LS engines in boats on here, but not many actually in use in an I/O application from what I have seen. Can you use a mercruiser outdrive and make it live behind an LS without spending a ton of coin on custom parts (Teague, Imco, MaxMachine, etc.)?

 

[RaceTec]

@Goodtime$ has used a number of LS based engines in his builds I think, he might know...

 

[evantwheeler]

@Goodtime$ has used a number of LS based engines in his builds I think, he might know...

Yes, the LSA build I referenced was one of his boats. I should have tagged him. Thanks!

 

[DWC]

Here’s some info from PSIRacing. They went after some big HP, high RPM’s.

 

[evantwheeler]

Here’s some info from PSIRacing. They went after some big HP, high RPM’s.
View attachment 990588 View attachment 990589

That's a bad ass boat, I think it's the 2JZ toyota in a Daytona? Those kind of numbers are way beyond anything that I could ever afford to do with an engine and drive package. I just think it would be easy to drop in a stroked LS3 in place of my current 6.2, but want to know what I would need in a drive to handle the power and RPM's. No sense in putting in an engine that has to get cut off at 5200rpm when it can make good power up to 6000rpm easily.

 

[Icky]

Subscribed

 

[Guest06]

I’d still absolutely love to do a 427-440” with a pair of 62mm’s, figure without getting retarded with the boost should make a solid 750hp and Upper 600’s tq spin its to 6400 all day long.

 

[evantwheeler]

I’d still absolutely love to do a 427-440” with a pair of 62mm’s, figure without getting retarded with the boost should make a solid 750hp and Upper 600’s tq spin its to 6400 all day long.

I think it would be hard to keep it under 750 with that setup!

Guy that built my LS3 is now building lots of 454 cu in small block LS engines. He sleeves them so piston doesn't leave the bore with the longer stroke. Not going to get the same bottom end torque as a similar cu in BB, but for a smaller lighter boat, I don't think it would matter.

My question is do you have to spend $15-$20k on an outdrive for it to live behind a reasonably powered LS spinning 6000-6400? I already have one toy with an $18k power transfer box (weddle S5d), I don't want another. Could a guy pick up a used XR from someone upgrading their boosted big block boat, and put it behind an LS and would it live?

 

[Melloyellovector]

XR should have no problem handling that power. How ever that’s not exactly a budget drive either at close to 18k range. Can you find used, sure, you can also find sc, scx etc.. used

 

[Guest06]

I think it would be hard to keep it under 750 with that setup!

Guy that built my LS3 is now building lots of 454 cu in small block LS engines. He sleeves them so piston doesn't leave the bore with the longer stroke. Not going to get the same bottom end torque as a similar cu in BB, but for a smaller lighter boat, I don't think it would matter.

My question is do you have to spend $15-$20k on an outdrive for it to live behind a reasonably powered LS spinning 6000-6400? I already have one toy with an $18k power transfer box (weddle S5d), I don't want another. Could a guy pick up a used XR from someone upgrading their boosted big block boat, and put it behind an LS and would it live?

Keep the boost low, and i say 750, but who wants to stop there.
I spoke with Alper on a build we spoke of 5-6psi as a place to start.
XR will handle it, but that is like a S4

 

[evantwheeler]

Keep the boost low, and i say 750, but who wants to stop there.
I spoke with Alper on a build we spoke of 5-6psi as a place to start.
XR will handle it, but that is like a S4

Alper built the engine in my sand car. It rips.

 

[Nanu/Nanu]

if you pull the trigger on this it will be awesome! I would think the blown LSA/Bravo 1 setup is more than capable of 70. I think it's just a matter of tuning through the motor, drive, and prop. That Daytona from pci did awesome at one of the LOTO shootouts couple years back.

Come to think of it... It's for sale at Eliminator right now might be easier to just have another boat. Haha

 

[H8Plow]

When I talked to Max Worx about my B1, he told me 500 was pretty much the limit on a B1 with the thin floor gears. The later model B1’s (thicker floored gear) could goto 600 but to be gentle on the hole shots.

 

[Goodtime$]

We have done a couple Lsa 540 / bravo 1 deals with no problems. Motor makes power

ls3 500hp bravo 1 deal Would be the ticket

tons of guys doing LS swaps in both jets and out drives.

6.0L iron block would be my base w nice pistons, cam , headers and prob a carb intake

 

[STV_Keith]

I'd ask Brian @ B & D Marine about this. I know he turns his Bravo's in the low to mid 6k range. @BDMar

 

[Racey]

It's torque that kills the drive, not HP and RPM....

Higher RPM with less tq and more HP is easier on the gear sets (the weak link)

 

[evantwheeler]

We have done a couple Lsa 540 / bravo 1 deals with no problems. Motor makes power

ls3 500hp bravo 1 deal Would be the ticket

tons of guys doing LS swaps in both jets and out drives.

6.0L iron block would be my base w nice pistons, cam , headers and prob a carb intake

just curious what your opinion is on why that LSA powered rig (242 skier I think, red and orange one) wasn’t more impressive from a speed standpoint. What RPM was it limited to? Like I said earlier, I have a very similar bottom as that boat on my Ultra 23XS and it can get to 62 with a stock 6.2. Granted that 242 is a bit heavier, but with 200 extra horsepower and more RPM (I assume) I would thin It would do a lot better than 70. I also acknowledge that that boat was likely not built or tuned for top end speed. Just trying to get a feel for capabilities of an LS powered boat and what components would be required to make things live.

 

[BDMar]

I'd ask Brian @ B & D Marine about this. I know he turns his Bravo's in the low to mid 6k range. @BDMar

My drives are IMCO SC's but have a lot of work I've done to them. They are basically an XR drive with stronger housings that keep the gear locations more consistent. Also when I run them to 6500, it's for seconds, not minutes. The reason Bravo XR style drives are recommended to stay under 6000 rpm's, is not because of the gears, it's the bearing temps. Anything over 6K and the bearing temps rise substantially.
The OP could get away with an XR drive if it was set up correctly for HP. Better choice would be an SC.

 

[Goodtime$]

just curious what your opinion is on why that LSA powered rig (242 skier I think, red and orange one) wasn’t more impressive from a speed standpoint. What RPM was it limited to? Like I said earlier, I have a very similar bottom as that boat on my Ultra 23XS and it can get to 62 with a stock 6.2. Granted that 242 is a bit heavier, but with 200 extra horsepower and more RPM (I assume) I would thin It would do a lot better than 70. I also acknowledge that that boat was likely not built or tuned for top end speed. Just trying to get a feel for capabilities of an LS powered boat and what components would be required to make things live.

LSA - 242 SKIER was for a family dude so it only saw a SKI PROP. Plus its an Aftershock 24 bottom so not made for speed really. Huge bow.
Ultra 23XS is much different bottom, trust me. We have that mold in our yard.

LS engines are designed to run at a higher RPM, LSA for sure. They are all that we are offered for JET POWER so here are some pics to help.

LSA - 242 SKIER

Goodrums crazy turbo 6.0 LQ4 deals

22 Domn8er Deck we did interior on (Placecraft style) bravo drive - He pulled his sandcar motor out and marinized it.

They make good power but.............LSA in a jet is 4600-5200 RPM of real world torque.
LSA - Bravo 1 in a 23 deck was tons of fun.
LSA - 242 SKIER was ok, definately much more torque power to a 6.2 mag but nothing crazy in a Vee Hull Skier.

6.0 L96
LS3
LSA
LT4
6.2 DI is what is offered.

If they had a 502 BBC with single 950 carb. I pick 502 all day

 

[SMPLV]

Alper built the engine in my sand car. It rips.

Damn, Jason is even popular on RDP! hahaha