TRS or Bravo even Bravo XR ?

[QBhoy]

I’ll keep this brief. Long story short. I’m trying to help a boating friend best I can with a ridiculous machine he has almost completed. But such a machine is not what I’m used to at all. Far from it.

He has one of only 18 built tunnel hull boats. They were made in the late 70’s and one came to the U.K. for the boat show.
This one had a big block with twin turbos in it. I really think more for the show than for actual reliable use. I think this because it has an OMC800 drive on it, which is thought original. It has a seemingly crazy 1.77 ratio.
I don’t know much about these drives...but I do know that looking at it, even my V8 small block MPI would likely blow it up in 10 minutes.

now...it’s sat all this time since it’s 1978 boat show.
It is now being fitted with a big block performance engine with thousands spent on its components and internals. New turbos too and is expected to run upwards of 500hp at close to 6000 rpm. There is no way that drive is going to cope with it.
Mathematics at 100 mph, 1.77., 6000 rpm and say 10% slip would suggest a 35” prop at that. Silly stuff really.

anyway. I’ve advised that performance boats of that period with some power would likely run a TRS drive. Modern day would be perhaps a Bravo XR.
the budget is tight now after the engine.

question would be....what kind of power could an old rebuilt TRS take ?
what kind of power could a standard single prop bravo take at say 1.5 ratio ?
will he need an altogether more serious drive ?

ps I’ve also suggested that at 6000 rpm...he might be in the category of needing a rebuilt engine after every outing.

all opinions welcome. Picture below of actual boat in about 1980

 

[alldodge]

How heavy is the boat fully loaded?

 

[QBhoy]

How heavy is the boat fully loaded?

Hi AD. Was hoping you’d reply.

I have no idea fully loaded. But I suspect it’s very light. If I was to guess at its weight empty as it is just now, it would safely be under 1500 lbs quite easily, without engine. Likely less by a fair distance.

he has been in touch briefly with a guy in the states who has one of the others still known to be left. I didn’t get any details on what is powering it or what drive he has...but I know that he has less power and very very quick. He thinks that 100 mph is a very safe bet when my friend told him what’s going in it. I dare say they didn’t discuss the drive it has.
I need to get more details what he has in his. But by the account I got, it’s quite normal power and not tampered with. Likely he is over 80 anyway.

 

[QBhoy]

This is the twin turbo big block that’s going in her.

 

[Scott Danforth]

the OMG stringer wont last. it was only paired with 260hp small blocks. it also wont run over 5000 RPM

you can heavily modify a production drive if you want. http://www.rlcperformance.com/project_tripledigits.html

however you should not be looking at production drives. maybe the NXT or similar drive

small blocks in endurance races spin much higher RPM's than 6k. they spin much closer to 10k.

you just have to build the oiling system properly. however at 6k, a wet-sump is more than adequate.

now back to the OMG drive. the hole in the transom and the setup is OMG specific. you can drive a buick into the transom hole.

any other drive will require a new transom, stringers and deck.

so why is there a high HP motor in front of the OMG stringer?

 

[alldodge]

With it being that light a regular B1 should do it. Going with a X or XR even better but don't think the boat will put that much torque on the drive. Sick Stinger on OSO will have some and he can ship across the pond with no issues, if unable to find local

That said, if the boat catches air and its not throttled back something is going to break

I wouldn't mess with the TRS only because of parts and expertise for rebuild.

 

[QBhoy]

the OMG stringer wont last. it was only paired with 260hp small blocks. it also wont run over 5000 RPM

you can heavily modify a production drive if you want. http://www.rlcperformance.com/project_tripledigits.html

however you should not be looking at production drives. maybe the NXT or similar drive

small blocks in endurance races spin much higher RPM's than 6k. they spin much closer to 10k.

you just have to build the oiling system properly. however at 6k, a wet-sump is more than adequate.

now back to the OMG drive. the hole in the transom and the setup is OMG specific. you can drive a buick into the transom hole.

any other drive will require a new transom, stringers and deck.

so why is there a high HP motor in front of the OMG stringer?

Presumed as much. Totally agree.

 

[QBhoy]

the OMG stringer wont last. it was only paired with 260hp small blocks. it also wont run over 5000 RPM

you can heavily modify a production drive if you want. http://www.rlcperformance.com/project_tripledigits.html

however you should not be looking at production drives. maybe the NXT or similar drive

small blocks in endurance races spin much higher RPM's than 6k. they spin much closer to 10k.

you just have to build the oiling system properly. however at 6k, a wet-sump is more than adequate.

now back to the OMG drive. the hole in the transom and the setup is OMG specific. you can drive a buick into the transom hole.

any other drive will require a new transom, stringers and deck.

so why is there a high HP motor in front of the OMG stringer?

Sorry Scott. Just read the rest of your post. It didn’t all appear initially on this phone.

ok so that’s a good point about the hole in transom. Well said.

im pretty sure the engine with the turbos (originally a small block) was fitted to it more to be a show piece for the boat show. Not so much for it being used in the real world. It was the only one to have this power plant. The rest had either small blocks in normal form or even a V6 outboard, by all accounts.

I think the drives of that era that could take that power would be a speedmaster perhaps. But they would be on much heavier boats I think.

 

[QBhoy]

With it being that light a regular B1 should do it. Going with a X or XR even better but don't think the boat will put that much torque on the drive. Sick Stinger on OSO will have some and he can ship across the pond with no issues, if unable to find local

That said, if the boat catches air and its not throttled back something is going to break

I wouldn't mess with the TRS only because of parts and expertise for rebuild.

Thanks AD. Sound advice there for sure. The XR here is about £7000 without the rest required. He wants to keep it looking of it’s own era too perhaps. Money is an issue now too.

agree about it being extremely dangerous too. Especially where it’s going to be used. 99% of the time the conditions will make it unusable. I really admire what he is doing though and will certainly hope to be there for its debut to the water here. Not anything like it here since Donald Campbell and co. Exciting stuff.

 

[Scott Danforth]

I think the drives of that era that could take that power would be a speedmaster perhaps. But they would be on much heavier boats I think.

plenty of high hp boats of that Era....... Just not a stringer.

its a V6 OMC outboard lower unit, connected to a 90 degree gear box via a cheap splinned shaft, driven by ball gears.

the dog clutches do not do well with a large load. however there are good things about the OMG drive..... just too many non-good things compared to others.