Stern Drive or Inboard for hi-power swap

[elwesso]

I posted this in the wrong forum and someone told me to post it here, so here goes

It has been my dream to swap one my beloved motors into a boat, however I dont have the boat yet so im debating on what would be the best.

Basically Im swapping in a Nissan V8, im not worried about getting it to work, I am wondering how it would be easiest... I am accustomed to inboards, whether they be V drive or direct drive and I dont really have much experience with stern drives.

This motor does not bolt to any marine gearboxes so im going to have to make it fit regardless...

Lets say for the sake of getting started that im going to be running about 400HP and im hoping to see 70MPH in whatever I use.

Questions..

1. Would an inboard setup work better or a stern drive? I dont know how stern drives attach to the motors, i woudl assume it has a bellhousing similar to an inboard setup. If stern drives only connect to the motor using the shaft/U joint coming off the back of it then that might be easier.

2. What kind of hull design would be good? I have access to a bunch of older cobalts, whether it be a single hull or a tri-hull design, just something thats going to be stable at high speeds.

3. can stock stern drives handle that kind of power?

Thanks for the help... Youd think being around boats my entire life Id know this stupid stuff but ive not been around stern drives enough.
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[superpop]

Re: Stern Drive or Inboard for hi-power swap

You are going to run into some major and very expensive fabrication and engineering to make this work. And then it still may not work. Are you talking about a Titan Motor, if you are you will need a custom bell housing to hook up to either a stern drive or tranny on an inboard. Then you have the custom manifolds and risers and then there is the ECU issues that will need to be addressed unless you want to throw in a custom made intake with a carb as well. Unless you have access to some serious engineering talent and some big boy machining toys you will just be wasting your time and money. An improperly cammed Nissan motor will run for about five minutes before it sucks in some water through the exhaust and implodes. Let me know if you have any success with this. I know that Toyota made a ski boat for a while that used a 4.7L V8 made by Toyota. That may be a better route to take, but if you are looking to go fast I would go buy a big block cheby motor and the appropriate drive, way cheaper and easier to find the parts.

 

[whywhyzed]

Re: Stern Drive or Inboard for hi-power swap

1. No Marine manifolds exist for a Nissan - expect to pay $10000 to $20000 to get some cast

2. No explosion proof electrical / ignition components exist - expect your boat to blow up

3. No marine fuel system components exist -expect your boat to blow up

4. No marine compatible ignition advance curve exists - expect the boat to be a dog and probably struggle to get on plane

5. Due to #2 and #3 above expect all insurance companies to refuse to insure it

6. Per my boat speed calculator program, 400HP / 70MPH reguires a very efficient hull and light weight -weighing around 1400 lbs.... basically you are limited to a 15 foot aluminum....

 

[elwesso]

Re: Stern Drive or Inboard for hi-power swap

Thanks for the feedback. I think I got the answer I was looking for.

The question of course is does a stern drive phyiscally mount to the motor or since the stern drive is mounted to the transom, does the motor and stern drive actually bolt together or does just the shaft slide into the motor? Im pretty sure Ive seen stern drive motors laying around our marina and thats the case...

Im simply asking if itd be easier to mount a motor to a stern drive or inboard, and from the comments it sounds like its not going to make much difference either.

I appreciate the other comments, im well aware of what Im up against but I dont think im going the traditional marine route. The motor will not be sitting under a cover and the exhaust will dump out of some stacks or something like that.. Meaning Im not planning on running risers at all, if the motor isnt going to be covered i dont really see the point. Id also be using a heat exchanger instead of raw water, as the aluminum block isnt made for raw water.

This is going to be a purpose built thing, not a drop in replacement. I already have a cruiser (Chris Craft Commander 23) so now im looking to make a purpose built screamer.

KJD- could you tell me where you got that calculator program?

 

[HT32BSX115]

Re: Stern Drive or Inboard for hi-power swap

I wonder about how accurate that program might be.​

My 1987 Four Winns 211 Liberator went 60 GPS mph with 340 crankshaft HP and a King Cobra stern drive.​

I know of another one that with 500 non-supercharged HP buried the speedo at 80 MPH (same King Cobra)​

It weighs 2200lbs without the engine/ stern drive, 21' long, 8' beam.​

Also you wouldn't need explosion proof stuff in an open type boat. NONE of the hot rod open engine boats have marine type stuff in them and they get insurance.​

You could either use water injected dry stacks or jacketed type stainless steel headers. $3000 PLUS for jacketed headers.​

If you want to use a stern drive, you'd need to use a BRAVO I or II drive since they are good for around 400HP. Merc has higher HP drives ....bring $$$ YOu'd also need to have access to a complete machine shop to make the bell housing and you'd need to put your flywheel on a vertical mill to index the holes to bolt a Bravo coupler to it.​

It's all doable. lot'sa time/money.​

a GMC V-8 would be a better choice since there's a LOT of 'off the shelf' parts available!​

Regards,​

Rick​

 

[whywhyzed]

Re: Stern Drive or Inboard for hi-power swap

I wonder about how accurate that program might be.​

My 1987 Four Winns 211 Liberator went 60 GPS mph with 340 crankshaft HP and a King Cobra stern drive.​

It's genearally accepted that
20HP = 1 MPH increase for most pleasure boat planing hulls

So, if 340HP = 60
To get to 70 requires 200 additional HP

550HP in your boat probably would have gotten you to 70

 

[HT32BSX115]

Re: Stern Drive or Inboard for hi-power swap

I would say it was even less than 340 since back then they rated everything at crankshaft HP and it was VERY optimistic. I would say that it was more like 300 propshaft HP!​

 

[HT32BSX115]

Re: Stern Drive or Inboard for hi-power swap

sloooow network causes double posts!!!​

 

[elwesso]

Re: Stern Drive or Inboard for hi-power swap

I wonder about how accurate that program might be.​

My 1987 Four Winns 211 Liberator went 60 GPS mph with 340 crankshaft HP and a King Cobra stern drive.​

I know of another one that with 500 non-supercharged HP buried the speedo at 80 MPH (same King Cobra)​

It weighs 2200lbs without the engine/ stern drive, 21' long, 8' beam.​

Also you wouldn't need explosion proof stuff in an open type boat. NONE of the hot rod open engine boats have marine type stuff in them and they get insurance.​

You could either use water injected dry stacks or jacketed type stainless steel headers. $3000 PLUS for jacketed headers.​

If you want to use a stern drive, you'd need to use a BRAVO I or II drive since they are good for around 400HP. Merc has higher HP drives ....bring $$$ YOu'd also need to have access to a complete machine shop to make the bell housing and you'd need to put your flywheel on a vertical mill to index the holes to bolt a Bravo coupler to it.​

It's all doable. lot'sa time/money.​

a GMC V-8 would be a better choice since there's a LOT of 'off the shelf' parts available!​

Regards,​

Rick​

Cheers my man, that is the info I was looking for!!!!

I know tihs may not be the best place to post about it, but i was looking online about some jet drives... I see a lot of really big HP boats, sorta what im looking to build, and im wondering if finding a boat with a jet drive but no motor might be the way to go...

Basically what im looking for is a platform that I can throw anything out... I want something that can take some serious abuse, because i plan to abuse it... Im really starting to think that a stern drive might be too finicky for me?

Thanks for the info about the bravo 1 and bravo II sterns, that is exactly what I was looking for. Is there an older equivalent to the bravo I in the mercruiser, because I know the bravo series stern drives didnt come around until after the boats I would be using if I went to a stern drive... Im not sure I've even seen a bravo I MerCruiser, ive only seen bravo II and bravoIIIs on our big boats. Like I said in my original post, itd probably be a late 80s Cobalt or something along those lines...

How much power can you expect an inboard direct drive gear to hold?

 

[j442w30]

Re: Stern Drive or Inboard for hi-power swap

Before the Bravo drive was introduced there was a drive called the TRS which is no longer available. The TRS was a non shifting drive and required a transmission but they were stout drives and were used on a lot of cigarette boats from that era, and you still see them from time to time. There is a company called Konrad that makes a newer version of the TRS drive (they are pretty bulletproof from what I hear), and this might be a good choice for you. You don't want a Bravo 2, thats designed for heavy cruisers, a Bravo 1 would probably be the best choice and I think they're good for about 400hp, but it all depends on how you drive it. I don't want to rain on your parade, you obviously have your heart set on this Nissan engine, but you would be out on the water sooner and much cheaper if you used a Chevy engine.

 

[180shabah]

Re: Stern Drive or Inboard for hi-power swap

I know tihs may not be the best place to post about it, but i was looking online about some jet drives... I see a lot of really big HP boats, sorta what im looking to build, and im wondering if finding a boat with a jet drive but no motor might be the way to go...

If you are looking for all out speed, skip the jets. They will take off like a raped ape, but are so inefficient that top end suffers.

How much power can you expect an inboard direct drive gear to hold?

Depends on the transmission and the shaft size.

 

[elwesso]

Re: Stern Drive or Inboard for hi-power swap

I know life woudl be easier with a chevy motor, but for my purposes and what i do, its not really going to get me very far. at the end of the day for me its not about how fast i drive, its how I drive fast.

I really appreciate the feedback... Thanks guys!!! I am leaning toward an inboard setup, it just seems more familiar to me plus with a direct drive packaging in the middle of the boat might be easier than trying to shoehorn it in the back of the boat.