Automobile Transmission, why not?

I want to take the engine from a rear wheel drive automobile and leave the transmission attached. Then, I want to run the drive shaft through the hull and affix the prop on the end. This would be cheap and the transmission would let you reverse, neutral and have several forward ratios to work with. Is the a hair brained scheme or might it just work? I am wanting to build a pleasure craft for my boy and me oh, and his mother. I am envisioning a craft about 17 feet long, having a flat planing hull with a top spead of about 25 to 30 mph. It would be used in lakes only. Please advise. Thank you in advance for any advice. Kg

[Misogynist]

It's been done... I've seen GM powerglides used that way... sturdy trans.... two speeds... plus reverse...

[kengasch]

Originally Posted by Misogynist

It's been done... I've seen GM powerglides used that way... sturdy trans.... two speeds... plus reverse...

Thanks. My first car was a '63 Chevy Impala with the powerglide.

[FAST FRED]

The only hassle will be installing a cooler for the tranny oil.

However reverse will be with a reduction gear , so it will take a few extra rpm while manuvering.

This might not work for a 24/7 vessel , but for a <200hr a year lake boat , why not?

FAST FRED

[gonzo]

There are a couple of problems. First, the transmission doesn't have a thrust bearing. Second, the engine is not rated for marine use. We have discussed that subject in several other threads. The main drawback you'll find right away, is that it doesn't produce enough torque at low RPM to get the boat up on plane. Third, the electrics are not spark proof. This is illegal and dangerous. The list goes on and is pretty long. In my opinion, the cheap solution is to buy a marine engine. If you are mechanically inclined, a power package needing rebuilding can be found for not too much.

[Misogynist]

I agree... it would be easier to find a used engine and outdrive combination. But he wanted to know if he could use an auto engine... I think either way... there is going to be hell to pay in the details. There is the obvious marinization of the engine, plus the plumbing of the trans cooler . Then there is the issue of the stuffing box, propshaft, rudder and controls, etc etc etc.... starter, battery charging system, If the guy is talking about a 17 foot boat... why not just buy a cheap used one and be done with it?

[Danielsan]

Hi Ken,

What kind of engine is it? Diesel or gas? If it is diesel you don't have to worrie about the electrics as they don't make sparks. (Starter and altenator do but you can replace them by marine ones). The thrust bearing is a detail, look at python-drive they have thrust, vibration resitent bearings I find them expensive. You could aswell design your own propshaft with thrust bearings in the two directions and the apropriate sealing. You can have the stainless steel parts machined + bearings all togheter for 200-300USD.

I think the marine parts are way to expensive, ass there is no big market compared to automobile. Ok I agree RPM - Torque is somehow different, but get you a good german Diesel engine and it will do the job. And if you really want to be sure, it is a bit heavyer but it will surely do the job even better get yourself an crane or stationary engine 1800RPM, Good HP, good torque, made for running all day long...

even 2nd hand marine parts are much more expensive than other and mostly in a bad shape, so you will have to do a rebuild right on.

Greetz,

Daniel

I don't want to make people harm them selves, but with some common sense and the right support from forums like these, local metalworkshop,... it can be done.

Safety comes allways first!!!

[Thunderhead19]

Merc Marine used to have a two speed automatic. Interesting stuff, let us know how it works out.

[asathor]

I had a 67 Impala 2Dr with a 287 and a powerglide 2 speed - it had a very wide power range so if you can get it to work try it! Just think about all the small block Chevy go fast parts out there - even nitrous - in a 17' that will not be a laughing matter. There aren't that many electric parts to replace on an older engine and you can surely find out if the whole thing works before you spend that money.

You should be able to use a 4WD center differential to reverse the power outtake and take the stress of the tranny - that way you can get the engine moved back a bit as well.

Cool!

You have just invented a new craze - you could rule the lake or crash badly so be careful, water is very hard at 70+ Mph.

Asathor

[gonzo]

The transfer case from a 4X4 doesn't have a thrust bearing. It will desintegrate in a marine application. "Go fast" parts for cars are not the same as those for boats. The torque curve and timing advance curve are very different. Other things like combustion chamber volume, valve material and sizes, etc. change too. There are marinized engines for sale everywhere. It is way cheaper to buy one than reinventing the wheel.

[asathor]

I have the advantage of not being a professional in this field so I can sympathize with Ken and encourage him to have some fun. I didn't really think a transfer case was a thrust bearing - I suggested using it for reversing the power flow so he could mount his motor further back. I do know a torque curve from a clothe line however and with both a Torque converter and a Two speed tranny and a lot of propsizes to choose from there is no reason you can't use an oversized car engine. With proper cooling there is no reason not to believe that such a rig can propel Ken at the desired 25-30Mph all day in a 17 foot boat - I don't think the power requirement is substantially different from running down the freeway at 75Mph in 100 degree weather with the AC on and the radio blasting as I frequently did in aforementioned Chevy. If I am wrong feel free to point it out.
So Ken forget about the nitro for the engine - just keep a small bottle around for yourself for when you look up what this would have cost you in marine parts.

[gonzo]

It would be the equivalent to driving your car uphill at 130 MPH. At highway speeds your engine is running at about 2300 RPMs a boat runs at 4600 RPMs at the target speed.

[asathor]

Correct, you would have to target a lower crusing RPM for an automobile engine like Gonzo suggest mid 2000 rpm would be sustainable. That is a common range of peak torque for domestic V8s and it would be a good RPM figure for calculating gear ratios and prop size as it would also yield the best economy. I do not remember the gear ratios or the torque converter ratios for the GM transmission so I cant help here.

The issue is similar to towing where you need a lot of torque combined with an appropriately low gear ratio to get out of the hole, peak horsepower is of little importance. You will have to dig some to see if you have the midrange power you need to stay on a plane at reasonable RPM.

Originally Posted by gonzo

It would be the equivalent to driving your car uphill at 130 MPH. At highway speeds your engine is running at about 2300 RPMs a boat runs at 4600 RPMs at the target speed.

Don't many inboard / IO boats cruise at 3,000 - 3,500 RPM?

[gonzo]

3500 RPM can be a good economy cruising speed if the boat is light displacement or the HP high enough. Many heavy boats fall off plane at 3000 RPM.