diesel on alpha gen2?

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telstar1

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Reading the comments re "im on a boat"s ideas on a large gas engine on Alpha drive,Im wondering if the same "take er easy" principles would apply with a diesel . The torque values on several adaptable diesels in the 200 hp range are in the mid 300's similar to a 5.7 sbc etc,is this the guideline to look for or is there something else("chattering" at idle maybe?)that makes the diesel unsuitable for alpha use.?
 
O-fishal

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Re: diesel on alpha gen2?

I heard this question before. IMO each manufacture makes a specific leg for their diesels for a reason, Volvo DPH or Dpr for newer motors 290 for the older ones (I think), Merc uses the bravos, they are built to hold the torque.
 
QC

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Re: diesel on alpha gen2?

And the same could be said for big blocks . . .

What rating and RPM range are you considering? There is no magic diesel thing that makes torque more destructive than a gassers. Could work but for gear ratio concerns needs to be a high speed variant.

moving to non-repair I/O
 
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Luhrs28

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Re: diesel on alpha gen2?

Having done this conversion with an inboard (old Paragon transmission), I agree with QC. There's nothing different about the torque from the diesel. Diesels usually have a more massive flywheel which makes for nice smooth power delivery at any speed above idle.

As long as it's rated for the torque the tranny won't know whether a gasser or diesel is driving it.
 
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telstar1

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Re: diesel on alpha gen2?

Thanks for the replies so far.sooo if one did do a diesel alpha match,and the concern is obviously torque,what would the better option for drive longevity be I wonder, a higher gear ratio with lower pitch prop or a lower gear ratio with higher pitch prop.Say the choice is between 1.6something versus something around 1.5 or so....Cant seem to get my head around this one.
 
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Luhrs28

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Re: diesel on alpha gen2?

Those ratios are so close I'd say the choice isn't going to affect drive longevity. I would see if you can find the HP/Torque curves for the diesel engine you intend to use. You're probably going to have to mess around with props a bit in the beginning, unless you just happen to hit it right. With my GM 6.2 diesel I was a little overpropped and could never get it above 2600 RPM. (max. torque for my engine was at 2400, max. RPM 3600).

Are you going to need shift interrupt capability? I don't know how that's done with a diesel.
 
QC

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Re: diesel on alpha gen2?

Luhrs28 said:
Are you going to need shift interrupt capability? I don't know how that's done with a diesel.
Click to expand...
Excellent point!!!! I missed that, and it is probably a deal breaker.
 
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Luhrs28

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Re: diesel on alpha gen2?

This has me curious now, 'cause I've seen several diesel conversions with outdrives on Youtube. Is there a way to do the shift interrupt with a diesel? (perhaps a solenoid valve in the fuel supply line?) Or did the guys on Youtube just not have shift interrupt?
 
QC

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Re: diesel on alpha gen2?

Well allrighty then . . . game on.
 
Don S

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Re: diesel on alpha gen2?

r.j.dawg said:
There is an old thread that discusses the shift interrupt issue.
http://forums.iboats.com/showthread.php?t=55533
Click to expand...

Well, you found a 2006 thread, and this is 2012. So before it goes too far, the older diesels did idle rough enough that the shift interrupt switch was not needed, with the newer, cleaner, smoother diesels, who knows. Merc doesn't use the Alpha with a 200 to 300 hp diesel, they use the Bravo drives with cone clutch, heavier gears and no shift interrupt system.
Same with Volvo, plus the developed an even larger drive for those 200hp+ drives so they would stay together and last a long time.
I guess the answer is, pick your engine, adapt it if you can, and see if it works.
It just seems like a big waste of money and time to adapt a big diesel to a little Alpha drive, just like throwing a big 400 hp gas engine on an Alpha. If you have to treat it with a tender touch like a little baby just so it stays together, what did you gain?
 
r.j.dawg

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Re: diesel on alpha gen2?

Don S said:
Well, you found a 2006 thread, and this is 2012. So before it goes too far, the older diesels did idle rough enough that the shift interrupt switch was not needed, with the newer, cleaner, smoother diesels, who knows. Merc doesn't use the Alpha with a 200 to 300 hp diesel, they use the Bravo drives with cone clutch, heavier gears and no shift interrupt system.
Same with Volvo, plus the developed an even larger drive for those 200hp+ drives so they would stay together and last a long time.
I guess the answer is, pick your engine, adapt it if you can, and see if it works.
It just seems like a big waste of money and time to adapt a big diesel to a little Alpha drive, just like throwing a big 400 hp gas engine on an Alpha. If you have to treat it with a tender touch like a little baby just so it stays together, what did you gain?
Click to expand...

+1^ I agree Don. Seems like a lot of pain with little or no gain.
 
QC

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Re: diesel on alpha gen2?

And my take is typically that there will never be a financial payback in a typical pleasure craft application. Need more info from the OP. Goals and engine.
 
r.j.dawg

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Re: diesel on alpha gen2?

QC said:
Need more info from the OP. Goals and engine.
Click to expand...
True, as the Op hasn't really said what diesel he is interested in, for all we know he could be considering stuffing an old Vivian in his boat. Now that would be interesting.
 
Don S

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Re: diesel on alpha gen2?

r.j.dawg said:
True, as the Op hasn't really said what diesel he is interested in, for all we know he could be considering stuffing an old Vivian in his boat. Now that would be interesting.
Click to expand...

My take is this is a wintertime, bored, whatif type thread.
 
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telstar1

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Re: diesel on alpha gen2?

Im looking at a FNM 225 hp, a used Volvo 41 or possibly marinizing a Navistar 7.3 non turbo out of a Ford P/U. Id think that the shift interrupt could easily be hooked up to the stop solonoid,should work same as spark cutoff? I too wonder how some engines dont seem to require shift cutouts while others do?If rough idling negated the need for a shift interrupt youd think 470's et al would be prime candidates but they seem to REALLY need the interrupt to shift .Also, outboards dont seem to require shift interrupt?Any logical explanation for this I wonder?
 
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telstar1

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Re: diesel on alpha gen2?

And yes it is difficult to achieve a payback with diesel and limited hours of use that is why Im exploring the Alpha thing.I happen to love these drives and believe that with care they can exceed the uses they are normally used for.A bobtail,with me doing the conversion machining etc, comes out many thousands cheaper than getting into a Bravo, then spending mega bucks for props if its a B3,etc etc.Yes Don this is somewhat What If but all ideas start out that way for me anyway. Exploring pros and cons,getting opinions etc.Thanks for ideas so far.
 
Don S

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Re: diesel on alpha gen2?

Im looking at a FNM 225 hp, a used Volvo 41 or possibly marinizing a Navistar 7.3 non turbo out of a Ford P/U.
Click to expand...

Any one of those engines will destroy an Alpha in short order. 1. there isn't a proper gear ratio for those engines. 2. A prop for them would put so much strain on the drives to keep WOT rpm in check, you probably couldn't get on plane. That alone will be killing the little gears and couplers of the Alphas. 3. Where do you expect to find marine adapter kits? Volvo doesn't fit a bellhousing for the rear mounts, no coupler, none of the necessary connecting parts. 4. On the automotive engines, how do you plan on converting the cooling systems.? It's not like there are closed cooling kits designed for them.

After all that work to adapt a diesel to a drive, why would you pick the lightest built, cheapest drive to do it to when there are drives out there designed for diesels.

If you can't afford the "then spending mega bucks for props if its a B3" then you can't afford the conversion at all.

If you want to putter around all day and slow speeds, then a small diesel adapted to an alpha will work fine, and in most cases the rough diesel idle will negate the need for a shift interrupt system. But ig you want to run a planning hull boat at more than 25 mph, then you need a boat and a drive that can handle that size diesel engine.
 
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telstar1

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Re: diesel on alpha gen2?

OK Don youyre saying its a bad idea I get that. Good chance youre right. Humour me here,and explain a bit further if poss? the FNM is a diesel with similar torque to a 5.7, at similar revs, where is the huge diff that would break the drive? A Volvo 41 with DP drive cruises a 24 foot boat at 3300 rpm,27 mph or so,so does a 5.7 with Alpha drive.How can the torques be so radically different if they run at similar revs for the speed? The torque curves Ive been able to track down are all around 350 ft lbs peak,same as for a 5.7. Of course Im not sure how the actual peak torque times might affect things.Again I tend to believe what you say Don but Id like a bit of meat on the bones of "it wont work"The adaptor plates etc I can build,that isnt a problem,the manifolds(for 7.3 only) are an issue I havent got worked out ... the 7.3 is likely going to not happen anyhow for a lot of reasons.However MC did use a 7.3 once and manifolds for that may fit I havent gone there yet. Thx
 
O-fishal

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Re: diesel on alpha gen2?

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I get a kick out of some of you guys trying to make frankenstien motors Just spend the cash and do it right!!!!
 
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