I had a converted OS.32F-H ringed. It was much, much quieter
than when ran on glow.
I have also ran a friend's OS .60FSR on Davis's Diesel
Conversion head and fuel. It too was very much quieter than
on glow. It handled about the same as my .32.
The smell and cantakerous nature of handling the fuel is
what made me return the engine to glow use, although it was
fun to operate it as a Diesel. If that engine hadn't been
such a fantastic glow engine, I would probably have left it
a Diesel and just toughed it out through the smell and
quickly evaporating fuel of the Diesel.
I have no experience of Davis diesel conversions, but do know of their
On this side of the pond, there are specialist diesel engine makers and,
over the years, I have had a wide cross section of these.
Generally speaking, diesels are considerably quieter than their glow
equivalents, can comfortably swing larger props at lower revs with therefore
less prop noise, and can handle a greater range of prop sizes because of the
variable compression. They are also, as a rule, much more economical with
The fuel isn't as agressive as glow fuels especially those with Nitro, so
"high spec" fuel proofer isn't needed.
There is a "down" side - the fuel is more expensive than glow fuel (partly
offset by the economy), and the exhaust residue is "dirtier" leaving black
streaks on the airframe.
Plastic film coverings suffer - wrinkle up, go slack and peel off. Solartex
seems to be unaffected but, unless given a coat of some clear lacquer soon
looks very grubby as the exhaust "gunge" sticks in the weave.
I had nothing but bad luck with the diesel heads and even
worse luck talking to the nitwit that owned the place.
"Sullen" "moody" and "grouchy" all come to mine when I
think back on my dealings with Davis.
I'd have to recommend looking elsewhere.
Judging by what has been said here, and on previous posts re Davis Diesels,
I would recommend going directly for a purpose made diesel. There is a
considerable choice of makers and capacities.
Just my two pennorth,
"Malcolm Fisher" wrote in
Having ran both purpose made model diesel engines and the
DDC (Davis Diesel Conversion) heads, I can understand why
people buy the latter.
First of all, they probably already have the engine that
they might convert to Diesel operation. The price of the
conversion head is much less than buying a comparably sized
purpose built model Diesel here in the USA.
Second, if they don't like Diesel operation, the DDC user
can return their engine to stock and then sell the DDC head
very quickly at a small loss, as long as they bought a head
for a popularly owned/used engine.
The DDC heads perform close enough to a purpose made Diesel
engine to let the owner/operator know if they want to
continue this type of operation. If the stink and finicky
handling required of model Diesel fuel doesn't turn you off,
the Davis setup will serve you quite nicely.
Purpose made model Diesel engines are expensive and
unfamiliar here in the US.
The down side of DDC conversions is that a converted engine
may not be as easy to set up/handle as a purpose made
Diesel. It is also possible that the glow engine that has
been converted may not be up to the task of handling the
higher cylinder pressure that is developed, IF the engine is
ran overcompressed for a lengthy period. Although, I have to
admit that the DDC conversion heads do not permit you to run
excessive compression ratios on the engines that I have
fiddled with. Higher than optimum? Yes. Damaging? Well, it
is less prone to damage the engine than were it fitted with
a conventional contra-piston setup.
If I lived in England, where there are/were a few
manufacturers of model Diesels, I might be tempted to go
with those engines instead of a DDC. But here in America, it
would be a close call.
I paid fifty-five dollars for my OS40LA, and I see that it would cost
me another fifty-five dollars to convert it into a diesel. To purchase
a cylinder head for the price of an engine seems unreasonable to me.
Who else makes diesel conversion heads?
The United States of Texas
The reason for the seemingly high price of DDC heads is
simply a matter of scale.
OS is a very large organization, relatively speaking, that
can amortize its R&D, machine equipment and labor over a lot
more engines than Mr. Davis will ever produce. The more you
make, the cheaper they get.
Well, thank you for the lesson in economics, Mister Notimprest, but
since I have the economic advantage of being already tooled up to
produce my own diesel conversion head, should I choose to do so, there
is no way in hell that I am going to pay that much. I am still looking
for those alternative diesel conversion head suppliers.
in my twenty-first year of business
Damn, Mike. I didn't mean to step on your toes.
Since you are a businessman, you know that you charge
whatever the market will bear. Right? If not, you won't be
in business for long. You make the money while you can
because it won't be long until what you are selling today
won't be in demand tomorrow.
But why am I telling you this? You already know everything.
Still, that doesn't explain the stupid question.
Hello, Mister Notimprest. That is a very impressive name, by the way.
Do you use it at your place of work, or only when you are socializing?
Well, Mister Notimprest, I am happy to inform you that you are quite
incapable of stepping on my toes. Whatever gave you the impression
that you possessed that ability? Please be specific, for I am finding
you to be quite entertaining.
Absolutely not. So far, I have worked in at least three seperate
service service fields where my tips _far exceeded_ my official
If not, you won't be
Mister Unimprest, I have been in business for twenty years, and I have
yet to set a single price. My customers set their own price, and they
compete against one another to do so.
You make the money while you can
Mister Unimprest, "Take the Money and Run" was a wonderful movie, and a
wonderful song. They were both meant to be comedies. Neither was
meant to be taken seriously. And my present service will be in demand
for as long as the grassn grows. How long do you think that wuill be?
No I do not, nor have I made such a claim. You are making an insulting
What stupid question? You have not made yourself clear. You obviously
percieve yourself to be speaking with authority, but I don't think that
anyone here could have any idea what the hell you are talking about
Mister Notimprest, anyone who would try to impress you would be a fool.
Should we all be trying to impress you?
| I paid fifty-five dollars for my OS40LA,
A pity -- it's not a very good engine. Oh, it works, but it's lacking
in power and I've heard they're finicky. A Thunder Tiger 36 or 46 at
$75 or $79 would be a lot better. But more money, so ...
| and I see that it would cost me another fifty-five dollars to
| convert it into a diesel. To purchase a cylinder head for the price
| of an engine seems unreasonable to me.
As suggested, it's very much a niche market. Davis wants to make some
money, but doesn't sell too many, so he charges a lot.
| Who else makes diesel conversion heads?
As far as I know, nobody. There's little demand for diesel R/C
engines (though our stock engines work on the same principle, except
that the glow plug helps the fuel ignite) so there aren't many sold.
Why? I know some people don't like the smell of the fuel. Beyond
that, I don't know, but it's true -- they're rare. I've heard that
the diesel conversion heads are very finicky to make work, but that
the engines that were designed as diesel from the beginning are not.
From what I can tell, you've got a very limited budget. So I'd
suggest not messing with diesel for a long time, if ever. You
mentioned you wanted to do it to keep the noise down -- well, if you
want something really quiet, you go electric or unpowered glider. But
you can quiet a glow engine too by using a prop on the larger end of
what's suggested, and sometimes you can improve on the muffler.
| Mike Mandaville
| The United States of Texas
Wouldn't we be the `United State of Texas'? Not that Texas is united
in anything, but ...
Thank you for your offer of pity. However, since I myself am pleased
with my purchase, your offer is therefore inappropriate. And now I
will return your offer. Doug, I pity you for imagining that I care
what you think about my engine. I honestly don't give a damn.
Whatever you paid for your engine, if it does what you want and YOU are
satisfied with its power output, whatever anyone else thinks doesn't matter
Don't waste your pity on those who think you should have gone to a higher
spec engine - you're right to "not give a damn".
"Malcolm Fisher" wrote in
What neither you nor Mike seems to understand is that what
Doug said was not meant as a put down. Pity.
Mike looks for issues to fight over, as I have recently
discovered. I have no time for that behavior or attitude.
And I really don't care if you don't like it, Mike, so save
your fingers some unnecessary typing.