After market Diesel Conversion Heads
11-04-2013, 09:31 PM
#26
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Just a quick update for any one interested.
I have just run my 40 FSR with a new fuel mix. I've updated my ignition improver to Amsoil Cetane Boost, and used Jet A instead of hardware shop kerosene. Thanks to Fiery for the heads up on the Amsoil product.
Starting and throttling is equally as good and power was up. I am now getting 13000 rpm on the same 10X6 APC (500 more than glow). I reduced compression by 3/4 of a turn.
I'm still running quite low compression settings (just high enough to stop the burping), so there's probably more performance there but I'm happy as it is.
Dave H
I have just run my 40 FSR with a new fuel mix. I've updated my ignition improver to Amsoil Cetane Boost, and used Jet A instead of hardware shop kerosene. Thanks to Fiery for the heads up on the Amsoil product.
Starting and throttling is equally as good and power was up. I am now getting 13000 rpm on the same 10X6 APC (500 more than glow). I reduced compression by 3/4 of a turn.
I'm still running quite low compression settings (just high enough to stop the burping), so there's probably more performance there but I'm happy as it is.
Dave H
Last edited by gerryndennis; 11-06-2013 at 04:27 AM. Reason: Thanks Fiery
11-05-2013, 11:45 AM
#27
Dave,
Got your post relayed through my email. (I don't look in here every day when things get a bit busy...) Glad to hear your success! The 40FSR is/was a pretty fine engine! Plenty strong, unless you manage to do something really dumb. I campaigned a glow 40 FSR-S in a CL Stunt model for a few years in the early-mid 1990's. The model gave out before the engine was at all stressed. Some 600 or so flights...
Bob D mentioned that he introduced stronger shafts for reed valve Cox 1/2As almost as soon as the heads came available. At the time, I was moving around in Army assignments, and probably missed that. He's very conscientious. I expect he tailors the fine specs to heads he offers for current engines, so even if a conversion head might fit an out of production engine, it might not be optimized to his standards.
You may have noticed, in this or other related threads, that some diesel-converted glow engines do not get much benefit from that last 15% to 25% of full throttle position. Some I've run had nearly no RPM gain from 3/4 throttle up. Could depend on a lot of things, like the characteristics of diesel fuels compared to glow fuels. Particularly in that methanol will burn in just about any conditions, while kerosene (Jet A, paraffin, however you find it) is a bit more fussy to the fuel-air ratio. ...And proper mixtures reflect the engine's air pumping capacity. Good, fresh, clean ingredients do make things much nicer...
Got your post relayed through my email. (I don't look in here every day when things get a bit busy...) Glad to hear your success! The 40FSR is/was a pretty fine engine! Plenty strong, unless you manage to do something really dumb. I campaigned a glow 40 FSR-S in a CL Stunt model for a few years in the early-mid 1990's. The model gave out before the engine was at all stressed. Some 600 or so flights...
Bob D mentioned that he introduced stronger shafts for reed valve Cox 1/2As almost as soon as the heads came available. At the time, I was moving around in Army assignments, and probably missed that. He's very conscientious. I expect he tailors the fine specs to heads he offers for current engines, so even if a conversion head might fit an out of production engine, it might not be optimized to his standards.
You may have noticed, in this or other related threads, that some diesel-converted glow engines do not get much benefit from that last 15% to 25% of full throttle position. Some I've run had nearly no RPM gain from 3/4 throttle up. Could depend on a lot of things, like the characteristics of diesel fuels compared to glow fuels. Particularly in that methanol will burn in just about any conditions, while kerosene (Jet A, paraffin, however you find it) is a bit more fussy to the fuel-air ratio. ...And proper mixtures reflect the engine's air pumping capacity. Good, fresh, clean ingredients do make things much nicer...
11-06-2013, 04:19 AM
#28
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Hi Lou,
Yes the FSR is a lovely engine.
I take your point regarding fitting a Davis head to an out of production engine.
Bob Davis also mentions the possibility of not getting any further power increase above about 80% throttle opening with some engines. I assumed this was to do with the engine and carb being optimised for glow fuel operation and fuel/air demands (and RPM as pointed out in following posts). So far both the 40 FSR and 20 FP seem to throttle quite linearly with rpm increasing right up to full throttle. I'll keep it in mind when I set up the throttle throw once I fit these engines to models though.
Dave H
Yes the FSR is a lovely engine.
I take your point regarding fitting a Davis head to an out of production engine.
Bob Davis also mentions the possibility of not getting any further power increase above about 80% throttle opening with some engines. I assumed this was to do with the engine and carb being optimised for glow fuel operation and fuel/air demands (and RPM as pointed out in following posts). So far both the 40 FSR and 20 FP seem to throttle quite linearly with rpm increasing right up to full throttle. I'll keep it in mind when I set up the throttle throw once I fit these engines to models though.
Dave H
Last edited by gerryndennis; 11-08-2013 at 03:01 AM. Reason: I forgot RPM
11-06-2013, 04:45 AM
#29
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Since, in most cases you are running a larger/higher pitched prop to take advantage of the Diesels higher torque, the rpm will be below the full throttle glow rpm. Only opening the throttle to the max rpm point will make the carb easier to set. Some like to run smaller carbs for that reason but there is no real reason to do that. The typical rc carb is a variable venturi so it doesn't care how far open or closed it is.
11-06-2013, 05:53 AM
#30
Hobbsy is bringing up a good point, reason the intake passages in a glow engine are larger than a true diesel in many cases, as stated
running a glow engine at night you will see a little flame out the exhaust without a muffler this just wasted fuel not a complete burn in ignition a diesel complete burn before exhaust port uncovered at bottom of power stroke,no flame, thus less fuel needed to be burned in the engine wide open throttle you may be drowning the engine most of mine are running "full bore" at the 75-80% open
you could run a smaller bore carb or sleeve down the intake cutting the throttle to below wide open will do the same thing.
this is most notable I have found in my Irvine 40s and 53s they will bog and cough at WOT
running a glow engine at night you will see a little flame out the exhaust without a muffler this just wasted fuel not a complete burn in ignition a diesel complete burn before exhaust port uncovered at bottom of power stroke,no flame, thus less fuel needed to be burned in the engine wide open throttle you may be drowning the engine most of mine are running "full bore" at the 75-80% open
you could run a smaller bore carb or sleeve down the intake cutting the throttle to below wide open will do the same thing.
this is most notable I have found in my Irvine 40s and 53s they will bog and cough at WOT
11-07-2013, 04:56 AM
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I've run the 20 on larger props (up to 10X6) and haven't noticed the effect yet, but the FP hasn't got an overly large carb throat either.
I haven't experimented with larger props on the 40 yet, but I intend to. I'll restrict the throttle opening if required.
I had noticed the lack of flame out of the exhaust due to the complete burn prior to opening of the exhaust port (running my Mills .75 replica at night), I presume this has something to do with the lower exhaust noise of a Diesel engine.
Dave H
I haven't experimented with larger props on the 40 yet, but I intend to. I'll restrict the throttle opening if required.
I had noticed the lack of flame out of the exhaust due to the complete burn prior to opening of the exhaust port (running my Mills .75 replica at night), I presume this has something to do with the lower exhaust noise of a Diesel engine.
Dave H
11-07-2013, 11:50 AM
#32
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I really like the RJL head. They shipped it the same day I placed the order and it arrived here in NZ about a week later. Shipping was a bit of a killer, about half the price of the head again, but that's still cheaper than the alternative. It seems to be pretty standard for anything I've bought from the States though, the box was big enough to fit 24 heads (I checked). Maybe United States air is really valuable because that's what the box was mainly filled with
It is shipped in a larger than required box intentionally. It helps to keep items from slipping through the cracks.
Dennis
It is shipped in a larger than required box intentionally. It helps to keep items from slipping through the cracks.
Dennis
11-07-2013, 01:47 PM
#33
AMB and Hobbsy,
Personal opinion: With glow, you have a very tolerant range of mixture settings - the alcohol will almost always burn. Nitro in the fuel, in effect, brings more oxygen to the combustion chamber than the engine could pump unaided.
Kerosene and ether do not form oxygen when heated. They rely on the oxygen the engine, alone, pumps. That is limited, probably never coming near the full nominal displacement (full stroke times piston area), or even effective displacement (stroke with cylinder ports closed times piston area.) Kerosene has almost twice the heat yield as the alcohols, per unit weight and is, IIR, slight heavier than alcohol. ...Given that these are burned most efficently - no unused oxygen; no unburnt flammables. And, we don't have that condition either...
As kerosene is more sensitive to the range of fuel/air mix, the amount of fuel the engine (as pump) can provide oxygen for is limited. Oversized - glow sized - fuel/air passages don't change that. IMO, that's why our diesels, other than the extreme ultra RPM and power examples, can use much smaller venturii/carb choke area, and smallish shaft and cylinder port volumes, and still give us very useful power.
Recall, too, that POWER is the rate at which Torque is delivered. Better torque from the kerosene burn characterisitics, at modest RPM is a natural consequence. We have to do things to modern glow engines to get their higher potential power to a useful RPM - like testing fuel, prop, load and plug. Similarly, for a diesel, testing for these - except there's no plug - will put a sport diesel at its optimal range. And the practical RPM ranges are pretty similar...
Personal opinion: With glow, you have a very tolerant range of mixture settings - the alcohol will almost always burn. Nitro in the fuel, in effect, brings more oxygen to the combustion chamber than the engine could pump unaided.
Kerosene and ether do not form oxygen when heated. They rely on the oxygen the engine, alone, pumps. That is limited, probably never coming near the full nominal displacement (full stroke times piston area), or even effective displacement (stroke with cylinder ports closed times piston area.) Kerosene has almost twice the heat yield as the alcohols, per unit weight and is, IIR, slight heavier than alcohol. ...Given that these are burned most efficently - no unused oxygen; no unburnt flammables. And, we don't have that condition either...
As kerosene is more sensitive to the range of fuel/air mix, the amount of fuel the engine (as pump) can provide oxygen for is limited. Oversized - glow sized - fuel/air passages don't change that. IMO, that's why our diesels, other than the extreme ultra RPM and power examples, can use much smaller venturii/carb choke area, and smallish shaft and cylinder port volumes, and still give us very useful power.
Recall, too, that POWER is the rate at which Torque is delivered. Better torque from the kerosene burn characterisitics, at modest RPM is a natural consequence. We have to do things to modern glow engines to get their higher potential power to a useful RPM - like testing fuel, prop, load and plug. Similarly, for a diesel, testing for these - except there's no plug - will put a sport diesel at its optimal range. And the practical RPM ranges are pretty similar...
11-07-2013, 01:59 PM
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Lou,
You've touched on an area I've been wondering about. No doubt as a Diesel the engine will turn a much larger prop better than as glow, but will this necessarily give better performance? Depends on the application a bit I would imagine. A slightly larger prop may give the best overall performance.
Davis' formula suggests that a 11X6 prop would be correct for my 40. I'll start experimenting around there. The proof will be in the flying.
Dave H
You've touched on an area I've been wondering about. No doubt as a Diesel the engine will turn a much larger prop better than as glow, but will this necessarily give better performance? Depends on the application a bit I would imagine. A slightly larger prop may give the best overall performance.
Davis' formula suggests that a 11X6 prop would be correct for my 40. I'll start experimenting around there. The proof will be in the flying.
Dave H
11-08-2013, 02:55 AM
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Yep understood, I didn't mean to sound like I was complaining. I'm sure the shipping cost is what it is, and is probably based on the weight not the size of the box.
As I mentioned I am very happy with the product and the service.
Dave H
