Author Topic: How much difference can different fuels make on engine performance? (Read 1001 times)

frank mccune · « **on:** August 22, 2020, 02:32:42 PM »

Hello all:

Yesterday, I fueled the tank on my HP .40 equipped with a Brian Gardner p&c with my regular fuel, 11,11 oil, 10% nitro and the engine hated it! Starting was difficult, needle valve adjustment was terrible, and once airborne, the engine sounded very different. It shut off after a few maneuvers.

I noticed my error and after arriving home, I fueled the plane with a fuel containing 20% synthetic oil and no nitro. This is the mix that Mr. Gardner recommend that is to be used in this engine. The engine started first flip and responded perfectly to the needle valve. It ran like a Swiss watch!

Question: WHY would an engine run so differently due to a change of fuels? It is only a engine consisting of three major moving parts!

Suggestions/Comments

Tia,

Frank McCune

Brett Buck · « **Reply #1 on:** August 22, 2020, 04:45:16 PM »

Quote from: frank mccune on August 22, 2020, 02:32:42 PM

Hello all:

Yesterday, I fueled the tank on my HP .40 equipped with a Brian Gardner p&c with my regular fuel, 11,11 oil, 10% nitro and the engine hated it! Starting was difficult, needle valve adjustment was terrible, and once airborne, the engine sounded very different. It shut off after a few maneuvers.

I noticed my error and after arriving home, I fueled the plane with a fuel containing 20% synthetic oil and no nitro. This is the mix that Mr. Gardner recommend that is to be used in this engine. The engine started first flip and responded perfectly to the needle valve. It ran like a Swiss watch!

Question: WHY would an engine run so differently due to a change of fuels? It is only a engine consisting of three major moving parts!

Could be a lot of things, but the most obvious is excessive compression. Some engines set up to run on FAI fuel are overcompressed on conventional fuel, your symptoms sound pretty typical. It is *extremely rare* to find stunt engines that are overcompressed - most are plenty good up with 25% nitro, and a lot the "Head Gasket Patrol" exists to throw head gaskets in until it will barely run, so usually the problem is that "improved" engines are grossly *undercompressed* to the point they are absurdly feeble.

In this case, one .005 or .008 shim would *probably* allow it to run on standard fuel (while giving up power unnecessarily on FAI fuel). But, given the other issues, I would very strongly suggest *leaving it alone* and just run the weak fuel, since it seems to work that way.

Brett

Steve Fitton · « **Reply #2 on:** August 22, 2020, 04:45:43 PM »

If you have an engine set up for no nitro fuel, it's probably gonna really hate 10%. the head is probably dropped way down.

pmackenzie · « **Reply #3 on:** August 22, 2020, 06:19:46 PM »

Quote from: Brett Buck on August 22, 2020, 04:45:16 PM

In this case, one .005 or .008 shim would *probably* allow it to run on standard fuel (while giving up power unnecessarily on FAI fuel). But, given the other issues, I would very strongly suggest *leaving it alone* and just run the weak fuel, since it seems to work that way.

Brett

I think Beelzebub is looking in his closet for a warm sweater!

Brett Buck · « **Reply #4 on:** August 22, 2020, 07:21:15 PM »

Quote from: pmackenzie on August 22, 2020, 06:19:46 PM

I think Beelzebub is looking in his closet for a warm sweater!

I think the reason I am always reticent is that everybody figures if .005 is good, .050 is 10x better.

Brett

Brian Hampton · « **Reply #5 on:** August 23, 2020, 06:30:07 PM »

Quote from: Brett Buck on August 22, 2020, 04:45:16 PM

In this case, one .005 or .008 shim would *probably* allow it to run on standard fuel (while giving up power unnecessarily on FAI fuel). But, given the other issues, I would very strongly suggest *leaving it alone* and just run the weak fuel, since it seems to work that way.

I do things the other way round because I only use zero nitro fuels (which doesn't necessarily mean FAI fuel). With my Enya 61 CXLRS I did about 40 flights with the standard head button (8.8:1 compression) before making a new head button giving 12.4:1 compression. With back to back runs on the test stand using the same prop/fuel/plug and peaked to max revs the HP increased by 26% (cube law thingy). I have to wonder how much nitro would have been needed to get the same HP increase with the standard low compression. I must admit I was aiming for 13.5:1 but took slightly too much off on the last skim off the combustion chamber bowl but figured, nah, that's near enough

.

Brett Buck · « **Reply #6 on:** August 23, 2020, 07:05:56 PM »

Quote from: Brian Hampton on August 23, 2020, 06:30:07 PM

I do things the other way round because I only use zero nitro fuels (which doesn't necessarily mean FAI fuel).

If you get no-nitro fuel here, it is almost always labelled "FAI". It is a special-order item.

Brett

Steve Thomas · « **Reply #7 on:** August 24, 2020, 03:38:39 PM »

Quote from: Brian Hampton on August 23, 2020, 06:30:07 PM

With my Enya 61 CXLRS I did about 40 flights with the standard head button (8.8:1 compression) before making a new head button giving 12.4:1 compression.

Interesting about your Enya 61, Brian. I’ve got one also, but it’s almost as if it left the factory already set up to run zero nitro. With 10%, it’d be generally unhappy and cut after a few manoeuvres (a bit like Frank’s HP40). With my usual 5%, it’d ping under load and run very hot. So, despite the potential disgust of Brett

, I did what I’ve never done before and tried head shims. With two, it’s now much happier and more civilised. I should perhaps have investigated more thoroughly by measuring the CR or trying FAI fuel, but was too busy at the time and just happy to get it running right.

I wonder if they released them with different compression ratios?

Brian Hampton · « **Reply #8 on:** August 24, 2020, 08:09:46 PM »

Steve,
This only applies to the first ringed version with the head button but Enya did have a higher compression button which I believe was fitted if you ordered/bought one with an RC carb. AFAIK the distinguishing feature is a small dimple near the plug seat indicating low compression.

Air Ministry . · « **Reply #9 on:** August 24, 2020, 10:15:31 PM »

H P are European . Theyre generally fairly stingy with the Nitro. Particularly back in the 70s .

Most Euro engines of that era needed decompressing to run Nitro , and most American engines needed higher compression for the ' straight ' or whopping 5 % nitro generally available there .

The H P , as a rear induction motor , was generally set up for F.A.I. Pylon . Zero Nitro . The front induction ( pattern ) motor generally , in the earlier series at least , were similar .
THOUGH in the tests , it stated , I think , that they came with a 5 & a 8 thou. gasket , to set comp. as necessary .
Chinn also prattled on about ' production tolerances ' on early examples , and how liner & head clearnce hights varied , and would need ' custom setting ' for optimum clearance .

Just put the Royal 46 guts in a OS SF case . Spat the prop off about six times , and tryed gnawing the didgits . So I figure its a bit close in the head department now .

Brett Buck · « **Reply #10 on:** August 24, 2020, 10:43:41 PM »

Quote from: Steve Thomas on August 24, 2020, 03:38:39 PM

So, despite the potential disgust of Brett , I did what I’ve never done before and tried head shims. With two, it’s now much happier and more civilised.

Changing the head clearance is a very useful adjustment, for fine-tuning. Unfortunately, for some strange reason, people do it by reflex. "I only got 13 appearance points, so I added .045 worth of head shims", that sort of reasoning. But if you are running 4-2 break engines for competition, then, knowing when to adjust it either way is pretty much mandatory. If you are already close to the right range, small changes (like +-.003-.005) are very powerful adjustments.

Unfortunately, it is generally not needed in almost any situation for sport fliers, only in the odd situation that Frank has. I have seen maybe 5-6 cases of misfires, etc, caused by excess compression, if your engine is not misfiring or quitting, it probably doesn't need more head shims.

And I emphasize again - FAI/ no-nitro fuel is almost unheard of in the USA, even 5% is rare and hard to find, either special order or make it yourself. 10-35% is extremely common and available anywhere. Almost all engines sold in the USA are intended to run on 10% or more and don't need more head shims to run correctly, and in the vast majority of cases, people would be *far better off* never taking the head off.

Yes, it comes with an Allen wrench, but that does not compel you to use it!

Brett

frank mccune · « **Reply #11 on:** August 25, 2020, 09:08:45 AM »

Hello All:

Thank you for all of the replies.

Much of what you posted made sense. As a provincial sport flyer, I strive to have:

Easy starting.

Consistent needle valve setting.

A steady engine run for each flight that is repeatable.

I have a HP Silver Star equipped with a Byron Gardner p&c that does this while using fuel that contains 20% synthetic oil and no nitro. I also use a HP .40 Gold Cup that does while using 11% synthetic oil, 11% castor oil and 10% nitro. This HP has a ring fitted by Mr. Bowman. This engine also all of the requirements listed above.

I have found that these engines perform best in a wet two cycle mode. I am using a 10-6 on the SS due to lack of prop/ground clearance and an11-5 on the GC. Life is good. Of course, there is always the small gremlins that seem to frustrate one on some days. Lol

Be well,

Frank McCune

Ken Culbertson · « **Reply #12 on:** August 25, 2020, 09:23:50 AM »

Quote from: Brett Buck on August 24, 2020, 10:43:41 PM

and in the vast majority of cases, people would be *far better off* never taking the head off.

Yes, it comes with an Allen wrench, but that does not compel you to use it!

Brett

George Fruhling · « **Reply #13 on:** August 25, 2020, 12:01:57 PM »

My Fox .36 "Combat Special" ran GREAT on Fox "Missile Mist" fuel. I believe it was 25% nitro. Had my Voo Doo hitting close to 100 MPH. Great for half A too. When it went over 20 bucks a gallon in 1979 I quit buying it though...

Author Topic: How much difference can different fuels make on engine performance? (Read 1001 times)

frank mccune

How much difference can different fuels make on engine performance?

Brett Buck

Re: How much difference can different fuels make on engine performance?

Steve Fitton

Re: How much difference can different fuels make on engine performance?

pmackenzie

Re: How much difference can different fuels make on engine performance?

Brett Buck

Re: How much difference can different fuels make on engine performance?

Brian Hampton

Re: How much difference can different fuels make on engine performance?

Brett Buck

Re: How much difference can different fuels make on engine performance?

Steve Thomas

Re: How much difference can different fuels make on engine performance?

Brian Hampton

Re: How much difference can different fuels make on engine performance?

Air Ministry .

Re: How much difference can different fuels make on engine performance?

Brett Buck

Re: How much difference can different fuels make on engine performance?

frank mccune

Re: How much difference can different fuels make on engine performance?

Ken Culbertson

Re: How much difference can different fuels make on engine performance?

George Fruhling

Re: How much difference can different fuels make on engine performance?