Author Topic: Brodak 40 on FAI Fuel (Read 2168 times)

Motorman · « **on:** January 13, 2020, 12:19:55 PM »

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Geoff Goodworth · « **Reply #1 on:** January 15, 2020, 10:58:10 PM »

My Brodak 40s were a bit temperamental until somebody suggested that I try running them with FAI fuel — all Coolpower.

Perry Rose · « **Reply #2 on:** January 16, 2020, 12:05:36 PM »

I have found that Chinese, Japanese and most modern European engines run very well on my 2% nitro home brew fuel. Give no nitro a try it won't hurt anything.

Leester · « **Reply #3 on:** January 16, 2020, 02:33:18 PM »

No hobby shops in my area carry or can get FAI fuel. Sig carry's it and at just under 18.00 a gal. not a bad price but !! Hazmat and shipping brought the price to 46.00 a gal. and they don't carry it in quarts. My local hobby shops don't order enough from Sig to buy it. So I had Walt do his thing and if the weather has a break in it lol !! we're expecting snow then ice then back to snow tomorrow then the deep freeze !! I'll run mine ASAP.
Thanks again Walt.

Brad LaPointe · « **Reply #4 on:** January 16, 2020, 02:53:59 PM »

No nitro fuel is very easy to blend . If your local hobby shop carries Klotz great ,if not most bike or cart shops do .You can then buy methanol at most big box stores . I would not use straight castor in an AAC engine.

Brad

Geoff Goodworth · « **Reply #5 on:** January 17, 2020, 04:13:36 PM »

Can somebody explain how I tell which head is which?

Al Ferraro · « **Reply #6 on:** January 17, 2020, 06:51:28 PM »

Quote from: Geoff Goodworth on January 17, 2020, 04:13:36 PM

Can somebody explain how I tell which head is which?

The early Brodak 40 has a squish band at the bottom of the head chamber that is approximately 3/32 wide. The new version does not have a squish band. The head chamber is opened all the way to edge.
Al

Robert Zambelli · « **Reply #7 on:** January 18, 2020, 07:43:51 AM »

I have the oldest Brodak 40 in the country.
It has never been apart and is exactly as it was shipped from the manufacturer.
I have used it on a number of different aircraft and it has always performed perfectly.
If anyone is interested, I can remove the head and photograph it.

Bob Z.

Al Ferraro · « **Reply #8 on:** January 19, 2020, 11:17:52 AM »

The early high compression is on the bottom.

Al

Dennis Toth · « **Reply #9 on:** January 19, 2020, 03:49:54 PM »

How much compression is needed for stable no or low nitro fuel to work?

Best, DennisT

Al Ferraro · « **Reply #10 on:** January 19, 2020, 07:12:35 PM »

I found that the early Brodak 40 dose not have the same power as newer version, even though it has the higher compression head. Using a APC 11.4x5 prop, the early Brodak has trouble swinging it on a 50oz plus plane. The newer version has no problem doing that even on windy days. I tore down both engines and timed them to see what was difference between the two are.
1: The early version has a smaller muffler outlet .325 the new .425 "POWER ROBBER"
2: The early version has a higher compression head that if you use it on a new version the engine, it will break real hard going into a two stroke from four.
3: The early version has SPI when the piston is at TDC. "POWER ROBBER"
4: The early version does not have the cut outs in the piston skirt to help to get the fuel flow up the intake ports. "POWER ROBBER"
5: The early version intake boost port opens before the side intake ports. "POWER ROBBER"
6: The early version case intake channels is one large area the all the intake ports draw from. The new version each port has its own channel.
7: The early version has shorter threads on the crank shaft.
I timed both engines to find timing to be similar.
I installed a new style piston & liner, and cylinder head in a early case with a Fox 40 muffler drill out to .375. My updated engine run just like the new one with lots of power using a APC 11.5x4 prop in a Smoothie.

Al

Dennis Toth · « **Reply #11 on:** January 20, 2020, 11:19:55 AM »

Al,
My feeling is that you are getting most of the power boost from the larger exhaust opening in the muffler. The simple test is to try the new style muffler on one of the original engines and see how it runs, or try the old muffler on one of the new ones.

With the new engine/muffler how is it setup to run i.e. 4-2-4 or 2- 2+ -2? The original was designed to be a drop in for the Fox35 with the same run (classic 4-2-4) at around 9500 rpm but with a little more power to turn say a 1/2" more diameter prop. The new one may be tuned for more constant speed on a low pitched prop. Let us know if you do any additional tests.

Best, DennisT

Leester · « **Reply #12 on:** January 23, 2020, 04:23:00 PM »

Just received my High Compression Brodak 40 head (5th engine sold by Brodak 8/2002) after it's rework by Motorman. Looks Fantastic !!! wish I'd have done a before picture now !!

Brian Hampton · « **Reply #13 on:** January 26, 2020, 08:35:11 PM »

My 40 has the wide squish band head but measured compression is only 9.9:1 which is much lower than the 13.5:1 that I consider optimal for zero nitro fuel.

Brian Hampton · « **Reply #14 on:** January 27, 2020, 05:31:38 PM »

I use a 1ml syringe with .01ml graduations filled with turps then lay the head flat on a window sill close to the flyscreen then start filling the combustion chamber. When it's almost full I wet the squish band so the turps will flow easily onto the squish band and not form a meniscus on the inner edge of the squish band. Then I start carefully adding more turps but now I watch the reflection of the flyscreen which initially shows a distorted grid pattern. Adding very small drops from the syringe this grid goes flat and then I can take a reading from the syringe to find the exact combustion chamber volume. In the case of my B40 head, this was .61ml (cc).

Next step is to measure the squish clearance, calculate its volume and add that to the combustion chamber volume. In my case, with the .2mm shim, the squish volume was .13cc so total combustion chamber volume was .74cc. Then you have all the figures necessary to calculate compression.

I use a spreadsheet set up to enter all the necessary figures, including swept volume, which automatically gives the final CR. Then it's simple to play with adding or removing shims to instantly see what effect it has on the CR.

Lauri Malila · « **Reply #15 on:** January 28, 2020, 10:07:26 AM »

Or, as I wrote earlier, you can measure it more easily from an assembled clean engine, piston at tdc, with whatever amount of shims. The rest is simple calculation of cylinder volume above piston and the volume altered by each shim.
And mind you, head volume and squish clearance (when notable squish area) are 2 different variables.
In stunt one should allways aim to minimum safe clearance, I'd guess in this case it is about 0,15-0,20mm,
The head volume should be made correct according to that. L

Brett Buck · « **Reply #16 on:** January 28, 2020, 11:18:46 AM »

I know I am going to regret asking this, but - if the engine was not already misfiring/quitting on regular fuel, why would you want to hog out the head? You just give up power on an already pretty weak engine. If it's too aggressive on the break (which I have never seen on any Brodak 40), it takes something like .005" of shim to make a pretty big change, tripling the head volume is 10x more than that.

I don't understand - In the entire 40+ years I have been flying stunt, I have seen stunt engines "overcompressed" for conventional fuel exactly twice - Discovery Retro that wouldn't run properly on even 5% (2004 WC) and ST46s with extruded head gaskets that still ran OK about half the time. Otherwise, I and other people have run 25-35-40% nitro in otherwise completely standard stunt engines with no ill effects except for running out of fuel after the triangles. Stunt engines, and even RC sport engines, are generally nowhere close to being "overcompressed" and it just about never needs any changes just to get it to run. But adding all that head volume, or adding 20 head gaskets, or whatever, just kills the power. What is it that people think they are accomplishing?

The later Brodak 40s are pretty good runners with OK power, if you get a proper venturi. Is this all trying to get it to run with the stock insanely oversized venturi?

I am really not trying to be a smart-ass, but I just don't understand where this obsession and abject terror of being "overcompressed" came from, Brodak 40, or any of the hundred of other engines that people seem determined to stack 20 head gaskets into (that patently don't need it).

Brett

Brian Hampton · « **Reply #17 on:** January 28, 2020, 04:59:08 PM »

Many years ago I did an experiment with an Enya 60X to try to find out how much compression it could handle using zero nitro fuel simply by progressively raising compression while monitoring peak revs. When there was no more rev increase I backed off to the previous setting. Original compression was 8.8:1 (which is about normal for most engines) and final compression was 13.5:1 while revs increased from 11.7K to 12.5K meaning a 22% increase in HP. I've never used nitro (hence my interest in determining an optimum compression for zero nitro) so I've used that figure as a basis.

The only engines I have that Brett might reluctantly agree could be classed as stunt engines are a VF46 (with a compression of 10.7 so could do with a boost), an Irvine 40RLS (12.5 so close enough for .gov work) and an Enya 61CXLRS (8.8 so could use a boost). The only engine I have that doesn't need any mods is my brand spanking NIB Irvine 61RLS with a compression of 13.6:1 but it's a bit too heavy for stunt work.

However, the Enya 61 uses a head button so it's easy to make a new higher compression button. So I did, eventually, and ended up with 12.4:1, mainly because on the last pass in the lathe I slightly overshot the final skim but once again near enough for .gov work. But first I flew with it as standard for some time before modding it and taking some before and after figures on the test stand. Probably the figures of most interest is that with the LC standard button the 4-2 break point ranged between 7.8-7.9K revs while with the HC head it ranged between 7.5-8.2K revs. Peak revs went from 8.8K to 9.5K which was a 26% increase in HP.

In flight with the standard button it gave a very nice 4-2-4 switch but with the HC button the switch was faster and more powerful. It was a delight to fly.

@Lauri..the reason I do my particular volume check is because whenever I get a new engine (even a used one) I remove the head so I can check all the port timings and squish clearances etc.

Peter in Fairfax, VA · « **Reply #18 on:** January 28, 2020, 07:41:04 PM »

Ok, Brett. What size venturi is good? I'm planning to campaign a Brodak 40 myself this season in a Vector, so I'm curious.

Last season, another club member here at NVCL had a good running Brodak .40, so I know that at least some models of it are good. All the different heads are a little confusing.

Peter

Peter in Fairfax, VA · « **Reply #19 on:** January 29, 2020, 07:04:44 AM »

I think my head is the late model, based on a fellow club member looking at it externally. He said the finish is more polished on the late model.

Reading older posts, and measuring my venturi, I think I have the .305. I see that Lee Machine offers a .285, which sounds better.

Peter

Al Ferraro · « **Reply #20 on:** January 29, 2020, 09:39:47 AM »

Quote from: Peter in Fairfax, VA on January 29, 2020, 07:04:44 AM

I think my head is the late model, based on a fellow club member looking at it externally. He said the finish is more polished on the late model.

Peter

Not true, mine look exactly the same. How big is the exhaust hole in the muffler?
Al

Peter in Fairfax, VA · « **Reply #21 on:** January 29, 2020, 10:17:18 AM »

Al,

Exhaust about .378" ID. Are your measurements ID or OD?

thanks,

Peter

Peter in Fairfax, VA · « **Reply #22 on:** January 30, 2020, 09:59:37 PM »

Well, looks like I have the small one. It's opening is .378 at the end, but there is some flashing on the casting at the base of the final outlet that puts it closer to the .325 that Al got. Plus, it matches the dimensions/proportions taken off the excellent photo Al sent. If I could find my 1/64" graduated drill bit set, I'd try opening it up.

However, I just calculated the cross section area vs. a tongue muffler I've run all season. Even at .325, the smaller Brodak 40 muffler is bigger than the tongue muffler opening.

Al Ferraro · « **Reply #23 on:** January 31, 2020, 06:30:11 AM »

Quote from: Peter in Fairfax, VA on January 29, 2020, 10:17:18 AM

Al,

Exhaust about .378" ID. Are your measurements ID or OD?

thanks,

Peter

All my exhuast measurements are ID. The newest version Brodak .40 engine muffler exhaust is .425 ID. The 2nd version engines the mufflers were about .375 ID. If yours is .325 ID then it sounds like you have 1st early engine which has less power then the newer ones.
I have no problems using the stock venturi with a uniflow vented tank. I do use the Brodak venturi filter or one layer of panty hose. I also recommend at least a 4-1/2 oz tank to complete the pattern using 10% nitro fuel.
Al

Leester · « **Reply #24 on:** January 31, 2020, 02:24:39 PM »

Motorman, mine being a 1st batch engine my muffler opening is .3105 ID with .3945 OD Good , Bad or Ugly

Al Ferraro · « **Reply #25 on:** January 31, 2020, 07:52:42 PM »

Quote from: Motorman on January 31, 2020, 09:27:52 AM

I had the big hole and had to run the engine rich to get my lap times and AAC was too cold to run good.

Motorman

Sounds like you were running the wrong plug and fuel. There must be 5 guys in my club running the Brodak .40 the way I do with great results. When someone did have a problem it turned out to be the tank. We have a spare known good running engine that we plug in if someone has issues to help troubleshoot.
Al