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Briggs & Stratton 993cc "Big Block" engine info/no theory, just the facts!

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Jay Dub

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This is very similar to the thread I started on the Briggs Vanguard 627cc engine:

We call this "Experimental Aviation" for a reason. If you are a theory person or a "thrower of wet blankets armchair engineer", please don't reply to this thread. We only want to know what does or does not work by experience in the air not by some idea in between your ears. Just the facts ma'am, just the facts on the Briggs & Stratton Vanguard 993cc engines that have flown or are flying.

A lot of these engine threads become theory threads with "armchair engineers" saying why it can't be done, or people throwing "wet blankets" on ideas like "TV will ruin everything", or "it's not as good as certificated", or "stick with Rotax or Hirth", and showing spreadsheets to try to prove their theory. Naysayers keep quiet, what we do know is that others are experimenting and flying them successfully, albeit with some issues, and learning how to make it better. I want to know in the real world what has and hasn't worked so far so this can be somewhat replicated by others.

Who flew, what was their setup, and what worked and what didn't work:

Parazoom from Germany has many of the 993's converted and flying in trikes. From their own information:
Light 2-cylinder 4-stroke sports engine, tuned, with approx. 50 HP
Technical data:
- Approved for DULV, noise measurement + sample test possible without problems because very, very! quiet !
- approx. 1000 cc
- approx. 50 HP
- approx. 135 kg stand thrust
- Approx. 58kg weight including gear!
- Ribs - belts - reduction already installed (price is without propeller)
- designed for 1.6m 3 blade helix propeller
- including forced fan cooling, oil cooler, alternator, electric starter and manual (reversing) starter
- Fuel consumption 4.5 - 7.5 l / hour = 1.2-2 gph

Kleber in Brazil has also successfully flown the 993. There are some photos on the web. I don't have much info from him but I do have:
This engine is original internally and I added two carburetors that generated 115 kg of thrust, using the 1.8:1 redrive from ace aviation, I modified the pulleys from 14 to 16 ribs on poly v-belt, working perfectly!

I know the Vanguard 993cc engines are a bit heavier than the Subaru/Robin/Generacs that Valley Engineering used, but it seems like this might be a viable option to pursue for the 50hp needs or for those of us in the Western US that have high density altitudes in the hot summers.

Jay
 
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Jay Dub

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Trying to keep with the facts, I'm going to share some of what I have learned on this engine. This is a side note as this doesn't come from flying examples but good examples none-the-less. Interestingly, looking at the mud-motor guys that use these engines hard, running full loads for long periods of time in the hot Gulf Coast Summers (great test bed for us) it appears there are some problems and some good things to be gleaned.

One problem it seems they have had is there can be leaking at the gasket between the crankcase and the cover when these engines are turned up above 4500 RPM. Some have reported the case covers cracking when "turned up" at high RPM. Currently the "Marine" versions, especially the 40hp EFI engine, has a beefed up crankcase and cover according to Briggs.

The interesting part of the Marine 40hp EFI is that it has a hotter cam in it and some say the heads are machined down (two popular mods on the 993's). I don't know about the machined down heads as the compression ratio shows the same for that model as the other 993s: 8.5:1. The 40hp rating is at 3600 RPM but the engine comes with the 4750 RPM high speed CDI, heavier "pink" valve springs, all steel pushrods, etc that you find in a "high rev kit". Some say it comes with forged aluminum connecting rods so they should be stronger than billet. The normal 993 pistons do not fit the forged connecting rods so if you bought the rods you'd have to get the pistons and wrist pins too. This thing comes "hot-rodded" from the factory with a 3 year warranty. Some are claiming 50+ hp dyno'd at 4500 rpm which seems possible if you had the EFI system re-mapped and the ECM retuned.

While all this sounds good, the big problem for us is with the EFI. It is a closed loop system that shuts down when certain parameters are met which means it would not be a good choice to avionize and use the OEM EFI. That's a bummer as the EFI would reduce intake icing and automatically compensate for altitude.

However, all the "hotrod parts" for the 40 hp (the cam, valve springs, keepers, pushrods, etc) are available through Briggs dealers. It seems (assume) you could use OEM parts to easily get 50+hp out of one reliably. I'd try to put the 40hp marine cam and high rev parts into a magnetron ignition motor with a stepped flywheel key to advance the timing and dual motorcycle carbs for better control of the fuel. This has not been done that I know of so this is based on assumption. This way you'd keep the simple ignition system and simple fuel system but get some of the gains from the Briggs R&D team.

Back to the facts, does anyone know of anyone flying the 993, what they did to "avionize" it, and what problems they have encountered?

Jay
 

TLAR

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All the grey matter ingianeers are gonna be so disappointed 😢, lol setting in their lazyboy building airplanes
 

karmarepair

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I've been digging in this area, although my test stand will be running brand K.


Another difficulty for EFI on these engines is that the use teeth on the flywheel to sense crank position. Eliminating the heavy cast iron flywheel is the key to getting the weight down, as well as eliminating torsional problems from ANOTHER big torsional moment on the other end of the crank. There is no easy, off the shelf, bolt on solution for crank position on EFI small V-twins I'm aware of.

There isn't much of an aftermarket yet for the Big Block Briggs or Kohlers yet, but Briggs owns the Mud Boat market, and I expect the aftermarket for that engine will explode. I'm told it's ten times the size of the garden tractor pulling market currently driving the Kohler aftermarket.
 

Protech Racing

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How many trigger teeth does the OE flywheel have?

Most of the time; the system is a VR system if the trigger has 2 wires. The trigger makes volts and a square wave that the ECU reads.

The 3 wire system is usually a hall sender. The trigger is magnetic and the makes almost a square wave signal.

Any Ford 36/1 tooth crank wheel and focus crank trigger may work. If the OE system uses a VR signal . Mount behind the prop.
If it uses a hall sender, use flying bolts or 2 tooth wheel . You will need 2 separate ignition systems for this .Due to the uneven firing order . But either way, it should be easy to duplicate the OE trigger system with a little thought .
FWIW I use 2 bolts into the front of the crank wheel on one of my race cars. The $30 Hall trigger reads the bolts and triggers a VW ignition module, fires the Bosch coil back through the OE distributor.

Keep in mind that the front mounted trigger rotates the opposite direction as the flywheel end.

The Microsquirt can be set up for any trigger and avoid limp mode . You can set it up for warning lights tho.
 
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TLAR

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Midwest Horsepower 40hp EFI Mud Motor ....... is this what you are starting with?
 
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Jay Dub

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I appreciate the interest in the topic but I see this is drifting from "just the facts of what is working." I really want this to be a thread of just what we know is working, not ideas nor conjecture. There is already a thread with 72 pages or so with everyone and their brother's ideas on these industrial v-twins so if you have ideas, that is a great place to put them. I would like this to be a thread with information that doesn't need to be waded through for hours and hours to find those "golden nuggets" of what works. I'm doing research and posting here to make it a one-stop-shop thread of solid information of what is working so any of us can replicate what we are comfortable with.

For facts the mud motor guys have a lot of useful information that I think we can find useful. Midwest Horsepower has several YouTube videos of their projects. Watching some of their videos on the dyno brings some very interesting numbers. Mud motors are not like motorcycles or racing karts as mud motors run at high power settings for long periods of time in hot weather while motorcycles and karts run bursts of high power. From watching 2 dyno videos about builds for mud motors here's what I wrote down:

Midwest HP used a new, 0 hr, no break-in, 35hp carbureted Big block 993cc engine in it's stock configuration to get a baseline. They did have the cooling fan removed and on the dyno they measured stock was 36hp with a stock OEM marine muffler. I would guess the fan would reduce that 36 at least 1 hp.

Stock Engine with just a muffler change to their MHP muffler they got 37.5 hp @3946 rpm & 63.3 ft-lb @ 2546 rpm.

They changed to a MWHP (different) Muffler 38.7 hp @3996 rpm & 64.3 ft-lb @2646 rpm

They installed their big-bore kit (bored cylinders, oversized pistons, billet rods, and changed cam, all lower end stuff) but kept the heads stock and the stock marine muffler and got 48.2 hp @ 3746 RPM & 79.6 ft-lb @ 2546 rpm.

They again did a muffler change to the MHP muffler and got 51.7 hp @3846 rpm, 82.9 ft-lb @2746 rpm on the baseline big bore kit.

Next they measured the Big Bore kit bottom end, their billet intake, Mikuni 42 HSR carb (165 main jet), MHP muffler and measured 65.7hp @ 4096 rpm, 65.7 ft-lb @3496.

Added their 1.6:1 roller rockers with stock heads and got 65.9 hp @4646 rpm, 87.9 ft-lb @3346 rpm. Not much difference on HP with those rockers.

To this they changed out the heads from OEM to their bigger valves & ported oem heads (reworked oem heads) and 1.6:1 roller rockers and got 75.4 hp @4646 rpm, 87.6 ft-lb @4196 rpm with stock oem muffler.

To this they changed to their MHP muffler and got 77.2 hp @ 4696 rpm, 94.3 ft-lb @ 3546 rpm.

Stock OEM 4750 rpm coils on all these dyno runs.
Their cam specs .350” lift
.256” duration
105 degree LC

To boil this all down it appears the tuned muffler can give you a just a couple of horsepower at the most. That style won't work for our application. The Big Bore kit can give you about 12 hp if you do nothing else. They gained about 14 hp by ditching the stock carb and putting in their intake and a Mikuni carb. The 1.6:1 roller rockers didn't appear to do anything for power. They gained about 9.5 hp by going to reworked OEM heads with larger valves. Of course these increases were in conjunction to the previous mods so YMMV. I wish they did the dual carb setup on the dyno as I think you would see a little more HP. It was also interesting to me that they did not put a "high rev" kit in this engine during any of this or at least I don't recall it mentioned. As you can see none of this HP is at insane RPMs.

For something really wild: Midwest Horsepower made a dual carb stock head build that made just over 90hp, then they made their own heads out of billet and got 120hp @6500 rpm. Then they took them out on the water in mud boats. No, I don’t see anybody running them that hard on a plane but it’s interesting to see the actual power made via a dyno and see them in a boat running around. I'm sure longevity is much shortened when they are worked that hard.

You can see and hear them here:

These are real world numbers on a dyno made for an application that will use them at high power settings for periods of time which would be similar to what we would use them for.

The videos where I got the numbers from are here:

and
 
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Vigilant1

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Midwest Horsepower has several YouTube videos of their projects. Watching some of their videos on the dyno brings some very interesting numbers.
....

They installed their big-bore kit (bored cylinders, oversized pistons, billet rods, and changed cam, all lower end stuff) but kept the heads stock and the stock marine muffler and got 48.2 hp @ 3746 RPM & 79.6 ft-lb @ 2546 rpm.
Jay Dub,
While watching the videos, did they show an extended run at these HP levels, and were the CHTs included in the stats? Thanks.
 

Jay Dub

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Keeping with just the facts, no, I think these were just peak numbers, not sustained.

Another Youtuber is Devin Daniels testing several of the MHP engines on video. In this video he is using the 75hp big bore with a single mikuni carb (that was in the dyno video I got the stats from) going 37 mph. The tach shows 4550 rpm with both CHTs showing just between 300-325F. I don't know the redline CHT on these engines but Lycoming recommends for longer life stay below 435F with a never exceed 500F. So by the looks of it the fan system does give good heat rejection at 75hp. On their dyno run with that engine they were getting 77.2 hp @ 4696 peak. Was he running at 70hp there and had been for a while? Was it 60hp? Either way that is impressive to me.

75hp MHP at 4550 rpm 320F cht.png

Jay
 
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Vigilant1

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FWIW, probably the most popular aero application of similar big block V-twins was the Valley Engineering Big Twin and Big Bad Twin, based on the 990cc Generac. Gene Smith lavished a lot of work and development time on the engines and their PSRU. They claimed 40 HP takeoff for the Big Twin and 50 takeoff HP for the Big Bad Twin. They were open and honest in noting that both engines were capable of 32 HP max continuous (based on heat rejection and resultant head temps).
Of course, every application is different. And CHT measurements depend a lot on where the thermocouple is placed.
 
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poormansairforce

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Jay, thanks for the info. I have pointed out a several times in the various threads that if you modify these engines you'll need to keep the fan. The Big Bad Twin had it's fan removed so much less horsepower capability due to less cooling air.
 
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