# Briggs & Stratton 993cc "Big Block" engine conversation thread

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#### BBerson

##### Light Plane Philosopher
Listed at 35hp here 613477-0255
Where do you find the 40hp and 46hp version?

#### karmarepair

##### Well-Known Member
There's the 25 lbs that I need to lose from the engine. Thanks for taking the time to measure. This should be an easy 35 to 40 HP at 3600 RPM. The stock 993 EFI motor is 37 HP.
Don't forget there is shrouding, a governor (not much weight there) and an air cleaner you probably don't need.
And you can start with a carbureted version, like this one, that comes with the fat output shaft 613477-4201
I sometimes see big block Briggs used on E-Bay, but rarely the Godzilla 993cc version.
Boy, those 810/49 series sure are a screaming deal. Half the price of the horizontal 993/61 series.

#### Vigilant1

##### Well-Known Member
Here's a video on the 40HP EFI marine engine. It's got different conrods and some other different tweaks from the other 993cc engines.

Boy, those 810/49 series sure are a screaming deal. Half the price of the horizontal 993/61 series.
The 810/49 are a deal. They're cheaper than the 23HP 627cc/38 series, and only 9 lbs heavier (out of the box), with 5 more stock HP. It'd be great if they came in a horiz shaft version at the same weight and price.
Whatever engine I use will drive from the PTO shaft and the flywheel will be removed.
Are you going for the tapered PTO shaft then?

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#### Ken Powell

Yes, tapered crank with generator taper. I believe that Arrowprop will build a prob hub for $119.00. I need to talk to them before placing the order. #### BBerson ##### Light Plane Philosopher The Generac 993 was about 78 pounds without flywheel and starter. I don’t know why the Briggs 993 is 22 pounds heavier. Should be some areas to lighten. #### Vigilant1 ##### Well-Known Member It will be interesting to compare a B&S 993 V-twin powered MiniMax to ones powered by an "O-63" (1/2 VW from Casler,$3850 with re-used case, 1037cc, 38 HP, 85 lbs hand start).
The heads on the 993 stick up about 10" above the crankshaft and span about 20", so the engine and cowling will be a chunky thing. It would be useful to know how much it will affect visibility once an appropriate length prop is selected and sufficient clearance beneath it is provided, but I'm sure Ken has looked into that and is satisfied.
Now, flip the engine over and run it heads down and it is a whole 'nuther animal-- a low cowling over the prop, no bumps needed, and easy to get the prop hub higher for a longer, more efficient prop (as TiPi is exploring for the SD-1). But, more weight and unknowns (lube setup, need for dry sump, oil consumption, possible plug fowling, maybe hydraulic lock, etc).

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#### Ken Powell

##### Well-Known Member
The minimax thrust line is 5.25" below the top longeron and the 2-stroke Max usually runs a 60" prop. I plan to drop the engine another couple of inches and run a 54" or 56" prop. The top of the front deck is curved and is ~3" above the top longeron. Sight lines shouldn't be a problem.

#### Vigilant1

##### Well-Known Member
Just to mention it: Valley Engineering was commendably honest about the ratings of their 993cc Generac-based-with-PSRU conversions. All of them had a continuous rating of 32 HP (due to cooling limitations). The B&S models may be able to make more stock HP continuously using a fan, but unless we keep the cooling fan or are operating a plane fast enough to match the static pressure of that fan, we probably shouldn't count on the same continuous HP as they are making (just based on the ability to keep CHTs reasonable).

Baffling/ducting could be important. Just hanging the heads out in the breeze might not get the job done at high power levels using these cylinder heads.

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#### Ken Powell

##### Well-Known Member
Yes - just part of the development process.

#### BBerson

##### Light Plane Philosopher
Is it FAR103 or EA-B?

#### Ken Powell

##### Well-Known Member
EA-B. It will be N numbered.

#### Vigilant1

##### Well-Known Member
Sight lines shouldn't be a problem.
View attachment 119929
Yes, these things are very airframe specific. The MiniMax distance from prop to pilot is relatively short and the pilot's eyes are well above the top longeron and cowl.
With a plane like the SD-1, the heads of an upright V-twin are closer to the horizon as seen by the pilot. The longer nose does mean they block less area than if the engine were closer.

#### rtfm

##### Well-Known Member
I bought a Valley Engineering "Big Bad Twin". They claimed it could produce 50hp. I weighed mine with exhausts, redrive, oil in the sump - basically ready to run.

#### Ken Powell

##### Well-Known Member
I just tested positive for Covid-19. I may be a couple of weeks before I get back to this project. In the meantime, can anyone identify the taper on this 993: 61E377-0027

I think its a 10:1. Is a 30mm taper the same as a 10:1 (I think they are the same)? Arrowprop is set up for a 30mm taper so that would be good.

#### samyguy

##### Well-Known Member
Where are you guys getting these Aluminum flywheels made ???

#### TiPi

##### Well-Known Member
I just tested positive for Covid-19. I may be a couple of weeks before I get back to this project. In the meantime, can anyone identify the taper on this 993: 61E377-0027

I think its a 10:1. Is a 30mm taper the same as a 10:1 (I think they are the same)? Arrowprop is set up for a 30mm taper so that would be good.
B&S has no useful info on shafts. This is from Honda for taper shafts (V-type):