# Briggs & Stratton Vanguard 23hp build

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#### bl_dg

##### Well-Known Member
Supporting Member
OK, starting a thread for my engine conversion. I just purchased a Vanguard 23hp engine. (386447 series) The goal is to minimize weight and maximize -reliable- horsepower. This will be a direct drive installation, so I do not forsee pushing the engine much past 4,000 rpm. Looking for incremental improvements. No billet spark plugs!

I will be mounting the prop on the flywheel end, because.. that's what Briggs (Europe) did on the ULTRA UAV. Since I won't need the PTO end, I was able to save some money by getting a 'generator' model with the internal spline PTO. I also bought an oil pan/engine cover from a vertical shaft engine so I can 'more directly' mount the engine to the firewall, rather than using a bed-mount engine installation.

But first is getting some base line info on the engine. So unless I can find someone with a dyno, I will be building some Eiffel clubs.

See attached photos of the engine.

#### Attachments

• 386447.jpg
1.1 MB · Views: 4
• 386447 - PTO end.jpg
1.2 MB · Views: 5

#### Vigilant1

##### Well-Known Member
Supporting Member
Bl_dg,

Admin question: Do you want to take comments/questions here? That can get messy, but everyone is gonna have questions.
The alternative is to start your "just my own comments" thread in the "Build Log" subforum (no one else can post on it there), then leave this here retitled as your Q&A thread.

Mark

#### bl_dg

##### Well-Known Member
Supporting Member
I'm fine with this being a 'discussion' thread. I can do a build log afterwards.

#### Tiger Tim

##### Well-Known Member
I also bought an oil pan/engine cover from a vertical shaft engine so I can 'more directly' mount the engine to the firewall
Alright, that’s just clever. Are there any internal differences between covers that may affect oil distribution inside the case?

#### TiPi

##### Well-Known Member
Supporting Member
OK, starting a thread for my engine conversion. I just purchased a Vanguard 23hp engine. (386447 series) The goal is to minimize weight and maximize -reliable- horsepower. This will be a direct drive installation, so I do not forsee pushing the engine much past 4,000 rpm. Looking for incremental improvements. No billet spark plugs!

I will be mounting the prop on the flywheel end, because.. that's what Briggs (Europe) did on the ULTRA UAV. Since I won't need the PTO end, I was able to save some money by getting a 'generator' model with the internal spline PTO. I also bought an oil pan/engine cover from a vertical shaft engine so I can 'more directly' mount the engine to the firewall, rather than using a bed-mount engine installation.

But first is getting some base line info on the engine. So unless I can find someone with a dyno, I will be building some Eiffel clubs.

See attached photos of the engine.
Thanks for starting the new thread
bl_dg, sorry to tell you that the sump from the vertical engine is very unlikely to fit on the case of the horizontal engine. The vertical engine has the oil reservoir in the sump, so the sump has a deeper space. The crankshaft and camshaft are most likley too short for the deep sump.

Camshaft, oil pump, cover (sump) gasket and many more parts have different P/N between vertical & horizontal.

#### Vigilant1

##### Well-Known Member
Supporting Member

- With the prop on the PTO end, what's your plan for the flywheel and the stuff that is on the OEM flywheel (alternator, ignition, starter ring gear)?

- Will it be heads up or heads down? From the oil pan discussion, I'm guessing it'll be heads up.

I like your approach of measuring the HP of the stock engine first, and in a reliable way. That seems a very good start.

Thanks again for sharing your efforts here.

Mark

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#### cluttonfred

##### Well-Known Member
Supporting Member
I'll be following this with interest as I would love to see the steps involved to gauge how hard a project it would be for a non-engine guy like myself as well as the final time, effort, cost, weight, and power. It would also be great to see how much of an impact an Ace redrive ($800 delivered to the USA) would have on the real-world pulling or pushing power of the engine. #### Vigilant1 ##### Well-Known Member Supporting Member It would also be great to see how much of an impact an Ace redrive ($800 delivered to the USA) would have on the real-world pulling or pushing power of the engine.
That's a tough bit of information to measure if we care about thrust at climb and cruise airspeeds. We'd need two very similar planes, one with direct drive and one with a PSRU.
Lots of folks measure static thrust, but that is not indicative of the situation at typical flight speeds.

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#### cluttonfred

##### Well-Known Member
Supporting Member
That's a tough bit of information to measure if we care about thrust at climb and cruise airspeeds. We'd need two very similar planes, one with direct drive and one with a PSRU.
Lots of folks measure static thrust, but that is hardly indicative of the situation at typical flight speeds.

I was actually thinking of the same engine on the same plane and then just compare real-world performance with and without the redrive.

#### Vigilant1

##### Well-Known Member
Supporting Member
I was actually thinking of the same engine on the same plane and then just compare real-world performance with and without the redrive.
That would be close to ideal.

#### BBerson

##### Light Plane Philosopher
Supporting Member
Not really. Redrive is for slow, high drag aircraft. Direct drive is for fast or low drag airplanes.

#### Vigilant1

##### Well-Known Member
Supporting Member

#### Vigilant1

##### Well-Known Member
Supporting Member
Your Briggs is the lightest industrial V twin that will pull or push a small airplane into the sky, but it will take modification in the neighborhood of about $500 to$1000 to get the thrust you'll need. Most of the flying 23 hp 627cc model 38 Vanguards are modified to put out 30 to 35 hp at 4300 to 4500 rpm with maximum torque at 4000 rpm.
And, it is worth keeping the end goal in sight when choosing a starting point. If we want 30hp or more, the required modifications, cost, and RPMs may be lower if we start with the 810cc engine as our base engine. The steps to turning it to the horizontal shaft orientation are well known and not hard, the engine will be under less stress and the heads under less heat load. As a bonus, the 810s are about the same or cheaper to buy. Weight of the 810cc ready to fly (Spacek) is 77 lbs, a modified 627cc engine (Spacek) is lighter.

There's nothing wrong with the Vanguard 627cc engines. Like every engine, it'll have natural limits. They can be stretched with money and effort, but they'll still be there.

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#### Vigilant1

##### Well-Known Member
Supporting Member
What is the least-cost method of doing dyno testing? The Eiffel clubs are within my abilities - just need a planer and a jointer. (\$!)
That's the best way to go, IMO. Accurate and not subject to "helpful', optimistic dyno calibration. You likely know the details, but they are in the attachment here.
Maybe look around for a MakerSpace, Vo-tec school, or a woodworkers club near you to fabricate the clubs? It seems a shame to buy a jointer for this alone (unless you secretly want one anyway!). At the small widths involved, you can probably get by using a jointer, no need for a planer (again, unless you want one anyway.)
Mark

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#### llemon

##### Well-Known Member
I read Fred Weick's propeller book recently and he makes this interesting point about gearing;

The formula for Cs is;

23hp engine @3000 rpm;

The speed where it goes over 1.3 is ~94mph

#### Vigilant1

##### Well-Known Member
Supporting Member
I read Fred Weick's propeller book recently and he makes this interesting point about gearing;
View attachment 130010
The formula for Cs is;
View attachment 130011

23hp engine @3000 rpm;
View attachment 130012
The speed where it goes over 1.3 is ~94mphF
Thanks for that.

FWIW, at 3600 RPM (and sea level) C2 crossover point is approx 101 mph.

Of course, the magnitude of the direct drive vs PSRU difference at the airspeed of interest has primary practical significance, rather than the particular crossover point.

It's probably worth mentioning the mechanical losses from the belt drive (shown in belt and bearing heating). It's not a lot, but it ain't zero, either. Gates Corp says the loss is from 2-5%, and if it is at the high end of that we're losing about 1hp to PSRU friction.

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#### rv7charlie

##### Well-Known Member
Supporting Member
NB! The props are optimized for 50mph, so there would be differences as we get farther away from the design point of the props. But, at higher speeds we know that the thrust advantage of a larger prop diminishes.

Direct drive: 46"dia, 14.7" pitch. Expected thrust: 95lbs (approx).

PSRU: 1 : 1.5 ratio, 65" prop dia, 24.5" prop pitch. Expected thrust: 106 lbs (approx).

The difference in thrust is equivalent to about 2.6 HP of engine output at this airspeed.
What's the thrust difference at say, 30 mph? What's the difference at 100 mph?

Everything's a compromise. If an extra 8 lbs (for a redrive) pushes you out of pt103 and that's important, then it's an unacceptable compromise. If the weight can be tolerated and it cuts the takeoff run by 30-40% and doesn't reduce cruise or top speed, then the compromise would look pretty good to me, unless I was flying something with UL performance from a long paved runway and had no interest in off-airport operations.