# Briggs vanguard conversions

Discussion in 'Firewall Forward / Props / Fuel system' started by Hephaestus, May 12, 2019.

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1. Jul 11, 2019 at 4:47 AM

### Vigilant1

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For someone looking for a new 810cc B&S Commercial series engine with EFI, this $975 price (+$67 freight in the CONUS) is the best deal I've seen.
That's the typical price for a carbureted model, the EFI versions are usually several hundred  more. It might be a typo, it would be best to check with the retailer.
Note: I have no commercial relationship with this company.

Edited to add: This appears to almost surely be a typo. The text says the engine has EFI, but the model number is for an engine with a carb. Sorry . . .

Last edited: Jul 11, 2019 at 5:39 PM
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2. Jul 11, 2019 at 5:46 PM

### blane.c

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Thank you.

I am wondering a few things about this engine, It is commercial not Vanguard and what does that mean to the internal parts like forged rods, crank, etc.? I also noticed it has a 1" dia. shaft and the engine has models available with 1 1/8" dia. shaft, I "assume" this is just the PTO side and is unimportant to those who do not intend to use the PTO side for anything major, but does it affect the flywheel side taper dia.? Because that would matter.

It would be nice to have a small engine expert to talk to. Obviously much concern is small potatoes but a stinkin' rotten potato in the soup is really going to taste bad on a small budget.

3. Jul 11, 2019 at 6:30 PM

### Vigilant1

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FWIW, I added a bit to that prior post, as I'm now fairly sure the listed engine is not EFI.
I don't know the specific differences between the 810cc B&S Commercial engines and the 810cc Vanguard engines. From previous discussions here (and a look at a scanned photo of a commercial 810cc conrod), I >think< the Commercial rods are cast. The literature says the Vanguard rods are forged. Regarding the flywheel-side taper, we could probably look at the part numbers for the various Commercial engine flywheels--if the same flywheel fits both engines, then it's probably safe to assume the crankshaft leaves the case with a 1 1/8" diameter.
Yes, it would be great if B&S would answer tech support emails, or if we could see the actual info provided by B&S to OEMs who are shopping for engines. For example, I think we'd all like to know if they can run at the rated HP nonstop, or if B&S has time or external environmental limits (temp) for the rated HP. Similarly, are the Commercial and Vanguard engines built to the same clearances, balance tolerances, etc.
It >does< appear that MiniSport starts with the B&S 810cc Commercial engine, and that this apparently is giving good service when a prop hub/extension is mounted to the (modified?) flywheel. So, that's something.

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4. Jul 11, 2019 at 6:54 PM

### blane.c

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B&S supports marine engines. These engines are generally "Mud Boat" engines. But I surmise that possibly "Airboat" would be in the same general class.

I have had several crankshafts magnafluxed by a machinist in Fairbanks Alaska who magnafluxed the majority of crankshafts for everyone in the area, for racing engines, airboat engines, and for those willing to call there airplane crank an airboat crank those aircraft engines. Thing is he magnafluxed a lot of cranks and new what to look for, the mere cost of his inspection enabled me to reject two cranks before purchase. They were airboat cranks of course. O-290 D2 and O-235 airboat cranks lol. Point is B&S isn't going to talk squat to airplane anybody/anything, but may talk airboat and certainly will talk mudboat. So most things we need to know about for an airplane engine are the same things needed by a mudboater and if they will talk airboat even better.

We could use some help here from some of our members who are in mudboat and airboat country and have "friends".

5. Jul 12, 2019 at 8:10 AM

### Armilite

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There is nothing Magical about the Briggs Van Guard Engines, and any of these Cheaper Clone V Twin Engines can be Upgraded. The Small Block Van Guard 627 comes in 21hp, and 23hp and 23hp EFI. IF you can handle the extra Weight, the Big Block 993 is more HD and with even more CC makes more Hp. For Airplane use, they all need the Governor and Low Oil Sensor removed. They all need a Billet Rod, a Hi Rev Kit even if only turning them 3600rpm, a better K&N Style Air Filter, and a Tuned Exhaust, with a Bigger Carb/EFI. I would also use Needle Bearing Rocker Arms. To turn it over 5000rpm you need a Billet Flywheel or to just Save Weight. With just these few mods (K&N Style Air Filter, and a Tuned Exhaust, with a Bigger Carb/EFI) the Engine will make more HP at same 3600rpm.

The Honda GX390/420/440 Clone Singles use the same Stock CAM .246 Lift, never looked up these V Twins CAM Specs, but also probably a same Small Lift CAM.

Most of these Engines use the same Head with the same Small Intake and Exhaust Valves.

The Single Cylinder Cylinder versions can be Big Bored +12mm, so the Twins probably can be also.

A Harbor Freight PREDATOR 670 ENGINE 8.2cr. (78mm x 70mm) 669.2cc. A Big Bore +12mm (90mm x 70mm) 891.0cc Small Block!
$749.99. Rated 22hp@3600rpm. With Electric Start! ACE 623 Belt Drive USD$649 +Shipping $109. ACE 993 Belt Drive USD$699 +Shipping $109. The Small Block Van Guard 627 making 23hp@3600rpm is 85% Volumetric Efficient! The Predator 670 making 22hp@3600rpm is 79% Volumetric Efficient! 670 at 79% at 5500rpm = 34hp All of these Industrial Engines are HP Rated at 3600rpm, so you need to figure out what they did to get 2hp more at same 3600rpm. both use the same 8.4:1cr, so either Carb Size or CAM most likely. All of these HD Racing Parts are Cheap! To make HP you have Options: 1. Just Turn the Base Stock Engine with those Upgrades a Higher Rpm, 3600rpm to 5500rpm. A 670 at 79% at 5500rpm = 34hp. 2. Raise the CR and use a Bigger Lift CAM and use the same 3600rpm which will also raise your Volumetric Efficiency! A Predator 670 at 100% ar 3600rpm = 28hp, at 3600rpm at 110% = 31hp, at 3600rpm at 120% = 34hp, at 3600rpm at 130% = 37hp. 3. Use Bigger Intake & Exhaust Valves, do some Porting will Improve your Volumetric Efficiency. 4. The 670 V Twin Crank is only 70mm Stroke, the Singles have Crank Strokes up to 86.5mm. The Stock CAM's used in these Industrial Engines aren't Optimal for Airplane use either. A Marine Engine CAM is much better. Most Airports only carry 100LL so you can run about any CR you want too, within reason Max 11.8cr. A Predator 670 upgraded with all the Bells and Whistles and turned 5500rpm could probably make 52-55hp. The Rotax 912UL 80hp/100hp is rated at 5500rpm. Engine Durability depends on the Parts used, the Oils used, the Octane Fuel used, WHO Machines the Parts, WHO put it together, WHO maintains it, WHO Stores it, and WHO Flys it. Almost all Engine Failures are Human-related. Learn the Failure Points of the Engine of your choice. On most 4 Strokes it's the Valve Train. So WHY start with an Expensive Van Guard Engine that you're going to throw a quarter of the parts away anyway. A Vegas Cart 625 Single using 9.0cr, (96mm x 86.5mm) 626.3cc is rated 23hp@3600rpm, cost$850. It can be Big Bored to (100mm x 86.5mm) 679.6cc.

6. Jul 12, 2019 at 9:54 AM

### mm4440

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It is an open question whether the retained B&S parts are of different quality between their different lines. We could use inside information.
The stock cams have a torque peak about 2400 rpm and need to be upgraded for max power even at 3600 rpm. Tuning the engine for max power at around 5000 rpm is not too extreme. Can it produce that power continuously without overheating is a question.

There are super/turbochargers and intercoolers available the right size for these engines on e bay for the adventurous. Modest boost and rpms will be the easiest on the engines. They will still be cooling limited.

7. Jul 13, 2019 at 10:00 AM

### Armilite

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=========================

There are many things to look at when Building and Engine. Most Engine Parts very rarely Fail no matter what Brand Name or Cost. As I said, Engine Durability depends on the Parts used, the Oils used, the Octane Fuel used, WHO Machines the Parts, WHO put it together, WHO maintains it, WHO Stores it, and WHO Flys it. Almost all Engine Failures are Human-related.

On Parts used, like the Factory Stamped Rockers are a very Poor Choice for Racing or Airplane used. The Stock Valve Springs are very Low-Pressure, marginal for even the Stock 3600rpm. The Stock Push Rods are marginal for even the Stock 3600rpm. Just like you have different Types of Pistons, Cast vs Forged. The main drawback is that cast aluminum is limited in terms of ductility. In other words, an over-stressed cast piston will suddenly and destructively break when it fails. Detonation in Engines is a problem. You have to look at what causes these different Engine Parts to Fail. It's usually traced back to Human Error, or just being Cheap, or Negligent. It's like if the Head Rotax Engine Designer says 85% of all Rotax 2 Stroke Failures is from Detonation. Then you have to ask WHY haven't they either Lowered the CR on their 2 Stroke Engines as Hirth, Simonini has or supported using 100LL in their 2 Strokes Engines as some other Engine Manufactures have. All the while making Millions on Repairs over 40 Years. These Honda/Clone 4 Strokes face some of the same Problems.

Part 103 Aircraft even with 5 Gallons can Fly 50-90 miles depending on Engine and Speed used!

Kitplanes have No Fuel limit Restrictions other than Max Load!

While Turbos do have their place, they're not worth the extra Cost & Weight for most People using Small Planes.

These Stock Industrial Honda/Clone CAMs are terrible for Racing, and for Planes. This guy is one of the best Honda Clone Builders on Youtube. Watch his Video on CAM's.

No Piston Engine is run at it's Max HP Rating, continuously without some overheating problems. Most are used at 75% Power. Over Heating is a problem with even Certified Engines. Each Airframe they're put on is different so different issues to deal with. Today, you have better Oils, different Engine Coatings to Help, better Bearings, better HD Parts, etc.

Racers who use these Honda/Clone Engines, push them to their Extreme Limits, can give you the best insight on their weak points.

RPM used is what turns a Prop, so HP & Rpm go hand in hand when figuring Prop Thrust.

Every Plane has a Stall Speed, just as it has a Max Full Power Speed with X amount of HP based on Prop used. Like a USA Part 103 Ultralight has a Specified Minimum 24 knot (27.6mph) Stall Speed, so what Minimum Hp/Rpm does it really need? If a USA Part 103 has a Full Power Speed of 55 knots (63.3mph) what Max HP/Rpm is really needed? Each Type of Airframe will vary +/- a little.

With Planes, it always boils down to Weight vs Hp vs Cost.

TBO (Engine Durability) usually boils down to the Parts used, the Oils used, the Octane Fuel used, WHO Machines the Parts, WHO put it together, WHO maintains it, WHO Stores it, and WHO Flys it.

8. Jul 13, 2019 at 2:11 PM

### pictsidhe

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The ports are lousy on the intek engines. Fix those, the torque peak will increase significantly. Valves are already large enough. You need efficient ports for good BMEP.

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9. Jul 13, 2019 at 7:19 PM

### mm4440

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Max continuous power means what it states. This is tested with engines running at that level often with adverse operating conditions for many hours at a time. When we hot rod these engines we are eating into the margins built into the stock engines. the max continuous power of the modified engine will be determined by how well they are cooled, how much fuel you want to add for cooling and cht. Max power is needed for TO and initial climb, one to two minutes.
The question for me is can a B&S be modified to replace a 35 hp two stroke paramotor engine for a self launching sailplane/motorglider.
It is going to weigh more and it is looking more costly in dollars when I start putting some value on time spent. For my application the two stroke wins but for other types of aircraft a reasonable cost and weight four stroke is definitely worth working on.
Low boost and moderate rpms are the easiest path to power. A turbo adds more heat to the engine so a supercharger is looking more attractive, search: AISIN AMR 300, & 300

10. Jul 13, 2019 at 8:44 PM

### pictsidhe

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Do you have a reference for turbo engines running hotter than super engines? Super engines run higher bsfc and burn more fuel per horsepower. That will at least partially offset the higher back pressure of turbos.

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11. Jul 13, 2019 at 10:00 PM

### Hot Wings

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For a self-launch glider the paramotor is probably the better choice. I'm betting (SWAG)that the B+S is a better option for a light motorglider.

12. Jul 13, 2019 at 10:11 PM

### pictsidhe

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There are pros and cons to both engine types.
For me, a big reason to go Briggs is so I'm not flying behind an angry wasp.
Yes, that's a lousy engineering argument...

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13. Jul 14, 2019 at 1:41 AM

### mm4440

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If you have seen turbo engines on a dyno at high power the exhaust is glowing orange to bright yellow. That increases heat flow into the heads. In an aircooled engine it could limit power more than a blower with a free flowing exhaust.

14. Jul 14, 2019 at 4:23 AM

### pictsidhe

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Much like heavily supercharged engines, then?

15. Jul 14, 2019 at 9:50 AM

### Armilite

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========================

Most Engine Companies only give you the Max Hp made at Sea Level for a Specific Rpm! For 2 Strokes used on Airplanes, Industry Standard is Max 6500rpm. Some Small Para Motors exceed that rpm.

Since each Airframe offers different Cooling problems, depending on Engine used, Prop used, has different Cooling needs. You could take a Standard 503UL rated 50hp@6500rpm, actually, Dynoed Max 49.8hp@6250rpm http://www.rotaxservices.com/dyno.html#6, and put an R&D Aero Tuned Pipe on that now it makes 62.3hp@6500rpm and doesn't Over Heat. http://www.rotaxservices.com/dyno.html#7 That's a 12.5hp Increase 49.8hp to 62.3hp!

To Answer your Question, "The question for me is can a B&S be modified to replace a 35 hp two stroke." Yes, but it's probably going to Weigh more. Can you afford the extra Weight? You don't say which Brand Engine or CC Size you're trying to replace. A Honda/Clone/Predator 420 Single can make 35hp@5000rpm. Best Bang for your Buck is a Duro Max 440cc Single, Stock 18hp@3600rpm, with Electric Start, $299.95. 1. Use a 34mm Flat Side Mikuni Carb.$40 eBay
2. Use a K&N Type Air Filter. $25 eBay 3. Use a Tuned Exhaust.$40
5. Use a Billet Rod $125, & Billet Flywheel.$175.
6. Use Needle Bearing Rocker Arms. $225. 7. Use a better CAM for 5000rpm.$65.
8. Install Hi-Rev kit for 5500rpm. $90. 9. Use an Ace Belt Drive or equivalent. 10. I would Install a Billet Side Cover.$150.
11. Use the different Engine Coatings to fight Heat.

For most Small Kit Planes and Part 103 Ultralights, Weight Saved is very Important. So a 2 Stroke is usually a Better Option! If People put in some research on How to Build and Improve their 2 Stroke, How to make even more HP, and How to keep it Cool, they would be better off. Many of these things they could do themselves to Save Money.

A General Rule for 2 Strokes that use a Good Designed Wide Band Tuned Pipe Designed for 6500rpm and use 11.5cr, it takes on Avg 7cc to make 1hp. So you can flip that info, If you want 35hp x 7cc = 245cc Minimum. There are many, probably 20+ Snowmobile Single Cylinders out there. Not all have the Bolt Holes around the PTO to attach a Gear or Belt Drive. The Rotax 277 and most of the JLO, and the Sach Singles do. There are others. JLO alone made about 14 different Singles, 100cc to 395cc.

All Rotax's and Hirths, use Mufflers, Simonini, and Polini use Tuned Pipes. Rotax uses many different CR's, the other Engine Manufactures are Standardizing on 9.5cr.

Tuned Pipes are probably the most misunderstood 2 Stroke Engine Improvement. Each Tuned Pipe is Designed for a Specific Max Rpm, using the Engines, Bore & Stroke, Exhaust Port Spec's, Engine Port Duration. You can have a Narrow PowerBand or a Wide Power Band. They can be Designed Increments of HP Increase. That Stock 503UL Dynoed 49.8hp and with R&D Aeros Tuned Pipe it made 62.3hp@6500rpm, Stock 49.8hp + 25% = 62.25hp (62.3hp). A 503UL is 496.9cc/7cc = 70.9hp. Stock 49.8hp + 30% = 64.74hp, Stock 49.8hp + 35% = 67.23hp, Stock 49.8hp + 40% = 69.72hp. Now if you raised the 503UL CR to 11.5/11.8 vs Stock 10.8cr what HP Gain would you see?

When you look at these New 2 Strokes from Hirth, Simonini, etc., and their ridiculous Prices, I'll pick a Good Used Rotax 277UL, 377UL, 447UL, 503UL, 532UL, 582UL, 618UL, any day, and rebuild it, or their counterpart Skidoo Engine. They can all be Rebuilt fairly cheap. My best Trade was a Used Pistol I had $250 in, for a Good Running Rotax 277UL with a Gear Drive, with CDI off a Scat Hover Craft. I have bought Good Rotax B Gear Drives for$220. You can completely rebuild these Rotax Singles for less than $250 in parts, most Twins$600 in Parts.

Improvements for 2 Strokes for more HP:
1. Wide Band Tuned Pipe. For Plane use Max 35%.
2. A CR Bump for some engines, for Planes Max 11.8cr.
3. Porting & Polishing.
4. Turn 6500rpm for some.

For Durability & Better Cooling:
1. Use a Higher Octane Gas!
2. Use the different Engine Coatings
3. Use the Full Synthetic 2 Stroke Oils.
4. Use the Hybrid Crank Bearings.
5. Use Evans Coolant(Doesn't Boil)

16. Jul 14, 2019 at 5:35 PM

### Hephaestus

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Compression alone will ensure air heats... The turbo housing being near egt temps generally ensures there is a bit more heat exchanged.

The difference is negligible, either way a modern turbo you'd use an air to air intercooler to reduce that some. Just as you would with a supercharger.

I don't think anyone here is building a race engine, you're not going to have exhaust glowing red hot in our application.

17. Jul 14, 2019 at 9:25 PM

### mm4440

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EGTs run ~1400-1600 F when producing power. The turbo is a bit of a cork in the exhaust system increasing heat flow out of the exhaust manifolds compared to a NA engine. I assure you that inside the cowls of turbocharged aircraft engines under power there is a pleasing orange glow. Little engines might run cooler, maybe below incandescent but still hot. As an amature welder I have to relearn that occasionally.

18. Jul 15, 2019 at 8:33 PM

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