# Briggs vanguard conversions

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

1. May 15, 2019

### Vigilant1

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Wood/wood core props should be run no higher than 850 fps tip speed (That is helical speed, not circular speed. They won't be much different below 100 mph.) Another reason not to go crazy with the RPM on a direct drive installation. You'll probably do fine with a smaller prop at these modest HP levels, even at relatively low airspeeds. What airspeed would you optimize your prop for (and would that be climb or cruise)?

2. May 15, 2019

### BBerson

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Stock Briggs thin tin mufflers (off a single) don't weigh much. How much does a turbo system weigh?

3. May 15, 2019

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Here is an article I translated from french on the use of club props. I posted this in my build thread too, but I can't seem to find it in there

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4. May 15, 2019

### mcrae0104

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Why would "Extreme Cold Wheather Conditions" be more conducive to carb ice?

Last edited: May 15, 2019
5. May 15, 2019

### pictsidhe

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Don't be silly, any fool knows that ice needs temperatures below freezing to form.

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6. May 15, 2019

### Vigilant1

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Some numbers from Jan Carlsson's prop program, for consideration.
Assumed:
40 HP (just because people are hoping for this), prop optimised for 70 mph cruise, 2 blades, 4500 RPM.

44" dia=870 fpm (loud, inefficient, marginal safety in wood), pitch 17",
61.3% efficient.

42" dia= 831 fpm tip speed. Pitch 17", prop efficiency at that airspeed: 61.4%

40" dia= 792 fpm tip speed, pitch 17", prop efficiency at that airspeed 61.1%

Take aways:
- You can't run a wood/wood core/similar prop longer than about 44" at 4500 rpm.
- At these power loadings, a longer prop doesn't get you significantly better prop efficiency. 40" is fine.
- As a bonus, the shorter prop has wider blades. You don't want wispy thin blades if you'll be turning them very fast and using an engine with power pulses like a V-Twin has.
-If the engine puts out less than 40 HP (likely), most of the above points are even more germane. The blades get wispier, the power loading is lower (so efficiency changes even less with prop diameter).

Last edited: May 15, 2019
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7. May 15, 2019

### poormansairforce

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I'm curious about the thrust at those speeds/rpms? Care to share? Thx.

8. May 15, 2019

### Armilite

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

Carb Ice has probably caused more Accidents then is known account most People don't realize what the problem is and it melts soon after a Crash or Engine Out Landing.

I have visited Valley Engineering, and while the Dad nice guy, the real Brains behind the Company has passed away over 2 years ago now, the kids are running it today. Have you ever visited them? Since they don't really have much Snow or Extreme Cold in Rolla, Mo. I seriously doubt it's been Tested under those Extreme Conditions YOU & other People might Fly in. They don't offer the Big 993 Twin today, Why is that?

Factory Spec 3600rpm is for what Industrial Tools are run as Industry Standard is supposed to run, it's not the Engines Max Rpm!

The Valley Engineering Big Twin Four Stroke from their Web page!

"The engine is a Four-Cycle, two-cylinder, 990cc, V-Twin developing 40 hp at 3600 rpm.
40 HP @ 3600 rpm (peak) 32 HP ( continuous ) 120 lbs COMPLETE*

By some Modifications, Tweaking and Tuning we've upgraded the 40 hp Big Twin to the 50 hp Big Bad Twin. The extra power makes a BIG difference too. All dimensions the same as the Big Twin with a little bit more fuel consumption."

Did they ever Dyno this Engine and post it? Do they give a Continuous use rating for the 50hp, No?

So, HOW DO YOU THINK THEY DID THAT, 36hp to 40hp and then to 50hp with the same CC Engine? They didn't start with the 37hp EFI 993 Engine either! They don't state at what rpm it made that 50hp either!

Stock 993 with a Carb was 36hp@3600rpm = 85% Volumetric Efficiency!
Stock 993 with a Carb making 32hp @ 85% = 3200rpm.

993 with a Carb making 40hp@3600rpm = 95% Volumetric Efficiency! Probably just added a better Air Filter, Bigger Carb, a better Tuned Exhaust for +4hp!

993 with a Carb making 50hp@3600rpm = 120% Volumetric Efficiency! For this way, IF using 3600rpm, Probably just added a better Air Filter, Bigger Carb, a better Tuned Exhaust, and would have needed a CR Bump & probably a Bigger Lift CAM if they wanted to use low 3600rpm!

993 with a Carb making 50hp@4500rpm using their 95% Volumetric Efficiency! For making 50hp this way Probably just added a better Air Filter, Bigger Carb, a better Tuned Exhaust, a Hi-Rev kit, and just used a Higher 4500rpm!

The Rotax 912, 4 Stroke, 80hp is rated at 5500rpm! The Rotax 912 100hp is rated at even Higher 5800rpm. It's not a Magic Engine. Just because You and your Racing buddies can't figure out how to Cool an Engine doesn't mean the rest can't.

9. May 15, 2019

### Vigilant1

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I just apply the standard thrust formula and use the prop efficiency above. In imperial units:

(Engine HP x prop efficiency x 375) / (airspeed in MPH)

So, we'd expect something like (40 x .61 x 375) / 70
= 131 lbs of thrust at 70 MPH for a 40HP engine and this prop

When we look at graphs or use a propeller program, we normally see that the optimum efficiency we can obtain with an optimized fixed-pitch propeller goes up with higher airspeeds. But the airspeed in the denominator of the equation above assures that, within normal bounds of prop efficiency, actual thrust still goes down with airspeed, though prop efficiency may be increasing.

Also, a fixed-pitch prop designed for a particular airspeed loses efficiency at airspeeds faster and slower than its design speed. The dropoff in efficiency is less dramatic at airspeeds below the design speed, but can be very sharp at airspeed higher than the prop's design speed.

Last edited: May 15, 2019
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10. May 15, 2019

### pictsidhe

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For direct drive at 70mph, the 810 would work a lot better. 29% more displacement to swing a bigger prop at lower revs. Heavier crank. I want to use the 627, but with a redrive.

11. May 15, 2019

### mcrae0104

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Could you please explain why snow or extreme cold are related to carb ice? Thanks.

12. May 15, 2019

### poormansairforce

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Ok, I thought Jan's program spit something out but that works as well. Thanks for the explanation.

13. May 15, 2019

### Vigilant1

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I think his program might do it if I could make it give me the raw data (there are some macros that aren't working for me). The program does give a thrust vs airspeed graph, and at the prop's design speed it matches the math I did above.

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14. May 15, 2019

### Hephaestus

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I'm not even entertaining the 810 guys. Different fully unknown block. More weight, a thousand dollar price premium, and lacks the aftermarket support that makes this a bolt together project.

But I'm still working on bore/stroke options (because turbos are great but there is no replacement for displacement).

Whereas this one even just with the turbo hits the numbers for the ranger. Which is kind of the point.

Bberson - the factory tin exhaust is restrictive and wouldn't work in an aircraft. But turbo does very effectively muffle an exhaust. So likely just routing to a decent place is required. The turbo is around 3kg with all the extras needed to add it.

15. May 15, 2019

### BBerson

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What does the turbo system cost? And all other parts?

16. May 15, 2019

### Hephaestus

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350$for the turbo, bits and pieces likely another hundred or so, will depend on what oil pump I use (50-500$+), not finding a high volume for the briggs, not sure I'll get enough pressure / volume from the factory one for the turbo...

Hard to fully put the number together before the building really starts. A lots going to depend on how/where the turbo gets mounted.

17. May 15, 2019

### Hot Wings

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Search eBay with RHB31. Save yourself $200? 18. May 15, 2019 ### Hephaestus ### Hephaestus #### Well-Known Member Joined: Jun 25, 2014 Messages: 567 Likes Received: 122 Location: YMM Possible I wanted a known entity, we know how eBay purchases can go... After shipping the difference runs less than 80$ Canadian between unknown source eBay and known source...

19. May 15, 2019

### Vigilant1

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I understand your position, but just for others who may be weighing a similar choice with similar objectives:
If the goal is to get a particular HP at 5800' MSL, and the options are a turbonormalized Vanguard 627cc or a NA Vanguard 810cc:

Power: The air density at 5500' MSL is 85.4% of the air density at SL (standard conditions temps, which include the temp. lapse rate). The 627cc engine displacement is 77% of the 810cc engine displacement. So, if the 627cc is truly turbonormalized, it will be receiving 8% less O2 than the 810cc at 5500' MSL and will produce 8% less power.

Weight: The "stock" horizontal Vanguard 810cc engine weighs 91 lbs out of the box. The horiz 627cc weighs 77 lbs out of the box, so 14 lbs less. We know both will weigh a lot less once plastic shrouds, fans, etc are removed, but let's assume that these things are proportional and that there remains a 10 lb difference after the stuff is stripped off. Hephaestus says the turbo is 3KG = 6.6 lbs. And we need a bigger oil pump, and oil lines to service the turbo, and more complicated air induction routing, as well as more complicated exhaust routing, fittings for same, a few ounces for the boost gauge and wring, etc, etc. Even adding in a muffler for the 810cc, it could easily be about the same weight.

Cost: The 810cc Vanguard is about $1300 retail in the US (I frequently see it for a few hundred less). Forged crank and conrods, beefed-up pistons and rings, etc. We'll want a new CV carb of some kind. A Vanguard 627cc Horiz engine is about$1700 retail in the US. If it doesn't have a forged crank and conrods, those will definitley need to be added to the price IF we'll be exceeding normal HP or RPMs (maybe not necessary for true turbonormalizing). Add in $300 for the turbo, and whatever aftermarket carb/EFI you'll need (same cost as the 810cc), the costs for additional mounting hardware and fittings for the turbo, a boost gauge and sensors, etc. The 627cc was already$400 more before we bought anything custom or turbo, so we could easily be at close to double the price of the 810cc installation by the time we get done.

Now, if someone found a great deal on a 627cc Vanguard, that's super. But we could look around and find a used 810cc as well, so to compare a used version of one to a new version of another is not quite right.

In the bargain, the 810CC is beefier: Larger crank, larger journals, larger bearings. More importantly, will have a head designed large enough by the factory to shed more waste heat than the smaller head on the 627cc. IMO, this may be the constraining factor on both engines WRT continuous HP.

Again, possibly for use by others.

Last edited: May 15, 2019
20. May 15, 2019

### Hephaestus

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But then you're also taking a full clean paper design not building on some known with the 810cc.

To me when I started with "turbo normalized" I meant to bring air density down to sealevel. Less cooling same charge - reproduceable numbers. Meaning hp I start with is same as the rest of you are likely to see, but with a cooling deficit. It'll be boosted but intention is to start at sea level and work up so the heat issues are well known and documented, before we start adding power to bring it to where I want it.

The 810 is a new design not the dihatsu original. Parts don't exchange. I want it largely off the shelf as a build. We don't know what the flywheel bearing is, don't know if it will take the load of any prop without failure.

The turbo is 2.65kg I'm adding weight to allow for extra parts.

But I think you guys have shown me where I've gotten sideways... Kinda need to toss things aside and go back to the start again - drop the RPM range morr, skip the redrive, keep it direct and make the power it needs in the range it needs for the ranger design. I don't want it screaming at 6000rpm on a redrive to swing a bit prop slower - that's just more weight and points of failure. But I'm pretty sure that the end goal of direct over 40hp is probable. It's just getting the details right to make it.