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810 Briggs Rabbit Hole - New Head Branch

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Hot Wings

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Forked off from another industrial engine thread.

Decided to take a few hours to see how much potential a new head casting for the 810 B+S engine might open up. The sketches below have all of the essential original B+S parts in their original location (+/_ 1mm or so).
The block in the assembly is the standard B+S ParaZoom block as found on GrabCad - not the 810 block.

What I think I discovered is that there is some improvement available for aircraft use but a lot of the orientation of the ports depends on if the engine is going to be used upright, inverted, and if the flywheel side will be facing the incoming air or if it is on the trailing side.

I'm not likely to get time to be serious about this project for a year or more but I thought others might like to see how much open space there is available for additional cooling once the OEM restraint for a simple die casting is removed.
810 with vert bare block.JPG810 head valley side.JPG810 head flywheel view.JPG

Edit: Exhaust ports shown are best for inverted. Upright would probably be rotated 90 deg.
 
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Vigilant1

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Wow, thanks for the graphics and the insight.
Dual plugs. Cool. Maybe have the OEM magnetrons for secondaries, use a modern EI (Speeduino, RusEFI, SDS, Megasquirt, etc) as primary so we can have variable timing and idle lower.
A nit: maybe add a dedicated tapped hole for a CHT thermocouple so everyone can be using/referring to the same location for their readings.
So, any reason not to add fins on that big slab top? Too much trouble to make that?
Thanks, again.
Mark
 
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TiPi

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Nice🙂
The dual plug location might not work, you need a squish zone in one location. An Italian builder must have dual ignition and is welding and re-machining the heads for side-by-side dual plugs similar to the Jabiru heads.

The original head is severly compromised in 3 main areas:
- valve size due to the head being sized for a 74mm bore, not the 83mm of the 810 (IN 34mm, EX 31mm)
- intake port length and sharp angle (short-turn radius)
- exhaust port with right-angle intersection and sharp corner

Your design addresses all 3. But the actual head height (combustion chamber) will need to increase as the combustion chamber is 13mm deep (will probably end up about 10mm with the wider chamber) and there needs to be quite a bit of meat above to prevent bending of the head.
 

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A nit: maybe add a dedicated tapped hole for a CHT thermocouple so everyone can be using/referring to the same location for their readings.
So, any reason not to add fins on that big slab top? Too much trouble to make that?
Not a nit - Good idea
This was just a very basic sketch to visualize how much room there really is to work with.

The dual plug location might not work, you need a squish zone in one location.
<< >>
But the actual head height (combustion chamber) will need to increase as the combustion chamber is 13mm deep (will probably end up about 10mm with the wider chamber) and there needs to be quite a bit of meat above to prevent bending of the head.
There is a nice squish zone - just not shown in the posted pics. There is enough room for dual 8mm plugs on the stock side. The plugs shown are 8mm in 10mm holes.
<< >>
This is going to be a problem. The head I measured has the valve seat face and chamber roof at 12mm. Leaving that height as is (to keep the original valve parts) doesn't leave a lot of room to work with. With flat top pistons the best I was able to get was a 9.5/1 compression ratio. Anything more would severely shroud the valves around the perimeter. Moving the roof down to the 10mm range may be the only practical solution. With a reground cam and stock length pushrods everything might work out OK. Shortened push-rods or shimmed rockers are the other obvious fixes.

As drawn the combustion chamber has a thickness of 12mm. The bolt pads are not quite as 'filled in' as the stock. Once/if I get serious about this SW does an acceptable job of FEA for this kind of investigation. The cooling fins should stiffen the rest up pretty well.
 

Vigilant1

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Out of curiosity (and ignorance)--projected benefits of a new head design? The dual plugs would be nice, re-orienting plumbing for easier routing, etc. Lighter weight? But the major items would be breathing and cooling. Given the induction and exhaust limitations of the present head, how much is being left on the table? And, with better fins/etc, how many additional continuous HP could be supported?

In the Type 1 VW world, the aero engines have pretty much topped out at about 75 HP continuous due to cooling limitations. Better heads (with better cooling, smaller valves) would be great and make the engine more reliable and reduce maintenance, but (IMO) there's not much additional reliable HP to be had even with those changes--the bearing saddles in the magnesium cases already get worn from the pounding, the cases themselves eventually crack, etc. So, at some point the various limiting factors add up and it's not reasonable to ask more from the engine if we want reliable long-term use use in aircraft.
Is there a sense of where that limit is for the B&S 49 series, or other industrial engines? On the face of it, if we can get 28-30 HP continuously from a direct-drive, affordable 49 cu in. four-stroke engine, that seems pretty good. Very good, really. If the head is made to breathe better and more HP results, there will be more stress on the rods, bearings, crankshaft, etc. If the RPMs are raised, then the valvetrain eventually needs attention, etc.

Signed--Mr Wet Blanket
 
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TiPi

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This is a table comparing some of the industrial engines that have been used or proposed for aircraft use over the last 10 or so years.

If you compare this data to "proper" aircraft direct-drive engines, the achievable power is around 40hp/lt and maybe 43hp/lt with everything optimised. The power/displacement is normalised to 3,600rpm and based on max power (not all manufacturers have max cont power advertised).
1596530849451.png

Aiming for 43hp/lt (35hp out of the Briggs 49) is already at the high-end. A set of new heads optimised for flow at the lower rpm might improve the output but I'm not sure by how much and if it is worth the effort. It would be very nice to try.
 

Vigilant1

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I suppose the magnitude of any cooling issues/challenges will become clearer as TiPi's engine research continues. As far as I've heard, the SE33 seems to be doing okay in service, but I'm a bit uncertain about the claimed "33" part.
 

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A set of new heads optimised for flow at the lower rpm might improve the output but I'm not sure by how much and if it is worth the effort. It would be very nice to try.
Pretty much my presumption as well. For my personal use the motivating reason is mostly from a packaging point of view for use in an aircraft in the inverted orientation. Way down another rabbit hole - I'm at 5000 ft and density altitude gets to be a significant factor. Thus turbo normalizing is a real option in the future. Cooling then becomes more of a factor in the thin air while producing sea level power.

I'm also looking at uses where direct drive is a better option than a PSRU.
 

poormansairforce

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This is a table comparing some of the industrial engines that have been used or proposed for aircraft use over the last 10 or so years.

If you compare this data to "proper" aircraft direct-drive engines, the achievable power is around 40hp/lt and maybe 43hp/lt with everything optimised. The power/displacement is normalised to 3,600rpm and based on max power (not all manufacturers have max cont power advertised).
View attachment 100003

Aiming for 43hp/lt (35hp out of the Briggs 49) is already at the high-end. A set of new heads optimised for flow at the lower rpm might improve the output but I'm not sure by how much and if it is worth the effort. It would be very nice to try.
Notice the UL 260 and the Jabiru 2200 are at 40 hp/lt and make their horsepower with low compression ratios. This means they flow well at target rpms and therefore those are the heads we should be imitating.

Edit: see my post below.
 
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Vigilant1

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Notice the UL 260 and the Jabiru 2200 are at 40 hp/lt and make their horsepower with low compression ratios. This means they flow well at target rpms and therefore those are the heads we should be imitating.
They also have a considerably higher fin density and volume than the industrial engines, which may also play a role in achieving higher continuous power levels. That may be another thing to emulate.
The stock B&S 49 series engine is already above the average power density for the engines TiPi cited. His goal of 35HP would be a higher 3600 RPM specific power level than any of the engines he charted, it is suitably ambitious.
 
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Hot Wings

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I would be elated to achieve 35 continuous sea level Hp. That would be better than the first generation of VW conversions.

The Aeronca E-113 has always been my benchmark for this class of engine. If we could emulate the Aeronca's RPM as well then PSRUs become a redundant item.
 

pictsidhe

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This is a table comparing some of the industrial engines that have been used or proposed for aircraft use over the last 10 or so years.

If you compare this data to "proper" aircraft direct-drive engines, the achievable power is around 40hp/lt and maybe 43hp/lt with everything optimised. The power/displacement is normalised to 3,600rpm and based on max power (not all manufacturers have max cont power advertised).
View attachment 100003

Aiming for 43hp/lt (35hp out of the Briggs 49) is already at the high-end. A set of new heads optimised for flow at the lower rpm might improve the output but I'm not sure by how much and if it is worth the effort. It would be very nice to try.
Some of those hp numbers led to Briggs being taken to court for overly 'optimistic' power ratings. Even considering that the then SAE standard let them claim up to 20% more than the real number They lost that case. Since then, their engines 'lost' a surprising amount of power... The current SAE standard is with no fan and needs to be within 10% of actual power. Other manufacturers were also playing with their numbers, though I don't know how much. We need real numbers, not advertising BS.
Saying that, 43hp/l is possible, though may be a cooling headache. I favour a modest continuous power and water injection for takeoff/fun to deal with cooling.
 

poormansairforce

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Notice the UL 260 and the Jabiru 2200 are at 40 hp/lt and make their horsepower with low compression ratios. This means they flow well at target rpms and therefore those are the heads we should be imitating.
Actually, those engine numbers are not correct. Based on that the CH1000 would be the head we want to investigate..... assuming those numbers are anywhere is close to correct.
 

WonderousMountain

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I'd suggest keeping the 10mm plugs,
IRL 8mm high life cycle surface gaps
Are surely hard to find. Anyone know
If Kawasaki V-twin uses a forged crank?
 

Hot Wings

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8mm plugs aren't generally stocked at the local auto parts store but are pretty common anymore. The only real problem is the lack of broad heat range.
The bigest advantage of the 8mm is that the socket to remove them is smaller and lets us package things a bit tighter.

Finished todays tasks ahead of schedule. Took a bit of time to redo the ports. The flanges are now stock B+S size and I moved the intake port 90 degrees. This should make manifolding easier for either upright or inverted engines.
I'm only updating one head so the mirror head is not matching.

810 invert block.JPG810 iso.JPG810 air view from outside 'V'.JPG
 
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Vigilant1

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While we are down this rabbit hole: Are the stock valves in the 49 series the best size for the job, or are they (like the head) not-quite-optimum bits from the predecessor 656cc engine? If a from-scratch new head for the 49 series ever does come to pass, a deliberate decision on valve diameter would make sense, especially if there is a suitable candidate out there that would have the right overall length so that the rest of the valve train can remain unchanged.

On substituting parts: I recall the helpful advice in a Jaguar repair manual: "Remember that if factory replacement valve shims for the 3.8 liter engine cannot be found, the shims for a Lotus Cortina are also suitable.” Great! Pep Boys is sure to have those.
 
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TiPi

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I haven't looked too much yet into what the ideal valve sizes would be. I don't think it would be much bigger, maybe a couple of mm. The problem with low rpm engines is to find the balance between intake port size and intake air velocity. A minimum velocity is required to move the fuel and to get the intake column inertia for the cylinder filling towards the end of the intake stroke.
One thing I haven't completely discounted yet (if I don't get the desired output) is the re-doing of the intake ports. The existing port can be removed and a bend similar to your design welded in. I will have access to a MIG/TIG welder once our move is complete, so I might have a go. I have a Vanguard short-block engine on order (P/N 835183), judging by the price, it will be without heads so I will need to get a set of extra heads as well. But I wait till I see this short-block engine (4 months from now).

The power ratings of these industrial engines has always been a contentious issue. I believe Kohler was taken to court as well. The new Kohler ratings (from 2014 onwards) are in line with the B&S rating adjustments.
1596593820079.png
1596593756061.png
 

Hot Wings

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There is plenty of room in the head for larger valves, especially if the center to center distance is moved a couple of mm. But.........

If we are going to stick to 3600 rpm or less what is there is already pretty good. Besides, using the stock parts and then selling the original head saves a little cash, and makes the replacement parts more universal. Would be nice to have an iron bin of junk B+S (and other industrial engine) parts to compare/measure.

Did some checking on B+S pushrods. Seems there are cut to length steel versions available from the racing world. Shortening the stock aluminum intake pushrods is easy. So that means the valve seat face and the combustion chamber roof can both be moved down and maintain stock valve train geometry. This gives more options for combustion chamber shape and helps keep the volume low for higher compression ratio. If one wants lower compression a simple cut of the squish area, like VW did with their low CR heads, is possible.
 

pictsidhe

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Industrials have much larger valves than would be optimum in better ports. Smaller valves in new ports would be the way forward.

Something that I'd likely do if I was going to cast new heads is buy a recent 2 valve car head such as an LS and copy the ports. Stock heads are cheap at scrapyards and from those upgrading to hotrod heads. 2 valve V8 heads are well optimised now.
 

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I haven't done the math...........Won't until I get serious about this. Already probably spent more time on this than I should have for now.

The last VW bug head used 33 intake and 30 exhaust. This is smaller than the previous engines. They made plenty of power in the same rpm range as a stock industrial engine. 810cc is pretty close to half of 1600cc. The Briggs has a slightly lower bore/stroke ratio.

The head I'm using as a pattern has 30mm intake and 27.5mm exhaust. Even smaller than the VW - and VW could have used any size they wanted on the last head. This is one area where even if the theory says there is an improvement, unless it is on the order of 10% or so, it just isn't worth the extra effort.....IMHO.

Something else to consider:
Moving the peak torque up closer to the original 3600 RPM power rating also moves us closer to running on the back side of the torque curve - kind of like flying on the back side of the power curve.
 
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