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

[TiPi]

I was a member of that group, then I wasn't, and now I can't even find it in Facebook. The guy who set it up did not seem to know what he was doing, but it did have some good information.

V-Twin aircraft conversions.

www.facebook.com

 

[Protech Racing]

Part numbers for cams .springs, total head CC chamber sizes etc will be helpful.

 

[itggouveia]

Good evening All,

I was following your thread and though it is a Briggs thread, I didn't see anybody bring up the Kohler V-Twins. They have a pro series for the 600-700cc series and the big V-twins 980 to 1000cc. They appear to be more robust and seem to be more favored by the industrial/commercial mower and garden crowd. There is also a large following in the tractor pull arena where they use lawnmower (barely) to pull small sleds. Kohler also posts the service manuals online for rebuilding the engines. Kohler also posts dyno-ed power output - attached below

Here are a couple of links for performance parts and lightened flywheels.

Midwest Supercub - Catalog

Lakota racing - Lakota Racing

I am building a Quad City Challenger and plan to use a 25 HP motor and a 38HP motor as test beds - 25 for ultralight broomstick flying, then upgrade to the 38 HP for Light sport when I get tired of the UL limitations.

I am seriously looking at the Ace Aviation Redrives due to their cross compatibility between the 25 and 38 hp motors ( the bottom pulley appears to be the only difference due to the 1" straight shaft and the 1 1/2" taper shaft).

Does anyone have any feedback on these redrives or direct comparison between B&S or Kohler motors?

 

[karmarepair]

Good evening All,

I was following your thread and though it is a Briggs thread, I didn't see anybody bring up the Kohler V-Twins.

Some links:
Search results for query: Briggs TiPi has done a lot of comparison. This post in particular has a useful comparison. B&S 49-series (810cm3/49ci) - TiPi's conversion for aircraft use

For the same displacement, a Kohler will be a little heavier, and has a cast iron crank and a hollow cast iron cam, and will be a few kG heavier than a Briggs. Kohlers, as you've noted, have more hop-up gear available.

The scuttle butt on the Ace redrives is they take forever to get, but they are well machined, and if you're OK with NO torsional isolation, they are as good as anything comparable on the market. They drive from the PTO end. Use the lightest possible flywheel or NO flywheel to avoid breaking the crank from two big rotating masses on either end of a cast crankshaft. But nobody makes the flywheel we'd really like - low moment of inertia, but WITH magnets for both ignition and charging and a starter ring gear. If you're OK with a direct drive, the SD people in the Czech Republic will sell you the demon tweaks you need to build up a Kohler from a domestically sourced CH25-CH750 engine. I have a CH25 I plan to put on a test stand, but my progress has been very slow, finishing my Sonex has a higher priority. I post in IO.Groups when I have something to say. Small-4-stroke-engines groups.io Group

The big block Kohlers have bupkus for hop-up stuff. The big block Briggs has taken over the mud boat market completely, and I expect to see lots of stuff available for them in the next few years, but right now there is not much, in part because you can buy an EFI engine from the FACTORY set up to run up to 4500 RPM with a year warranty, so why bother taking it apart?

There are several Koher threads, use the search function to find them, or oh hell, here: Search results for query: kohler

 

[Herbgh]

The word on the Big Twin conversion is that the fan and shroud must be kept. The engine overheats and the head will be damaged; typically a burned exhaust valve...I have a friend who had one on a pusher , Thunder gull....Guessing they are ok in Tractor? Both experiences I know of were used in Pusher config..
I have one of the 1 liter Generac's . Its off of an 18kw home back up generator..Like new...and for sale...

 

[itggouveia]

Thanks for the responses, I will take a look at those

 

[Ken Powell]

Does anyone have the weight for the Briggs 993 EFI-motor flywheel and starter? My minimax 1600R is ready for cover and I would consider the 993 direct drive without the flywheel by running a ford Edis-4 or GM 4-pin HEI ignition along with no starter if I could get the 993 under 100 lbs. Use 2 pickups for the ignition - one set at 12 degrees and the other at 28 degrees. Hand prop with the 12 degree pickup then switch to the 28 degree pickup when running. This might save as much as 30 pounds from the engine (20 lb for the flywheel and 10 lb for the starter - ignition weight is a wash). Everything depends on the weight of the flywheel.

Also, I'm assuming that the flywheel is not a balanced part of the rotating assembly and can be removed. Is this true?

 

[TiPi]

The flywheel is not part of the crank assy durign balancing so it can be modified or removed.
I don't have the exact weight of the flywheel for the 61-series but the 49-series flywheel is 6.8kg.
Removing the flywheel will also remove the alternator. It can be replaced by a lightweight magnet holder of the same dimensions as the original alternator magnet ring. Replacing the alternator with a small motorbike alternator won't work as the engine doesn't rev high enough, so you would need to keep the original alternator stator and find a way to mount the magnets on a lightweight carrier/ring.

 

[Ken Powell]

Thanks for the reply. I have been following your conversion and would probably go in that direction if we could get 35HP out of the 810 with direct drive. I wonder if the 810 could make 40+ HP at 4500 RPM using a redrive? I have questions about the 810 due to the restrictive porting. The Honda iGX800 (788cc) is also temping even though you would have to scrap the ignition system if you used a redrive and spun it up to 4500 RPM. Whatever engine I use will drive from the PTO shaft and the flywheel will be removed.

 

[TiPi]

Thanks for the reply. I have been following your conversion and would probably go in that direction if we could get 35HP out of the 810 with direct drive. I wonder if the 810 could make 40+ HP at 4500 RPM using a redrive? I have questions about the 810 due to the restrictive porting. The Honda iGX800 (788cc) is also temping even though you would have to scrap the ignition system if you used a redrive and spun it up to 4500 RPM. Whatever engine I use will drive from the PTO shaft and the flywheel will be removed.

35hp out of the 810 is a stretch (my goal), requiring quite a bit more work. If my 20% flow increase so far do translate into the same increase in torque, I will get 33hp. To get more might require a bit more work on the heads (intake ports at a 45deg angle to the seat instead of nearly 90deg). I now have the milling machine to do it so w'll see.
The 810 would make 40hp at 4,500rpm, but the rods would need to be replaced with billet ones and possibly another cam and valve springs. The re-drive will add a lot of weight as you need to keep the flywheel, or at least a lightened or an alu version.

 

[Stuffengineer]

I think the big block Briggs flywheel is 19lbs. I will confirm when I get out to my shop. Have one laying there.

 

[Stuffengineer]

TiPi mentioned the alternator issue. The EFI system will also require a crank position sensor and 23 tooth trigger wheel. Not sure how the ECU will react with a different ignition timing that it is not controlling.

 

[Ken Powell]

I'm going to ditch the starter, stock EFI and ignition. I plan to use either a Ford Edis-4 or a 4-pin GM HEI for ignition. Two pickups will allow for a retarded timing for hand propping and a 28 degree advance for max power. If that 993 flywheel weighs 19 lbs then this project will be a 'go'. I haven't decided whether to use an alternator system or a total loss ignition. We are talking about a MiniMax so endurance is not real important. A low-voltage warning like this one make a total loss ignition practical - LowBat 12v Low Voltage Monitor and Alarm LOWBAT-XL. A wind driven alternator would also be easy.

 

[Stuffengineer]

TiPi mentioned the alternator issue. The EFI system will also require a crank position sensor and

I'm going to ditch the starter, stock EFI and ignition. I plan to use either a Ford Edis-4 or a 4-pin GM HEI for ignition. Two pickups will allow for a retarded timing for hand propping and a 28 degree advance for max power. If that 993 flywheel weighs 19 lbs then this project will be a 'go'. I haven't decided whether to use an alternator system or a total loss ignition. We are talking about a MiniMax so endurance is not real important. A low-voltage warning like this one make a total loss ignition practical - LowBat 12v Low Voltage Monitor and Alarm LOWBAT-XL. A wind driven alternator would also be easy.

Will you run twin Mikuni’s? The 20amp John Deere style alternators are light. Have you considered a aluminum flywheel to run standard Briggs mag ignition? Might be lighter than the edis as it still needs crank sensor and control.
Should be interesting

 

[Ken Powell]

I will probably run two 32mm Keihins because I have so much brass (jets and needles) to dial in the jetting but I have an extra 38mm Mikuni on the shelf. I'm open to the ignition side but lightness is important since the 993 weight is the upper limit for a minimax 1600R (really need to keep the engine weight under 110 lbs with under 100 lbs better). I can make the Max a flat rear deck instead of a fastback and not use a cowling to save weight to manipulate the weight and balance.

 

[Stuffengineer]

I will probably run two 32mm Keihins because I have so much brass (jets and needles) to dial in the jetting but I have an extra 38mm Mikuni on the shelf. I'm open to the ignition side but lightness is important since the 993 weight is the upper limit for a minimax 1600R (really need to keep the engine weight under 110 lbs with under 100 lbs better). I can make the Max a flat rear deck instead of a fastback and not use a cowling to save weight to manipulate the weight and balance.

8.2 kg flywheel
3.2 kg starter

 

[Ken Powell]

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.

 

[BBerson]

What does the 993 Briggs weigh stock out of the box with flywheel and starter?

 

[Ken Powell]

Briggs claims 125 lbs. I hope Stuffengineer knows; he is the only guy on the internet who seems to have any numbers.

 

[Stuffengineer]

Briggs claims 125 lbs. I hope Stuffengineer knows; he is the only guy on the internet who seems to have any numbers.

Out of box it’s 125. If I get a chance tomorrow I can strip one down and get the weight for one converted. Regarding horsepower they are 40hp at 3600. The marine version has a high rev kit and gives 46hp at 4750rpm.