# GM 1.6l Turbo Diesel (LH7)

### Help Support Homebuilt Aircraft & Kit Plane Forum:

#### ivanhoyt

##### Member
I want to be able to use a production automotive engine with 100+ hp at 2700 rpm. I'm a proponent of keeping things as stock as possible. In my research I run across the LH7 GM turbo diesel and after looking at the hp/torque/rpm (dyno) chart, I wondered if this could be used to driving a prop directly off of the flange end of the crank through a BMW drive shaft vibration damper. The prop hub would require its own bearing, of course. One concern is the low placement of the crankshaft which would create a ground clearance problem for the prop. If there was a way to run this engine upside down it would resolve that but my goal is to keep it stock. Definitely not a stock situation (-;

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Inverting the engine is not usually treated as a big deal. Steve Wittman had plans out there for inverting the Buick/Rover aluminum V8.

One way is to use the valve cover as the sump, probably having to enlarge it and including an oil pickup to the oil pump.
Another way is to run a scavenge pump to evacuate oil from the valve cover to a remote tank, and connect the oil pump to the bottom of the tank.

Nothing about injection systems is messed up by inverting the engine.

The biggest issue I see is that air and gyroscopic loads from the prop must be carried. Air loads on the prop shaft are thrust and P-factor. There are ways to estimate these. Gyroscopics will require estimation of prop mass moment of inertia, prop speed and rotation speed in pitch and yaw axes. Try to be cognizant of pitch-yaw rotation speed due to control movements, spin entry, snap rolls, etc. Once you have a pretty good idea of what your airplane are, you can design the bearing set and propshaft. Take a look at the old Sport Aviation articles on Steve Wittman's Buick V-8 adaptation.

Billski

#### ivanhoyt

##### Member
I was envisioning this engine in a pusher configuration. with an aluminum plate bolted to the block / flywheel housing. a BMW or like driveshaft damper between the crankshaft flange and the bearing assembly / prop flange capable of handling all the loads mentioned above. This assembly would be bolted to the aluminum plate through appropriately sized spacers. The only force placed on the crankshaft would be the rotational force normal to the automotive application.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
It could work. You will still have to size engine side inertia based upon the spring rate of the Giubo chosen, prop inertia, and shaft spring rate, then set your min idle speed high enough above resonance to be safe.

#### galapoola

##### Well-Known Member
That torque looks nice and flat were you'd be using it. Can you shed some auto accessories to trim the 250# weight?

#### Rik-

##### Well-Known Member
I would not use a BMW Guibo connector. They are a failure point on the cars.

Take a look at something substantially stronger that we use in the boating world.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
I would not use a BMW Guibo connector. They are a failure point on the cars.
Lets put this perspective. In RWD manual trans cars, first gear is about a 4:1, and you can raise the revs and drop the clutch. Conservatively, a Giubo on the drive shaft an be subjected to 8 times max engine torque. If it is on a half shaft, it can be around twice that again (multiply by final drive ratio, divide by two for there being two torque paths). Say you have 200 ft-lb, that is 800 ft-lb for the driveshaft or 1600 ft-lb on a half shaft. Yeah, wheel slip will cap it some, but a 3500 pound car will hit tire limits around 1000 ft-lb per tire or around 500 ft-lb on the driveshaft. In an automatic, max possible torques are similar. That driveshaft Giubo will be safe at 2.0-2.5 times more torque than this 1.7l Diesel will make, and a half-shaft giubo will be safe at somewhere around 4-5 times the nominal torque.

Yes, a much more serious analysis is appropriate, but I suspect that the driveshaft gadgets will be fine on strength, and we already know some of them have about the right spring rate for isolating the engine torsional vibe from downstream components.

On the Teton Aircraft project, we had the boat drive devices and I modeled them to include them in our analysis. Pretty stiff. Let's remember that the gadget is supposed to be a springy element...

Billski

#### Rik-

##### Well-Known Member
Lets put this perspective. In RWD manual trans cars, first gear is about a 4:1, and you can raise the revs and drop the clutch. Conservatively, a Giubo on the drive shaft an be subjected to 8 times max engine torque. If it is on a half shaft, it can be around twice that again (multiply by final drive ratio, divide by two for there being two torque paths). Say you have 200 ft-lb, that is 800 ft-lb for the driveshaft or 1600 ft-lb on a half shaft. Yeah, wheel slip will cap it some, but a 3500 pound car will hit tire limits around 1000 ft-lb per tire or around 500 ft-lb on the driveshaft. In an automatic, max possible torques are similar. That driveshaft Giubo will be safe at 2.0-2.5 times more torque than this 1.7l Diesel will make, and a half-shaft giubo will be safe at somewhere around 4-5 times the nominal torque.

Yes, a much more serious analysis is appropriate, but I suspect that the driveshaft gadgets will be fine on strength, and we already know some of them have about the right spring rate for isolating the engine torsional vibe from downstream components.

On the Teton Aircraft project, we had the boat drive devices and I modeled them to include them in our analysis. Pretty stiff. Let's remember that the gadget is supposed to be a springy element...

Billski

Your little example is cute but a very very small amount of power and the rubber guibo hates oil and heat. Been through those enough to know that I don't want to use some cheap ass BMW part when there is a far stronger and simpler item available for like  and being every pilot is a cheap ass, why are we even discussing this?

#### Dana

##### Super Moderator
Staff member
Lighten up Rik, Billski was just explaining that the guibo is loaded a lot less than it would be in a car driveshaft, so failure is a lot less likely, and that the "far stronger" boat version is also far stiffer, defeating the purpose.

#### lelievre12

##### Well-Known Member
HBA Supporter
Certified TDi aero conversions use dual mass flywheels to soften the more severe Diesel crank pulses (eg Thielert/Continental/Austro). Any coupling of a direct drive or PSRU should therefore connect to this flywheel and not the crank itself.

All the prop loads and the coupling have to be contained with their own bellhousing downstream of the flywheel which makes things a bit more complicated than you might like.

Last edited:

#### rv6ejguy

##### Well-Known Member
HBA Supporter
I've owned 5 BMWs, one oil soaked guibo was going bad at 350,000km of very hard driving and track use. The ones on the other 4 cars look like new still. 2 of these cars have been tracked also and all driven hard on the street but I don't do burnouts. Pretty robust parts from my experience. The SPG gearboxes all use these and they seem to work fine.

#### ivanhoyt

##### Member
That torque looks nice and flat were you'd be using it. Can you shed some auto accessories to trim the 250# weight?
Not sure yet but it would be great if I could.

#### ivanhoyt

##### Member
Certified TDi aero conversions use dual mass flywheels to soften the more severe Diesel crank pulses (eg Thielert/Continental/Austro). Any coupling of a direct drive or PSRU should therefore connect to this flywheel and not the crank itself.

View attachment 116350

All the prop loads and the coupling have to be contained with their own bellhousing downstream of the flywheel which makes things a bit more complicated than you might like.

#### ivanhoyt

##### Member
This particular diesel engine is called the "whisper diesel". Supposedly the fuel injection happens in multiple pulses thus minimizing the sharp vibrations typical of diesels.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Certified TDi aero conversions use dual mass flywheels to soften the more severe Diesel crank pulses (eg Thielert/Continental/Austro). Any coupling of a direct drive or PSRU should therefore connect to this flywheel and not the crank itself.

View attachment 116350

All the prop loads and the coupling have to be contained with their own bellhousing downstream of the flywheel which makes things a bit more complicated than you might like.
Remember the "soft element" I keep talking about to bring the system natural frequency down? This is one of them that is being used in cars and trucks with manual transmissions.

The part with the ring gear on it (you can only see a little of it) is bolted solidly to the crankshaft, and accelerates with every bit of motion the crankshaft has.

The part closest to us is sprung and thus isolated from firing pulses. Normally the clutch cover (pressure plate assembly) is bolted to the threaded holes around the periphery, while the friction material contacts the large smooth flat area that runs around the middle area.

This assembly is the current production soft elements, so were easily sourced with the engine once the aero engine maker had confirmed that the soft element appropriately lowered the first natural frequency of the system in the airplane and also confirmed that other modes were not dragged in. They might have selected different springing for aero use than would be used with the particular road vehicle engine. Mix and match works too.

Billski

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
I want to be able to use a production automotive engine with 100+ hp at 2700 rpm.
You said 100+hp, 2,700 rpm, GM L-something-or-other with a BMW vibration damper (ausgezeignet!), but all I heard in my own head after that was Corvair.

These specs (sans Deutsch damper) been woked out and demonstrated with reliability, but kudos should you choose to blaze a differnent trail that takes you to the same destination.

#### mm4440

##### Well-Known Member
I've owned 5 BMWs, one oil soaked guibo was going bad at 350,000km of very hard driving and track use. The ones on the other 4 cars look like new still. 2 of these cars have been tracked also and all driven hard on the street but I don't do burnouts. Pretty robust parts from my experience. The SPG gearboxes all use these and they seem to work fine.
Porsche used one on their aircraft engine.

#### ivanhoyt

##### Member
You said 100+hp, 2,700 rpm, GM L-something-or-other with a BMW vibration damper (ausgezeignet!), but all I heard in my own head after that was Corvair.

These specs (sans Deutsch damper) been woked out and demonstrated with reliability, but kudos should you choose to blaze a differnent trail that takes you to the same destination.
Not a Corvair but an inline 4 cyl Turbo Diesel. I would be interested to find out about anything aeronautical done with this particular Diesel engine. No need to re invent the wheel.

#### wsimpso1

##### Super Moderator
Staff member
Log Member
Not a Corvair but an inline 4 cyl Turbo Diesel. I would be interested to find out about anything aeronautical done with this particular Diesel engine. No need to re invent the wheel.
Please use the Advanced Search Tool and start typing. Diesel Gazaile brought up hundreds of posts from a multitude of threads, like these;

When you ask folks for something that has already been talked to death, most of the knowledgeable folks on the topic don't even look twice. Once you find the existing threads on the topic, you can learn tons. Then when you have more specific questions, post a new thread and look for results.

Now I am going to give my \$0.02:

Any car engine in direct drive will need a prop shaft with bearings. Folks flying Volkswagen and Corvair and other engines in direct drive have found out the hard way that you can not hang a prop on a car crankshaft and expect it reliable performance. The prop produces bending moments in the end of the shaft that it will not usually stand for long. P-Factor and gyroscopics. Both can be calculated pretty easily and have been talked about plenty. You can EITHER look up the various VW and Corvair suppliers for us airplane nuts and learn what they did to beef up the cranks and bearings at the output end, OR go for a shaft and a pair of bearings and a housing attached to RFOB, and they all have to carry all the thrust and moments and be sized and designed for long life. Both are daunting exercises. The VW and Corvair guys have gone custom crankshafts and bigger plain bearings and such. The inverted V-8 guys (Steve Wittman et al) went with an extension and bearings and clutch hub spring sets.

Getting perfect alignment between the prop shaft and the crankshaft is tough to achieve if you go the Steve Wittman way. You will likely need some compliance between prop shaft and crank shaft.

Once you have a shaft, you also have some torsional compliance and now the natural frequency between prop and engine side inertia with will likely be inside the range of firing frequencies during engine running. If so, you will need a soft element between engine and prop shaft to bring the first torsional mode safely below idle firing frequency. There are ways in the vibration textbooks to calculate the range of needed spring rate. This is where the radial/axial misalignment device can also be a soft spring for torsion. A flywheel on the crankshaft with a manual trans clutch plate bolted in or a manual trans dual mass flywheel are usual paths. Spring rates and inertia must all go into some math to figure out what engine side inertia you will need with the available spring rates.

Now if somebody has already plowed this field, great, lets hear part numbers for the soft elements and bearings and shaft dimensions, etc. Or let's see the crankshaft end dimensions and bearing part numbers used there.

Billski