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Why is engine and gearbox inclined?

Why is engine and gearbox inclined?

Why is engine and gearbox inclined?

Do some or all cars have the engine and gearbox at an incline of a few degrees? If so then why? Is it purely to get the engine and gearbox into better positions to fit in the car or is there more to it?

I've only worked on two cars in my life but both seem to have them inclined. I'm now building a custom chassis and wondering if I should do the same. There's zero fall (gradient/slope) in the sump of the Lexus V8 engine that I'm using, where the shallow area of the sump lets the oil flow to the deeper end of the sump, and I'm wondering if the incline of the engine is what's supposed to create the fall, so I need to mount my engine at an incline in the new chassis?

RE: Why is engine and gearbox inclined?

The incline is there to reduce the size of the driveline hump in a passenger car.

Mike Halloran
Pembroke Pines, FL, USA

RE: Why is engine and gearbox inclined?

It is to maintain the correct angle to the differential pinion which will always be lower than the center line of the engine since it is usually below the centerline of the rear axle centerline. Of course things are a bit different on the independent rear suspension type cars. I was mostly referring to straight axle arrangement's as found in some SUV's and pick up trucks.

RE: Why is engine and gearbox inclined?

The diff pinion is usually below the axle centerline because hypoid gears (non-intersecting axes) have become nearly universal in cars and light trucks. Hypoids are quieter, and I think stronger, than bevel gears or spiral bevel gears (intersecting axes), and they're in volume production, so they're cheaper than doing anything differently. Hypoids were invented in the interrest of packaging, like Greg says. Even aftermarket intake manifolds for carbureted front engine/ rear drive cars come with an angled carburetor flange. Fuelies don't care.

I have a big SUV with IRS. I think the axle is a hypoid, partly so that the third row seats can fold into the floor.

In a custom car, you have the option of mounting the engine with the crank level, but you may end up with a tall tunnel in the floor pan, and the driveshaft may be above the input flange to any axle you can scrounge, unless you go for an antique part.

Mike Halloran
Pembroke Pines, FL, USA

RE: Why is engine and gearbox inclined?

Lots of useful info there. I had also wondered about the rear axles where the axis don't intersect.

I did notice in my Suzuki Vitara (Sidekick/Tracker some parts of the world), the incline of the engine/gearbox lowered the rear driveshaft and hence lowered the driveshaft angle and wear on the driveshaft UJ bearings.

RE: Why is engine and gearbox inclined?

dicer, given that the angle of the diff nose is easy to set, that is scarcely a consideration. OK I have worked on a car with leaf springs amd torquey engines where we couldn't install the diff at the right angle as it would have hit the floor on WOT, so if we were worried about driveline angles we would have tilted the engine to compensate. But that's a pretty unusual case. Designing the driveline angles when we used to use Hooke's joints throughout was tricky.


Greg Locock

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