Is a Diesel Pusher just a Porsche in disguise?

[daveward]

Hi, I'm trying to get to the next level of detail about diesel pushers.  All the definitions and glossary listings mention the rear engine positioning, but none mention the position of the engine, transmission and the drive axle in relation to each other.  My questions are: 1.  Compared to a "normal" passenger car with a longitudinally front mounted engine, like a 60's muscle car, is a diesel pusher''s rearmost-mounted engine pointing frontward or backwards?  I assume it's pointed backwards, like a Porsche 356 or 911, right?  2.  If the engine is pointing backwards, then the transmission is too, right?  3.  If I'm right on questions 1 and 2, then is there a shortie driveshaft linking the transmmission with the drive axle?  I hope someone can clear this up for me.  Thanks.  Dave

 

[Ned]

On a diesel pusher, the engine is mounted behind the drive axle so the transmission is forward of the engine and behind the axle.  The drive shaft is very short as you would expect.

It doesn't have quite the performance of a Porsche, however

 

[Gary RV_Wizard]

And there are diesel pullers too, called a FRED (FRont Engine Diesel) and available from Tiffin (allegro) and others.  And shortly there should be a gas pusher - Workhorse has a chassis that accepts either gas or diesel in a reae engine configuration. The diesel version is out now and the gas version due later this year.

 

[daveward]

Thanks for the quick responses...they help quite a bit.  Could you verify for me that the engine is in fact pointing rearward, meaning the radiator fan is bringing up the rear...right?  Also, with that heavy engine/trans assembly hanging off the back, doesn't that create a rear-heavy weight distribution situation?  I imagine that could contribute to a feeling of light steering, if that's possible on a beast like a diesel pusher.  Would that be so?  Thanks again.  Dave

 

[Tom]

Could you verify for me that the engine is in fact pointing rearward, meaning the radiator fan is bringing up the rear...right?

Yes, the engine is facing rearward. However, in our case, the radiator is side mounted although some coaches have rear mounted radiators.

 

[29er]

Dave: Your thinking of the fan bringing up the rear may not be correct. An arrangement like that might clog the exterior of the radiator pretty darn quick (more like put a paste on the cooling fins).

Or I could be wrong. (Cat 330 - radiator is last)

 

[rhmahoney]

Wt distribution is well compensated and handling is near effortless. I hav edriven Country Coach, Hawkins (now defunct), Monaco, Foretravel.

 

[BernieD]

Dave

I'm not sure what you are trying to prove with the Porsche comparison. It sure isn't to get around corners faster. The rear pusher design has a number of advantages. The front axle can be placed farther forward, increasing the wheelbase. The rear axle can be placed closer to the rear of the coach, reducing rear end swing out on turns and extending the wheelbase. when properly designed and maintained, the shorter drive shaft can reduce power loss of a longer drive shaft. And having the weight of the engine over the drive wheels give better road contact. On the other hand, the Porsche, and VW, engines are flat, and have horizontally opposed cylinders. Diesel pushers have in-line 6 cylinder engines. The diesel engine may weigh as much as the whole Porsche car, but the ratio of torque to hp is much higher for the diesel.[/font]

 

[Gary RV_Wizard]

doesn't that create a rear-heavy weight distribution situation?  I imagine that could contribute to a feeling of light steering, if that's possible on a beast like a diesel pusher.  Would that be so?

Yes, a DP is heavier in the rear. But so is a gas front engine chassis - it's just a matter of degree. DP's have the heavy generator mounted in front to offset the engine weight, whereas front engine rigs mount the genset in the rear for the same reason.  Whether it is light in the front is a matter of design, floor plan and cargo loading on any individual coach, but generally this is not a problem.  It is, however, to weigh the rig occasionally to make sure you are not exceeded axle capacity, especially in the rear. You need the axle (or better yet, individual wheel) weights to properly set the tire inflation anyway.

Coaches have dual wheels and even tag axles in the rear to carry the weight - you can't do that in the front! So by design, more weight is distributed to the rear because that's where it is feasible to carry the load.

 

[daveward]

I'm not trying to prove anything with the Porsche references, I just find it useful to use real-life and fairly well-known examples when comparing/describing things.   

Anyway, as I mentioned in my initial post, I'm just trying to gain some knowledge about the diesel pushers without finding one to lay under.  These responses have been quite useful.  Thanks again.  Dave