Cummins repower

[martin300662]

There have been several threads on swapping to diesel power, most typically using the Isuzu or Cummins 6 cylinder (5.7 or 5.9L) engine.

For me the main driving would be fuel consumption (others may have different priorities), but these 'donkeys' whilst being better than the small/big block motors in our MH they aren't designed for fuel efficiencies.

So I started looking at alternates, and have gone through LPG (same mileage cheaper price for fuel), modern diesel (Mercedes and BMW diesels fit but have massively complex engine management systems that need to be replicated), older/better diesels (no better than a Isuzu/Cummins), a modern petrol (Ecoboost 3.5L with 10 speed) and even EV (price is currently north of $100K). But it seems the easiest way to achieve my fuel consumption objective is to use something available 'off the shelf' ie a Cummins R2.8 (a little 2.8L 4 cylinder turbo intercooled, https://www.cummins.com/engines/repower) and a Quick Draw transmission to a standard Chevy transmission.

Anyone else considers this swap - I am worried when things look to good to be true, they probably are!

[uncle_bob]

Hi

161 HP and 310 foot-pounds isn't all that far from the power plant in a "modern" AS MH. I think the net result will depend a bit on just what "standard Chevy transmission" you go with.

Bob

[martin300662]

Originally Posted by uncle_bob

Hi

161 HP and 310 foot-pounds isn't all that far from the power plant in a "modern" AS MH. I think the net result will depend a bit on just what "standard Chevy transmission" you go with.

Bob

Its actually almost identical to the original 350 in Bella, although a little lower than the 454 in Peanut. However the torque curve is steeper and peaks much lower.

Certainly Bella has no shortage of get up and go so I'm not worried on that front.

Its a good point about the transmission as the early 350 only came with TH400 (replaced with a TH475 if the 454 was fitted) but Bella has the GV overdrive to reduce the revs when cruising. Maybe it will also need a taller rear end gear.

[uncle_bob]

Hi

These "bicycle" transmissions with their 6 to 10 speeds ( on an automatic trans no less ...) are a big change from "back in the day". They most certainly help get a good level of performance out of the modern engines. I would at least look into it ....

Bob

[martin300662]

Understood, but the R2.8 is designed specifically to use the original transmission under the 're-power' badge. That said all the extra ratios do is add more steps between lowest and highest ratio so allow the engine to stay in the appropriate rev range, and the under/overdrive of the GearVendors does that as well (gear splitting) so the biggest issue is the rev range of the final drive. Currently the final drive is selected for a higher reving petrol engine not a low torque diesel.

[jeffmc306]

Martin, I watched the video on the Cummins site - they did their homework and put together quite an impressive package.

I’ve had two VW diesels, a 2 liter four and a 3 liter six and both had plenty of grunt thanks to the torque. Let us know if you decide to go ahead with it!

[Boom Sounds]

Has that Cummins 2.8 got enough grunt to power my 250?

I know it bolts onto the 4L80E.Do you think you could get 30mpg out of a UK Gallon with that set up?

I suppose I would be concerned about the number of European cities who are banning diesel but an interesting option nevertheless.

[martin300662]

Originally Posted by Boom Sounds

Has that Cummins 2.8 got enough grunt to power my 250?

I know it bolts onto the 4L80E.Do you think you could get 30mpg out of a UK Gallon with that set up?

I suppose I would be concerned about the number of European cities who are banning diesel but an interesting option nevertheless.

This is the 'magic' of modern engines. It maybe a 2.8 but has the same HP/more torque than Peanuts 454 and more than HP and torque than Bella's 350. It is actually very similar to a old school Cummins 6BT (torque curve much lower than a gas engine) and more than a 4BT (which is 3.9L).

Its not going to have more grunt, just achieves that from an 'auto sized' 4 cylinder so has much better fuel mileage and is much lighter.

The biggest challenge is 'I dont think it has ever been done' so all of this is 'one paper' not proven.

My logic around the number of cities banning diesels is simple.....I wouldn't want to take Bella/Peanut into the city anyway, I would be leaving it and using public transport/rental car, none of the European cites can cope with a 8ft 6in wide vehicle anyway.

[martin300662]

Quick update.....

Basically using an approach to simply swap in a R2.8 is not going to achieve what I want. The issue is it will still be spining the same rear drive ratio (we think it is a 4.10) which means even with the GV overdrive (0.75/4th gear) it would be, as described by the shop I approached to do the swap, "reving its nuts off".

His recommendation would be couple the engine swap with a big reduction in drive ratio and live with the fact Bella will not compete in a traffic light Grand Prix, but use the torque to accelerate but also keep the revs low on the highway, as the R2.8 has more torque near tickover than the current 350 has at 3000revs. His charts showed I could drop to a 2.73 final drive ratio with the diesel.

However he did make an important observation, if I am changing final drive ratio and relying on increased torque/low engine revs I can get that with an appropriately built stroker conversion/EFI/electronic ignition to the 350 and stay with the 'gasser' and his feeling is a low rev'ing 383 could easily achieve 18-20mpg again with the 2.73 final drive swap (although I'm not sure he is fully accounting for the 'pushing a brick through the air' aerodynamics of a motorhome!

Then he started talking about 5th gen LT1/8L90E Connect and Cruise engine swaps to match the 2.73 rear drive ratio and my mind glazed over!

[martin300662]

Just for giggles, I ran the numbers and a LT1/8L90E/2.73 final drive would give a 165mph top speed if it could pull to the red-line.

Bonneville here I come!

[bkahler]

Originally Posted by martin300662

stay with the 'gasser' and his feeling is a low rev'ing 383 could easily achieve 18-20mpg again with the 2.73 final drive swap (although I'm not sure he is fully accounting for the 'pushing a brick through the air' aerodynamics of a motorhome!

18-20mpg will never happen, even with an imperial gallon. If it was that easy to get that kind of mileage manufacturers would have been all over that option.

Just my $0.02 of course

[mikeajana]

My opinion, gearing is the focus.

I recently put a Cummins 12 valve engine in a Ford Excursion. It's an awesome setup, but fuel efficiency was not my primary objective.

The project included an Allison 1000 transmission to tie everything together and I am immensely impressed with it. A final drive ratio of .61 and 6 speeds is key.

I'm still trying to determine a plan for our 24, other than a 20 foot replacement, but an Allison 1000 is going to figure heavily.

[martin300662]

I agree Mike but I think final drive ratio is the critical factor, as well as having enough ratios to keep the engine revs in the most appropriate part of the torque curve.

Something has got to give as current fuel prices in the UK are $9 a gallon or putting it another way nearly a $1 a mile.