Why are people scared of big blocks.

[Ziegelsteinfaust]

A friend i did a side job with. Told me a friend he has got a older RV that he, and his wife plan to restify. Not sure what it meant, but probably keeping the 70's charm on the outside. Then polish up the interior.

The 454 runs fine according to the story, but he wants to get rid of it for better mpg. By installing a 350 that will have a few nice things. I get it if a Cummins was installed better mpg would be assured.

The RV is a huge Winnebago box. It is litterly square. There will be no mpg to speak of. With the big block it will get 8-12 depending on terrain, and no small block will do better. The load is to great on the engine at just highway speed, and it is a lot to overcome.

Personally I would do the bolt-ons to the 454, and tune it. Or maybe add efi of some kind to get it started to better reliability. Then if I like the RV a lot I would add a 4L80E, and rear end regear to match the combo.

Are my friend, and I right he is crazy to replace a running 454 with a 350 in a RV?

[cwcarpenter98]

I would think that the factory built the RV using the 454 for a reason. Might just be me though

[weq92f]

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Depending on the specifics of the RV in question, folks may find it a major effort to remove the existing engine regardless of its displacement! In some cases it seems they built the RV around the power plant with no regard to future R&R activities!

-klb

[Ziegelsteinfaust]

Originally Posted by weq92f

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Depending on the specifics of the RV in question, folks may find it a major effort to remove the existing engine regardless of its displacement! In some cases it seems they built the RV around the power plant with no regard to future R&R activities!

-klb

I helped a friend years ago along with a few others tear apart of 1/2 rotted 24 footer roughly to get the industrial 440/727 out of. It was a insane amount of work to get rid of the rv body portion. The engine while would be a big pita to remove with out destroying the RV if needed. Compared to a traditional car or truck. It would however not be unreasonable if one purchased or rented the needed equipment. Then removed the front axle to make it all easier.

So I don't see why this guy is hot to do the swap unless absolutely needed.

After we cleaned up my friends driveway I asked him if it was worth it. Pretty much his exact words were I have $1500 in it with the rv, dumpster, and you guys. Its not worth it now, and it better be when I drop then engine in tomorrow.

He had a D100, and it was already for the swap. With most of the nessacary parts already bought.

[Steeveedee]

Originally Posted by weq92f

.
Depending on the specifics of the RV in question, folks may find it a major effort to remove the existing engine regardless of its displacement! In some cases it seems they built the RV around the power plant with no regard to future R&R activities!

-klb

Pretty much. Some are delivered as a "Chassis-Cowl" and then the body gets dropped on. The only way I'd take the engine out is if the body was rotten.

[Dead Parrot]

Some things want torque. Like large heavy vehicles. Very possible that the 350 will give worse mileage due to having to spin at higher rpms all the time. Depending on what is meant by 'older', 8~12mpg is probably overly optimistic.

Another vote for keep the 454 and apply a few modern updates.

[special-K]

We don't know the size of this one, but as they get bigger they go to big block

[67ChevyRedneck]

I'd leave it alone. I have a 2015 Silverado and by the time you put a trailer behind it to match the weight of the RV it's only going to get 10-12 mpg. Unloaded I average 15 city and can get 22-24 highway, but all the extra weight is a mpg killer. That's also a 6 speed with 2 OD gears and EFI.

Plus, it's like a giant brick.

I agree about the only thing that would improve mileage is something like an older Cummins and OD swap.

[mongocanfly]

I also think he will regret it...my C30 came with a 350... my buddy's square dually had a 454...we both got under 10mpgs empty...but he could leave me in the dust when we were loaded...the bb just kept pulling....
Any kind of engine swap wont come easy..

[LS short box]

I'm a big time LS guy but I agree with above you need torque to move that RV. It has all the aero of a brick. If he puts in the 350 he will have that gas pedal buried most of the time. Unless there problems with the big block I would do basic maintenence and let it buck. Buy the time they build or buy a 350 that money will buy a lot of gas.

[1976gmc20]

Just pulling my little camper trailer upwind to the mountains dropped it down to about 7 mpg! That's with a 350 and SM465. That pickup used to get 15-18 empty.

[gvw5400]

Years ago I work for a RV rental / sale dealer. On 31 foot class A motorcoaches the gas mileage was the same on 454's with a T- 400. 8 to 9 with a Q-jet or TBI.
But when you had a 454 with TBI and a 4L80E mileage was 10-11.
The 21 foot Class C motorcoaches with a 350 TBI and a 4L60 mileage was 9-10.
Just leave the 454 installed. The cost per mile will never break, even let alone save costs.
All the Best,
Dirk

[truckster]

You might get away with a small block in a smaller class C motorhome. If you put one in a class A motorhome you'll be hating life.

I've owned motorhomes with Chevy 454s, Ford 460s, and now a Cummins 6BT 12 valve. You might get 12 MPG out of that big block... coasting downhill with a tailwind. On cross-country trips, my 36 and 40 foot big block rigs averaged right around 6.5 MPG. My Cummins (also in a 40 footer) averages about 9.5, but the Allison AT545 has a lot of slip in the TC.

Replacing the big block with a small block would be a huge mistake, and as others have said, it would be an absolute nightmare of a swap.

[Ziegelsteinfaust]

Originally Posted by gvw5400

Years ago I work for a RV rental / sale dealer. On 31 foot class A motorcoaches the gas mileage was the same on 454's with a T- 400. 8 to 9 with a Q-jet or TBI.
But when you had a 454 with TBI and a 4L80E mileage was 10-11.
The 21 foot Class C motorcoaches with a 350 TBI and a 4L60 mileage was 9-10.
Just leave the 454 installed. The cost per mile will never break, even let alone save costs.
All the Best,
Dirk

I know the guy who has "plans", but not very well. Either way I am staying out of the project of the engine swap. My knees are F'd so I don't want to deal with the extra pain, and frankly it's stupid to remove what appears to be a good running engine from the RV. Yes it needs to be cleaned up, and tuned. But it could take a few guys 2 days to pull out, and a bunch of tools that very few home guys would have.

He is coming at it as a recipe for disaster. Or atleast to big a initial rebuild, and setting failure up at every turn.

Remodeling the inside is going to be a 10-15K dollar job with enough complexities to pass you off. There's no reason to go further that soon.

[Sheepdip]

Well I have it in my mind that should the 350 in Otis ever go south that I would replace it with something similar to this https://paceperformance.com/Big-Bloc...8778-F2X-.html

Not necessarily this exact one, that decision would be made at the time it's needed. Have even entertained a LS Conversion but that's a lot of extra work I'm not up to.

[Tom]

Title of thread is very misleading. He isn't scared, he just wants gas mileage. Not unusual to think an engine with 100 cubic inches less might get better mileage. In this case it won't, be its not a scare thing.