chevy 454 and 350 4 bolt main.

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Why? By the time you built that 350 to have the torque and power of a big block, you will have to be running 5 to 6000 rpms all the time. And if you think you have bad fuel mileage now, wait until you start running the snot out of the 350 to do what the 454 will do normal running. If the 454 needs work and you have a 350 on hand, sell the 350 and use that money to do up the 454.

To answer your question though, yes it will swap. You obviously will need small block exhaust manifolds or headers, and maybe different motor mounts, depending on the individual swap. You may also run into issues with radiator hoses, but that's no biggie either.
 
I've often wondered about this equation. An '84 carb'd 454 was 230hp and 385lb ft, but, say, a '96+ Vortec 5700 is 235/335 (an LT1 is similar) - not a *huge* deficit. If you were going to put in the work, a mildly built (like, maybe just an RV cam) modern 350 would probably outperform a tired '80s 454. Might even be cheaper to do that, since 350s get all the attention anyway. ;) You might run into problems with gearing - I'm sure the TH400 and rear end are expecting a lot more grunt a lot earlier than the 350 will deliver and it might be a little rough with only three speeds.

Unless you're in it for the science, I would tend to agree with kdbgoat and just go get another 454. :)
 
Here's a good way to compare:

https://www.gearvendors.com/cghptorque.html

The charts could be done better, but...

Look at the L31 5.7 vs the L29 7.4. That 7.4 starts with great gobs more torque off idle compared to the 5.7. The torque curve for the 7.4 is relatively flat, where the 5.7 starts low, goes to a peak, then drops like a rock.
 
Yeah, but that's comparing new stock motors. That '84 454 isn't new, and the 350 was theorizing about wouldn't be stock. Even assuming an '84 454 made it thirty years losing only 10% of it's power (which seems unlikely) it'd be in the ballpark of a 350 with a cam or heads or headers. New vs. new, no comparison. But old vs. new and lightly built? Might be pretty close. I can't tell much a difference between my friend's old 454 Suburban and my Vortec 5700 Suburban - I know we're not talking about 10,000lb motorhomes, but he's got an old, tired motor that wasn't the pinnacle of GM engineering to start with, and I've got a young (by comparison!), healthy motor that was pretty darned good. ;)

Stock vs stock, new vs. new it's not much of a conversation. But once you factor in time & wear and the plethora of cheap upgrades for 350s and the water will get murkier.
 
That 350 will never have the torque needed to power a MH. I've been a small block guy all my life and I'm an old man now. The Chevy small block in my opinion was the best engine ever made. But they just don't have the torque necessary for a MH. The flexplate will be different and the mounts will need to be modified, but the trans will bolt up to the 350. I personally would find another 454, as they can be found pretty cheap now a days. 
 
Considering they actually built 350-powered cutaway Minnie Winnies back in the '80s, we know it *can* work. ;) And you can buy *right now* 5.4l Triton-powered Class Cs. And since this guy has a 24' - the same size as the Minnie Winnies - I think ya'll are making mountains our of molehills. ;) It's not like he's trying to repower a 40' Workhorse with a small block. ;)

 
Thank you I'm probably going to go with another 454. I had a mechanic tell me a 350 would work better and bolt right up and match. But it didn't sound right to me. I know they can be built with an RV cam but it seems like it would be pushing a constant high rpm.
 
That mechanic probably doesn't know what he's talking about, but I appreciate his enthusiasm. :)

I do think sticking with the 454 is the right answer, but I'm also very confident you could build a 350 to do the same job easily. Chevy and Ford both sold van chassis with small blocks that were turned into motorhomes (the aforementioned Minnie Winnies were common), and Chevy even sold the P-series chassis with small blocks. There is no difference between a 10,000lb Class C motorhome and a 5,000lb C1500 pulling a 5,000lb trailer and that is *hardly* uncommon. My old Suburban towed a 5500lb trailer+race car all over California without issue, and that's way over 10,000lbs. Heck, my little bitty Ford 300ci six can do that. Will a 454 give a better experience? Probably. But will a 350 fail? Definitely not, especially given the huge aftermarket for those motors. What you can build cheaply in 2016 is 10x better than the factory could produce in 1985. :)
 
brandon.bjf said:
Thank you I'm probably going to go with another 454. I had a mechanic tell me a 350 would work better and bolt right up and match. But it didn't sound right to me. I know they can be built with an RV cam but it seems like it would be pushing a constant high rpm.
      You can check both and find the price diff. little and besides all the stuff around it will bolt back up. You may need new mounts anyway? Collapsed or weak. The big block with the right cam will last 200K?
 
I just had one mechanic come look at my rv and he's saying that it would be best to go with a newer 454 SBC but that doesn't seem right either. And it would cost me 3,200 for the new motor
 
Folks have stated that a 350 can be comparable to a 454 in performance, they may be looking at the peak torque and horsepower numbers. The 454 starts with good torgue and horsepower off idle, while the 350 starts and ends low with it a narrow peak point higher up in the rpms. Where talking about motovating a motorhome, not drag racing. Two completely different applications.
 
On a 24' I have to say I would try it, 5.7 fuel injected and RV cam. correct torque converter and a decent th400 possibly a gearvenders under/overdrive.
 
I have seen one rebuilt 350 with an RV cam for sale on craigslist in the Seattle area so I know people do it. But I eventually want to pull a small storage trailer also.
 
This is what I'm working with right now. I don't know a lot about engines other then the basics so I didn't notice that it had the wrong fuel pump, just that it probably shouldn't of been mounted to the right valve cover. Which most likely caused my engine to overheat from to much fuel getting pumped into the carb and destroyed the bearing
 

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That's a mess... find a good tech. in a smaller shop (Mom and pop) that would be willing to do it right could be your best bet? Or a truck shop.Buy a target(GM) long block or AER (ford) yes ford builds GM engines too. With a good warranty! Not sure what took out the old motor but having the right fuel pressure is important. Sounds like the pump failed(diaprham) and pumped gas into the crankcase and washed out the bearings? Seen it many times But a 454/502 is the best way to go. Finding the shop may be the hard part? most auto repair shops don't want to fool with larger trucks. That looked like a filter to me on the right valve cover?                  Stay away from jasper engines NOT so good and replace all hoses, belts water pump ect. Good luck. Will
 
Yeah it's a electric fuel pump mounted on the right valve cover. I just talked to another friend last night who has some good pull on a small mechanics shop near me that shouldn't charge more then 3 grand to put a new 454 in it.
 
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