Thread: a 454 to a 350

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i currently have a 454 in my 89 gmc dually i have seen them stock with 350 motors is there alot involed swapping them as far as parts being different the 350 i think will get beter gas milage any info would help thanks jay

gas mileage in tehory would be better, but if you are working the 350 hard then the mileage may not improve much. what are you getting now? how are you using the truck?

check out http://www.fueleconomy.gov/
i see an 89 350 getting about 14 city, 16 hiway. a dually will probably lose a few mpg to drag and extra weight. 4wd will be worse too. rear gear ration will make a difference as well.
I didn;t see the 3500 or 454 lised.

as to changing it over...to install a carbed 350, crate motor, yo'll spend $5000 or so, and unless you drive gobs of miles you'll never make that back in fuel savings.

if you do the work and go to a junk yard 350, umm used motor, you may be able to get by on $1000. you can do the math and see if that would save you anything at all.

then you mayhave emmissions issues, but the truck may be over the GVWR to need that test.

the motor mounts will be different, no biggie there., the exhuast will differ, not too big a deal.

the trans...bolt pattern may be differernt, the cluthc or TC will be different.

not sure that this would make economic sense...unless you were gonna put the 454 in a t-bucket for weekend fun!

I have to agree with screamer. By the time you save enough money on gas to pay for the swap; you'll be ready for a new ride anyway (unless you already have the motor in hand). Also, if you use the truck to haul anything, you will miss the hell out of that 454. There is no way you will pick up a 350 that puts out the kind of torque your 454 already does for the $1000.00 junkyard motor that screamer mentioned.

Anyway, if you do get one out of junkyard, make sure it is a carb to oil pan motor (may as well get the exhaust manifolds as well) and not just a long block. Otherwise you are looking at buying a new intake manifold and exhaust manifolds/headers and possibly having to modify the exhaust system beyond that to make 'em fit. Then all ya gotta do is hope the motor you get from the junkyard lasts.

One final thought and I may be way off on this one, so please forgive me if I am, as I'm not trying to offend you; but, I can only assume that since you are asking the question, you wont actually be the one doing the work to change the motor over. If that's the case, you can add labor to your bills as well.

Anyway, I do wish you the best of luck with it.

Cheers,
Firechicken

yes i will be doing the work myself thats no big issue i dont use the truck to pull anything more hten a boat. the junkyard around here i can get a 350 for about 300 mabye 400 with low miles on it. im asking if the throttle bdy fuel injection carb i have on the 454 will work on the 350 and i know the exhaust manifolds will change but will the y pipe be different and the trans its a turbo 400 in there now ? thanks jay

Stay with the 454. It will work alot less than a 350.

Why not just put an RV cam in the 454 and give it an exhaust that can breate easy. You'll pick up a few MPG and get more torque out of the beastie.

Abe

yeah i actually replaced all the plugs today they were dirty i noticed a little difference i mean before when i got the truck it was eating gas like it was its job lol but i drove it before and i can see a difference . mabye i will leave the 454 sounds like a good idea hey thats why im here asking the experts. i have one other problem what would the normal idle be on that motor it seems to high like if i go from park to r is bangs and sounds high the throttle screw is at its lowest and after running the idle will seem to come down a bit someone said it could be a sensor or this or that just wondering if someone had this problem thanks again jay

That sounds more like a choke issue. If it were a carb, I would recommend a rebuild, but being injected, it might be the injectors, but it could also be oxygen sensors or timing. Go from cheapest fix to most expensive(timing to sensors to injectors). Just my little suggestion, take it for what it's worth.

You must set the idle with a computer (i think there may a work around on this but not sure on GM cars). The computer will set the idle and make the mixture richer ('digital' choke so to speak). Same thing for timing on most engines as well - twist the dist 1/3 of the way around and the timing marks don't move!

the idle screw as you call it may have nothing to do with idle speed. also, idle will kick up with a/c on, cold start, and possibly with the power steeering turned all the way (added load causes teh computer to kick the idle up).

if the check engine light comes on with thte key in the ON position (before starting the engine) then the bulb and circuit are ok. this may also happen if the thermostat is stuck open or too low a temp one is installed.

if the light is NOT on when the vehicle is running then the major systems are OK. Pre-1996 car computers are not very bright. You should be able to get the computer read at an autozone parts store for free.

there will be (or was) a sticker under the hood with the idle speed - warm idle in park/neutral is usually 600-700 RPM, maybe more if it is a stick shift.