454 to inline 6 swap in a crew cab c20

[dragn91]

I bought a 80 Crew cab 454 truck a couple months back and it's a lot of fun but the gas mileage does suck I didn't think I'd drive it as much as I do but I really like the truck. I found a truck cheap down the road that's a 292 inline 6 and it has a really nice bed mine is junk. Would I be crazy to drop the 292 down in my crew cab or would it be a complete turd? I'd like to keep the 400 turbo until I can find everything to convert it to a manual column shift or take the 4spd out of the donor truck as well. There both c20 trucks I figure an extra set of doors and couple feet of cab can't weigh that much right lol. And this should pretty much be a bolt in job right as long as I keep the trans where it's at? Or would I need to shorten or lengthen it?

[tucsonjwt]

In my experience, once you have a 3/4 ton pickup you can expect poor gas mileage regardless of the engine size (unless you have a diesel.) I think a 3/4 ton has about 1,000 lbs. more dead weight to carry around. I have had two 454 C20 regular cabs - mpg ranged from 11/13 to 8/13 city/highway with 4:10 rear axle. A six will have to work harder to pull that dead weight around, so you won't get the gas mileage you would in a 1/2 ton truck.

Plus, there will be the conversion cost.

For reference, new 6.0 LS engines in new GM 3/4 ton trucks are advertised at 11 mpg city by a Phoenix commercial truck dealer.

If you never plan to carry a decent load in the box and stay off the highway you might get a slight improvement in gas mileage - but then I would ask why you have a heavy duty pickup.

[mud.man.rj]

I was thinking the same, conversion cost is always more than you think in the end, then loss of power with the heavy truck plus mileage may be slightly better but way less fun as also less usable for towing, stick with what you have and make it better, really a dual exh with larger pipe size plus a better intake and KN filter kit will help more than you think, maybe even a vacumn gauge to keep your foot out of it when driving. Figure with the correct setup should get at least a few mpg better than now and cost way less.

[enaberif]

Inline 6 in your truck wouldn't be a good idea. 350 might be ok but the 454 unfortunately is the best bet.

[gmachinz]

Now, if a twin turbo build is in the works....that little 6 would sure wake up! At least it'd be different from everything else I've seen on here.

[Edahall]

You could increase your mileage more by putting in a manual tranny and installing a rear end that decreases your rpm's to around 1900 rpm's at cruising speed.

[Oregoon]

Originally Posted by Edahall

You could increase your mileage more by putting in a manual tranny and installing a rear end that decreases your rpm's to around 1900 rpm's at cruising speed.

Absolutely. Overdrive is the inliner's best friend.

[Ziegelsteinfaust]

I would consider a Vortec 350 and 4L80 swap to be my personal fav for mpg, a 6.0 or maybe a 5.3 LS would be a good choice. Especially hooked to a 6L80, and a 14 bolt SF.

[mud.man.rj]

What you will spend to upgrade would be a major amount, would be a lot of big block gas mileage to catch up to that, and more labour.

[donut]

Or you could do a cheap and easy swap and park the thing on the front lawn with a "for sale" sign on it, then purchase what you want.

Honestly, a big block crew won't get the mileage your looking for...
6 cyl, prob not (most my 1/2 ton 6's would average about 15. tops..) Vortec and OD, not bad, but still doesn't have the torque (I really don't care about the "advertised" ratings, I have driven both. Advertised torque is kinda like advertised mileage in the '80's)
Lot's of good ideas, but IMO, the smile on your face won't be as wide.

[slotard]

If you want to do an engine swap in order to get good mileage I'd look for a 4.8/4L60E. The tranny should do pretty well behind the 4.8, and mileage on them is very reasonable.

[86c20]

gears gears gears. like was said if your cruz speed is higher then the peak of the motot your done. my c20 with 350 and sm 465 with 3.42 rears and stock size tires adn at 65 i have got over21 now my truck is stock right down to the qjet but i have pumped the timing some. now my c30 with 454 465 and 4.10 gets 10 up hill down dont care gets 10 run the pto and its down to 8.
the 400 is a great trans but if you want mpg dump it and get a lockup or get a od standerd trans just remember anytime the motor revs more then is turning the wheels its wast. carbs make a big diff too.

[tucsonjwt]

X2 on 3.42 rear axle, and low horse 350 (like a stock goodwrench engine) for relative fuel economy, but I don't think a SM 465 adds much. I have a gear vendor behind my SM 465 and I would be exaggerating to say that it adds 2 mpg - and that is on the highway only.

I got better mpg with my 73 454/TH400 and 4:10 rear axle - it was much faster also. With a SM 465 you really have only two gears useable most of the time - 3rd and 4th - 1st is never used and 2nd just gets you rolling a short distance from a stop. So city mpg has never been good with a SM 465 for me.

I suppose a 3:42 rear axle might help. GM now has a 3.23 rear axle option on its trucks - with a V6 1/2 ton that would get good gas mileage. I got 19 city/23 highway on a 2000 Silverado work truck with V6/auto - but it I had to use tow/haul if I had any kind of load on it which killed the gas mileage.

Just drop $30K and buy one of Keith's new gas saver Silverados and be done with it. You might have a $500/month payment but you will save $30/month an gas.

[dragn91]

This trucks just a 500 beater I needed a crew cab and it came up cheap so I snagged it. It's a low mileage truck and runs great but I really don't need it to be a 3/4 ton they just didn't offer a squarebody crew as a half. I only drive 3 miles to work so the big block doesn't absolutely have to go but I figured the 292 with maybe a 700r4 or a 5 speed from a 90s silverado would save some gas idk. I love a 3 on the tree so I'd love it to just have a inline 6 with a 3 on the tree and ditch the extra tank and huge stack of springs I don't really need maybe even swap it over to half ton. If it still gets ****ty mileage oh well it'll be what I want and I'll have the low mileage 454 400 combo for a future 57 chevy project. I have a (sorry)f450 sitting in the driveway if I ever need to haul some serious weight but this c20 is perfect for dump runs and picking up stuff from the hardware store and still have room for my kids. It sure beats the hell out of the minivan I had to drive after my 66 got totaled lol

[Speeding Dakota]

Originally Posted by dragn91

This trucks just a 500 beater I needed a crew cab and it came up cheap so I snagged it. It's a low mileage truck and runs great but I really don't need it to be a 3/4 ton they just didn't offer a squarebody crew as a half. I only drive 3 miles to work so the big block doesn't absolutely have to go but I figured the 292 with maybe a 700r4 or a 5 speed from a 90s silverado would save some gas idk. I love a 3 on the tree so I'd love it to just have a inline 6 with a 3 on the tree and ditch the extra tank and huge stack of springs I don't really need maybe even swap it over to half ton. If it still gets ****ty mileage oh well it'll be what I want and I'll have the low mileage 454 400 combo for a future 57 chevy project. I have a (sorry)f450 sitting in the driveway if I ever need to haul some serious weight but this c20 is perfect for dump runs and picking up stuff from the hardware store and still have room for my kids. It sure beats the hell out of the minivan I had to drive after my 66 got totaled lol

Maybe finding a 1/2 ton 6cyl donor and swapping over everything (like the suspension) would be best way to reduce weight. I'm not to far away if you do decide just to sell it.

[dragn91]

Oh and the donor trucks only 600 bucks it's a one owner mid 70s c20 longbed and vomes with a decent slide in camper. My neighbor allready offered me 500 for the truck minus bed and engine so I figure I can't loose

[Oregoon]

Go for the 292! They're torque monsters, dirt simple to work on, very long lasting, and a joy to drive. And if you want to get creative, check out Clifford Performance or CL. Find a new intake, a 390 cfm 4bbl and a header, and they wake right up.

You'll never get great mileage out of a crewcab, and a 292 is a thirsty girl for an inliner. That said, nothing beats the gear-whine of a big six going to work.

I've owned all sorts of V8s, and a lot of sixes, and for the last 15 years, I go for the six every time.

Also, one could get a 292 in a crewcab, though I believe they were fleet vehicles only? I've seen in a few ex-Forest Service rigs and military stuff. Personally, I think they're GM's best engine, with the 250 being a close second.

[andrewmp6]

Throw a 6.2 diesel in it or a cummins if you want mpg.

[SCOTI]

Originally Posted by andrewmp6

Throw a 6.2 diesel in it or a cummins if you want mpg.

x2 & add a OD trans.

[Bigstevex4]

I put a250 6 in a 65 panel guy had a 396 built he wanted too much for cost me 15 bucks for motor mounts and 50 cents for piece all thread (throttle) to swap it. God i love GM.