Inline or V6 Vs 350 comparison?

[thatK30guy]

I had a truck with a 250 and a 4 speed. I can't say anything for mileage but the engine was 0ver 40 years old and had plenty of power. I like the Inline engines but the shared intake and exhaust mounting setup seems stupid to me

I had an '81 SWB once that ran a 250, 4 speed and 3.73 gears. Went everywhere a V8 did. Got me 18 mpg on the highways to work. Could have gotten better with a good tune up and better carb but back in the mid-90's gas wasn't such a concern. I miss that truck.

Anything but an 8.1

Who cares about MPG with an 8.1!!!! I'll tow and drive this truck any day, all day, rather than be concerned about MPG. After all you gotta pay to play.

 

[dyeager535]

I had a 305 (305/Q-jet/700/308/3.08/31" tires) in an '83 K5, and it netted the same mileage the '85 truck in my signature gets. Even with an old-school 350 this truck got the same MPG. 305 might have been a BIT easier to get the higher MPG's out of (overall MPG might have averaged 1 or 2 higher with the 305) but under ideal conditions, they all got the same. The 305 and 350 both seem to get the same off-road. I don't think the displacement difference is enough to make the huge difference in economy.

Given a heavy truck, the ONLY time a smaller motor is going to get better economy is cruising on the freeway when relatively little power is needed to keep the truck moving, assuming gearing is right. Under other conditions (starting, climbing hills, towing) the smaller engine is going to have to work that much harder and economy is going to suffer.

Look at what the trucks in the 80's were getting for MPG (not sure "official" numbers exist for the 70's or earlier) and what they get now. The economy gains are not exponential. They are there, but with the massive technology differences between an LS-series motor and a carbed 350 from 1981, one would think the MPG difference is equally massive. It's not. Average car in 1974 probably got 25 on a good day. Econobox of today is easily a 40MPG vehicle, roughly 38% better. If you figure trucks in the 80's got 18MPG (figuring high) and a modern GM truck with similar size engine gets even 23MPG (2015 5.3L in a 1500, per GM) your efficiency gain is 22%.

That's a pretty big disparity in efficiency gains, but reflects that being much lighter, more aerodynamic, and with an exponentially smaller engine, is where the gains are. Not a more *efficient* engine, per se. The LS-series motors ARE more efficient, but the engine efficiency just isn't where most of the MPG problem comes from.

 

[thatK30guy]

Dorian makes good points with MPG comparisons of old and new but where I'm at with using old versus new lies mainly with wanting to use the simplicity of a carbed motor and not having to mate/hookup/hassle with the wiring of computers, etc.
I have thought about another 250 SWB truck but with a TBI topping it off to see if the gains can be had. But I'm getting old now so that's a dream.

 

[campfire]

Is there any beating the tried and true? That I guess is my bare bones question....

Mileage-wise, the 6.2 will beat the sbc hands-down. I have a pretty good stock setup on my K10 and get mid-20s mileage numbers regularly on the highway (19-20 MPG in town). There are rigs out there that beat those numbers, but that's what I get in my automatic.

So you can see a large mileage increase simply by buying a diesel truck (they are out there). And for less work than trying to swap an engine, a few efficiency mods to a good 6.2 truck could probably raise the mileage figures even more.

I went through the same dilemma with the current rig, and a potential 6.2L swap. 25MPG is very inviting, but the work to get there after what I have invested in EFI, and how little I drive the rig, not worth the tradeoff.

Rather than try to swap one out, why not simply buy one already assembled at the factory? 6.2 trucks aren't that rare yet...

 

[diesel4me]

The I6 prolly just had a lower rpm torque curve than a V8. Making them feel like they could pull harder

This is true..
A 250 six reaches its maximum torque at a mere 1800 rpms...
A 292 six makes its maximum torque at 1600 rpms !..that almost at idle speed..

The 292's longer stroke is the reason,those engine can pull just as hard as a stock 350 4 bbl will,but they also get the same or worse gas mileage too..

I like straight sixes,and would swap one for my diesels in a heartbeat..
Not so much because I'm not a big enthusiast of the 6.2's,I just like them for reliability,and most of all, EASE to work on..and the fact you rarely DO have to work on them...they take some punishment without complaint and yeah,you might not be able to boot it up to 65 mph like a 454,but so what.

..As I've aged,I ended up regretting taking many straight sixes out of trucks and putting V8's in them--yeah,the power and rapid acceleration was nice,and that 454 did impress more folks at cruise night,but for all the labor entailed,I look back now and realize the straight sixes were pretty cool too..

I had this '79 Bonanza for 5 years with the original "camel humper" 250 six with the not so great "integral head" design...I also had two more of those engines,one in my '81 G-10 van,and another I kept from a '78 C-10 a friend had that "hated that POS grandpa eggbeater"--it only had 35K oringinal miles on it--he ripped it out in favor a a 350 he had..had a three speed manual behind it too..

I eventually lost the #6 piston in the Bonanza at 117,000 miles..the top ring lands litteraly came apart and went out the tailpipe..those engines always had spark knock and no amount of fiddling with the timing seemed to cure it ..(one mechanic stated he thought the engines were so overworked,the exhaust valves turned red hot and pre-ignition resulted)...

I found after I adapted the 500 CFM Edelbrock to the intake the pinging stopped..those "Vara-Jet" 2 bbls were one of GM's worst carbs ever..
I gained about 2 mpg by unhooking the secondaries on the Edelbrock..
The tiny six seemed to be smothered when you booted them open..
It ran way better with the Edelbrock than it ever did with the stock carb..

When I took the engine out,I came across a 305 from an '86 G-10 ,so I swapped that in it..in my opinion it went better with the 250 !..but the V8 did give slightly better mpg,I got about 15 highway with it..the six was good on gas "sometimes",but on windy days on the highway you could feel it struggling to maintain 65 on grades..and it would drink!..

 

[chevyfumes]

Mileage-wise, the 6.2 will beat the sbc hands-down. I have a pretty good stock setup on my K10 and get mid-20s mileage numbers regularly on the highway (19-20 MPG in town). There are rigs out there that beat those numbers, but that's what I get in my automatic.

So you can see a large mileage increase simply by buying a diesel truck (they are out there). And for less work than trying to swap an engine, a few efficiency mods to a good 6.2 truck could probably raise the mileage figures even more.




Rather than try to swap one out, why not simply buy one already assembled at the factory? 6.2 trucks aren't that rare yet...

Now do the price of diesel vs gas equation....

 

[campfire]

Now do the price of diesel vs gas equation....

The diesel trucks don't fetch any particular premium in my area, and the cost of fuel is within 2 cents/gallon at this point in time. I have seen it larger, though. It has occasionally gotten to the point where the cost per mile was only slightly better than a comparable sbc, but overall it has been quite a bit cheaper to drive.

 

[diesel4me]

Huh,your lucky..
Diesel fuel here has always been 50 to 80+ cents more than gas,only recently has the margin fallen some,I just got fuel yesterday ,it was 2.80 a gallon for diesel--gas for my lawn mower was 2.65 a gallon..

My 6.2 averages between 15 and 22 mpg,and it doesnt seem to care if I'm pushing snow,driving with an empty bed,or a full load..

While I wont complain about the MPG,I have had gas powered trucks that got close to 16 mpg with engines ranging from a 250 six,to a 454...(one '74 454 I had with a Holley Economaster carb would get 14-15 mpg on my commute to work 65 miles away)...the diesels might beat the gas engines for MPG,but is it really worth having to drive something that sounds like a stone crusher to get a few more miles to the gallon?..

 

[dyeager535]

Rather than try to swap one out, why not simply buy one already assembled at the factory? 6.2 trucks aren't that rare yet...

Anyone here buy a rig they didn't feel the need to modify? lol

 

[dyeager535]

This is true..
A 250 six reaches its maximum torque at a mere 1800 rpms...
A 292 six makes its maximum torque at 1600 rpms !..that almost at idle speed..

Check out the 4th page here: http://brochures.slosh.com/index.shtml?1981

At least in 1981, the 250 and *305* reached peak torque at the same RPM (2000) and the 305 was +40ft lbs.

Even with the 292 (I could read the engine specs there for 1980), it's peak is less, and coupled with an automatic, RPM where peak is made is less consequential than with a manual. Obviously getting moving the 292 might feel stronger than a 305 and a manual, IF the 305 curve isn't real flat.

No replacement for displacement is unfortunately apt when it comes to normal aspiration.

 

[campfire]

Anyone here buy a rig they didn't feel the need to modify? lol

I didn't say to avoid modding the truck...I recommended buying a 6.2 truck and then modding that truck to get better performance/mileage.

Intake/turbo upgrades come to mind most quickly...

 

[campfire]

Huh,your lucky..
Diesel fuel here has always been 50 to 80+ cents more than gas,only recently has the margin fallen some,I just got fuel yesterday ,it was 2.80 a gallon for diesel--gas for my lawn mower was 2.65 a gallon..

It's not always that close. Last fall (when gas prices fell so dramatically) the difference was enough that the diesel wasn't a whole lot cheaper overall. But that was a short-lived situation.

And I'm confused by your "always been 50 to 80+ cents more than gas" comment. I'm still pretty young, but I remember when diesel was steadily cheaper than gasoline (pre-2007 regulations). Surely you remember those days, right? Or are things that different on the coast?

My 6.2 averages between 15 and 22 mpg,and it doesnt seem to care if I'm pushing snow,driving with an empty bed,or a full load..

While I wont complain about the MPG,I have had gas powered trucks that got close to 16 mpg with engines ranging from a 250 six,to a 454...(one '74 454 I had with a Holley Economaster carb would get 14-15 mpg on my commute to work 65 miles away)...the diesels might beat the gas engines for MPG,but is it really worth having to drive something that sounds like a stone crusher to get a few more miles to the gallon?..

A 6.2 better set up for mileage should get better numbers than your 3/4-ton with TH400. And a few mods should make things better yet, for those so inclined.

As for whether the sound is worth it, that is completely up to the vehicle's driver (and passengers ). I really enjoy the sound, so it isn't a drawback to me at all. For others, they may or may not want to have such a sound.

Squeezing mileage isn't typically the end goal of truck owners (there are waaaaaaaay better options out there for that), but for owners like me it makes a difference. A 15MPG truck in my driveway would spend just about all its time parked. I'd rarely get enough enjoyment from it to find the operating cost worthwhile on the street. It's easier to talk myself into a 22MPG hobby. Or an offroad hobby.

 

[diesel4me]

When I said "always" ,I meant since I got a diesel powered vehicle..my first one was an '86 VW Jetta I got back around 1995...before then,yes,diesel "used" to cost less than gas,as much as a dollar less..then when it went "low sulpher"they jacked it way up..(and diesel powered cars and trucks soon were available quite reasonably for awhile,just as the big block gas hog land yachts were after the first gas crisis in the late 70's)..

Today I noticed diesel was selling for 2.65 a gallon at a station that recently re-opened,and gas was 2.67 for regular..this marks the first time in nearly 20 years diesel has cost less than gas..but most of the other stations are getting 2.80 to 3.06 a gallon...

I dont "hate" the diesel noise,in fact it is kind of cool..sometimes my truck sounds like its going to chuck a rod,today I noticed it was suddenly much quieter than usual,the "diesel knock" was hardly audible..might be due to the hot weather and high humidity..just this weekend it was a lot noisier..
sometimes I get weary of the noise though,it seems to make a short trip feel much longer somehow..

Any passengers I carry dont seem to be too enthused about the rattle and diesel "stink" though..one woman I gave a ride to almost barfed when we rode a few miles with the rear slider open..when I'd goose it to take off from a stoplight,the smell would enter the cab and she'd gag..guess I'll never get her to go on a date in my truck......

My truck "might" do better on fuel if it didn't weigh 6300 lbs "empty"--and if it had overdrive.....there have been times I have filled the tank right to the top,driven it 180 miles over the course of a few weeks on local trips,shopping,paying bills,etc,no highway runs over 50 mph to speak of--and when I went to fill it again,it only took 11 bucks to fill it to the brim again,which equaled out to just over 5 gallons at the time..

I'd say that's pretty good for an ingot with the areodynamics of a brick..

Since I don't go far away very often,I don't really mind driving something that gets 15-20 mpg..more would be nice though..

 

[swettysblazer]

I know around here, Diesel started being priced higher than gas about 8-10 years ago.

 

[black dawg]

I was wanting to try a 292 with tbi, but then it hit me that a 300-6 would be easier, being that it is already injected (and port injected) and serpentine belt. Just have to adapt the ford bell to my 465.

 

[diesel4me]

The 300 Ford six is a very durable engine..having fuel injection and the serp belt is a plus,as you noted..there are adapters available to let you bolt one up to a GM bellhousing,but they are almost 500 bucks..

Putting a 292 in a GM vehicle ,even one that had a 250 six originally,isn't a "bolt in" deal either--you'll need to source the motor mount brackets for the passenger side,the 292 has a taller block,and the fuel pump and distributor swapped places,so the mounts are completely different..

I imagine these parts are probably getting scarce now,and any left for sale will be priced accordingly..

I always liked the GMC 305 and 351 V6 engines used mostly in larger trucks and busses--we had a '71 GMC 3/4 ton 4x4 at the junkyard that had a factory 305 ,coupled to a SM465...there was a few busses and a C-60 that had one too..those engines were one of GM's best..

I think all ended up scrapped because the 2 bbl Stromberg carbs on them proved to be a pain..you could swap a Holley or Ford Autolite carb on them with an adapter and they ran much better..

 

[Blue85]

The I6 prolly just had a lower rpm torque curve than a V8. Making them feel like they could pull harder

I've always figured the I6 came by default with lower gears, but I have no data.

 

[diesel4me]

Mostly in the older trucks (pre-70's) and the 3/4 & 1 tons with a straight six almost always got the lowest rear end gearing,usually 4:56's or 3:90's..
That alone would tend to make them feel more powerful..

But many of the 71 & up trucks got 3:08's or even 2:73's to save on fuel..
My '79 Bonanza had 3:08's and it didn't feel that gutless really--if anything the engines peak torque at a low RPM was well suited to the higher gearing..
My '81 G-10 also had 3:08's originally ,I swapped in a 2:73 rear axle and was rather discouraged ,I wished I had gone "up" to 3:42's or 3:73's instead..
It wasn't that bad with the 3:08's..

I had a '80 El-Camino with a 267 V8 that had a TH350 and 2:56 gearing,posi too..that thing would barely spin the tires on sand!..but it got great gas mileage and it'd go 80+mph in second gear once you got it rolling..it wasn't too doggy,being so light..put anything in the bed though,you'd notice it right away..

 

[vandelay industries]

1) The question i would ask is how much driving you are going to be doing and/or how much weight will you be hauling/towing?

i am in the middle of a 4.3 swap---from an 8. The 4.3 actually makes more hp than stock 305's---LG3 and LG4's. It also makes almost as much torque (albeit at 400rpm higher). So, the 4.3 should have no problems moving the truck along---and the 305 could move the truck along at 80mph without too much trouble.

2) Now as far as the mileage thing:
a) one thing to remember is that some (perhaps all?) of the new gm pickups use cylinder deactivation so a lot of the time the truck is just running on 4 cyls. And they don't seem to have any problems on the highway when in 4 cyl mode.

b) Here's where i think the v-6 will achieve better mileage despite concerns that the engine "will have to work harder" compared to the 8:

You do have less cubic inches(this alone generally means better mpg), but you also have less rotating and reciprocating mass---crank and cam are shorter also two less pistons, rods etc.. And LESS FRICTION---less cubes, that alone means less friction, but you also have less main bearings (i think one less?) also less lifters against the cam, less rockers.

Also, it is lighter than the 8. Okay only 125 lbs, but it's a start.

i will be observing and recording my mileage very accurately with the new engine.

Looking back i think it would actually have been easier to swap to a 6.2/6.5 because i think that is actually more of a bolt in swap compared to the v-6 believe it or not.

I always liked the GMC 305 and 351 V6 engines used mostly in larger trucks and busses--we had a '71 GMC 3/4 ton 4x4 at the junkyard that had a factory 305 ,coupled to a SM465...there was a few busses and a C-60 that had one too..those engines were one of GM's best..

I think all ended up scrapped because the 2 bbl Stromberg carbs on them proved to be a pain..you could swap a Holley or Ford Autolite carb on them with an adapter and they ran much better..

i love those gmc v-6s also, but think about this: By like 72 or so gmc had completely switched over to chevy power in the light trucks. i think this may have to do with the gmc 6 was just too thirsty.