anyone swapped 6cy to 8cy and regret it?

[davidh]

1. I was wondering if anyone had swapped a 6cy to 8cyl and regretted it? If so why?

2. Anyone converted from 8cyl to 6cyl because they wanted a straight 6?

3. For mpg. c10, 283, 2bbl Hei, 3speed, 3.08 gears. Think there would be some mileage?

[TP from Cntl PA]

Originally Posted by davidh

1. I was wondering if anyone had swapped a 6cy to 8cyl and regretted it? If so why?

2. Anyone converted from 8cyl to 6cyl because they wanted a straight 6?

3. For mpg. c10, 283, 2bbl Hei, 3speed, 3.08 gears. Think there would be some mileage?

I fall under #2, for atleast TWO engine swaps...........First one was a SB 350 for a Inline Cummins Diesel................Second one I am currently working on and hope to finish up soon, BB 454 for a 250 I-6.

The first one is really a non-issue, I got so much more in the end it wasn't funny, heck you couldn't even hold a candle to the "BIG C" even with a Big Block of any make, as far as towing and MPG doing it.

As for going from the BBC to the Inliner, I really was looking for overall longevity. The 6 I am putting in the truck has been totally re-worked and will last a LONG time, heck, we had worn out 250's here on the farm that you couldn't break, they'll stand up to alot. I imagine it will get a tad better fuel mileage in the end, but I could have probably did alot better mpg wise with a SBC...........As far as power, the 454 didn't impress me at all for the fuel it sucked up. Not to mention the 6 is different in both looks and sound.........

I guess I should add having both turned wrenches on, and driven OTR truck along with heavy equipment, I have seen the PROVEN dependability of Inline power day in and out............Their are very few V-type diesels that are even generally reguarded out there, most are considered boat anchors at best. So my thoughts maybe a bit exotic to most on this board for that reason.

[Longhorn Man]

MPG poll;
http://67-72chevytrucks.com/vboard/s...d.php?t=172346

I've only swapped strong for stronger...not once have I regretted it.
Well, i tried installin a 305 in place of a knocking 350, but the 305 was a knocker too. It's all good though, just speed up the Longhorn progress.

[bryanw1968]

All depends on what you're trying to do. Longevity or go fast!
6 cyl are cool. They are a little better on gas and run forever. If you're going to have a stocker just to cruise around in than a 6 may be the way you wanna go. If you want to be spanking imports and hanging with what's quick on the street, then a small block is the way to go in my opinion.
Good luck with whatever you decide.

[davidh]

I got another truck that's V8 for power. This would get a next to stock small block if the 6cy was rebuild. Curious, what's the weight difference between the 292 and a small block? If I keep the 292 I'd really like to get power steering.

[danny7139]

I believe a small block goes great accross the board. It makes more grunt than a 6. But gets slightly less gas mileage. When I talk about a small block I'm talking about a 350, IMO don't bother with a 305 makes less power than a 350 and doesn't make much better mpg than a stock 350. Big blocks are fun and all but in the long run it doesn't pay off to have a 8 mpg ride. Unless of course this is a racing ride? But even then, I wouldn't want the added weight with the big block. A very healthy 4 bolt small block can give good grunt for the track. Add fuel injection to a sbc and some other intake/exhaust goodies to a 350, different gearing ratios and you will have a power horse that makes good gas mileage.

[bean]

I kept my 250 for the sake of gas mileage and unfortunately it seems like people pull them in favor of a sbc. The 250 goes to scrap... I think they're unique. I used the petronix ignition so I don't have to change points anymore runs great and get great gas mileage.

[davidh]

Originally Posted by bean

I kept my 250 for the sake of gas mileage and unfortunately it seems like people pull them in favor of a sbc. The 250 goes to scrap... I think they're unique. I used the petronix ignition so I don't have to change points anymore runs great and get great gas mileage.

How is your truck set up? 1/2, 3/4 ton? What gears? What kind of mileage too? I think I might have found a ps pump/brackets for my 292.

[bean]

Mine is a stock 250. I rebuilt about 5-6 years ago. Stock 3 speed. Don't the gear ratio in the rear. My truck isn't a show truck or anything just something fun to fart around in on weekends and when the weather is good.

[ThatOneBlue67]

My truck has the original 250 and I'm keeping that in. Right now I'm just doing small thiings like putting on a more dependable carburetor and exhaust headers.

They're not fast engines. People have had to tell me that enough that I think some of them are becoming unhappy with me....

And I've just about accepted that just about anythign can ebat me. But I'm still trying. And I get GREAT gasmileage! I've found that the main reason was poor vacuum pressure. So I've put a hoseclamp or ziptie on just about every exhaust port and found that I get pretty dern good MPG's.

The thing about inline sixes that I like, is that they're such an easy engine to work on! And unique.... 'cus no one uses em anymore! And they look really cool with some chrome and other dress up.

I'm bout to dump 800 bucks into a new exhaust system with headers and dual 18" glasspacks. Supposedly the sound will be outstanding.

After that, it'll be 700R4 time. That means lower first gear (for burnouts which are actually possible on these old 6ers!) and overdrive for when I take my truck across the country next spring.

So, honestly, they're not fast. Not slow.... but definetly not fast. They can be if you completely rebuild them with high performance parts, but by then you're only matching the speed of a V8 with decent headers and a 4bbl Holley.

So, when people ask me if my 250 is fast I be honest and say:

"No, she's not that fast. But if you ever get stuck in the mud, I'll be the one of few lightweight pickups that can pull you out."

[davidh]

so, am I guess 15mpg out of bean and thatoneblue67?
That would be good in town. I've rebuilt the carb on mine already. I noticed when I got the carb kit it was like 1942-1967 and 68 up were different.
I've rebuilt the carb, change points, plugs, condensor, and the previous bad intake/exhaust it runs much better but still has a slight miss. Thought about adding a valve job for now.

[mudpuppie]

okay , working on putting my 283 back together ,,,,, would a 292 6 be better than 283 8 cyl ?

[Longhorn Man]

not in my opinion

[wibilly]

a 292 would be better if you were going to tow heavy loads up big hills all the time but otherwise i would go with a v 8

[Palf70Step]

Even though I have not driven mine with the 350 yet, there are times I think I should have stayed with the 250, mainly cause it was different. I am sure once I hear the roar of the 350 and step on it, I'll be glad I swapped.

Who knows on the next truck/go round.

[409biscayne]

I absolutely loved my 70 short step w/ 292 auto , 4:10 posi . Bullet proof engine , but it got no where near 15 mpg , more like 10 or 11 . Some of my friends have built 283's for mileage , i think the trans and rear gears have as much to do with economy as anything else . Chevy was notorious for putting weeny 4.3 v6's in trucks with rear end ratio's like 2:76 , these ended up getting crap mileage , imho .
Later ................................. 409

[ThatOneBlue67]

Most people get better gas mileage on the freeway..... I get worse. You figure running at 3,500 RPM and you're still in the slow lane. :laugh: That's California for you.

Somewhere in between 10-15 MPG nothing overly spectacular.

But I'm happy. It took me like 5 minutes to siptie all of my possible hose leaks and that gas gauge needle takes a lot longer to get to E.

[Bob B.]

I would consider swapping a V-8 for a GMC V-6! Certainly not for fuel economy, however.

[ThatOneBlue67]

I got my resto packet from GM and was suprised to find they had V6's that long ago!c Were they gasoline or diesel? Still haven't found out.

[shelby987]

diesel engines converted to gasoline is my understanding, GMC ran 305 and 351 V6's in their c20/c30 trucks, the 351 has TONS of torque, I have driven one with a stick shift, and still regret not buying it! (NOT GAS FRIENDLY AT ALL)

[JAKES 68GMC]

I'd swap my V6 for a 350 SBC. The V6 is driving me nuts and the 350 would be more fun.

[Longhorn Man]

Shelby, they were in C/10's too.
They weren't diesel engines converted, this was before diesel had proven it's self. This was a gas engine built specificly for trucks, and to be indestructable. In that essence, it DOES have a lot of diesel traits, but that's just to make it bullit proof.

[shelby987]

my mistake, did they later re-design them to handle diesel then? I seem to remember these V6's and V12's being tied to diesel, either on the front end or back end of their lives.
Not to hi-jack the thread, but if I ever come across another 351 with an SM420 behind it, it's coming home with me! To get back on topic, I would be with the right balancing of the engine, a more economy friendly carb, and some tall gears (like 3.08's), possibly a manual trans with O/D, you could eek reasonable mpg out of an engine like that.

[67ChevyRedneck]

1. I kinda wish I had just put a NV3500 behind the old six... but I'm kinda happy I yanked it for the 350. The pedal stompin is just too much fun!

2. Nope

3. Maybe, if you drive like a grandma

[TP from Cntl PA]

Originally Posted by danny7139

I believe a small block goes great accross the board. It makes more grunt than a 6.

LOL, 350 in my 3/4 ton wouldn't hold a candle to our little inliners.............SBC has NO low end. Low end to me is down around 2000 rpm, you pull a SBC down to there and it dies. I really hated it for that reason. About the only way to correct it was to pop in a 5 spd so I could run it higher up in rpms while towing. I didn't really want to fart around with that and still have a towing turd...........Put a Cummins in the truck, now I can't keep the GM drivetrain behind the engine in one piece for too long. It seems around this place I either don't have enough engine or too much.

As for the V-6's.............They are awesome! I wish I could find a old '69 GMC 3/4 ton 4x4, and then a 351 V-6/4spd for it.............IMO it would make one HECK of a rig for pickup truck pulls!!!!!!