250 vs 292 and 700r4

[Awann99]

Let me run an idea by the experts.
I thought 3.08 gears were nice until I started driving another truck with 4.11s. So I'm redoing the drivetrain on my 69 1500 2wd, I want the get up and go of those gears but it will need overdrive. I'm wanting to instal an inline 6 because it's what the truck originally had. I'm a sucker for inline 6s they are borderline unkillable.
I have a 700r4 to rebuild. I'll have 3.73 gears in the back so the engine will be moving around 2100 rpm at 70.
The only question is should I go 250 or 292? Fuel economy is the goal. (Don't say ls swap) the 292 would have more torque but I hear it's kinda hoggish on fuel. The truck will just be a cruiser. Maybe carry 500 pound of camping gear a few times a year. Anyone out there have the 700r4 on an inline 6?

[c10sport]

Personally, I'd go for the 250 for fuel mileage. Unless you can get a hold of an MPFI 250 from South America...

[tutone]

I have about 2500 miles on my last build (305 stock/ 700r4/3:73 rear gears.
Like you, in 3rd gear (1:1), it has the get up but in od it calms down to about 1700 rpms. The 305 still has enough low end torque to keep from lugging the engine.This is based on 55 mph manual switch lockup. Now while you are researching the difference, I would take a hard look at the powerband if a 250 . I will guess that at 17-1750 it's gonna be lower on torque than a v8. The 292 wull be "torquier" for sure. Will it like that rpm range? I dont know. But there is a reason GM put 3:73s behind the 250 without the od.

['68OrangeSunshine]

The 292 [L25 is the RPO] is the big block of the L6 world. It is a power/torque monster for its size.
Not an economy engine at all.

[Accelo]

1955 thru early 1959 cars came with a 4.11. In mid 1959 the O.D. cars were switched to a 3.70. GM did it so you can you.
BTW GM dropped the O.D. Transmission in 1969.

More information below;
http://67-72chevytrucks.com/vboard/s...d.php?t=496578

I could not confirm it but I believe the OD ratio in the 4l60 is slightly steeper at .7:1 than the GM manual transmission with OD. You would make up any difference by having the additional advantage of a modern torque converter. If you were in WY or CO I would recommend the 4:11's. Quite sure you can do the 3:70's and be just fine. This is the stock ratio of maybe 90% of the 6cyl trucks built in the 60/70 time frame. Expect the cab to be a lot quieter as a second hand benefit.

[MikeB]

For the kind of driving you're describing, a fresh 250-six will work fine. Just make sure it's not a later model with the integral head/intake manifold, which is prone to cracking. Some also had PAIR, which stands for "Pulse Air Injection Reactor" which puts chambers, air valves, and plumbing on top of the valve cover. Stay away from that setup! The only thing good about that engine is it had a dual outlet exhaust manifold. It also had a 2-bbl carb, but it was a nightmare of emission controls.

There are lots of aftermarket parts available for the earlier 250, such as 4-bbl manifolds, headers, and even cams.

Unless you do sustained driving at >70 mph, I'd say a 250 with a TH350 or manual trans would be just fine with a 3.08 - 3.42. Heck, a 292 six would probably be OK with a 2.73 - 3.08. That's for tires up to 28'-29" tall.

Keep in mind that you add some complexity with a 700R4. You MUST understand exactly what the TV cable does, and the importance of proper adjustment. You will also need a "geometry correction" throttle bracket for the carb, as well as some kind of scheme to lock & unlock the torque converter.

Photo shows the infamous 250 with PAIR and integral head/intake manifold. You can barely make out the dual exhaust pipes.

[MikeB]

Originally Posted by Accelo

1955 thru early 1959 cars came with a 4.11. In mid 1959 the O.D. cars were switched to a 3.70.

A 55 car with a 265 and 3-speed manual trans came with a 3.70 axle. I think Powerglide cars used a 3.55, and OD cars had a 4.11.

In 56, a 3.27 ratio was added, but I don't know what engine/trans combos it was used on. That ratio was available only in 56.

A 57 car with the larger 283 went to slightly taller gears. I think 3.55 was used in 3-speed manual cars.

I still remember installing 4.56 gears in my 57 Chevy with a fairly hot 292 (283+.060") and M21 Muncie. With tires probably no taller than 26", that car was virtually undrivable on the freeway, but man would it kick butt in a short street race!

['68OrangeSunshine]

Originally Posted by MikeB

For the kind of driving you're describing, a fresh 250-six will work fine. Just make sure it's not a later model with the integral head/intake manifold, which is prone to cracking. Some also had PAIR, which stands for "Pulse Air Injection Reactor" which puts chambers, air valves, and plumbing on top of the valve cover. Stay away from that setup! The only thing good about that engine is it had a dual outlet exhaust manifold. It also had a 2-bbl carb, but it was a nightmare of emission controls.

There are lots of aftermarket parts available for the earlier 250, such as 4-bbl manifolds, headers, and even cams.

Unless you do sustained driving at >70 mph, I'd say a 250 with a TH350 or manual trans would be just fine with a 3.08 - 3.42. Heck, a 292 would probably be OK with a 2.73 - 3.08. That's for tires up to 28'-29" tall.

Keep in mind that you add some complexity with a 700R4. You MUST understand exactly what the TV cable does, and the importance of proper adjustment. You will also need a "geometry correction" throttle bracket for the carb, as well as some kind of scheme to lock & unlock the torque converter.

Photo shows the infamous 250 with PAIR and integral head/intake manifold. You can barely make out the dual exhaust pipes.

Not entirely sure, but I think the Lower Ends of those later 250s are usable, if you mount an earlier head [63 - 74]. 250 and 292 use the same heads. Those can accomodate after market intakes [Clifford, Offenhauser] and exhaust manifolds [12-Bolt /Fenton type] or headers. I have Clifford headers [from 1978]. I don't know if they still carry the long-tube 292 type. Other makers [Flowtech, Hedman] also have headers for the ''Late Chevy L6''.

[MikeB]

Originally Posted by '68OrangeSunshine

Not entirely sure, but I think the Lower Ends of those later 250s are usable, if you mount an earlier head [63 - 72].

I think you're right. It's just that everything above the short block was crap!

Mine was in a well-used 82 C10. I thought about rebuilding it, using an earlier head and intake along with a cam and headers. But ended up installing a 350 and TH350. Actually worked pretty well with the truck's 2.73 axle. Believe it or not, that was the standard ratio for the 250 in 1982! It did have a 3-speed manual with a very low 1st gear (3.50 I think), so that got the truck moving.

[68 P.O.S.]

How about the GMC 305 V6?

['68OrangeSunshine]

Originally Posted by 68 P.O.S.

How about the GMC 305 V6?

Great engines in their day, but parts are really hard to get now, and there's no aftermarket of hi-perf parts to support the ''M'' engines. Also the OP said he wanted to stay L6.

[Dirt's72]

I have a 250 and a 292 pretty much original. The 292 loves gas though. I'd go with the 250.

[68 P.O.S.]

Originally Posted by '68OrangeSunshine

Great engines in their day, but parts are really hard to get now, and there's no aftermarket of hi-perf parts to support the ''M'' engines. Also the OP said he wanted to stay L6.

Yeah, I know. It's an engine that's kind of different, which makes it cooler to me lol. He could go with the larger 351 v6 too.....or even the 478 hahaha.

[Awann99]

So it looks like the 250 is the better bet for my plans. I'll keep the 292 for a k10 in the future. I didn't think about going all the way to 4.11 gears but with the overdrive it would probably perform better over all. Better off the line. The 250 is a great engine but it needs a good gear to help get the truck moving.
I may try the 250/th350 with 3.73 and then go with the 700r4 if I feel like it needs it.
I liked the suggestions of the gmc v6. Cool engines but not so great on gas and all the specific stuff for them would be way too much work to find.
Thanks for the suggestions fellas.

[caseyjones]

Thought I'd add a data point - I had a 64 C10 with a stock 292 (stock rebuilt carb), NP440 overdrive manual transmission, 3.73 rear gear, and 255/70-15 tires. The NP440 is geared just like a 700r4. The truck got 13mpg with a mix of city and highway driving, but it was a great combination for a get-around type of truck. Never felt like it needed more power and it could comfortably cruise at 70 in OD.

[MikeB]

Originally Posted by Awann99

I may try the 250/th350 with 3.73 and then go with the 700r4 if I feel like it needs it..

Sounds like a good combo for around town, but I think you'll find yourself trying to find another gear above 50-60 mph!

Compared to the truck you drove with 4.11 gears, the revs with a 3.73 would be approx 10% lower, assuming tire height is the same as what's on your truck.

Just be sure to build that 250 with revs in mind -- carb, intake, exhaust, and cam.

[kwmech]

I'd be looking for a manual 5 speed trans if you want mileage and simplicity, like an NV3500. With a 4.10 rear ratio, this 5 speed in 5th (.75) will give you a final drive of 3.08

[kwmech]

Originally Posted by 68 P.O.S.

How about the GMC 305 V6?

Gas hogs....been there

[72 tigger]

As a side note, I didn’t realize until I l read a article today on a K20 that the 292 was still used in 1978- thought they were discontinued earlier.

['68OrangeSunshine]

Originally Posted by 72 tigger

As a side note, I didn’t realize until I l read a article today on a K20 that the 292 was still used in 1978- thought they were discontinued earlier.

The L25 went on for a long time. Later ones were made in Mexico. They called them 4.8L L6. I guess '88 was their last year in production.

I have never seen or heard of a 292 from the Factory in any K/5s. I'm sure it was possible to order any engine you wanted from the dealer's wishbook -- especially if money was no object -- but if one exists, it's a rara avis.

[67 twins]

Originally Posted by 72 tigger

As a side note, I didn’t realize until I l read a article today on a K20 that the 292 was still used in 1978- thought they were discontinued earlier.

The one in my truck came out of an 85 and as 68OrangeSunshine pointed out was made in Mexico. The Mexican blocks are said to be better.
They did stop putting them in 1/2 tons some time earlier, I don't know what year.

['68OrangeSunshine]

Originally Posted by 67 twins

The Mexican blocks are said to be better.

The Mexican blocks are said to have thicker casting and are less prone to water jacket cracking. You can also bore them deeper, I am told. .060-Over is the max you can safely get out of a Flint block.
[They were trying to go light on the castings].
I have a Mexican 350 Goodwrench from 1998 in my Jimmy. Still runs fine.
Leo Santucci likes Mexican 292 blocks in his ''Chevrolet Inline Six Cylinder Power Manual.''
I have no experience personally with the South of the Border L6s.

[Although I might kill for a Brazillian L6 Head and Quadrajet intake.]

[Richard]

2000-2200 at 65 is what I shoot for comfort and street performance with OD. IMO fuel economy will be about the same no matter what you do. My 94 and 2000 truck both get around 13-14 mpg. Expect the same from my 72 with the LS swap, maybe a little more? In stock form it averaged 10 mpg empty or loaded. Same as my 72 K20 with stockish motor. Just saying, make the vehicle comfortable to drive. The difference in gearing will probably not matter as far as mpg. The motor choice in MPG is splitting hairs as well IMO.

[MikeB]

Originally Posted by '68OrangeSunshine

The Mexican blocks are said to have thicker casting and are less prone to water jacket cracking. You can also bore them deeper. I have a Mexican 350 Goodwrench from 1998 in my Jimmy. Still runs fine.

A lot of the 1985 and later 5.7L one-piece main seal roller cam blocks were "Hechco in Mexico". I've built up several junkyard versions, many for use as 383s, and I used a couple of the "880" blocks in personal vehicles. It's not uncommon for the bores to clean up at .010", or even .005" overbore, so GM must have used a different alloy on these later model blocks.

And there was almost no core shift compared to earlier blocks, so crank and cam ran smack in the middle of the engine. Also, for whatever reason, the black paint was more like an epoxy coating.

All hose positive traits, and yet I still hear folks talk about the cheap Mexican castings.

[Palf70Step]

MY 81 had a 250 with T350C (lockup converter) and 2.73 gears from factory. It did great around here and on the highway it would go all day at 75. Now granted most of down here is flat, but when I went to north MS or Louisiana for truck meets had no issues keeping up speed on the highway. You will not see much better MPG than 13-15 I would say, no matter what tranny rear gear combo you have at today's highway speeds. Oh BTW, that was with AC running and power steering on it.

I don't have my book handy, but believe the 292 ran thru mid 80s, although it was really rare to see them.