350 to 250 swap i

[Awann99]

My truck originally came with a 250/3speed. The PO swapped a 350/350 into it form the 70s so the engines sits way back like a 4wd truck. I’ve added a sm465 so it is a manual again. But I want to go even further and rebuild a 250 and swap it back where it should be. The 350 in a great motor. It’s a goodwrench crate engine. It’s makes about 195 hp. Do you think I would see a large drop in power and fuel economy swapping to the 250? The truck has factory 3:07 rear gears. I love the sound and the look of I6 motors so I really want to do this swap. You don’t see I6 motors anymore. Plus with a 250 you have so much more room to get in the engine bay and work on it.
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[72c20customcamper]

A few minor mods and a 250 really wakes up . My 68 stepper is a 250 4 spd (granny) with 4.56 or 7 rear . Plan on doing intake cam headers and some port work in the future

[truckster]

I wouldn't call a SBC in a 67-72 Chevy truck engine bay "crowded". When people look at mine, they usually comment on how much room there is.

Anyway, I think you're going to give away a lot of torque and it's going to be noticeable, especially off the line, and especially with 3.07 gears.

[68Gold/white]

I agree with Truckster...

If you a want an inline 6, go for it!!! Until 1955, you got no choice in a pickup.

['68OrangeSunshine]

If you want to go L6 there are many possibilities. Some websites:
www.inliners.org
www.12Bolt.com
www.cliffordperformance.net
Have fun, and remember
6=8

[67 twins]

I say if you want to go inline 6 go for it. I personally prefer to drive my 250/4speed truck over my 283/5 speed truck.
Might I make a suggestion however? Since you don't already have the engine get yourself a 292 instead. You'll still have an inline 6. You'll have a 40+ cubic inch advantage over the 250. All the same performance parts that fit the 250 will fit the 292 as well. & to top it all off you get a truck engine in your truck. The 292 was the only one of these engines designed solely as an engine for trucks.
That is what I am doing with mine. I have a refreshed 292 that will replace the 250 if I ever get caught up on all those little things that crop up to rob your time.

[franken]

If it was an I6 from the start I'd guess a low original rear ratio. Might want to check.
Trucks have a ton of room under the hood so that's not a concern.

[MikeB]

Below are some numbers that I found for 1969 truck engines. These were still "gross" numbers back then before the switch to "net".

250 six: 155 hp, 235 lb/ft
350 V8: 255 hp, 355 lb/ft

I think GM is now calling your base Goodwrench 195hp crate engine a "350/265", because it's always been known to make 260-something horsepower with a 4bbl carb and dual exhaust.

Anyway, with a 250 six, you'd be giving up ~100 hp, and more importantly in a truck, ~120 lb/ft torque! So, you just need to know that and be prepared for it. Also, that 250 won't be too happy with a 3.07 axle, especially with the usual 29" tall tires. That means shorter tires or a 3.42-3.73 ring & pinion. And don't plan on taking highway trips with a 3.73!

Sure, that 250 six can make more horsepower with aftermarket components and cylinder head work, but most mods like that actually give up some torque at lower RPMs.

Bottom line, if you're stuck on a six (which I actually think is cool) I'd try to find a 292, which in perfect condition would probably be OK with your 3.07 axle ratio, and make as much torque at a 307 V8.

[MARKDTN]

I would not go to all the work and expense to change back to a 6. For what you will spend fixing the 6 you can build a healthy V8. You also have to realize that the crate is rated Net HP while the original was Gross HP. The difference is noteworthy. If I was to do it, I would find somebody who wanted a V8 and do the swap side-by-side. That way you both have all the little things that are hard to think of. Exhaust, transmission mounting, etc.

[Awann99]

I thought the 3.07 ratio was strange as well but it’s the only mechanical option on my SPID. The serial number has an “S” in it so I know it had the 250. I guess it was made as a highway cruiser? I have a 292 sitting in a 70k mile parts truck. The only reason I was leaning away from the 292 is because I’ve heard it was a gas hog. It is a powerhouse but would it be a decent highway driver? This truck is my cruiser. My truck that has a 350 in it is sitting on i6 mounts so I don’t have to change anything but the exhaust, clutch mount, and few other things.

[GASoline71]

You'll have to put your foot in it more to get the truck moving, so any I-6 is gonna be a gas hog.

Inline 6's have their place, but if there is already a V8 in there, your gas mileage is probably the best it's going to see.

Gary

[MikeB]

Originally Posted by MARKDTN

I would not go to all the work and expense to change back to a 6. For what you will spend fixing the 6 you can build a healthy V8. You also have to realize that the crate is rated Net HP while the original was Gross HP. The difference is noteworthy. If I was to do it, I would find somebody who wanted a V8 and do the swap side-by-side. That way you both have all the little things that are hard to think of. Exhaust, transmission mounting, etc.

I'd be surprised if the 195 HP number is net. I think it's probably gross, given the very low compression (7.8:1 actual) and crappy heads. But I don't know how they came up with the number. Was it with a 2-bbl carb and single exhaust?

And it's said the 260-265 HP rating is with a 4-bbl and dual exhausts. Was that using headers or cast iron manifolds? And were the exhaust pipes 2", 2-1/4", or 2-1/2"? How about the mufflers -- stock high-restriction, or performance low-restriction?

Just occurred to me that the L31 350 with EFI, Vortec heads, and 9.4:1 compression is rated at 255 HP net. To me, that really says the Goodwrench engine is definitely rated in gross HP, because no way is it anywhere close to the L31 output.

But even a totally stock Goodwrench 350 engine with a late 60s Rochester 2-bbl and single exhaust will have more of everything than a 250-six.

[pjmoreland]

I had a 67 with a 250. It had 4:10 gears and an overdrive from the factory. That engine was quite wimpy, but it got good gas mileage on the highway, which may have been mostly because of the overdrive. I installed Clifford headers combined into a single 2-1/2" pipe and a Flowmaster 40 series muffler. Sounded like a Honda Civic with aftermarket exhaust. I also installed a Clifford intake manifold and a tiny Holley four-barrel carburetor. Those add-ons did wake it up a bit, and I drove it that way for a couple of years. I ended up installing a mild 350 in it, and I was blown away by the difference in performance.

['68OrangeSunshine]

Originally Posted by 67 twins

I say if you want to go inline 6 go for it. I personally prefer to drive my 250/4speed truck over my 283/5 speed truck.
Might I make a suggestion however? Since you don't already have the engine get yourself a 292 instead. You'll still have an inline 6. You'll have a 40+ cubic inch advantage over the 250. All the same performance parts that fit the 250 will fit the 292 as well. & to top it all off you get a truck engine in your truck. The 292 was the only one of these engines designed solely as an engine for trucks.
That is what I am doing with mine. I have a refreshed 292 that will replace the 250 if I ever get caught up on all those little things that crop up to rob your time.

Second that motion. 292s Rule.
You will need to source a set of 292-only Passenger Side motor mounts. While the Driivers Side mount is the same as 230/250s, the 292 has appreciably more torque -- so GM engineers put the RH mount forward. Motor mount and fuel pump change places on the bigger L6.
My built 292 in the '68 C/10 has a lot more guts than a crate 350 in my '71 Jimmy.

[Dirt's72]

I have a 72 c10 that originally had a 250 3ot but did not have a motor in it when I bought it. The guy had a built 350 and 350 trans he was going to put in it. He had already had the automatic column in it. I sold the 350/350 combo and purchased a 250 motor. The first two 250 motors I bought had already been bored .60 over. Third one finally was rebuildable so had it done and installed the 3ot and 3speed saginaw. It has a 3.73 rear end. It does wrap out at 60. I bought a 3 speed saginaw with an overdrive to put in it in the future. I really am happy with it its fun to drive. I also have a 69 c10 with a 292/350 combo. Both have power steering which is a dream compared to not having it. I have to admit as of now I prefer to drive the 69. Mostly I guess cuz its so effortless with the auto trans. And I like the buddy bucket seats that are in it. The 72 w/250 just has a bench seat which I dont like. The bench seat will be going bye bye soon. They both feel the same off the line. The 292 loves gas. Both motors are stock.

[Carl Spangler]

I wouldn't swap my original 250 for a 350 but I also probably wouldn't swap a 350 back to a 250 even if a 250 was in the truck originally.

[Grumpy old man]

put a 292 in it .

['68OrangeSunshine]

Originally Posted by Grumpy old man

put a 292 in it .

Yeah!
292 Rocks.

[MikeB]

Originally Posted by Grumpy old man

put a 292 in it .

That's a beauty, man! Easy to work on, too.

[Awann99]

I guess a 292 is where I will go then. Here is the 292 I mentioned earlier that I have sitting with all the rare air cleaner stuff on it. I would Like to add AC one day so I assume 292 ac brackets will be extremity hard to find.

['68OrangeSunshine]

Originally Posted by Awann99

I guess a 292 is where I will go then. Here is the 292 I mentioned earlier that I have sitting with all the rare air cleaner stuff on it. I would Like to add AC one day so I assume 292 ac brackets will be extremity hard to find.

True. If you're OK with aftermarket [and have a rich girlfriend] They make some billet aluminum AC and P/S brackets for sale on Ebay, for around $300.

Or, look up Davis Speed Equipment.

[Wrenchbender Ret]

The 292 is a good tough engine but I think you are going to regret removing that 350 V-8.
The v-8 with a Q-jet carb & dual ex. will get you as good of gas mileage as either one of the other. With the3:07 gears it should be a pleasure to drive.
George