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Chevy 250 to 350 Engine Swap
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TOPIC: Chevy 250 to 350 Engine Swap

Chevy 250 to 350 Engine Swap 8 years, 6 months ago #8314

  • john_w
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I'm posting this for a club member I talked to earlir this evening who rarely uses the web site ...

Anybody done a straight 6 Chevy 250 to Chevy 350 V-8 engine swap? Specifically for a 1979? And if you did, do you have a write-up on it (similar to the 3.8 to 4.3 V-6 swap in the Fall 2008 newsletter) identifying what needs to be changed, such as radiator, engine mounts, transmission mount, drive shaft, whatever?

John W
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Re: Chevy 250 to 350 Engine Swap 8 years, 6 months ago #8321

  • captunderdog
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The 250/292 to 350 swap is pretty straight forward as GM didn't change a lot of that stuff. The bell housing, torque converter, flywheel doesn't care which Chevrolet engine it is bolted to. Except for the 400 small block and the 454 big block which both are externally balanced with weights on the flywheel. The driveshaft will not change at all since the transmission will not move. The motor mounts should be the same, they were in the Chevelles. The oil pan might be an issue, but so many pans are available for the 350 that is should be easy to cure. The only real difference will be the fan will be located on the same plane but approximately five inches rearward of where it was. The exhaust will have to be completly rebuilt.

Some of us old guys remember when there was a NHRA pro-street class for six cylinder engines. The rule makers tried to make the playing field level by imposing rules on the Chevy engines that nobody else had to comply with. But nothing worked and the class was totally dominated by the 292 Chevy. There was nothing else that came close, no matter how much engineering and money they threw at their Fords and Chryslers. They finally did away with the class because there was no competition for the Chevys. The 250 six is my favorite gas engine, probably because in the diesels, six cylinders RULE. The reason for this is that in a six there are seven main bearings, in a V8 there are only five. The crankshaft is much more stable and can stand way more torque delivered by each piston/rod assembly.

Years ago when I lived in Billings when gas was a buck fifty and propane was free (to all refinery workers and their friends) I built several propane motors. I built a 250 six for a 76 4X4 3/4 ton pickup. I used 12.5/1 compression pistons, an Edelbrock cam and balanced the lower end. In the head we put in the hard seats and stainless steel valves and smoothed up the passages a little. It ran strictly propane, it had too much compression to ever run gas again. When we were finished the pickup would out run any stock 350 and got 23-25 miles per gallon.

What I'm trying to say is I'd build an angry 250 before I'd swap in a 350, unless it was a Ram-Jet, huh Paul?
God Bless.
"not ashamed of the gospel" Rom. 1:16
1967 Marathon
1968 C10 Golden Anniversary Chevy
1983 Volvo F716 Service Truck
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Re: Chevy 250 to 350 Engine Swap 8 years, 6 months ago #8322

  • JiminGA
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Build up the 250! I've got one in my '79 Nova, and I plan to add Clifford Engineering headers, intake manifold (allows a small four-barrel carb), cam, and bore to a 305. The engines are nearly indestructible, fairly light, easy to work on and rev fast (and sound like a Porsche or something exotic when headers are on). If yours is in good condition and you don't feel like rebuilding it right now, then just add the headers and manifold, good for about an extra 50+ HP. If you do the full tilt, expect an extra 100 HP.

A note of caution though: The internals are plentiful, but good blocks are now nearly impossible to get. Locally, none are to be had. A long block rebuild is as costly as a V-8. The reason? Sixes aren't in great demand, so the junkyards sell them for scrap because they can get more in scrap price than reselling the engine. Make sure yours is crack-free before you start. And Clifford Engineering, from what I've read, has indifferent and slow customer service. You can find used stuff on eBay from time to time, but it bids as high as the new stuff. I've been consistently outbid on the headers and manifold.

I've got a 226 Continental six in my '63 Checker. I would dearly love to build it up, but alas, it's as obsolete as disco and polyester, so a small block is going into it eventually. I've given brief thought to yanking the six from my Nova and putting it in there.

Find some back issues of Nova magazine and see what others have done with their sixes. You will be amazed and shocked!

Jim In GA
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