motor swap question

gbs · Dec 27, 2011

going to change out a 350 chevy to a 250 6 cyl truck has 400 thm will the flex plate work off the 350 on the 250.

Bob Huntress · Dec 27, 2011

Usually if the years are close.

Goose · Dec 27, 2011

I swapped a 283 V8 into a '67 GMC pickup in place of a 250ci 6 cylinder once.

It had a manual trans, and I had to use the 6 cylinder flywheel. The V8 flywheel was too small diameter. Both engines were internally balanced, so it didn't matter.

Dean · Dec 27, 2011

No.

The 350 is externally ballanced. Not sure about the 250 but not likely and different in any event.

Dean

ericlb · Dec 27, 2011

the 400 sb is externaly ballenced, the 350 and the 6 are internal, depending on the year the 350 flexplate will work, but there were some exceptions, the main thing is you will need the harmonic ballencer that goes with the 6, from experience make sure that 6 is a 250, if its a 292, and your looking for better gas milage the 292 wont get you there, the 292 and the 350 are almost the same fuel economy wise, the 250 may be better unless you live in the mountains and will have to run the 6 at maximum power all the time,

Jon Hagen · Dec 28, 2011

The pre 86 model small block V8(except SB 400) is internally balanced like the 6 cyl, so the wheel will fit and balance.
After 86, the SB Chevys with one piece rear crank seals are a whole nother animal with a different balance wheel for most every size.

old · Dec 28, 2011

More info needed for us to be able to help you help your self. The older ones say before 1980 or so where all the same but some place in the late 80s or 90s things changed. Now of your swapping to save fuel the 250 will not help you any they loved fuel.

elmersooner · Dec 28, 2011

absolutely.

buickanddeere · Dec 28, 2011

Not going to gain any fuel economy with that swap.
How about a Gen III 5.3 Chev and four speed auto with lock-up torque converter from 1999 to 2004?
That will improve mileage. Any engine combo with a non lockup auto trans is not going to deliver mileage.

buickanddeere · Dec 28, 2011

The LM4 (VIN code "P") Vortec 5300 is a light weight all aluminum block and head version of the LM7.

LM4 applications:

2003–2004 Chevrolet TrailBlazer EXT
2003–2004 Isuzu Ascender
2004 GMC Envoy XL
2003–2004 Chevrolet SSR
2004 Buick Rainier

bradk · Dec 28, 2011

Dean,you're thinking of a 400 SB.

bradk · Dec 28, 2011

Didn't see that mileage gain was a top priority.My guess is that he already has a 350(pro'ly a carb engine) acquired for the swap.

Texasmark1 · Dec 28, 2011

Glad I stayed out of this one!

Anonymous-0 · Dec 29, 2011

I think it would work. But WHY would you want to change a 350 for a 250? Most people change smaller engines for larger ones. Good luck!

motor swap question

gbs

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Bob Huntress

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Goose

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Dean

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ericlb

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Jon Hagen

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old

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elmersooner

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buickanddeere

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buickanddeere

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bradk

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bradk

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Texasmark1

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Anonymous-0

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