I-6 to SBC swap

Hi there.

Iv'e been thinking of removing my original 250 inline six engine from my 1978 Bel Air sedan and dropping in a mild 275ish HP SBC. I have many questions regarding this and would just like some ideas if anyone has done this swap before.

I know the mounts will change but what frame holes are used? and I'll have to redo the exhaust but will the fan shroud still work?

I don't know if the cross member was the same part for both the 250 6 and both optional V8's so what would be my options if I was to add dual exhaust? I really dont want to notch the driver side of the X member.

Should I reuse the original drive shaft or is this a I-6 spec part?

Thanks

I've never done the swap.  I'm curious as to what can be re-used and what can't.  

This might help -




I'm betting you can re-use your drive shaft and trans x-member.  It just sounds like something GM would do to keep expenses down.

I've done dual exhaust with no mods to the x member by using mid length headers and routing both pipes from the collectors to the right (passenger) side.  Similar to the way the "Y" pipe from a stock exhaust is routed from the left side.  Granted it's more restrictive on the left side due to the bends, but it worked.  I ran both pipes down the right side and into Cherry Bomb glass-pack mufflers then over the axle and out the back.

Please keep us updated with your progress!

Sweet Seventy9 wrote:I've never done the swap.  I'm curious as to what can be re-used and what can't.  

This might help -




I'm betting you can re-use your drive shaft and trans x-member.  It just sounds like something GM would do to keep expenses down.

I've done dual exhaust with no mods to the x member by using mid length headers and routing both pipes from the collectors to the right (passenger) side.  Similar to the way the "Y" pipe from a stock exhaust is routed from the left side.  Granted it's more restrictive on the left side due to the bends, but it worked.  I ran both pipes down the right side and into Cherry Bomb glass-pack mufflers then over the axle and out the back.

Please keep us updated with your progress!

Hey thanks for the reply and posting that cool diagram, I like seeing stuff like that.

I'm not 100% sure if I will do this as I really do like the uniqueness of the 250iddy but it's getting a bit tired and needs a valve job but I really don't want to spend money on that dreadful integral intake cylinder head lol.

I'm pretty sure I'll need a donor car that had a SBC from factory.

Can I use any other X member from another B car or aftermarket?

78i6belair wrote:<snip>Can I use any other X member from another B car or aftermarket?

This might help

https://www.gmbbodyforum.com/t31-transmission-crossmember

Okay, so, taking me back a few years...

The motor mounts should already be in the right place on the frame if you're going from a 250 to a small block chevy (they were on my '79). Same goes for the transmission crossmember if you're staying with either a turbo 350 or a metric 200 transmission. If you go to a 700R4 or a 4L60E, you'll need a different transmission crossmember and driveshaft.

The fan shroud will 'work' but it sits something like 3 inches further forward, so the fan will be exposed (not covered by the shroud) You can pull a shroud off of a newer V8 car, but most of them use a radiator that is 2-3 inches narrower. Other than that, you have exhaust to figure out, the shifter linkage is the same if you stay with column shift. You will need different radiator hoses. The fuel line should be the same, though I'd take the time to inspect it while you have the motor out. Will be easier to replace. Same goes for the brake line that runs from the proportioning valve to the passenger side front brake. Much easier to inspect or replace when the motor is out.

the Power steering lines will 'work' but they won't be happy. I kinda had to really twist mine around to fit properly, but they'll work in a pinch. I would also look up a vacuum diagram for a v8. There are a ton of 'emissions controls' you can rid yourself of, but important things, like the power brakes, vacuum advance on the distributor, and heater controls (if you have air conditioning, the switching is all vacuum operated)

One other thing: I noticed that if you get the motor from a truck, the motor mounts won't always line up perfectly side to side. I had a motor out of a suburban and the brackets that bolt to the motor were about 1/4 to 1/2 of an inch too wide side to side. Just something to look at. I think I ended up using a set of brackets off a full size Chevy Blazer.

Oh, and you'll want to take a little time reorganizing the wiring harness. all the important stuff is there, but things like the distributor is on the front of the motor on the L6, and at the back on theV8. The alternator is on the other side. Little things that can be a pain in the @$$ later on.

One more thing: If you stay with the original transmission, make sure you get a flexplate (flywheel) that has dual bolt patterns. The L6 uses a smaller diameter flywheel than the V8's, and thus has a smaller diameter bolt pattern on the torque converter. Most Small block chevy flexplates have both small and large diameter bolt patterns, but I've come across a few that don't. Just trust me, this is one of those things that you don't want to come across /after/ the motor is in the car. You can use the L6 flexplate on most pre 1986 small block chevy's (ones with the valve cover bolts along the perimiter) but NOT, I repeat NOT, on anything 1987 or later, (center bolt valve covers).

Anyhow, let me know any other questions you might have.