Did 1970 Malibus come with single or dual exhaust out of the factory? Mine has the duals but I didn't know if that's how it originally was. Thanx.

Both. There are guys on this site that can give you exact numbers but generally speaking most of the big block cars had duals and some of the small block, four barrel cars did but not many. If you have a 300 horsepower or better, chances are it came with duals. Does your car have the original motor in it?

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Yeah, my malibu has the original 307 with a 2 barrel carb. I think they were measured at 200 horses. So I'm guessing someone added the duals later?

Duals are good. Technically they were optional on the L65 & L48 cars, not 307s. The reduced back pressure offered by duals is a performance must, and is said to also help with exhaust valve life. I guess it depends on whether you putt around or drive W.O.T.

In 1970 both I and my future wife bought each a new Chevelle Malibu. Hers was a 307 and mine, the 350 two barrel 250 horsepower version. Both came with single exhaust from the factory, hers from Baltimore and mine from Arlington.

Okay, so somewhere along the line someone had the duals added. Do you guys happen to know how much h.p. this adds?

I added duals on my 307. 2.25" w/super turbo mufflers. kept the stock exhaust mani's. with the engine stock, it didn't make a whole lot of difference.
After boring and rebuilding with a hotter cam and some performance upgrades, it made more of a difference.

you probably won't notice a big difference with the stock 307 and 2bbl carb.

The factory did offer dual exhaust as an option on at least the L48 equipped Chevelle. I don't know about any of the lesser HP engine combos. HTH