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Discussion Starter #1
Hi All,

My 351w is doing so-so at 178k, but I'm getting some white smoke out the tailpipe and I want it to be strong for 500 mile+ trips. I looked in to replacing the engine altogether instead of just the head gasket so I can keep it going for another 200k, but I started wondering if I could go smaller - for better mpg. I've looked around and there are some 5.0 to 4.95 I6 swaps on here but nothing comes up for 351 5.8 to 300 4.9. Could it be done? I'm not using the truck for hauling or anything that needs lots of power and would be stoked to get a few more mpg. Any advice is welcome.

S
 

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Yes the 300 can be swapped it just oposite of the 300 to 351 swap. Would i do it myself, no but its your rig. The cost of a rebuilt 351 long block isnt much. By the time you get the 300 and everything else for the swap i would be willing to bet the cost is comprable. That and a new 351 should get better milage then an older one.
 

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Roller rockers are gay
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Everybody assumes "white smoke out exhaust=headgaskets." *shakes head* Not always. And if it is a headgasket, you typically get no heat, no power, mis-fires, very fast overheating.

If it runs fine, has great heat, good power, doesn't overhead you're probably looking at an intake gasket. When they let go they can and will burn the coolant and make a milkshake of the oil since it drips right into the oil too.

I often wonder how many people unnecessarily pulled cylinder heads because they overlooked a simple intake gasket. Taking an hour to do a compression test, leakdown test and pressurize the coolant system will tell you a lot.

In my opinion, dropping a 300 into an automatic transmission is a waste of time, especially the C6 which is a black hole when it comes to torque and horsepower transfer. Fix/replace the 351w with another 351w if it comes to that.
 

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Sure you can do the 300 swap, a good used 300 will definitely be cheaper than rebuilding the 351 and if you drive with a lead foot it will probably get slightly better mpg, but don't expect 20+. I agree with everyone else about trying to work with what you have first.
 

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Discussion Starter #5
Thanks everyone, I checked out newer 351's before I looked into this and that was my first idea, since it's about the same price as a 300 and a straight swap. I drive pretty mellow, 55 on the highway and not much city driving but there are some hills around here. I get 9-10 on average, which seems low for driving so easy. There are tons of things that could be causing it from the looks of the mpg threads, the engine probably is one of the last things, but I'd like to trust it 100% and the swap would be educational for sure.

Steve83 I'll look into that newer engine and Quint's build, that thing looks mean!

TheUnforgiven I'll look at my intake gasket as well. We have a mechanic who comes out here to the farm and he should be able to give me a hand wth the tests. I haven't noticed too much milk in my oil, but I'm guessing if anything it's just a minor leak.

S
 
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