Engine rebuild or swap


Jun 24, 2017
When I started my 68 GT 350 for the first time this spring I had a knock in the motor. Knock went away as it warmed up with me trying to figure out where the knock was coming from. It's been diagnosed with at least three cracked piston skirts. So it's time to do something if I want to drive it. Sadly, all the engine builders I have contacted locally are booked. One told me it would be winter before he had time to get to it. Don't like that but can live with it to get my car back on the street. Doing some research on options. This is what I am thinking.
If I have to rebuild it I might as well add some HP and Torque. Be nice to have 300+ torque. Set it up for a street, low end torque motor as a weekend driver & show car.
1) My engine is a 68 Mexican block so it is NOT the original motor but what came with it when I got it in 1982 from the original owner. The prior owner told me the motor had be rebuilt. Don't know if it has been bored before. This motor is pretty much stock except for the cam, lifters, & springs. It has the infamous Ford Motorsport C90Z-6250-C hydraulic hipo cam and lifters that I bought from Ford about 1970. Love that lope of this cam and want to end up with that idle no matter what I do.
2) It's pretty hard not to consider getting a crate motor and just swapping. The 347 stroker with 400 HP and Torque Looks pretty nice. Be like having a different car. But I am concerned about buying a motor regardless of the warranty from someone 1,000+ miles from me here in MN. If I have problems I have to ship it back to the builder? Any one have experience with crate motors. I looked at what Ford offers. The Ford crate Boss 302 340HP ($7500) looks pretty good but I am not confident those heads would work with my Cobra intake and Tri-Y headers. This is another concern is finding a crate motor that drops in and allows me to use my existing parts like headers, intake and toploader. On Summit Racing's page I read about the Blue Print 347. $4600?? with a roller cam and aluminum heads. Almost too cheap. Wonder what the internals are? Built using Chinese parts was what one other builder said to me who wanted $8800 for a comparable engine. Jasper has some nice pricing and have a local shop to me in St Paul. But they don't do custom builds, off the shelf only. This whole crate motor deal is confusing for sure. Cheap is not necessarily better in this case. A local builder quoted me $9000 for a 1995 HO block 347 full of name brand parts like Edlebrock Performer heads (retails for about $1800 for the pair) & Ford E303 roller cam and lifters. forged pistons etc. All top end stuff. How can Blue print do it for half that price?
3) Then I have to deal with what to do with my existing 302. Inclined to see about just rebuilding it, adding forged pistons, new crank, aluminum heads. Is this cam too old tech to take advantage of the aluminum heads? Or the Shelby Cobra aluminum intake? Should I go with a roller cam set up in this old block and what does it take to install that?
If I go with a crate motor or roller cam I am going to have some parts I don't need.

You guys that have already done this please give me your thoughts and what you did. We all eventually end up here. I'd like to hear what you have done, how successful it was and are you happy with the results?
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I’m in the same situation. It really comes down to budget, time and what you want out of it. There are some really nice crate motors out there, but you’ll pay a premium for the ones built with quality parts and carry a decent warranty. If you have a local reputable builder who is decently priced and will warranty their work, well you have that option. The next question I tend to keep asking at that point is, how strong is my old block, that I have absolutely no idea the true mileage on it?

So I’m left leaning towards going crate motor, but that budget isn’t here yet, so for now I’m trying to just freshen up the old’ish 91-96 5.0 engine that the PO installed and keep her smooth until that budget appears.
It depends a lot on your goals for the car. I once did an idiotic thing. I rebuilt the original straight six that came in my 1970 convertible. Kicked myself quite a bit later.

Now the car has an old 302 from a highway patrol car. It's all stock except using a carb now instead of EFI. Well over 100,000 miles on it when I swapped it into my car in the 90s. Definitely even a worn 302 making 200 hp or so is better than a fresh 250 straight 6. And those late 80s early 90s 302s last virtually forever. It has enough power to be a fun cruiser.

A 302 is a good engine choice in my opinion because it leaves lots of room in the engine bay (easy to work on), makes decent power and parts are inexpensive. If building a 302, I would do heads from Jon Kaase in Georgia, stroke it to 347 (I like the Coast High Performance stroker kits), and go with a relatively mild cam. Either that, or I wouldn't spend the money to rebuild. I don't think it's worth spending a bunch of money and time for a freshened up engine if you aren't going to build it up.

Budget is usually important, so another option to consider is to just buy a used engine from the junkyard and swap it in. I would assume you can still find 302s from the 80s and 90s relatively cheap.

You might also want to spend a little time considering why you have a damaged engine. Any chance it got over-revved? Maybe an MSD box or something with the capabilities to limit maximum engine RPM would be a good investment along with the new motor.