I recently bought a 351m for $50 heads and all. It has a blown out cylinder wall in one hole. I want to sleeve it and r&r it. The question is in everyone's opinion what is the cross roads for hp and reliability.

 

Welcome to FTE.

Are the heads good? If so, just find another block. These are not rare motors and there are plenty around. If you are looking for power, you need to find a 400 anyway, as there is no practical way to make power with the 351M due to a lack of economical piston choices.

 

The heads are good they are at the shop

 

To be fair, the block is the same between a 351M and a 400, he would just need a crank and pistons (which he'd probably be doing the latter anyway). But if it's got a hole in it, I agree that I'd rather go get another one than try to sleeve it. There's saving money and there's being cheap, and with no shortage of available intact blocks, you might as well go get one of those.

 

Pistons are a PITA for the 351m so it's customs or a 400 swap with the kb2347 flat tops $444 after shipping (as of April 2017)

 

I agree - find another block, preferably a 400 with a crank. As was said, there are no pistons for an M that give more than 8:1 compression. But Tim Meyer, who is the king of these engines, has pistons for the 400 that yield essentially whatever compression you want: https://www.tmeyerinc.com/category-s/1877.htm.

As for your question, we need to know more about what you want to do with the engine. Most of us have them in trucks and want low-end grunt, at the expense of high-end horsepower. Tim dyno'd my 400 at 384 HP and 500 ft-lbs, but that was limited by the choice of cam, which was spec'd for drive ability and MPG.

 

Well, pistons can be had but it will takea lot of work, probably custom bore, maybe fly cuts in pistons, a lot of balance work. If your heads are good then a 400 crank and some good compression, as far as dependability, I feel that the best way to get a good engine that performs but is not a nightmare to tune and drive is in the 10:1 CR and shot for a cam that is around that 1500-5000 rpm range, or 2000-6000 rpm, that is about as radical as I would want to go and expect to be able tosit in traffic, hot rod a little bit, and still have vacuum for brakes. my 400 is just pistons, cam, and balance. It is a crower cam. It is quiet,snappy, throaty, rumbles, all kinds of torque, and very smooth. More cam would be acceptable, but Iwanted an engine to drive, sound, and run like a stockengine with more power. That is what I have. You would probablybe impressed with around a 270 cam, improved intake, bump the compression, adjustable valve train, GET THE RIGHTLENGTH PUSH RODS FOR THE BUILD, not just stock, headers, a 600+ 4 barrel, maybe some mild port work, like just port matching, and I bet the power would follow.