Good choice with the cummings, you just went up a few points in my book lol. I say custom fab a procharger onto a 300, then run 6-8 pounds, gain 50% TQ, putting you close to your 400 ft lb goal, and and around 275 on the HP. Stay outa boost and MPG will only drop round 1 or 2 MPG. Very streetable. Power on demand. MUAAHAH

 

^---i agree with that.

 

Rot, I dare say you don't know about the thickness of the cylinder walls in the block. From my measurements, original, unmodified cylinder wall thickness is only .135" in some areas of the cylinder wall. That's barely over one eighth inch. If you bore .080" a little core shift will make some areas paper thin. Nearly all obtainable 300 blocks are thinwall.

Rule of thumb for these thinwall castings is to bore as little as possible to clean up the cylinder and no more. Do not get fixated on a certain engine size-rather, just focus on getting a good, minimum, concentric cylinder boring job. The gain in cubic inches will produce minimal benefit compared to the other modifications you can make.

In addition, stroking it to any significant degree is also a bad idea, as the rod ratio is already poor. Additional stroke increases the sideloading on the pistons. Shortened engine life is the drawback. The gain in cubic inches from stroking is also negligible, even less than boring, as the formula for displacement is Pi radius squared times height.

A high cylinder pressure, high revving 300 with paper thin cylinders and increased sideloading on the pistons isn't what I'd call a motor with good longevity potential. BTW, I believe .060 over is the largest piston size I could find when I was looking to rebuild mine. Turbo it with a big overbore and it probably would have a very, very short life.

Think more like .030" over and leave the stroke alone. An extra 5 or 7 cubic inches is piddling small change and not worth compromising the integrity and longevity of the motor.

A NA motor with 400 lb. ft. at the wheels at a usable engine speed for offroading is very, very optimistic, unless you want a motor with no low speed torque at all. Better get a high stall speed torque converter if it's an automatic if you are going to try making those numbers. How about more like 325-350? Those numbers should be produceable at a useful rpm. Turboed I suppose it would be possible, but not at 312 cubic inches.

 

309, you are right as far as me not knowing the measurements and such. I gained that information from my machinist. I talked to my machinist again after reading what everybody had said here. He asked me what sort of application I intended to use the engine for, and I told him it was for my truck which is a daily driver/weekend warrior. Apparently he originally thought that I was going to be putting it in some sort of drag car , and said that I would be better off focusing on the core aspects of engine performance, and not so much on cubes. Told me that it is generally a bad idea to remove metal from the lower half of the engine if longevity is a concern. As you all know, I already plan on doing this, but as for boring it out and all that, I've changed my mind. So I am going with a new (modified) plan. I am still going to do most of it, but I am going to get a junkyard head in good condition (already know where it sits), and have the work done to it. I'm going to get all the engine parts I intend to put in/on over the next few months, and pretty much do an in truck rebuild. I'm also swapping in a ZF S5-42 in place of the M5OD. In case you're wondering, I'm going with a junkyard head to lessen the downtime. I figure if I can tear down and rebuild a Detroit 60 Series (and yes, it runs) in about 42 hrs, I can do a 300 in that or less.

p.s. its CUMMINS not Cummings!!!
proof~>http://powerstore.cummins.com/cgi-php/store.php?search=yes&detail=yes&category=2&subcat= 10&item_no=CI3572

 

hey man you were looking at spenging 7000 on this motor project.......i know you said you know what parts you want but i have an alternative for you and you may like it if you hear me out
i've run the inline six for quite sometime and i liked it, it truly did it's job, which was packing a punch and pulliing stuff around with the best econonmy but i've got a solution for you which is better spent with the amount of money you are going to spend. go grab a 351w block at .30 over and then get an eagle forged rotating assembly with a 4inch crank and 6.2" rods and 27cc dish pistons, that will put you at 408ci and a rating of 7000rpms then you could snag some brodix or jegs ALUMINUM heads that have 2.1" intake and 1.65"ex and 62cc combustion chambers that will put you at right about 9.2:1 compression which means you can supercharge or nitrous on pump gas(if you don't advance to far) if you don't though this setup will pump out 450hp EASY and handle it (remember you don't need H beam rods just some forged I beams) and trust me if you want different this is it, if you have ever raced a camaro ss in this setup and made him drop his jaw when a 95 EXTENDED cab XL wasted him at a red light, dude this is different TRUST me and money better spent because of the capabilities you have later on down the road and you are looking at about 6grand and you can always pull it out and use it in a mustang later if you want.....you definitly need aluminum heads and a mild hydraulic roller cam i wouldn't go solid. if you wanna do some real damage get a windage tray, knife edge the crank, have everything balanced at the machine shop, deck the block at .015, headers and a straight exahust then go get you a accessory bracket out of an old ford with the eight so you can hook up your a/c and stuff oh yeah don't go bigger than 235-245 ACTUAL duration or you might lose your ability to keep proper vaccum other than that maybe a big fuel pump and a vaccum pump that you can disconnect for long trips would be sweet but trust me.....alot of people don't put their money where there mouth is when it comes to building a motor so i PROMISE YOU WILL NOT SEE THIS IN A STREET TRUCK EVER unless you come see me or some of the other guys on the forum combo it up with a six speed tranny you will crap you pants every time you drive it.....and if any one is wondering where my I-six went.......you should see how good my mud boat pulls

 

all i can say is... LOL Sounds like too much fun!

 

I think everyone is getting confused, I said the TRUCK not the ENGINE is going to see about $7000. Although sapper_daddy's idea sounds great (seriously, I would love that setup, but HATE to pay for it, lol), it is not practical for me, nor is it what I am really looking for. That $7000 is for everything from a lift, wheels, tires and differentials to paint, interior and exterior mods and accessories, engine upgrades, a new tranny, and performance accessories like brakes, and a stronger clutch. I am going to do an entire frame and drivetrain swap (Including a Cummins ISB, a 5 or 6 speed manual tranny, and Dana 60s front and rear) once I am out of college and working. Thats where the $20,000 part comes into play. Buying the engine, tranny, axles, suspension and install/adapter kit, (or donor truck). Like I said, I am going to school, its not like I have a grove of money trees to fund my projects, but at the same time, I'm not going to just let that money sit and collect intrest when I could be doing what I love and making myself happy.

 

if you can find the right donor truck and a few extras you might be able to at least do a v-8 swap, do some research you might like what you see, especially if you are gonna pick that thing up in the sky you might not like the results that the six can give you because you are gonna be hurting on the top end, highway speeds are probably gonna be below 55mph, something to think about though. another thing too is that the six IS good for pulling but you could really hurt that slow turning motor in a low gear situation with some reserve for the mechanical abilities, but i'm not a preacher trying to convert you rather i'd hate to see you be disappointed after the truck is all jacked up (ever pulled a motor out of a truck with a ten inch lift?) and plus i really like to see people haul ***, cause that is always a good thing(unless you hit a tree or run over someone's grandma) the thing that the eight can do that the six can't is last a long time in a high strain high horse power appllication. once again, just do some research and see how many true off road trucks have a seriously modified six, not cause it can't be done it just is easier to do it with an eight, if you put your money in some good parts you can really show spectators what you are made of, don't be scared to mess up a block if it's worth it to you because after all a block is really inexpensive and then a new set of rings and pistons and slap them in and you are as good as new(yes easier said than done) but remember once you've got the head and cam combo you want, you've always got them