Will a 318 be ok to punch out to a 4.0" bore, cut a 360 crank to 340 mains, and build a stroker for a late model dirt car and hold 7K pluss RPM.

It could be done with the right 318 block. You need to have it sonic tested. Early blocks will be the thickest, I think they ended in 030 casting number and were produced from 67-71 or so. Another option if you wanted that bore stroke and main combo would be a poly 318 block with LA heads, they were very thick and have seen a few guys run them to 4.040 bore sucessfully, again get it sonic tested. Or another option would be a 360 with the crank turned down and spacers in the mains, but it would need very good bores to run at standard size. A 360 magnum block would be good for this purpose. A few years ago I had a bunch of 318s tested and only the early ones were any good, .030 wa about all I would have felt safe on the mid 70s and up blocks.

What we are planning on doing is running a chevy piston as there are a large variety of chevy pistons with all kinds of pin heights, and we can run a mopar rod with the small chevy pin size. Or we could even run a chevy 6.125 rod combo.

Just wondering??

Kasey

how many cubes are you looking for? how much $$ do you want to spend? some other thoughts, .060 over 283 pistons are .025" over 318 bore. 6" rods, 283 pistons and a 360 crank make a near or 0 deck stroker 318 that would be 348 CID (352 if you found .080 over pistons)....

or use some low comp cast 318 pistons, 318 rods, and 360 crank for a similar displacement.

Youhit it on the head, I figured a 348" stroker. Im glad you have the piston sizes now I dont have to work as hard figuring out the math.

Thanks

Kasey

well if you bore it to 4.0" and use a 360 crank you would have a 360,just use 360 pistons.

My concern is will an earlie 318 take a 4.0" bore, I dont want a weak thin block thats going to heat up all the time.

again, what's the budget, displacement limit, and what kind of RPM are we talking?

I'm not a fan of spinning a cast 360 crank to 7500 let alone for long periods.

W2s are the head alowwed, and we arent supposed to port, but :acid flowing" will be done. Oiling mods are going to be the normal trick mods, resizing oil holes, etc...

anyone make a 3.79" stroke crank anymore? .030 over 318 w/a 3.79" is 370CID.....

with KB forged pistons for a 4" crank and 6.25" rods, you have a short block with the pistons .010 out of the hole, diamond forged will be .002 OOTH....

or on the cheap, using .060 over jeep 4L pistons (3.935", 1.58-1.592 CH and .931" pin) and 6.125" chev rods will net you a 0-.012 out of the hole short block....but they have a 13-18cc dish in them....

The CI limit is a limit, we dont want to build right to that incase of a huge problem, so we would like to keep the 348-355CI range.

Kasey

I had a 4inch stroke 4 inch bore 68 318 ran real nice.

There is a guy on here with an even bigger bore bigger stroke 318 in his aspen.

If I was you I would just buy a steel crank for a 360 and put it in a 360, even .060 over will not be too many cubes. This will make more power because you valves will be less shrouded.

We dont want a 360 due to the large main bearings, We want a nice little buzzer, nothing with a crazy rod bore ratio, and no larger stroke than a 3.58 is allowed. W2 heads are it, 3.58 is it, and we can only run 1 intake, and it has to be a holley 2 bbl and make 450+hp to compete well.

Kasey

i have a brand new in the box mopar 3.51" forged crank,i'll take $350.00 plus shipping

I agree with dave, if you're limited to 3.58" stroke, you're better off using a 360. less valve shrouding....and if you only need 450-500 HP to be competitive, why do you need to buzz it to 7k+ RPM? why not build it for midrange power with a torque peak in the 4-4500 RPM range and a HP peak in the 5500-6000 range?

We need RPM for a 3/8 track. Its so short on the straight, and the cars are very wild suspention wise. They are constantly on and off the throttle. Its never at full throttle for longer than a few seconds, but its the decel that is hard on them. They get tossed in the corners really hard, and use engine braking to make the cars handle. If you havent watched these cars in action DO, they are AWSOME to watch, and they are a handfull!!

Limited late models, or just a local latemodel race is hair raising.

dirt track is my favorite roundy round to watch, but i haven't been to one in years, but I didn't think the wissota cars I used to watch up in Proctor or Superior spun that high.

I'd suggest talking to Jesse Lackman, I think he's had experience building dirt track motors, and I think Don (Moparsforlife) has friends who are heavy into the dirt track scene in N. Dakota....they might be able to give some advice.

what heads are allowed to be exact? aftermarket iron OK? I presume so since the W2's are class legal. for that kind of RPM I guess I'd be inclined to go short stroke/big bore to minimize valve shrouding and piston speed while maximizing displacement. a 383 with a crank destroked to 3.25" would net 369 CID, 374 CID at .030 over. add some indy SR's, and a small dome piston (~12cc) and you're in the 11.5:1 compression range.

with a 4.25" basic bore, you're looking at BBC standard bore sizes, so there's a ton of pistons out there that you might be able to adapt with some rework of the dome/valve pockets.

looking at the Kieth Black forged pistons for 454's, doing the math,

BBC pistons with a 1.27 comp height and 7.1" rods gets you .015 out of the hole

BBC pistons with a 1.52" comp height and 6.8" rods gets you .035 in the hole

BBC pistons with a 1.645 comp height, couple that with some BBC 6.7" rods and a 3.25" stroke, and you're looking at a piston sitting .010 in the hole.

granted main and rod journals (assuming using shelf 2.2" journal BBC rods) are bigger than an LA, but mains are smaller than a 360....

bummer things are so restrictive. I guess I'd use a .020 340 block, personally, or start scouting for a poly block with thick walls to bore out to 4.00 or 4.03.... then you could use KB107's and stock length rods with the 3.58" crank.

FWIW, a 3.58" crank, and 6" rods needs a 1.81" CH piston for 0 deck...which is the compression height of a KB167, or a KB 165 (chev 283 app, 3.875" bore, available .060 over, which would be a .025" over 318 bore)

KB165's are 488g/145g piston/pin, 167's are 507/132 (odd to me that the larger pin is lighter)

I would use these rods:

http://www.competitionproducts.com/prodinfo.asp?number=CPXPPF6000

that's for a set of 8....killer price, killer rod.

but spinning it that high, I'd probably do as long a rod as possible, and look at a shelf 4" stroker piston and a 6.35" long rod...

The rods look awsome!!

Has any of you guys on here ever use a howards rod?? The guy I talked to said they are 100% US made, in house with us 4140 blanks.
He also told me the powdered metal rods are just as ductile as the 4140 billets. They arent brittle like the oem style powdered metal rods.

I don't want to rain on your parade---but I think I should!

You are wanting to build a 480HP/two barrel/flat tappet dirt engine. Getting the 480Hp isn't a problem---getting it to live is a problem. Your weak point is the connecting rods/crankshaft. Get the best you can possibly afford---billet rods are the best choice---forget about Eagle, CAT, etc. You need something like an Oliver, King, or Crower seems to work well in this type of application. Why do you need this level of component? The dirt track gets rough---the cars "hook" so well---the vibration will kill substandard components.

Frankly, with a limited budget I would use a 360 block---don't worry about the larger main bearing. Use main and head studs!

Go on over to Moparchat---look in the circle track section---read the "Typical Oiling Modifications". If you follow the instructions, it will keep you out of trouble. While you are at it---prepare two blocks! A good 360 block will be good for 2000 laps!

The W2 heads will be fine with a good valve pocket work, shorted the intake guides 1/2", and make a cutter to machine the valve pocket down to the guide. If rules allow, use 2.06" BBC intake valves(shortened), the standard W2 exhaust is fine. If you can, 11/32" stems is nice but not absolutely essential. Set up a .050" seat width on both I/E. Check your intake manifold very closely for intake port alignment---most intakes require some TIG welding to properly align with the cylinder head intake runners. The heads should flow about 250-260CFM if properly worked.

With the two barrel(500CFM) Holley, you will need a cam with about .600" lift (AT THE VALVE), about 250 degrees @.050"(Intake), about 252 degrees (EXHAUST). Use a lobe separation of 108 degrees. Set the cam in at 104 degrees.

Use exhaust headers with 1 7/8" primary tubes/2" secondary/3 1/2" collector.

Use an MSD ignition, 32 degrees (Locked), 6AL box will be OK.

Buiding a good SB Mopar for limited late model is fun---just remember those chassis/tires are very hard on components.

I honestly think your budget needs to be at least $6K---with you doing all the engine work---and that's tight!

Good Luck!