QUICK! Can you bore a 5.2L-318 to a 340

[Dr. Righteous]

Will a 5.2L Magnum block stand up to a overbore to 4.04 bore? Stock bore is 3.91.

The idea is a Magnum 340 on the cheap. Minus the forged crank. Then you will have all the benefits of a Magnum engine (accessories, roller cam) and EFI if you want to make it work. There are plenty of goodies out there for Magnum engines so it really is an overlooked performance engine.

[AMR-Resto]

You would have to sonic check to know for sure but its highly doubtful that theres enough meat in the walls to go that far.

Why not just use the 318 .030" over (only 17 cubes short) or a 360 magnum (20 cubes bigger) ? Its not like 340 is a magic number for power.

[cudabob496]

My guess, no. Not enough cylinder wall.

[Paul Precht]

I wouldn't. Even if it held water, the thinner cylinder would loose power due to flex. Not worth the trouble, Paul.

[Dr. Righteous]

5.2L are cheap and plentiful, but because the 5.9L have the cubes for performance the salvage yards want a premium for them. Like 800 bones for the engine and all accessories. The 5.2L sell for $400. At least from what I have seen locally.

[AMR-Resto]

Theres no reason you cant build a strong running 5.2L. If the lack of cubes bothers you You can use a 4" stroker crank and pistons from Diamond to build a 390 cube small block.

[Ray Bell]

I think the magic of the 340 is in the bore/stroke ratio, its ability to breathe and rev (bigger bore unmasks valves etc)...

There's no doubt whatever that you can't bore a 318 to 340. And stroking will take some of that revving freedom away while not unmasking the valves.

We have Poly blocks, which should be thicker in the bores than LAs, and we've yet to confirm that we have one that will safely go to 4.0", so 4.03" is still a long way off.

One way would be to buy the main bearing spacers that enable you to fit a 318 crank to a 360, bore a 360 block 0.030" and you've got your 340.

[djswwg]

Ray, i have heard of these spacers, but have no idea where to get them. What's your source?............djswwg

[AMR-Resto]

Originally Posted by Ray Bell

There's no doubt whatever that you can't bore a 318 to 340. And stroking will take some of that revving freedom away while not unmasking the valves.

Its all a trade off. A high winding small block is fun but the torque of the stroker will easily make up for the .130" difference in bore size.

Also the longer stroke means the pin needs to be raised up in the piston which will make for a smaller, lighter pistons. Add in a set of aftermarket rods which are no more expensive then redoing stock rods or the smaller lighter magnum rods and you will have a very light bob weight.

Now you have more cubes and a motor that revs just as fast or faster then the 340.

Nothing wrong with the 340, I've built several from 300hp street motors to 500hp race motors I just dont feel that the "magic rod ratio" or big bore, small stroke is as important as other make it out to be. At least not in most street, strip motors.

I'll take torque fro the street over 7000rpm red lines every time.

[AMR-Resto]

Originally Posted by djswwg

Ray, i have heard of these spacers, but have no idea where to get them. What's your source?............djswwg

Mancini Racing has them but they are not cheap....

http://chucker54.stores.yahoo.net/mabesp.html

[Dr. Righteous]

Just something to muse about I guess. Like everything cost is prohibitive.
I read that early LA block (not poly) had thick wall castings and would stand up to a 4.04 overbore. In fact Hensleys Racing Ent. use to sell such a setup. Don' t know if they still do.

[cageman]

340 is a magic combination, I have many a 318, 273, 360, but I love my 340, and I crave more.
The big bore unshrouds the valve, and that allows better breathing, and it is in the heads is where you build power, If you can flow more air/fuel into the cylinder you build more power. simple enough.
Yeah, your screwed if you want a 340 and they charge that much for a core 360, and the crank spacers are 300, but what do you do.

[it's all dodge]

If you really want a 340, get you an older 318 block, like 1974 or earlier, punch it over, check the thickness first, than you can use your heads and above on it, should bolt in. Seen one like that run IMCE modified, and not breaking either

[it's all dodge]

Or, like you say, turbocharge it! Whatever, the 340 wil rev, rev, rev, yet not low end gutless like a boss 302

[AMR-Resto]

A good 340 will still make good torque, Just not as much as a 360 will.

[Dr. Righteous]

Originally Posted by it's all dodge

Or, like you say, turbocharge it! Whatever, the 340 wil rev, rev, rev, yet not low end gutless like a boss 302

I have dreamed of doing turbo projects for years now.
Seems like every time I get some money ahead to start a project, some kind of emergency wipes my stash out. With the wife not working seems like we can't stay ahead because of doctor bills and trying to keep our old vehicles on the road and keep the house from falling down around us. My project '72 Satellite is calling my name but I don't have the $$$ to invest in her right now, better let it set until then.

[cageman]

A 340 has no bottom end torque, compared to what, a cummins?

[rumblefish360]

Dr. Righteous; Oh man do I hear ya brother, man do I hear ya.
Oh, and ...

In fact Hensleys Racing Ent.

Takes sonic checked 318's out to a 4.00 bore and strokes them. If you could actually take a 318 out to 4.04, and the walls become thin, hardblocking half the block AKA the bottom end of it, would be a great help. Cooling should not be an issue since the heat issue is up top and and not as much of a problem on the bottom of the cylinder.
But I don't think you'll get that far. You might, buuuuutt.....

Clean, clear, hi flowing cooling system should be the min. High capcity should be the next step.

LOL @ cageman, AMR is right. The shorter stroke make s less torque. This isn't a 340 vs 360 thread, that is endless. But more arm for a street ride is nice.

[it's all dodge]

Just what weight vehicle are we talking??