Stoking a 340

[plymouthman72]

I am about to pull my 340 (or so I keep saying) to get the body work done. While its out, I am thinking of stroking it out but I have a possible hang up. Back when my brother had the car, a valve dropped into the #8 cylinder and the result was...... well lets just say the result was not pretty! My dad took the block to a machinist and he said the block could be saved but that he would have to bore it to .030 over and sleeve that cylinder. We rebuilt the engine (well my day did, I got to be the tool getter) and it has run great ever since. well until the dash caught fire in 04 but that's a different story. My question is if its safe to do a mild stroke on an engine that has a sleeved cylinder. I am hoping to achieve around 450 hp but not looking to do a large stroke to 416 (unless i should???) maybe a mild stroker with new heads, ect. I am open to any and all opinions. The only thing I would like to do is keep the 340 (sentimental value) since my roadrunner originally came with a 340.

 

[moper]

Once you change the stroke of a 340 it's no longer "a 340". So I'd have two points to raise in order of importance to you:
1. if this is the numbers matching block - there's financial and sentimental reasons to keep it "intact".
2. if it's already been bored +.030 there is potential to see issues even before it's machined - but after you've made some investment and disassembled it. What that means is there's a chance once you've got it "gutted" the block won't work well for you anyway.
Given those two concerns I would rather see you stroke another engine if you want the power, and shelf that 340. Even if you reuse all the tin and heads and stoke a 318 (makes a 390") you are "safer" all around and can reach your power goal. You're talking under 1.15hp/inch. That's easy to achieve with good machining and good value parts. I think it will be a wash between any old 360 and any old 318 in terms of costs to build with a 4" crank package. I would not plan to use the numbers block, even if it did check and test out ok.

 

[plymouthman72]

Hi moper, thank you for the info. This isn't a numbers matching block but a year correct 340. If it was numbers matching, I wouldn't even think about stroking it out. The only reason it's sentimental is that worked on it with my dad and it is the right type of engine that came with the car. I know its not technically a 340 anymore but I can still claim it is and I would badge the car that way . I have contemplated that very thing in stroking out a 360 and shelving the 340 but since the 340 is ready for the kit that why I was thinking it would be better and cheaper to use. If its safe for a sleeve that is. This may be a dumb question but is there a physical difference between a 340 and 360 block? Meaning could someone tell if the hood was up that it's not a 340 just by the appearance? Thanks again for the help!

 

[moper]

Understood. There is no structural problems using a sleeved block. But - any block getting a larger than factory stroke should get sonic tested by an experienced tester with good equipment. That's why I said you might get into it and find the block not worthy of the power levels you want. Do not believe any of the "thick block" BS. That's all wishful thinking because the guys actually casting the blocks didn't care much about quality. Mopars suffer from core shift which leaves thinner sections of cylinder walls. When you step up and almost double the output with a lower rod ratio the bores are stressed more. They flex more and can crack over time. So they need to be thick as possible for longevity and power production. In terms of how I build them, I always will install main studs. So even if the walls are thick enough (I own a very good sonic tester) there will be machining in terms of line honing.
There is no visual differences between the 318, 340, and 360 that are all outfitted the same way in terms of manifolding and tin. but - the 318 and 340 share oil pans. The 360's is unique to 360s. So if you were to use a 318 block, everything would transfer. If you use a 360, you'll need an oil pan.

 

[plymouthman72]

Thanks a million! I actually just found out from my dad that only the #8 cylinder was bored out and then sleeved back to stock so that changes everything. I will still have a sonic check to make sure its safe but I really don't want bore out the 340 if its not already done. Do they make stoker kits that use the standard bore or can I achieve 450 from stock stroke? I definitely plan to have it sonic checked either way.

 

[moper]

My impression is you will be able to get 4.04 bore stuff but there will be an up-charge. No different than the higher prices for the 318-based pistons. Most stuff is available in 4.03 or 4.07 bores. So std bore or anything more than +.030 is more $$.
I'm also going to strongly advise you not to do the stroking bit unless you completely machine the block. IMO you are asking for trouble long term. A good engine needs the right dimensions, the right surfaces, solid parts choices, and careful assembly to run well for a long time. If the block is still std bore, at best you have factory tolerances for the basic machining which sucked. And you have wear on the bores and probably another re-hone for the last time it was fixed. The bores are most likely too big and not straight or round anymore. IMO - it's a waste of cash to build it as a stroked package. You're asking for noise, possibly smoke and leaks, and just a grumpy engine. Leave the 340 if the budget is that tight and save more cash.

 

[plymouthman72]

I 100% agree with that and will either just leave the 340 as is or find another engine to rebuild. I don't really want to mess it up. If I did use it, I would spend the extra and have it professionally looked at and cleaned up. I wouldn't drop serious cash into without making sure it's not capable of handling it. I would go big block but there is just to much involved for it and my car was never a big block so that's where the interest is at in keeping the 340 block. Plus I already have all the accessories. Chances are, I will rebuild a 360 and use 340 badging and maybe build the 340 to stock specs for the day I want to go that route.

Thanks for all the advice!

 

[moper]

Don't give up on a 318 either. Might be free or cheaper to get depending on your local availability. The smaller bore requires a little pricier piston but with the power level you want that's about the only down side.

 

[mutt71]

Not to hijack this thread, but, I haven a 318 2v that I have replaced all of the top end and camshaft, etc. with Edelbrock parts including a 4bbl. Pretty much the best that they had to offer for that engine. I was told by the last owner that the block was rebuilt, but there is no paperwork to that effect. The current mileage is 31K. I am thinking of finding another 318 to use as a replacement, to use for a stroker motor. Thoughts on this, in addition to the above advice moper? Thank you for all of the above advice and any more that you can offer.
BTW I live on Cape Cod, MA and would love to visit your shop, if you have one.

 

[moper]

No, it all is the same thing. If you want to reuse as many parts as possible go with a 318 or 340 core block. don't over pay because all you need is the block. Any 318 or 5.2L Magnum will work. In fact if you're interested in a hydraulic roller cam, an 85-92 LA 318, or 5.2L Magnum will allow that with minimum fuss. But - the only thing you'll need different is the oil pan if you score a 360. The parts, the labor, it's all the same.
I recognized Mashpee. My parents have lived in Rock Harbor/Orleans. for 15 years now. You're about 80 minutes from me traveling "off peak"...lol. As for my "shop", that's my home garage. I own a small private horse farm and have to live with a small budget...lol

 

[mutt71]

I really appreciate the assistance. Ahh Orleans. I will be there visiting relatives tomorrow. I used to get down there a lot more often, than I do now.