This is for 340 builders

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66silverfish

66silverfish

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All right guys, need your ideas.
I have built a lot of engines, but I have always used matching parts. I'm presently restoring my Fathers 66 Barracuda. He has owned this since day one. Step Sister had the engin rebuilt 17 years ago when she had it. Garage took out the 273 and put in a 318. I get the car last year and it has not run in 15 yeares and was in her barn all this time. Engine is frozen tight.
So I will replace it with a 340. I have a 71 340 block .040 over.
Here is my question; have any of you used a 318 crank, rods and pistons in a 340? Crank is forged, as well as the rods. All journals are near factory stock. Block has light surface rust, can still see cross hatch hone pattern. Same with the crank. no pitting. The guy we got everything from has a lot experience building MOPARS. His garage is a MOPAR guys dream. and he is selling everything on craigs list. He said he always used 318 parts in 340's and never had any problems.
I have not done this and I'm on the verge of throwing out the crank and rods and getting 340 stuff.
Let me know what you think.
Thanks for your help.
 
crank is the same, 318 rods are usually light duty, i would go with 340 rods, pistons will not work.
 
In short, what he said, 318 and 340's shared the same crank (dimensionally speaking), but I'd go a little safer on the rods and forged pistons.
 
The 340 has a larger bore than the 318 so using 318 pistons is not an option, you`ll have to use 340 pistons. The 340 has a heavier rod, the 273 and 318 used a lighter rod. It may be possible to use a 318 crank but with larger/heavier (340) pistons you would have to add weight to the crank to re-balance it, not cheap. In all it`s not really feesible.
 
Pistons are going to be replaced. Was going to balance the entire rotating assembly, dampener, flex plate and conveter. Sounds like I will be replacing everything. If I do keep the crank, heavy metal will have to be added during the balance. Do they still use lead or is there something else they use these days?
 
Sounds like it's time for a stroker kit then.

Cranks are balanced using Mallory metal and it's very expensive.
 
66silverfish said:
Pistons are going to be replaced. Was going to balance the entire rotating assembly, dampener, flex plate and conveter. Sounds like I will be replacing everything. If I do keep the crank, heavy metal will have to be added during the balance. Do they still use lead or is there something else they use these days?
Click to expand...

I've had over a dozen 340's and the cranks are the same, you will have to have the rotating assembly balanced anyway so the weight difference won't matter but most new pistons are lighter than the stock ones so the weight difference won't be much if any. To add weight they just drill a hole and insert a tungsten weight and weld it in. Adding weight is common when balancing an engine, especially if you go with pop up pistons or the engine was bored because the pistons are heavier than the originals.

As far as the rods, the rods that come in most 318's are a lighter rod, Most steel crank 318's came out of trucks and the rods in the 318's with steel cranks are usually the same as the 340, there is a part number on the side of the rod that tells you what they are. Also most pre 72 truck engines had full floating pins and they are most of the time the same 340 rod.

I have a set of 69 340 rods I had redone for another engine, I will see if I can get the number off of them but the part numbers did change frequently over the 6 year run of the 340 so that might not help much, I know I've seen several different part numbers myself. There is a Direct Connection book that was published back in the late 70's that has most the small block engine part numbers and tells you which ones are which and which ones to use.
 
Also. The dampener, the flex plate and the converter won't need to be balanced so make sure you use a good machinist when you take it to be balanced, some machinist want to balance them also which is fine as long as they keep these parts at a neutral balance so if you ever have to replace any of these parts, you can without any issues. I have heard of idiot machinists that thought differently.
 
Blown fish you seem pretty knowledgeable about this stuff so i myself have a question on this same subject. i have heard that old 318 y blocks all had steel cranks in them and are the same as a 340 crank. do you know if this is true?? if so i need a good kick in the *** for the ones that i have sent to the scrap over the years!
 
the 340 steel cranks had the center of the rod end board out to make that end lighter. I beleive that would give you quiker response and require less weight on the outher end to balance it. ill bet if you bought an after market 340 steel crank it would look exactly like an old 318 crank. i have a 340 with an old 318 crank in it and it loves high rpms with no problem at all. I am not a moter builder but thats what i learned when i put mine together.
 
Cranks swap and work to a point, the steel 340/273 crank is stronger but only matters with obscene compression and over 6800rpm.

If you are going with lite weight pistons, I think the lil 318 floater rods will handle it just fine under 6500 rpm, but it's your choice.
 
ron spilman said:
Blown fish you seem pretty knowledgeable about this stuff so i myself have a question on this same subject. i have heard that old 318 y blocks all had steel cranks in them and are the same as a 340 crank. do you know if this is true?? if so i need a good kick in the *** for the ones that i have sent to the scrap over the years!
Click to expand...
Bend over and brace yourself. I use them in my LA engines.
 
I dont plan on racing it. I'm not going to make it fast, 12 to 11 second in the 1/4 is all I'm going for. Combression around 9.5 to 10:1 max.
This car is stock other then the motor and wheels. Looks like it came from the factory and placed in a barn for 17 years in Washington. The only thing missing is the stock gas cap and the H in Plymouth on the hood.
So since I do not see many 66 Cudas here , I will build it to look stock. I'm going to make a sleeper. I will try to also keep the engine looking stock as possible.
The part number on the rods is 3418645. My books show this as a 74 - 80 318 forged rod or a 71-80 360 forged rod. Still loking for the number on the crank. The crank is forged due to the 1/2" wide forge flash. Cast cranks have about a 1/4" wide cast parting line.
I"m really getting good info here on these part swaps. I feel good about the crank. Still not to sure on the rods. The information I found out on the rods I haveis that they do not have any offset, but 340 rods have a .100 offset. Also the rist pin is .0362 smaller then the 340. The center to center length is the same.
I dont have any info on rod beam thickness for the 340.
I want to stay with steel rods, will get some nice flat top pistons with valve reliefs. Has any one used pistons from Eagle?
Thanks for all of the good info.
 
I didn't know that about the old 318 crank, good info. I never thought to look into those engines.

Are your rods floaters? or press in pins?

It's been quite a while since I messed around with stock 340 parts but from memory, the 340 has a .984 floating wrist pin from 68-late 71 and some of the cast crank 340's had floaters but a few of the cast 340's I had just had a press in pin which are smaller in diameter than the floaters if memory serves me correctly. It sounds like yours are press in.

I had twelve 340's sitting here at one time that I gathered over the years but didn't see the need to keep them anymore and sold all but four off. I practically gave a few of them away, I guess we all make dumb moves now and then.
 
The rods I have are pressed in.
You are right about the 340 pin diameter.
I was always building big blocks. But the 69 Dart I did with my son turned me into a firm beliver that the 340 is one of the best small block to build.
Hind sight is 20/20. Most people did give them away. Everyone coulsd afford to build big blocks. But to keep a street car a sleeper, 340 is the way to go.
 
Just make sure the convertor fits into the hole in the crank. I used a 273 HIPO crank in a 340 and the convertor didn't fit the crank.

I was young and STUPID. I made it fit, but it had a vibration. After checking the crank rod & main journals I thought all was OK, but it should have been balanced.

If I were to build another 340 I would go for a stroker crank. If you have to have much machine work on the crank the little extra will get you a new stroker crank. And unless you are going to build an extreme engine you don't need the forged crank.
 
I used a 318 crank in a 1972 340 block. Check to be sure the crank clears the main webs. Second, I used the floating pin rods from a 318, and .030" 340 pistons. I don't see where there will be a problem balancing the rotating assembly, since my set up works fine.
 
what are the issues with floating pins verses pressed. on my 340 i used 360 rods press fit pins. my machienest didnt see any point in spending the money to make them floaters for my application.
 
Press fit works well for stock and lower output motors that do not require frequent disassembly for freshening up. Their main advantages are simple assembly, cheaper pistons (no locks or extra machining) and they rarely come loose. In performance applications they require extra clearance to prevent pin scuffing.
Only draw back is some times the spring locks break and the pin slides out. I had a 383 that this happened to and it sure cut a nice key way in my cylinder.
 
I would find a Mopar Performance 360 Crank with Small mains. I found one for 275.00 just recently brand new in the box. Get some Eagle Esp I Beam Rods 280.00 and some 360 pistons, I got mine for $220.00 at Mancini. You will have a VERY CHEAP 367 Stroker Motor. Use the same heads you have just clean them up and do a good valve job. You could build the whole thing for about 1300.00 or less + machine work since you already have the block and heads. Should make just at 500hp or so depending on how much air you get flowing thru those heads.
 
Mad Dart;
Now there is a plan. I had not thought of doing that. I have 360 heads, but would like to get a set of 340 TA heads with the 2.02 valves. The 360 pistons are they the same as the 340's. with valve reliefs cut in?
 
66silverfish said:
Mad Dart;
Now there is a plan. I had not thought of doing that. I have 360 heads, but would like to get a set of 340 TA heads with the 2.02 valves. The 360 pistons are they the same as the 340's. with valve reliefs cut in?
Click to expand...

No the compression Height is different and YES the valve reliefs are cut in them. The 360 piston will be what you need to build a Nice budget Stroker using the 3.58 stroke 360 crankshaft with small mains using the 340 block. As far as the heads go the 360 heads should work fine as long as they are not cracked. Have them magnafluxed. You can always have the intake valve brought up to 2.02, cost would be cheap compared to buying a set of 340 TA heads. 894 X or I think 915 J heads will do the trick just fine. You are attaching a BIG name with the TA heads and the price is also up there. You could buy a set of INDY/RHS X heads ready to install that outflow all of them I mentioned out of the box for right around 1k and they will take a .540 lift cam without modification to the spring pads or seals.

Here is the link to the heads with 1.92 intake valves that are fine enough with the 367 stroker combo and they flow mad out of the box. http://www.hughesengines.com/Index/...cw==&level1=Q3lsaW5kZXIgSGVhZHM=&partid=25741

Here are the pistons $208.00: http://chucker54.stores.yahoo.net/36072cc98to1.html

Here are the rods on sale cheap $239.00: http://chucker54.stores.yahoo.net/eagchryssbib.html

Hope this helps.
 
You mentioned that your bore will be .030 over. So you need to call if you order the pistons, they will be 4.070 size and then you will be 372 Cubic inches.

FYI
 
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