340 parts interchange & performance Q

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'68-340-S

'68-340-S

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Just wondering if any one knows what the interchange is between a '73 340 and the older ones ( '68-'70ish )? I want to breath new life into my 340 and let it live up to the CID reputation it was origanaly born with in '68. I'm getting a set of rods, pistons, bearings and windage tray from a member here and thought that I might have a problem with the internal vs external balance change over... I don't remember when they changed over and if it effects my '73 340 or not. My engine is a '73 340 block cast 8/8/72, every thing on the bottom end is stock ( even the stock bore ).
My plans with this engine are: I'm going with '69 pistons (to help the CR), change the "cleaned" up 360 heads to a set of mildly ported X or J heads (2.02's), Edelbrock performer intake (already cleaned up), performer cam & lifters, I want to use zero gap rings, and a double roller timeing chain. If I run across one that I can afford I'll use a stock forged crank. Any one have any input on this combo... what it'll put out and any sugestions?
I already have the cam& lifters, intake, timing chain, will be getting the pistons, rods, and windage tray soon ( from a '69 340 ). This is just a back burner budget build that I don't have anything to put into yet.
 
The stock cast pistons are the same weight for the high compression and low compression motors so it should not upset the stock balance if you use the '69 stuff in your block using the '73 cast crank. The stock balance though has a lot to be desired so a re-balance is always a good idea. I balance all of my motors regardless if it is a "race" motor or a "daily" driver.


Chuck
 
If it were me, I'd swap to a forged crank and neutral balancer while you have it apart. Sell the one year only crank and balancer and lose the future headaches. As Chuck said, have everything balanced.

Why such a mild cam and intake?
 
I have to ask the same question... Why so mild on the cam and intake?? Also, why use Edelbrock Cam and lifters?? Much better choices are out there for about the same money. I know that, NOW, you already have the Edelbrock Performer setup but you could have been much better off on your choices unless you are planning on staying as close to stock as possible with just a touch of performance.

If it were me, and actually at the current time it is because I too am buidling an engine for my Dart Sport, I believe you should have looked a bit higher as far as lift/duration on your cam. The other item I would have changed is to go to an Edelbrock RPM Air Gap vs the Performer...this is a MUCH better intake than what you are planning on and it still will give you the benefits...plus more, that you will get out of the performer intake. Because of the dual plane setup your fuel flow will be more efficient when it enters the cylinders but by adding the Air Gap under the plenums you cause them to not heat up which keeps the fuel mixture denser as it enters and getting you more bang for your buck. The other thing is that the RPM Air Gap is designed for a much better power range of of 1500-6500 instead of idle-5500 which will give you optimum fuel flow at all ranges instead of just the low end up to just under cruising speed.

Of course, it is your car and engine, and this is just my opinion, but if performance stats is what you want from this build, these couple of changes alone will benefit you greatly.
 
I know there are more potent combos out .... but I'm also not sure what this will end up in. I'm also not planing on hitting 6500rpm. Something a little over what a 68-70ish 340 came from the factory with is good enough for me. If I was 18 again it would be a differant story. I'm not looking for something to set any records with, just something that will live up to the reputation that a 340 has come to be respected for. At a later date that may change, but for now a step above stock is good for me... apx. 300HP and I'm content.
So I shouldn't have any problems using the older stuff in my '73 340? Personaly I would feel ALOT better knowing my engine has a "fresh" balance on it and that it's blue printed to optimize the power potential. I would rather used a forged crank, mainly because I prefer the "Tim Allen" treatment.... don't just do it... Over do it!!! And I would rather be safe than sorry.
Any one have a prediction on what this combo will put out?
 
not a thing wrong with that cast crank,,,all the 360 and 360 crate engines run a cast crank,,,unless you have a forged crank laying around,,,like from a junk 273/318 use what you have for a street driver or a mild streeet strip car,, the new 5.7 hemi uses a cast crank,,,,the 6.1 uses a forged crank,,

to much hype about cast vs forged on the street,,its proven to live at over 600 horse power in a 360..save your money,,use the cast if its in good condition,,
 
Yeh, I'm not out looking for a forged crank, But if I find one I would rather have one. That way as plans change ( and we all know how that goes lol ) I'll be ready for what ever i deside on.
 
The reason I suggested getting a forged crank is that the 73 340 cast crank is a one year piece. The balancers are all old and I wouldn't want to trust them. It's not balanced the same as a 360, so you can't steal one of their balancers, either.

With so many people building stroker motors right now, you can probably get someone to give you a stock stroke 340 crank. I was even thinking about looking to see what I had to give you.
 
Didn't the 73 340s drop to 240HP instead of 290HP at stock?? If so, you're looking at doing more than what you plan to reach 300HP. Also, you cannot use a 318 crank in a 340, the main journals are different sizes and these cranks wll not interchange. Otherwise everyone would buy 318 blocks and put 340 cranks in them for an on the cheap build.
 
Nevermind part of what I said, the parts you are using from the 69 340 should drive your HP up as well, I forgot what was totally going into your build.

But, the crank statement still remains the same.
 
318's have the same main size as the 340. I have a 318 poly forged crank in my '73 340 in my Valiant.

The HP ratings were net in '73 and not gross number like the older ones so the HP really isn't much different between the low comp and high comp motors. probably only 10 - 15hp.


Chuck
 
273 318 340 Use The Same Crank,,, Only 360 Is Different,,,
There Use To Be A Crank Called The 318-3 Is Was Used In Trucks And Vans,, I Forget Exactly,, But There Is An Oiling Advantage To Using This Crank,, It Is Right In Black And White In The Direct Connection Race Manual,,,
 
I agree grab an early 318 or even a 273 forged crank and a early 340 balancer.
I dont think the Performer cam and intake will make as much power as the stock 340 parts would.

I would either use the stock iron 4bbl or an Eddy LD340 or RPM and a 650 Eddy AVS. For a cam the Comp Cam XE268 is a great step up from the factory 340 grind.

If its an automatic the Turbo Action "Medium" 10" converter works great for the 340 with 355s or 391s.
 
I have no idea what this engine will end up in ( more than likely an A body), what ever ends up happening it'll have a 4spd behind it... I wish my '68 was a 4spd. Being how I already have the cam & intake i'll use them, that wont be a problem to upgrade as that project moves along. I'm more than likely just going to pick up a Dart or something, drop the engine in to enjoy for a little while and use the whole thing to help finance another long term project.
 
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