340 head questions

[Oldmanmopar]

Have in my notes they are 915's.

That is what they should be if they are O's Don't see them that often but I already had a 70 dart engine with one O and one Z they were original to the car.

 

[RustyRatRod]

When the heads are 72cc chamber, do the math and the static lands around 9.1-1 or less.
Stick a 280 flat in it and use 8553 head gaskets.. and it'll be cranking 140 psi if you're lucky.
For 91 octane with a typical 280 dur flat tappet cam. ..all the open chamber heads should be milled at least .025 to bring them down to around 67cc when used with a 340 stock replace 10.5 piston n your average hot street cam/280 cam.
If they are 1.88 valves to begin with, going 2.02 stainless nail head style valves will lower the chamber volume as well... its a you'll know when you get there kinda thing.

I'm just curious....what's the range of 340 chamber volumes you've seen? Lets' say all of the "letter" castings anyway. I've measured from about 65 to about 78 cc.

 

[Dart Frog]

I wouldn't worry about compression that much on a cast iron head. A true 10 5 to 1 would not be happy with modern premium gasoline. My X heads came in at 72 cc's. With a small cam and pump premium that's about all it would take with decent timing. It would still detonate if it was hot and I luged it at all. My aluminum heads are true 10 5 to 1 and never a ping to be heard.

 

[nutz]

Ill check the casting #s tomorrow
I know the ones are done
If its got harden seats then done right
And my guy will clean and pressure test
If the seats aren't done then just looking for the smaller chambers..
The seller only knew what his brother told him ...
Not sure what the short radius looks like
Not sure what to compare too

 

[nutz]

I wouldn't worry about compression that much on a cast iron head. A true 10 5 to 1 would not be happy with modern premium gasoline. My X heads came in at 72 cc's. With a small cam and pump premium that's about all it would take with decent timing. It would still detonate if it was hot and I luged it at all. My aluminum heads are true 10 5 to 1 and never a ping to be heard.

Easy enough to cc..
What # valve springs should I use on a stock cam ...my guy was saying around 60#
Does that sound right

 

[nutz]

That is what they should be if they are O's Don't see them that often but I already had a 70 dart engine with one O and one Z they were original to the car.

Wizard of Oz engine

 

[MOPAROFFICIAL]

I'm just curious....what's the range of 340 chamber volumes you've seen? Lets' say all of the "letter" castings anyway. I've measured from about 65 to about 78 cc.

As for the head that actually came off a 340, 72cc is the largest I've measured .
I spec some will have somewhat sunken exh valves and could be a hair more, but 78 cc ?? Not in my experience.
I cc them with stock spark plugs in and wired wheeled chambers free of carbon.

78 cc is what the 915 440 heads measured iirr.

I have some 2.02 915 J heads off my old 1970 340 duster that measure 72cc and all thats ever been done was a vj and .002 mill. The seats cut compensate for the .003 mill in that case

 

[Dart Frog]

Easy enough to cc..
What # valve springs should I use on a stock cam ...my guy was saying around 60#
Does that sound right

I would say closer to 100 on the seat. Remember Mopar small block valves are 3/8 stem and a little heavier than some.

 

[nutz]

Ok ill tell him
I see new springs just didn't want too much tension on stock cam

 

[nutz]

So both are 915 castings

 

[Dartswinger70]

Yeah the X ,O U J etc. is a casting mark the actual casting number 915 etc. is what matters prob more so with the 915 casting as the X heads were their own number.

 

[nutz]

Thanks

 

[340sFastback]

Easy enough to cc..
What # valve springs should I use on a stock cam ...my guy was saying around 60#
Does that sound right

This article talks about springs on a stock cam 340:

1970 340 High Performance Mill Dyno - Mopar Muscle Magazine 1970 340 High Performance Mill Dyno - Dyno Derby 340

 

[MOPAROFFICIAL]

This article talks about springs on a stock cam 340:

1970 340 High Performance Mill Dyno - Mopar Muscle Magazine 1970 340 High Performance Mill Dyno - Dyno Derby 340

I have a big box full of mopar muscle and mopar action magazines.
This post right here just made me feel so old and honestly.. made me remember my anticipation of the next months rag to learn or read about something new. Those guys inspired the **** out of me ..and man.. Bob looks so much younger then. Last I seen and spoke with Bob was 2018... very old by that time.

 

[nutz]

Yea i remember that rag...thinking 80s

 

[Dartswinger70]

I had a book "How to Hot rod small block Mopar engines" years ago but I lost it .It had a build recipe section that I think those build plans would still work today if you can get the parts .

 

[nutz]

My plan is close to stock everything...
Have the intake, exhaust, carb,dist
Just need to find a stock grind cam

 

[CFD244]

My 1971 340 is pretty much stock everything (68 manifolds and 2 1/2 inch TTI).....Running a XE262 cam. 16* initial, 34 all* in by 2500. Runs great....I've only used 91 octane in it. No heat issues, no pinging, starts and idles well.......16mpg too!

Forgot to mention 180lbs cranking pressure.

 

[furrystump]

I’m pretty sure my untouched x’s were in high 6’s

 

[nutz]

Lucky me pulled the heads and no rust on the bores

 

[Swinger 340]

That is what they should be if they are O's Don't see them that often but I already had a 70 dart engine with one O and one Z they were original to the car.

I also have a 70 340 with both "0" and "Z" heads. I thought they came from a 70' Challenger. Why miss match heads? I'm not sure, but I have heard of it before. Both are 2.02's.

 

[nutz]

Would think it was a change over time and no one cared to look

 

[mayhem]

I also have a 70 340 with both "0" and "Z" heads. I thought they came from a 70' Challenger. Why miss match heads? I'm not sure, but I have heard of it before. Both are 2.02's.

Just tell the Chevy boys you have the special 'Oz' heads and that's why your car out performs their junk. See how fast and how many of them jump on their phones to research 'Oz' heads.

 

[Oldmanmopar]

How about a sticker on the fender for the early Elon Musk rocket design X heads. But the woke bastards would probably key your car.

 

[Woody500]

How about a sticker on the fender for the early Elon Musk rocket design X heads. But the woke bastards would probably key your car.

What are you talking about