340 head questions

[nutz]

so I have a set of 0 heads 202 valves that need rebuilding
I just bought this 340 with rebuilt j heads 202 valves
going to build a 69 340 ,trying to build it as close to stock as possible
what's the difference between them ...does it even matter to me ??
what head came on the 69
thanks

 

[Professor Fate]

'69 340s came with X heads.
Js and Os are close enough that you'll never notice the difference.

 

[RustyRatRod]

With the 2.02 valves, you'll never feel the difference and I seriously doubt you'd even see it on the dyno.

 

[nutz]

Ill have my machinist check out the j heads
They have been redone just sitting for years

 

[Dartswinger70]

CC the chambers to find out the combustion chamber size. Rumor is they are all over the place while the X heads were smaller... a trick is to mill the heads to tweak compression ratio. I'm going by memory which isn't good but for example an x head may be 65 cc while a J and others can be up to 72 cc etc.

 

[nutz]

Haven't figured out pistons yet
Still gathering parts
This engine was built as 10.5 so might just go with those ...

 

[furrystump]

Stock build doesn’t really matter.

 

[dano]

Whichever set doesn't have the seats pounded into the casting.

 

[nutz]

Was going to have hardened seats put in the others
If these are done ...win win
If not still less labor...I can see new springs
The cam has purple paint on it ....
Is there an id on it somewhere?
He said steel crank...but I have one that was cut .....
What compression did they run in 69?
Oh and I guess the heads are off a360
Has 360 cast into it

 

[Dartswinger70]

Well these engines are well known for stacked tolerances... in 69 the 340 was advertised at 10.5:1 but until you measure everything that may vary maybe to 10:1 etc.thats why I mentioned cc ing the heads if you really want to know the true CR. the heads can be milled to make the combustion chambers smaller to raise cr etc.

 

[jeff alder]

Keeping it as close to stock is probably out the now that you have 360 J's. I had good experiences with those heads in the past.

 

[Oldmanmopar]

Last 3 digits of the casting 894 are 68,69 and some early 70's . Casting number ending in 915 are 70-72 . 72 having 188 intake valves.

all 894 engines had a 10.5 -1 compression rating. all 915's had 10.3 - 1 Except 72 with 188 valves came on 340's were 8.5 - 1.

All 894 heads when going to use an intake from 915's including the six pack the intake must be cut to fit properly. If you ever tried to fit a 70 up intake or a six pack on an 894 headed engine it is very hard to get the bolts started, Can be done but difficult.

 

[Dartswinger70]

I imagine the late 340 late flat pistons was the compression killer? and the 360 with the dish pistons naturally yes Id think.

 

[1MeanA]

You're not going to get 10:1 easily as I have stock 340 pistons and I calculate 9.75:1 after reducing the combustion chamber to 63 cc by adding 11/32 nail head type valves. I don't know much has been taken off the head but not a lot as the rebuilder wasn't keen on hogging them.

 

[NC Engine Builder]

Yeah that factory rating doesn't mean jack. The "10.5-1" engines were usually not

 

[MOPAROFFICIAL]

Ill have my machinist check out the j heads
They have been redone just sitting for years

When picking any of these heads pay attention to the height of the short turn on the exhaust. Some J heads have next to no short turn and would/could be a poor choice over what you have.

 

[Dartswinger70]

Yeah that factory rating doesn't mean jack. The "10.5-1" engines were usually not

I agree I am assembling an early piston 340 with 2.02 j heads and plan on cc'ing the chambers just to find out where its actually at for CR. I know I dont have to and it will run but Id like to know for sure if its 10:1 or 9.75:1 etc.

 

[MOPAROFFICIAL]

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.

 

[jawbone]

Don't here much regarding O heads. My 70 340 came with a set. Combustion chambers were cc'd at 65.6. Compression ratio calculated at 9.687:1.

 

[MOPAROFFICIAL]

Don't here much regarding O heads. My 70 340 came with a set. Combustion chambers were cc'd at 65.6. Compression ratio calculated at 9.687:1.

How many times have those heads been rebuilt AKA machined. From the factory they all came 72cc chamber. Change to nail head valves and they get smaller, typical mill when recon'd and they get smaller.. .0048 per 1cc

 

[jawbone]

How many times have those heads been rebuilt AKA machined. From the factory they all came 72cc chamber. Change to nail head valves and they get smaller, typical mill when recon'd and they get smaller.. .0048 per 1cc

Cannot give a good answer to your question. Purchased all the equipment to perform the task and that's what it came out as. Still only 9.7:1 CR.

 

[MOPAROFFICIAL]

Cannot give a good answer to your question. Purchased all the equipment to perform the task and that's what it came out as. Still only 9.7:1 CR.

65.5 isn't small enough apparently.. and I've no idea how far the pistons come out of your block, .018 or .024 or ?
Head gasket?
Factory head gaskets were around .020 thick, roughly.
I build more for a particular cranking PSI AKA dynamic effective, and i know what works on the shitty 91 octane we have here in California. 170psi is pushing it with open iron heads, 160psi is nice, much below that and it loses its kick/punch.

 

[jawbone]

65.5 isn't small enough apparently.. and I've no idea how far the pistons come out of your block, .018 or .024 or ?
Head gasket?
Factory head gaskets were around .020 thick, roughly.
I build more for a particular cranking PSI AKA dynamic effective, and i know what works on the shitty 91 octane we have here in California. 170psi is pushing it with open iron heads, 160psi is nice, much below that and it loses its kick/punch.

We've got 93 octane available but due to the fact the car does not get run much have loaded it with 89 ethanol free at the moment. Plan is to mix 100LL aviation fuel with it and a proper addition of Marvel Mistery Oil. Some will say I'm heading into trouble but this is what engine builder/racer recommended. Thoughts?

 

[Oldmanmopar]

Don't here much regarding O heads. My 70 340 came with a set. Combustion chambers were cc'd at 65.6. Compression ratio calculated at 9.687:1.

O's U's J's backward J's , Z's They are all 915's All 894's are X. Did you look at the casting number? 894 or 915.

 

[jawbone]

O's U's J's backward J's , Z's They are all 915's All 894's are X. Did you look at the casting number? 894 or 915.

Have in my notes they are 915's.