The Dodge Challenger Message Board

In lists there are two different cc sizes 63-72,5cc the year 1970 on the 3418915 smallblock T/A heads.
How can you recognize the volume, are there any numbers on the casting?

jimi, Are those heads you speak of have a 2.02 intake valve in them? If so they are the 340 1970 heads. If they are 1.88 intake they are possibly 72-73 340 head and possibly the 360 head. 360 never had the 2.02 intake valve from the factory. All the intake ports are the same except the 340 T/A 'J' head had both 2.02 intake valve and the 'meat' around the intake ports was significant and the pushrod holes were bigger. This allowed for porting to be done on the 305 CID T/A Keith Black competition engine that Sam Posey and the Cudas ran in Trans Am racing for 70 only, at least this is the understanding I have. Please correct if wrong.

I am 'prepping' this 915 late 70's 360 truck engine head for porting and some runner mods. I want some dual springs, bronze guides, trick valve job, cut for compression, relieved chamber on the intake side, ect.. I got em cheap, they had a exhaust fastener broke off and painted over, I removed it carefully without resorting to an oversize hole or e-z out heli-coil. Next thing is to measure the valves,(height), place them on a layout bench and instal checking springs then off to the flowbench to establish a baseline and see what they flow at .300- .500 lift. I'll post my results to help Jimi.

It is the X-Head that had the small cc closed chambers. This was not the TA head which had open chamber J heads.

This might help.

http://challenger.mpoli.fi/forum/viewto ... 5269#15269

"The 68'-71 X-head had large intake valves, 65cc closed chambers, and ample intake and exhaust runners (ports)."

Thank you guys!
I have seen information saying the cc volume could be different, and i felt that was a bit strange. I can expect 72.5cc from j-heads 1970 T/A style then. Can you tell me how much you can cut to get the comp? I understand this is invidual based on different engines, gaskets, pistons etc, but if you have any room for suggestions?

Thanks!

I would get the compression by using pistons if possible. After decking the block to make sure it is level.
It is not wise to cut very much off the deck or heads. It is best to take as little as possible off.

Otherwise you start getting into cutting the intake manifold and valley ends.

good thinking Dave, Thanks! I do not want to cut in my new manifold thanks! The link you posted, i understand that he cares of the J heads, do he writes that every 340/360 head has the same runners and ports, but i wonder if that is thrue. Do you have experiences of this? From the numbers i have found on the internet, the J heads do seem to have a slightly difference that can be better. But they are more expensive. In other hand it feels better to have the valve size already from factory without having to machine them... My question is: Are the J heads to prefer? Do they have different ports and runners etc? Wich one will after a good portjob likely be the best choise? 587/596 J head 1.88 or the 2.02 J heads?

Second question, does anybody know maximum lift with stock springs in the J heads?

http://www.1962to1965mopar.ornocar.org/ ... ticle.html

"For 1971 and 1972, 340 and 360 engines were equipped with 3418915 heads, so-called "J" heads, because of the cast-in J in three locations (backwards in one place) on each head. These were either equipped with 1.88 inch/1.60 inch valves, or 2.02 inch/1.60 inch valves, and have "open" chambers with volumes of 65-73 cc. Open chambers have a circular margin. The heads I examined had the larger valves and an average chamber volume of 71 cc. The ports are large, averaging 69 cc (exhaust) and 149 cc (intake)."

"Average chamber volume"(?) Is it not precision enough of the casting to set a volume that IS a fact on each one from this year/ casting number etc?
Can somebody explain, is it then "most likely" "about 71cc" ? Or is it 65cc in some and 73cc in others(??)

The guy that wrote that knows a lot more about these heads than me. I would be inclined to believe what he says. There is a lot of bullshit spoken about "special" and "rare" heads.
J heads with 2.02 intake and 1.60 exhaust will obviously flow more than J heads with the smaller valves.

I really do not know anything much about the LA engines. I am a 440 RB man myself.

Head cc does vary from head to head. Also from one end of a head to the other if you have a bad one.

dave-r wrote:The guy that wrote that knows a lot more about these heads than me. I would be inclined to believe what he says. There is a lot of bullshit spoken about "special" and "rare" heads.
J heads with 2.02 intake and 1.60 exhaust will obviously flow more than J heads with the smaller valves.

I really do not know anything much about the LA engines. I am a 440 RB man myself.

Yeah, my question remains about the J heads 2.02" compared to the regular 340/360 1.88" or J head 1.88" heads with bigger 2.02" valves installed. It seems to me that he recommend to keep the J heads for the guys that need them to restore to stock, and take a set of the more regular 587 or 596 etc. heads and port them instead because they are the same. I kneed to know if the 2.02" J heads are better/ will give the best flow to port then the others or if they really are exactly the same when installing 2.02" and portjob as he say?
I maybe did not type the words correct for understanding me right. You got to have patience, i am not an member of you english talking guys I know you are not in to the smallblocks Dave

Only the real T/A heads had extra "meat" around the ports for porting on the race versions (they had to have production blocks and heads). Otherwise the port shape and volume was the same I am sure.

dave-r wrote:Only the real T/A heads had extra "meat" around the ports for porting on the race versions (they had to have production blocks and heads). Otherwise the port shape and volume was the same I am sure.

So..? Can i buy a set of cheaper heads, like 596 or 587 etc and believe that they will perform the same after a good portjob and 2.02" valves as the J heads i have found?
The casting on the set J heads i found is: 3418915
Or should the 3418915 heads be better then the "others" after portjob?

If they are professionally ported it will not matter what heads you start off with.

You just have to decide how big on the ports you want to go. This depends on final use and cam selection.

I agree with Dave. I dont think there is much to gain by seeking a rare 340 X head unless you are restoring a rare 340 engine or T/A 340 SixPack engine. Any of the early 340/360 heads are good and can be made even better with some porting in the right places. I didnt know the X head had closed chambers, I thought all the small block heads had the open chamber except the swirl port 318 heads and 273 heads. I thought the X head had a recessed chamber with a piston that protruded into the chamber approx. .100-.120 on the factory 68-70 340? Wouldnt this be an open chamber with a squish or pop up type of dome? Just curious Dave, thanks.

I thought they were all open chamber too actually but like I said I really don't know much at all about small block parts.
I have a couple of books at home that might have more details.

Yeah, I am 're-learning' more about them everyday. I used to use a 340 on the street in the late 70's but went to B/RB cause I cant get enough torque!

Hopefully next week I can get this '915' 360 head on the flowbench and establish a baseline. Then I am going to attempt to street port this and increase flow in the all-important .100-.550 lift or ruin them. I am trying to learn what increases flow and velocity without killing the swirl, which is just as important as flow. I will reveal all data and post pics.

Don't touch the floor of the port!

I've heard that Dave. I think I will head your advice! Tomm. for 3-4 hours the SF bench is mine!!!

So what were the 73' Head's called? Are they Crap? I can't find the number's on mine.

You have to take a valve cover off to see the casting number.

i bet you got the "587" as i do... (3671587)

I coudnt put these heads on the flowbench for 2 reasons. One is the amount of carbon in the intake ports and chamber. The other is I measured the installed heights of all the seats and they vary .100 on the intakes to .050 on the exhausts! They are all over the place. Looks like someone ground the seats and not taken account of the depth they ground the new seats. Perfect opportunity to install 2.02 and new seats on the intakes. The valves 'appear' to be sunken from too many valve jobs perhaps. The springs had 55-80 lbs. on the seat,(closed). Not nearly enough to control a heavy 3/8 " valve! Time for some new springs and bronze guides as well!

Looks like I'm gonna re-build these heads first,(bronze guides, 11/32 valves, hardened inserts, then port carefully for max street flow.(.550 max) without touching the floor of course, and the short side radius on the intake, a goodson 3angled cutter with a cutting radius will remove 80% of the throat anyways for a bigger valve so thats what I'm gonna do, followed by a smoothing of the cut.

I can't wait for the follow up. more posts, more posts, more posts!

I had a quick read up on small block heads last night. By quick I mean less than a minute. But I picked up a few pointers.

But it seems there were no production closed chamber LA heads.

The 340 and 360 heads both flow quite well. But of course the big valve versions flow better.

They seem to respond to porting well and bigger is better.

The roof of the ports needs to go up. In some cases the floor is raised.

Going wide you are limited on the intake by thin walls at the mouth of the intake runner. The T/A head had extra material and offset rockers/pushrods. But the stock head can be brazed thicker on the outside so that the port can go wider.