Big Valve X Heads on Low Comp 72 340

-
Dustine

Dustine

Member
Joined
Jan 3, 2021
Messages
18
Reaction score
10
Location
Massachusetts
Looking at possibly putting a set of 2.02 X heads on my 72 340 . It is bone stock cast crank low compression factory cast iron intake factory exhaust manifolds 600 Edelbrock factory torque converter 904 auto I recently put a set of 3:73 gears in it . Just curious if I will feel any HP gains adding the X Heads with a thinner head gasket . Will the “ Juice be Worth the Squeeze “ . No future plans on rebuilding the bottom end she runs strong may consider a good set of headers down the road but I’m pretty happy with the factory cast iron exhaust manifolds for now .
 
The 2.02/1.60 X heads should flow slightly better than 1.88/1.60 valve size. I believe there both 915 head castings. Combined with some headers you should notice a difference. 65'
 
What cam are you running?
Honestly, you'll probably be able to tell zero difference with your setup. If you put 2.02s in your existing heads instead of the stock 1.88s, there would functionally be no difference in the heads at all.
Aside from the resto crowd, the only advantage of X heads over, let's say J heads, 308s, or 576s is possibly the amount of meat available for porting, the port sizes and general profiles remain basically the same;
so in a mild build like yours you'd likely not notice any seat-of-the pants difference, as I doubt your cam can really take any meaningful advantage of the 2.02 valves over your current 1.88s.
If you plan on further building your motor, save the X heads for that time.
 
Thanks for the input . Was thinking the same thing I will probably wait until the bottom end needs rebuilding . Do you guys think by just adding headers to my current setup I will feel any noticeable seat of the pants power gains ?
 
Dustine said:
Thanks for the input . Was thinking the same thing I will probably wait until the bottom end needs rebuilding . Do you guys think by just adding headers to my current setup I will feel any noticeable seat of the pants power gains ?
Click to expand...
Adding headers will make a difference, a noticeable difference
 
Since you’ll have to drain the coolant to remove the end exhaust studs to facilitate installing headers… why not go for more gain if you put a performer rpm or a budget air gap intake on it. I promise you won’t be disappointed!
 
the 587 head does flow better, over the 915 head, best to install sst one piece valves, that helps flow and velocity. in stock, low comp 340 are as fast as, the higher comp 340's. just food for thought, i've found the 1.88 valve has more velocity over 2.02.
 
Ditch the carb get more doing that then the heads
heads carb intake headers= big smiles
 
Depends on if the Xheads are ready to bolt on? With everything else that's been listed here to replace (intake, carb, headers) Why not do the heads?
 
The X heads are 894 number.
They do flow a bit better stock and
chambers are bit better aligned to block.

However, on a stock low compression 340
you will never feel the difference in performance.

I have done extensive research and testing on these
different heads for 50 years. If you gained 10 HP that
would be a lot. The headers would probably add much
more for less trouble and expensive. The intake and carb
if properly tuned and adjusted work quite well and aftermarket
parts would only add a small amount as well = although save some
weight.



OK, time for my enemies on this site to flame away and throw
rocks at me!!
 
May as well run the car as is I don't think you gonna gain nubs. Open chamber heads, HEAVY *** pistons, ZERO quench, low compression, short stroke. If you happy with it now then just run it as is enjoy the car.
 
GTX JOHN said:
The X heads are 894 number.
They do flow a bit better stock and
chambers are bit better aligned to block.

However, on a stock low compression 340
you will never feel the difference in performance.

I have done extensive research and testing on these
different heads for 50 years. If you gained 10 HP that
would be a lot. The headers would probably add much
more for less trouble and expensive. The intake and carb
if properly tuned and adjusted work quite well and aftermarket
parts would only add a small amount as well = although save some
weight.



OK, time for my enemies on this site to flame away and throw
rocks at me!!
Click to expand...
John, when I think of you I think of Paul. Simply because we spoke of Paul when we ate together. In the mopar sense, you’re often right and sometimes persecuted! LOL!

I always seriously consider what you have to say and value your experiences. Paul was lashed, beat, stoned, shipwrecked and imprisoned. If Mopar is with you who can be against you?
 
GTX JOHN said:
The X heads are 894 number.
They do flow a bit better stock and
chambers are bit better aligned to block.

However, on a stock low compression 340
you will never feel the difference in performance.

I have done extensive research and testing on these
different heads for 50 years. If you gained 10 HP that
would be a lot. The headers would probably add much
more for less trouble and expensive. The intake and carb
if properly tuned and adjusted work quite well and aftermarket
parts would only add a small amount as well = although save some
weight.



OK, time for my enemies on this site to flame away and throw
rocks at me!!
Click to expand...
Yeah but if ya got X heads for sale all the ppl that think there is some magic in them is a blessing.
 
As long as there is no positive deck height, and a stockish cam, would a set of thinner gaskets help get a little bump in compression, like a set of .027 metal gaskets? I recall that the 440's came stock with those.
 
Thanks for the Kind Words.

I could never even hope to be a thousand
of the witness that Paul was.

Even thou he was a fabulous witness he said =
"My righteousness is just like filthy rags".

Except for the Blood of Jesus my plight would be
absolutely hopeless.

Son of David = Have mercy on your pitiful servant!
 
I had forgotten to mention that if you have the stock ignition, you’ll want to recurve the distributor as well.
 
If you are going through the cost and effort to change the heads, why would you not put in a new cam that can actually take advantage of the potential increase in flow? Seems like the definition of a half measure. Even with the lower compression of the 72 piston, I would think that the bigger intake valve has a lot more flow potential and a smart cam grinder can put together something that would work a hell of a lot better with it as well as any exhaust improvements you make. Biggest improvement is going to come from a better cam, better heads, and exhaust improvements.
 
Stock 1.88 valve j heads will support 400 hp. You will need to do a lot to the motor to gain anything
with x heads. The J heads may have better acceleration on the street to well past highway speeds,
but you will win all the parking lot races with the x heads.
 
You probably can get 400 hp out of a stock 273/318 head with enough cam and cr don't make it a good choice for that much horsepower.
 
headers and a carb swap would net you way more for less lift. swapping the manifold for something aftermarket would be splitting hairs power wise, but it *might* have better manners down low and would shed a bunch of lbs.

unless you change the cam, you're not going to see any appreciable gains from bigger valve heads, especially on the street.
 
If your were to do a good valve job with some bowl work along with cam headers intake all together be worth while up grade.
 
I like how the poor guy said he was happy with the stock bottom end and exhaust manifolds, and just asked if the heads would make a difference.
Now everybody wants him to port heads, add headers and intakes...
:BangHead:
Not every thread is looking for a max power build.
 
Professor Fate said:
I like how the poor guy said he was happy with the stock bottom end and exhaust manifolds, and just asked if the heads would make a difference.
Now everybody wants him to port heads, add headers and intakes...
Click to expand...
People are basically saying the head upgrade by itself ain't worth it, so leave it stock or you got to do more to make it worth it.
 
Heywodja said:
As long as there is no positive deck height, and a stockish cam, would a set of thinner gaskets help get a little bump in compression, like a set of .027 metal gaskets? I recall that the 440's came stock with those.
Click to expand...

not sure its worth the trouble.. when my block was at the machine shop they indicated that a full compression point would only gain maybe 40 hp. don't think you'll get a full point from thinner gaskets. this is what i'm using on my 360, .028 compressed.. Mr. Gasket 1121G Mr. Gasket Head Gaskets | Summit Racing
 
You must log in or register to reply here.
-

Back
Top