Small valve 340 J heads on a stock 318

-
65Vart

65Vart

Well-Known Member
Joined
Feb 13, 2009
Messages
3,145
Reaction score
91
Location
Waterdown, Ontario
Heys guys , any advantages/disadvantages to small valve (1.88 1.60 340 J heads on a '71 318 motor. I can get a great deal on a set (complete). For the cost of machine work on my 318 heads I may as well bolt these on. Let me know of any problems. please and thankyou.
 
the lost of compression is the big deal.....if your 318 with the pistons way down in the hole and use an open chamber J head...your compression will be in the 7s...
 
70aarcuda said:
the lost of compression is the big deal.....if your 318 with the pistons way down in the hole and use an open chamber J head...your compression will be in the 7s...
Click to expand...

Perfect for some boost
 
This question gets asked over and over and the answer is always that they will make the motor lazy, truth is ...the larger combustion chamber will lower the compression, but if you simply mill them down...they will make more power all around over the stock 318 heads by means of increased flow.
That's fact.
 
I agree. I ran a stock rebuilt 318 with J heads on it in my mud truck. Would lnot wind up but it had great torque!!!! I would not recommend it - find some decent 318 heads and run it
 
before you take it as gospel that the J heads will lower your compression a lot. measure them.

I measured the chambers in my virgin unmilled 1973 318 heads and got 66.5cc

I then measured my 915 J heads with 1.88" intake valves and they came to 70.5cc

I then installed 2.02 valves and the chamber was reduced to 66.5cc with NO milling.

I have no sure way of knowing how much the J heads were milled before i bought them.

but I highly suspect the difference in chamber size between stock 318-360 heads is greatly overestimated.

in any case the difference is nothing that some milling can't compensate for!
 

Typically .006" milled off will reduce chamber volume 1cc. You can also use the thin head gaskets, which are around 6.5 cc in volume as opposed to the 12cc volume of the usual FelPro 8553 replacement gaskets. I have milled 596 heads down as much as .050". That along with aftermarket stainless valves got the chambers to 57.5cc.
 
skrews said:
Typically .006" milled off will reduce chamber volume 1cc. You can also use the thin head gaskets, which are around 6.5 cc in volume as opposed to the 12cc volume of the usual FelPro 8553 replacement gaskets. I have milled 596 heads down as much as .050". That along with aftermarket stainless valves got the chambers to 57.5cc.
Click to expand...

Dont you also have to mill the intake?
 
Actually,HemiMark, you can mill the intake side ,of the head down.Takes a good machinist,or a mock up after milling,and a angle gauge. Car Craft,had a small section on it, in the last couple years.The Mr Gasket 1121 head gasket compressed, .025 .Compared to stockie .040 - .050 compressed gaskets,picks up 2 to4 tenths to start.
 
Wally,you call around the local wreckers and see if you can find a 360 mag. out of a write-off vehicle($500).I,m sure Bill and I could help get it in on a weekend.:D
 
O.P.,that is a sweet offer.....As a Magnum convertee,I would highly suggest this option....
 
Soon as I sell the 65 (if). there will be a built 360 under the hood of the 71. This was just a stop gap solution for now since the 318 in there now needs some head work and these Jheads were a good deal. I also need the 65 gone so I have room to work.
 
You must log in or register to reply here.
-
Back
Top Bottom