Just Bought a 360

['64 Cuda]

I just bought a 360 block with crank, rods, etc. on ebay (I hope it turns out to be what he said it is) with a .030 over bore with flat top pistons (Sealed Power H116cp) with about .006" positive deck height. Can anybody tell me what approx. compression ratio would be with my stock J heads?


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[rumblefish360]

I just bought a 360 block on ebay (I hope it turns out to be what he said it is) with a .030 over bore with flat top pistons (Sealed Power H116cp) with about .006" positive deck height. Can anybody tell me what approx. compression ratio would be with my stock J heads?

Hum, I'll have to break out the calc. A zero deck with a 72cc chamber (My J heads) worked out to be 9.8-1.
What gasket are you useing? Bore, thickness?
And how many cc's your J's are?

 

['64 Cuda]

Thanks rumblefish. I havent cc'd my heads yet. They're still laying in the shop waiting for me to clean them up. I was just trying to get an idea of where I might be at. Gotta' decide if I want to run these heads as is & wait for a seat to fail from unleaded gas, replace the seats when I have the valves done, or look for a later head with hardened seats & a smaller combustion chamber. I've read the newer heads will work better because of the combustion chamber design, but I already have the J heads & they're in good shape. They were pulled in the mid 1970's & had a valve job done on them & have never been used since then, but I think the guides might have been knurled so they probably should be replaced.

 

[rumblefish360]

Well, if I were to replace my J heads, it would be with a set of 308's or Magnum heads. As far as factory stock heads go. I have both sets and just await the forth coming spring to fool around with them.

I'm currently screwing around with a 318. And will test several heads on top, just to see and play with. No other reason than that. Just spend money and burn rubber and gas. Oh! And then post about it.

Anyway, with those pistons sitting at zero deck height, think about a slightly thicker gasket to make pump gas a bit easier to run without retarding the timing to do so.

Fel-Pro has gaskets @ .054 and then theres Cometic in what ever you spec to them. A slight shave of the ratio would be good IMO for most case build on the street.

 

['64 Cuda]

Well, if I were to replace my J heads, it would be with a set of 308's or Magnum heads.

I'm planning to run a six pack so the magnum heads are out. I don't want to go through the trouble of adapting the manifold to them. But.....there's always Eddy's or those Mopar Performance Commando heads. It's only money, right?

 

['64 Cuda]

rumblefish,
I've been thinking about things & I guess I never really thought about how much the different stroke of the 360 (compared to the 340 I was going to build) would affect the compression ratio. :-k In my mind, I was thinking flat top = lower compression than domed. Good thing I'm still in the planning stage & haven't started assembling things yet. :toothy5: I've been playing around with a compression ratio calculator & even with the .054 head gasket you mentioned I'm at about 9.85. :read2: Of course, I'll have to cc my heads to find out exactly where I stand. My concern now is with the cr I'll have. How much can I get away with using J heads & pump gas. This is mainly a street car & I'm going to talk to Hughes about a cam, which will affect the dynamic cr. My question now is how thick of a head gasket can I use before I have manifold sealing problems? :scratch:


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['64 Cuda]

Hum, I'll have to break out the calc. A zero deck with a 72cc chamber (My J heads) worked out to be 9.8-1.
What gasket are you useing? Bore, thickness?
And how many cc's your J's are?

I've cc'd the heads and I'm getting about 72. I've plugged everything into a calculator using these numbers.

Heads 72cc
Bore 4.030
Stroke 3.58
Gasket bore 4.15
Gasket thickness 0.54
Valve reliefs in piston 5cc
Deck height -.006 (This is per the seller, I haven't received the block assy. yet. He said "...approx .006" positive above deck height")


All of this gives me a compression ratio of 9.53 to 1. Will I be safe there? I hope it sounds reasonable for the street with pump gas.

The block is a 91 which is set up to use the LA heads & a factory roller cam. The car has an 8 3/4 rear with 3.91 gears. I have the options of the original cast iron trans (huge ratio change from 1st to 2nd & ball & trunion front joint, along with limited selection of speedo drive gears available), an aluminum case close ratio trans (already rebuilt with the 66 & later tailshaft for a standard front U joint), or an 833 OD (again, the huge rpm drop but more evenly spaced ratios overall. This is a truck trans so I'd have to swap the tailshaft or adapt it to fit the car).


Anybody have any ideas for a cam? Should I cam the engine for good torque & use the OD trans or go for something else & use the close ratio box? I'll probably keep it under 5500 most of the time & I doubt it'll ever see a strip, but you never know. With the 8 3/4 rear, I could always keep the close ratio box & swap to a different rear ratio for a long highway trip (I'm leaning towards this). I'm also still undecided as to whether to use my fenderwell headers or fix the fenders (I have the panels) & run a set of 340 Hipo manifolds that I have.


When looking at roller cam specs I have to keep in mind that the rollers are spec'd with the magnum 1.6 ratio rockers & my LA heads will have 1.5s. I was told that I also need the long snout on the cam for the fuel pump drive. I kinda' want a lopey idle. I'm a bit old school. Maybe a custom grind from Hughes?


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