New Member - 360 Tips, Suggestions

[T56MaxTorq]

Hey guys, new member. Been ghosting around the site for a while reading a lot of good stuff. Living in the Mopar truck world, have an 84 Ramcharger. Love it. Wanting to find an old Duster or something but I can never find one and have money at the same time. Have some questions about my 360 swap from the stock 318. It runs good, but has burned oil from the start. I thought I broke a ring or my valve stems are toast. Pretty sure now that it is the intake manifold not sealing with the heads. All plugs are dirty. I ran a compression test first and the results worried me on how low they were. No wonder I havnt noticed much change from the 318 to 360 with 3.23 gears and 32" tires and 5000 lb truck.

360 ci 4.030 bore, roller cam
KB 362 pistons @ zero deck
224/230 @ .050 cam, 110 LSA, 38 degree intake closing ABDC @ .006 lift.
My true compression ratio is debatable as the stock LA heads were machined, my guess would be no lower than 65cc chambers leaving a c/r of roughly 8.8-9.2
6000 ft altitude

I ran a compression test on the rings

Dry and hot engine
110 118
115 110
118 115
125 110
Front

Squirt of oil in cylinder
115 120
120 120
128 120
125 120
Front

Do these numbers sound acceptable for the worst case scenario #8 cylinder? I used a calculator online to check cranking pressures and came up with at 8.8 c/r would be 133 psi, and at 9.2 is 142 psi. I'm wanting to add some closed chamber heads in the near future. Thanks.

 

[Cudafever]

The only problem with them calculators, is that they are sea level calculations.
There are a couple of compression calculators on line that have a Altitude option you can add that helps a lot for us thin air breathers:cheers:

My 340 compression check went from 160-170 psi at 4000 foot to 130-140 at 7000 feet.
Nothing was changed but the drive!!!!!!!

You can get a way with a LOT more compression at that altitude.

The most important thing to look at, when doing a compression check is even of the compression.
If those compression ### would have had a 90 psi mixed into there then i would have be worried.

Do you have flat top piston or dished?
are you sure there not down in the bore .020" or more.
and last, i would bet the head cc"s are closer to 72cc then 65cc.
My heads were 74CC(340 X head)

One last note: High altitude likes more ign timing!

 

[T56MaxTorq]

Hey thanks for the quick reply!

I used a wallace racing calculator that had an input for intake valve closing degree and altitude.

They are step dish pistons w/ valve reliefs, 19.4 cc head volume
They're defiantly zero decked
I only guessed on the head cc. Stock is roughly 72cc and they were shaved an unknown amount.

Compression numbers look level so I guess I'm good to go for closed chamber heads?

A set of RHS heads with 62cc chambers brings the compression up to a true 9.3:1

I'm about to drop 4k into this truck as soon I get back from deployment with goodies like RHS heads w/ roller rockers, headers and exhaust, air gap intake, demon carb, and 4.10 gears.

How much ignition advance we talking about? I was thinking roughly 32-5* total.