AMC 360 Build for Propane

[msalaba]

I'm in the process of rebuilding an 85 360 for propane.

EDIT: My current build-
1973 Jeep CJ5 on CJ7 chassis
360 (1978) bone stock with the following upgrades:
- Summit K8600 Cam & Lifters
- Motorcraft Duraspark II Dizzy w/ MSD "BIG" cap
- MSD 6AL CDI
- MSD Helicore Wires
- Edelbrock Performer Intake (#2131) non-EGR
- Impco 425 Mixer & "E" Vaporizer (Propane)
- Added 4/28/09 - Valve Job & 0.038" Head Shave
(Running late heads w/ stamped steel rockers)
BW T15 man trans
D20 T-case w/ 3.15:1 Kit
(soon to be TH400 w/ Atlas 4-Speed)
5.86:1 Axle Ratio w/ 42" Iroks


Excerpt by Franz Hofmann-
Propane has a theoretical CCR somewhere around 12.5:1, and again, this depends on the purity of the fuel, usually between 90 and 95% propane, the balance being propylene, ethane, butanes, and other minor fractions. Of all these fuels, propane has the longest burn duration, and the highest octane, and the highest resistance to ignition. The other fuels tend to diminish the combustion quality of propane. Propane can and will work effective with higher compression ratios, but at some point, the added heat during compression, the detonation and risk of pre-ignition, and reduced power gains eliminate any possible gains from the increased compression ratio.


I have read elsewhere that Propane is happy at 10.5:1 to 11:1 Static CR, so – how to get there?


Forged pistons – 4.125 Bore comp ht 1.601 21.66cc inv dome
advertised 9.5:1 with 57.92cc head.
Summit K8600 Cam
1.6:1 Bridged Rockers
2.025/1.68 Late 360 Heads w/ 57.92 chambers
Factory Crank & Rods
Impco 425 Mixer

I calculate 9.21:1 Static CR with the following calcs:
4.125 bore
3.440 stroke
5.875 rod
4.25 x 0.046 fel pro gasket
9.195 deck ht
0.000 deck clearance
1.5 cc Top Piston to Top Ring
57.92 cc chamber
21.66cc Inv. Dome

Assuming a 0.060 mill on the heads for 48.32cc I come up with the following:

http://www.diamondracing.net/cocalc.htm
4.125 Bore
3.440 Stroke
5.875 Rod
4.250 x 0.046 Fel Pro Gasket
9.195 Deck Ht
-0.001 Deck Clearance
1.5 cc Top Piston to Top Ring
48.32cc Chamber
21.66cc Inv. Dome
10.19:1 Static CR
9.05 Dynamic CR

I am real close to my target of 10.5:1 Is there anything I overlooked to get another 0.5:1 CR bump?

Are my number correct? Or am I better off getting new pistons?

Should I upgrade to forged rods on an engine that won't see much of 5500 RPM?

[ironman_gq]

you can get your target with some new pistons and save a lot on the machine work.

[dan58]

Have you started the build? Other than a cam, intake, and headers, I have a stock 360 on propane. It has a ton of power. You could save a pile of money if the engine is is good running condition.

Whose propane kit are you planning to run? I'd HIGHLY suggest www.gotpropane.com and talk to Cary. :t:

[msalaba]

I have a 79 360 stock w/ RPM intake, K8600 cam and MDS 6AL ignition w/ duraspark dizzy. Had the heads off when I did the cam. #3 bore did not look good, others still had a nice cross hatch. Valve guides wore. Needs a rebuild.

Running GotPropane kit. Impco 425 mixer. Runs strong. Lost some low end torque. Smokes pretty good (wore out)

Figured if I'm gonna rebuild it, might as well increase compression to take advantage of propane's octane preperties and get back some of the lost power due to propane displacing some of the intake charge.

Oh - I just recieved the "Performance American Style" book. Got it off e-bay. Some really good information on parts interchangability and explores 4 different engine buildup "modes"

[msalaba]

Update:

I thought my engine was wore out due to the massive amounts of smoke from the exhaust.

I turns out I am an mechanical genius 111!!!

I ended up pulling the heads for a valve job. After pulling the intake manifold I noticed the intake ports in both heads were oil saturated. I thought to myself hmmmm I wonder if that's what caused all the smoking?

Turns out after I installed my summit cam, I installed the new intake gasket with ultra black around the water ports.

DON'T DO IT!

Turns out ultra black will cure well before you can get the gasket and manifold back on the engine. This kept the manifold from seating hence the smoke.

Ultra gray IS the weapon of choice for this. :!:
I wonder if anaerobic sealant would be better? :-|

Anyway, I got a valve job and had the heads shaved.
(0.038" IIRC was the max before hitting the valve seat.)

Strange thing- the valves were gone but the seats were in great condition. The springs were the wrong rate for the Summit cam (Summit sold me the wrong stuff #-o )

So, lots of $$$$ later, new valves, springs, gaskets, ultra gray, torque wrench and swearing.... The engine is back together and no longer smokes :lo1l: ON a compression check, psi is up about 10 psi from what I had before. Still light on #3 but is within spec.

Conclusion: beat it like a red-headed stepchild and fix what breaks. Being a Chebby fan, I really like this AMC engine!

New Problem: Due to increased compression, my cheap Chinese starter cries like a little girl. I forsee a gear reduction starter in my future.........

[msalaba]

I did not get around to CCing the heads as I was getting to crunch time for Memorial Weekend (Dresser, WI)

The Intake valve protrudes past the head mating surfase so I would have needed to spend a lot of time making a relief in a piece of plexi to be able to CC the heads.

What is the best way to get an accurate chamber volume on this engine?