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Will my motor survive a 12:1 CR?

Hogback Fabrication

Hogback Fabrication

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383 stroker, 400 crank turned down to 350 bearing journal size, 5.7" rods resized (from my old 350), KB hypereutectic pistons, 4 bolt main, vortec heads.

I'm going to propane soon and would like to bump the compression up. Will this setup survive 12.1?
 
High octane gas and a very light foot might make it last for a while. Why not just wait until you do the propane swap before you rebuild it for higher compression?
 
vortec said:
High octane gas and a very light foot might make it last for a while. Why not just wait until you do the propane swap before you rebuild it for higher compression?
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I won't be changing anything until the motor gets propane running through it (which is ~110 octane and should be fine at 12:1).

Higher compression is harder on the motor and I'm asking if my components are strong enough.
 
It depends on the time versus rpm . If your on it all the time in a mud pit it wouldn't last as long as just chugging over a rock .

Isn't propane cleaner too ? So your engine oil should last a lot longer protecting it anyway .
 
What does KB say about that compression ratio?

Of your parts that seems to me like it would be the only questionable parts, usually at that high of a compression ratio I believe you end up with forged, cast is too weak and hyper's are brittle.
 
pauly383 said:
It depends on the time versus rpm . If your on it all the time in a mud pit it wouldn't last as long as just chugging over a rock .

Isn't propane cleaner too ? So your engine oil should last a lot longer protecting it anyway .
Click to expand...

Propane does burn a lot cleaner which will keep the oil cleaner a lot longer. Right now I run Mobil 1 synthetic and change it twice a year.

Full throttle ascents will be in my future so I would like the motor to survive.
 
crack she strong break she gone
I ran 12:1 in my daily driver, a 84 3/4 4x4 400 smb bowtie heads, stock crank & and rods.I ran 5gal cam2 to 15gal pump gas and never had a problem and I punished the the truck hard,truck pull,mud bogs, hill climbing, the only trouble I ever had was a bent valve from drag racing it on straight pump gas.
 
I run 10.75/1 compression in my 383 and have approx 50,000 miles on it so far - all really hard miles (daily 6500rpm shifts) - so trail miles should not be an issue
 
38377k5 said:
383 stroker, 400 crank turned down to 350 bearing journal size, 5.7" rods resized (from my old 350), KB hypereutectic pistons, 4 bolt main, vortec heads.

I'm going to propane soon and would like to bump the compression up. Will this setup survive 12.1?
Click to expand...

here's a neat article on the characteristics of propane as a fuel - kinda wordy, but the section on engine efficiency ( or lack of ) with propane is enlightening.

http://www.naftc.wvu.edu/NAFTC/data/indepth/LPG/LPG.html

One thing to remember - that 110 octane number is research, not motor octane..motor octane for propane is 100. ( so R+M/2 = 105 octane)..this article, (and others I've seen) says the max CR for propane is 11:1 because of this..
 
The parts you listed will hold up fine but you're going to find that you aren't able to get a combination of parts in a 383 flavor to get 12:1 CR. I'm about to build a propane 383 stroker and the reseach i did without going to a custom made piston you just can't get 12:1. IIRC i was able to achieve 11.25:1 with a zero decked block. Naturally the combustion chamber of the heads will have alot to do with what you'll be able to get CR wise. The engine i'm building is going to be running a set of 68cc chambered AFR heads.
 
4X4HIGH said:
The parts you listed will hold up fine but you're going to find that you aren't able to get a combination of parts in a 383 flavor to get 12:1 CR. I'm about to build a propane 383 stroker and the reseach i did without going to a custom made piston you just can't get 12:1. IIRC i was able to achieve 11.25:1 with a zero decked block. Naturally the combustion chamber of the heads will have alot to do with what you'll be able to get CR wise. The engine i'm building is going to be running a set of 68cc chambered AFR heads.
Click to expand...

I'm running vortec heads which are 64 cc IIRC.

Are there valve/piston clearance issues or does nobody make a piston for it?

11:1 is ok with me but if I'm going to the trouble of increasing the CR I'd like to lose as little power as possible.
 
I don't think that with your application that the power gain would justify the cost/risk. If you are running 10 to 1 or so already then I would leave it alone.
 
JpEater said:
I don't think that with your application that the power gain would justify the cost/risk. If you are running 10 to 1 or so already then I would leave it alone.
Click to expand...

Running my current 9.7:1 CR I would lose almost 10% hp by going to propane.

At 12:1 it would essentially stay the same. The cost of a head gasket and maybe having the heads milled is worth it to me.

On that same subject will taking some material off of vortec heads (to decrease the combustion chamber size) change their performance?
 
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