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Discussion Starter · #1 ·
I decided to come to POR for some help on this subject.

I want to build up an AMC 360 and swap it into my YJ. To make things more interesting, I have everything needed to run this setup on propane. I know propane has a higher octane, and so I want to better utilize that, and bump up the compression to 10-10.5:1. I was hoping to do it by running a higher compression piston and keeping everything else stock (more or less). That way, if I FUBAR something, I just go to the boneyard and pull a block or a head, and bingo, back in the hunt. If I can't get the higher compression with pistons, then I got to deck the block or the heads (in reality, it would be a combination of the two).

So, (to the point) I need to find higher compression pistons (stock in mine is 8.25:1) to run in my 360. I can get "custom" forged stuff done up, for like $550, but I cannot justify that. I could BUILD a hi compression chevy for the pistons alone.

Anyone got ideas (other than using a different motor?)
 

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My understanding is that if you bore something like .065 over you can use stock-bore 400 SBC pistons. Not sure on the exact overbore, but I do know 400 SBC stock bore is 4.125". 'Course, none of this is of any help if you've already done your machine work <IMG SRC="smilies/frown.gif" border="0">

TEX
 

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Discussion Starter · #3 ·
Well, that's the thing.

I haven't done ANYTHING to the motor yet, as I didn't want to screw the pooch by machining it for something I can't do.

The motor ran, so I know that the thing is salvageable, but I don't want to start cracking it open until I have a clear game plan.

Anyone else? I have tried to contact places, and they refer me to other places I called. Big circle.....

If I can't make this happen, I will just have to cave and swap in a 350 or a 302 <IMG SRC="smilies/rolleyes.gif" border="0">
 

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propane is 103 octane or thereabouts, so i believe you could actually run 12:1 if you wanted.

as far as higher compression goes, if you can find an AMC 343, the pistons in that are flat top and have a 10:1 comp ratio.

stock bore is 4.08"

why get forged? too expensive. hell, buying longer connecting rods might be cheaper than getting new pistons.

BTW, i'm doing the propane conversion too, eventually <IMG SRC="smilies/wink.gif" border="0">. it should cost around $400 if you get used stuff and $1000 if everything is brand new. also, propane pays for itself after a year or two. $0.89 a gallon for propane vs. $1.17 for gas.

didja know that you can run propane and gas on the same engine?

oh yeah, and propane burns cleaner.

[ 10-29-2001: Message edited by: WillyPete ]
 

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Discussion Starter · #5 ·
Hey WillyPete,

Yeah, I got the mixer, vac break, tank, and regulator already for $300. Just need the lines.

12:1 is still good, huh? Hmmm......

I was worried about getting the thing to turn over and stuff like that. Get a good gear reduction starter I guess.

Got a price on longer connecting rods from Crower just a couple minutes ago (cosmic vibe thing), and they quoted me $1200 <IMG SRC="smilies/eek.gif" border="0"> <IMG SRC="smilies/puke.gif" border="0"> <IMG SRC="smilies/eek.gif" border="0"> <IMG SRC="smilies/puke.gif" border="0">

I am hesistant to start playing around with turning down cranks (like using a 401) 'cause that is usually the weakest link when everything is said and done.

Finding an AMC 343 is like looking for a DoDo bird. in some magical place they may be laying around, but not in frickin Maine <IMG SRC="smilies/biggrin.gif" border="0">

I might be able to pull it off using the 219 casting heads (have a 51 cc compression chamber as opposed to a 58) and some 9:1 cast Federal-Moguls, which were stock in 1970 I think. That should be around 10:1.

But 12:1, that sounds yummy <IMG SRC="smilies/jeep2.gif" border="0">

thanx
 

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KB and Mopar performance make 9.0:1 pistions. So with a little block and head milling 10-10.5 is no sweat.
Mopar Performance 9.0 Forged overbore Pistion # P5249908
KB info:
http://www.kb-silvolite.com/slvpg09.htm

KB's run ~325.00 for a set of 8

[ 10-29-2001: Message edited by: Old Scout ]
 

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Originally posted by themaddhatter:
<STRONG>

Finding an AMC 343 is like looking for a DoDo bird. in some magical place they may be laying around, but not in frickin Maine <IMG SRC="smilies/biggrin.gif" border="0">
</STRONG>

There's a pretty good AMC wrecker in PA - Erie if I remember right... I'll see if I can find their contact info.

Check this:
http://www.amxfiles.com/resource/junkyard.html

[ 10-29-2001: Message edited by: Mo ]
 

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Discussion Starter · #8 ·
Excellent guys <IMG SRC="smilies/biggrin.gif" border="0">

Will be a snortin beast when she's all done <IMG SRC="smilies/beer.gif" border="0">
 

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you MUST check out www.froadin.com for awesome info. also i believe if you bore a 360 .045 over you can run the sbc 400 pistons which were designed for an 18deg head. that should bring you up to 9.5:1 i recall a peterson's mag article about building a motor just like this but don't recall the issue
later
bob
 

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Originally posted by driller:
<STRONG>why not get a 390 out of an early javelin or such</STRONG>
do you know how rare javelins are? i don't think any classic car enthusiast (no matter what their brand of choice) would sanction ganking a 390. newbie <IMG SRC="smilies/rolleyes.gif" border="0">

anyway...

don't take what i say as gospel <IMG SRC="smilies/thefinger.gif" border="0">. 12:1 would be pushin it. personally i'd like to try a supercharger with propance. that way you could keep your pistons and the SC would give you that extra oomph... however, you would suck propane like a mutha. $1200 sounds insanely high for connecting rods.
 

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Discussion Starter · #12 ·
Yeah, in my research on LPG systems and motor longevity, most of what I came across states that, yes 12:1 is a reasonable compression for good propane, but of course you got various "grades" and purities of propane, depending on where you are and how you got it.

Because of that and some other basic engine design features, pushing up into the higher threshold just starts burning up the motor faster.

Think of it this way: a normal car with 8:5-9:1 compression and maybe 200 HP lasts ~ 100-200K miles.

A top fuel dragster has 14+:1 compression, makes 6K HP, and lasts a quarter mile (maybe).

I would rather design a motor that will last me 500K (which BTW propane will, just need to do the heads every 100K or so), and make 200-250 HP, then 350 HP and replace a longblock every 150-200K.

But, yeah, it would be da <IMG SRC="smilies/nuke.gif" border="0">

Here is a link discussing engine design and LPG.
http://franzh.home.texas.net/engine.html

He has a link to his email. Probably worth discussing supercharging with him <IMG SRC="smilies/biggrin.gif" border="0">

I have been reading up on this stuff for 8 or 9 months. I am not the kind of person to just jump on something. But, yeah, the 12:1 is tempting, just beats up the motor more. And for offroading, I don't know if I need that MUCH power (other than for showing off) <IMG SRC="smilies/smokin.gif" border="0">

Now are you doing up a FSJ? I had to put down 2 88 GWs to do this project. One had thrown a rod, and the other was running, but was sacrificed to the parts GODS <IMG SRC="smilies/biggrin.gif" border="0">
 

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ouch! 2 88s? those were the best years of the 80s as far as FSJs go. best engines anyway, with a 44 rear.

12:1 is just theoretical. i might actually keep my 8.25:1 comp when i convert. my motor was rebuilt about 10k miles ago, so i'm cool for the moment.

what're you shootin for? i want something in the range of 250-280 horse and 350+ ft lbs torque at a nice low rpm. the waggy is eventually gonna be offroad only. i figure on 35s, 4.10s, stock axles, spools, manny hubs, an atlas, and a few other fun mods.

what tranny are you planning on? 400/727 or manny?
 

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Discussion Starter · #15 ·
Willy,

Just found 343 pistons on the performanceamc link there, and they are $250 for 8. <IMG SRC="smilies/smokin.gif" border="0">

So, that will be stylin.

Yeah, the sacrifice of the GW was necessary. "Life feeds on Life"

One was fine. The Mrs thought it was "ugly". Came down to that or finding a new woman <IMG SRC="smilies/confused.gif" border="0">

But hell, throw in a higher piston to get a little more out of it, or deck the heads. Should get stainless valves (found a source for $13 a valve)

Let me know how the project goes <IMG SRC="smilies/biggrin.gif" border="0">
 

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Discussion Starter · #16 ·
Originally posted by WillyPete:
<STRONG>
what're you shootin for? i want something in the range of 250-280 horse and 350+ ft lbs torque at a nice low rpm. the waggy is eventually gonna be offroad only. i figure on 35s, 4.10s, stock axles, spools, manny hubs, an atlas, and a few other fun mods.

what tranny are you planning on? 400/727 or manny?</STRONG>
Well, I am figuring since I am keeping it torquey, with the higher compression, that yeah 300 HP and maybe 400 ft-lbs will be where it is at. And, I am running it for 4K RPM or less, so she should be gruntin good.

I have an NP435 with granny low, and am building an NP203/EB Dana 20 doubler to get a crawl ratio down in the 120:1 range. Gears will be 3.73s so will still go on Highway.

Should be a LOTTA fun (and something different)
 

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Originally posted by themaddhatter:
<STRONG>

One was fine. The Mrs thought it was "ugly". Came down to that or finding a new woman <IMG SRC="smilies/confused.gif" border="0">
</STRONG>
You know what I think about that.
 

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Discussion Starter · #18 ·
Yeah, well if you ever built your frickin garage, I would have to live up in the rafters.

That way ollie couldn't eat me alive
 

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OLLIE!!!!!!
He just wants to play!
Can you blame him!?
I'd be a snarling beast if I had to watch Charly playing with Jeeps, through a window all day too! <IMG SRC="smilies/wink.gif" border="0">

I have dibs on Charly's garage...he promised a "Fonzie" apartment for me...my ole' lady is gonna boot my ass if I bring home another HEEP. IF it werent for her, I'd have a collection. <IMG SRC="smilies/frown.gif" border="0">

MJ
 

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Discussion Starter · #20 ·
yeah, well then Charly is just gonna have to build a bigger garage <IMG SRC="smilies/thefinger.gif" border="0">
 
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