AMC360 Budget Build w/343 Pistons

[AMC_FAN]

One question. With the 343 piston being down in the hole a little, could you use a 343 block with a 360 crank to get pretty close to zero deck?

Oh, I also clicked on the Wiseco link that goes to Summit and it says "Not available". Just an FYI.

Great write up as always! Thanks for all the info!

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One question. With the 343 piston being down in the hole a little, could you use a 343 block with a 360 crank to get pretty close to zero deck?

Oh, I also clicked on the Wiseco link that goes to Summit and it says "Not available". Just an FYI.

Great write up as always! Thanks for all the info!

Thanks!
Years ago I built a 343 with a 360 crank, rods and pistons and I had to mill the top of the pistons to get zero deck.
So... if you use the combination of a 360 crank, rods , 343 pistons in a 343 block, the pistons would stick 0.005" ABOVE the deck surface - assuming not decking the block. That wouldn't be a problem but by the time you deck the block 0.010" you could end up with a 0.015" Pop-Up piston. It all depends on what you want to do. And, the 343 has the smaller 7/16" head bolts so, step dowels would have to be used with any of the Dog-Leg heads.

[AMC_FAN]

So, if you used the 343 block with the 343 pistons and 360 crank and went with the head gaskets you were using (.058 crushed), you'd wind up with a .043 quench, correct? Just thinking out loud.

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So, if you used the 343 block with the 343 pistons and 360 crank and went with the head gaskets you were using (.058 crushed), you'd wind up with a .043 quench, correct? Just thinking out loud.

I changed up and am using Fel-Pro gaskets that crush to about .045" and I always get the block decked by .008"/010" so, no.
I highly doubt that anyone would feel the difference in horspower because of .020/.030 difference in quench in a street car or Jeep. I would wager that you can't even measure the difference in horsepower on a dyno on a 300 hp engine. Just my opinion I guess. I have built a few 1970 390's with '71 401 pistons which puts the piston in the hole about .075". It is nice combo because it lowers the compression ratio down to the 9's with the 91c heads and will still put out a bunch of streetable power.

[Nikkormat]

Off topic, what's my best option for 9.25-9.5:1 compression on a .20 over 91 360?

Is a point of compressison even worth the effort? I'm looking for 300 useable rear wheel HP and gobs of tourqe in a Jeep with 3.08 gears and 31's on 87 octane.

I've heard that the late model heads can be milled to reduce the chamber size. Is that true?

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Off topic, what's my best option for 9.25-9.5:1 compression on a .20 over 91 360?

Are you sure it is 9.25:1? If it is, the answer would be no in my opinion unless, you are rebuilding it anyway. Then, the cost of 343 pistons are the same so it is a free bump in compression

Is a point of compressison even worth the effort? I'm looking for 300 useable rear wheel HP and gobs of tourqe in a Jeep with 3.08 gears and 31's on 87 octane.
If you are going to run 87 octane, the lower the compression the better.

I've heard that the late model heads can be milled to reduce the chamber size. Is that true?

Any cylinder head can be milled to reduce the compustion chamber size but I wouldn't recommend doing it for that reason. The only reason I get them milled is to get a fresh gasket surface and usually it is only .005" to .010". If you go much more than that you might run in to issues with the intake manifold fitting correctly. The intake may actually have to be machined as well to fit. At that point all you are doing is adding machining cost for little gain in compression

[Nikkormat]

It's worth mentioning that for me 87 is mid grade. Not regular. High altitude and what not.

Do you expect this motor at 9.5:1 to use premium?

[Gulrok]

It's worth mentioning that for me 87 is mid grade. Not regular. High altitude and what not.

Do you expect this motor at 9.5:1 to use premium?

What is octane rating?

Gas pump showing octane options
Octane rating is the measure of a fuel's ability to resist "knocking" or "pinging" during combustion, caused by the air/fuel mixture detonating prematurely in the engine.

In the U.S., unleaded gasoline typically has octane ratings of 87 (regular), 88–90 (midgrade), and 91–94 (premium). Gasoline with an octane rating of 85 is available in some high-elevation areas of the U.S. (more about that below).

The octane rating is prominently displayed in large black numbers on a yellow background on gasoline pumps.

https://www.fueleconomy.gov/feg/octane.shtml

( Just some general information about octanes for everyone to read. )

Higher elevation has less dense air, so less pressure when it fires. Less of a need for higher octane then.

[Cataldo]

Very nice write up. I am curious how it runs! I like the idea of building a 360.

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It's worth mentioning that for me 87 is mid grade. Not regular. High altitude and what not.

Do you expect this motor at 9.5:1 to use premium?

I run premium in all of my AMC engines even the ones with 8.5:1 compression ratio. There seems to be so much variation in fuel these days I would say it depends on where you live in the country and where you buy it. Not a fuel expert at all but the idea of this build is to stay below 10.0:1 so that you can still buy pump gas and then maybe play with the timing to see how low of octain you could get away with.

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Finally back on this project again...
When I started installing the push rods and rocker arms in I noticed that it was really hard to turn over. Naturally I thought that I had a valve train issue but no.... It turns out that the casting on the new water pump was hitting the vibration damper. I just ground some of the casting off of the water pump at the two lower bolts and problem solved. The irritation is, I shouldn't have to check for stuff like this..

[babywag]

x1000
Parts should just fit! I had a discussion via email about this, they need to fix this IMHO.

http://www.ifsja.org/forums/vb/showthread.php?t=169721

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Yea, I just might start sending original stock old ones to this guy to rebuild. At least they would bolt up with no issues and I don't have to deal with different hub heights. I haven't tried him yet but I know of a couple guys who have.
Dan Bailey
4706 Detroit St
Dearborn Hts, MI 48125
313-530-2893

[babywag]

GMB makes a nice one that is aluminum, the housing appears to be a quality piece. It fits without modification, and the hose sizes are actually correct.
Their cast iron offering is horrible quality though.

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I normally use the aluminum water pumps. GMB lists 2 sifferent ones through Summit but, they are identical. The hub height is 3 3/4 which is 1/4" longer than the older cast iron ones used on the older AMC cars with the 3 bolt vibration damper so, you have to find just the right water pump pulley to make it work. In this case the cast iron pump was supplied to me..