AMC V8 pistons

[jeepsr4ever]

They are offset guys this is a reminder for whoever is throwing one to gether .....look for the offset and make sure your putting them on the rods correctly

[XtremeOverKill]

With regard to your offset pistons a few questions and thoughts come to mind....

First off I'm glad you know your stuff! I mean, I have always valued what you say and take it in the highest regards.... BUT now you have really impressed me.

And I am so glad that you told me about using Chevy Pistons, for I was very close to doing just that. And as trouble would normally have it.... Now i am extremely inquisitive about the pros/cons of offset pistons, and how previous guys who run Chevy 400 pistons can get away with it??? I"m not trying to disavow your claim/findings, but I am interested in learning.

Now for the Technial side of things. Assuming AMC pistons - complete with offset. There is a direction, so to speak, of the orientation of how to insert the pistons into the block, relative to the Con. rods. Let us assume for a minute we are talking of the odd bank of cylinders, drivers' side. If the #1 hole is on my left, and the #7 to my right..... how shal I orienent the offset with regard to the rods. I know we can not just rotate these 180 degrees to compensate, and I would like to tell my Machinist -sp?- how to properly mount the rods to the pistons.

Is the offset with the Generous portion to the lower side of the block - away from the Intake Manifold?

Mike

[jeepsr4ever]

Mike, thanks

Guys need to know this stuff or they can have some strange engine problems down the road.

[Tigger]

From what I have seen with rebuilding engines if the pin is offset the piston top will have a direction arrow on the top something like >Front> and you just orientate the piston to the proper direction and you are done, takes the guess work out of it.

[jeepsr4ever]

Yeah most forged pistons have that, but i havent seen a cast AMC piston with arrows yet.......I dont know why, maybe it wasnt in their original tooling

[XtremeOverKill]

Glad to hear that forged pistons have markings on them. But in response to your comment about stock arrows..... it is my understanding that from the factory, and in the TSM, there are directional arrows explicitly on the piston.

Pointing towards the front of the engnie of course.

While we are on the topic of pistons......
The stock piston is Dished - Have no clue what the cc is, but it has almost NO Quench. I have read about getting quench from pistons, deck height, head gaskets etc.... but for purpouses f this matter, allow me to play dumb and ask, Where can I find AMC specific pistons, adapted with quench, and what range of quench would be safe. Taking into account the shifting or rocking of the piston, is 0.020 enough - EXTREMELY high quench, or would 0.040 - essentially Zero Deck Clearance, and a Proform Head Gasket, Be enough quench?

I have heard that to push a quench of 0.037 to 0.030 on non-alumnium heads will outperform Alumnium heads? What validitiy/reliability can you credit to this, and from your experience?

What are the extremes?


Mike M

[jeepsr4ever]

Mike to push a quench and get better prformance out of a stock head vs. a highly engineered alum head is possible with porting and polishing, the extremes? Alot of it depends on the bore, as engineering math goes it is a progressive number for each increased bore and in exponetially different for material (head type, piston, type of rods and in some cases wrist pin diameter) So where should we start? I mean a ballpark figure can apply to most situations but exact numbers are a completely different world.

[jeepsr4ever]

some good tech
http://www.raceseek.com/custom_piston_information.htm

[Mudrat]

Mike to push a quench and get better prformance out of a stock head vs. a highly engineered alum head ...

OK, color me stupid , I can quench hot metal and even temper it sometimes, but what is "Quench" in regards to piston position? I just marked mine and reinstalled them in the same hole??

Mudrat

[Tigger]

The quench height is the distance between the piston top and the cylinder head when the piston is at TDC. It is the sum of the deck clearance distance from piston top at TDC to block deck surface) and the compressed head gasket thickness. Ideally it should be around 0.040". This clearance is necessary to allow for stretching of the rods at high rpm, otherwise the pistons would hit the head with disastrous consequences. When the quench height is smaller, more gases get compressed within the piston dish/combustion chamber and there are less detonation-inducing hotspots. This allows the engine to run a higher CR and low octane gas without detonation. Emissions are also improved.