Author Topic: 31-33 Avs factory pistons  (Read 10841 times)

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Offline crazycraftsman

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31-33 Avs factory pistons
« on: November 21, 2015, 07:01:56 pm »
Are the pin heights the same on 31  and 33 Avs pistons?
owen
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Offline Rocket Ron

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Re: 31-33 Avs factory pistons
« Reply #1 on: November 21, 2015, 08:18:18 pm »
Yes. They are in the same place. But unforturely they are in the wrong position.
Ronnie McClain
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Offline crazycraftsman

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Re: 31-33 Avs factory pistons
« Reply #2 on: November 21, 2015, 08:36:22 pm »
Thanks Ron. How do they run for so long in the wrong position?
owen
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Offline BIG AL 202

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Re: 31-33 Avs factory pistons
« Reply #3 on: November 23, 2015, 01:29:00 pm »
Yes. They are in the same place. But unforturely they are in the wrong position.
WHAT DO YOU MEAN "WRONG POSITION"?
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Offline Rocket Ron

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Re: 31-33 Avs factory pistons
« Reply #4 on: November 23, 2015, 03:49:28 pm »
They are not .590-.620 comp. height
Ronnie McClain
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Offline crazycraftsman

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Re: 31-33 Avs factory pistons
« Reply #5 on: November 23, 2015, 09:17:42 pm »
So the piston doesn't come up to deck high enough? Sits lower than the 31 piston?
owen
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Offline BIG AL 202

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Re: 31-33 Avs factory pistons
« Reply #6 on: November 23, 2015, 10:14:54 pm »
They are not .590-.620 comp. height
OK THANK YOU.
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Offline Rocket Ron

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Re: 31-33 Avs factory pistons
« Reply #7 on: November 24, 2015, 06:36:51 pm »
Dah.. If you only understood rod ratio!!!  Ron.
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Offline crazycraftsman

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Re: 31-33 Avs factory pistons
« Reply #8 on: November 25, 2015, 12:27:28 am »
I'm not a engine guy!! I'm a transmission man. Always learning something new everyday:)
owen
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Offline chavez

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Re: 31-33 Avs factory pistons
« Reply #9 on: November 25, 2015, 01:33:22 am »
So Ron, what say you about using the short synchro rod with avs piston for something only turning 5400rpm. Forgetting the deck height issue, using stock cam, ports, intake and valve size.
Travis Callaway

Offline Jeff McKelroy

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Re: 31-33 Avs factory pistons
« Reply #10 on: November 25, 2015, 10:11:48 am »
What Ron is trying to explain is that basically connecting rod length plays a role in how the engine will behave. Let's look at the model 21 engine. Ever noticed why the intake is short with a larger i.d. than the 31/33? And why the combustion chamber so shrouded? Then answer is a shorter rod. A short rod will pull massive amounts of air into the engine, but not expel it very easily. Hence a larger induction system to lower port velocity. The combustion chamber is heavily shrouded for the same reason. Though valve curtain area is poor, you will still have moderately good swirl, and all the gases are 'funneled' to the exhaust valve. But this can be fixed. Enter rod ratio. By lengthening the connecting rod, you can find the desired balance between intake and exhaust events, i.e., appropriate flow through the cylinder head, not just one side of the head. Design engineers like to say a rod ratio anywhere from 1.2-1.8:1 is best. And here's where it will get costly, if you do not use the currently available off-the-shelf parts. Changing rod length means changing piston compression height. There IS a limit. Piston speed and the angles between crankshaft to connecting rod, and connecting rod to piston are all factors that must be considered. And bigger is not always better, as you will find with broken skirts and crankpins.

Offline Rocket Ron

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Re: 31-33 Avs factory pistons
« Reply #11 on: November 25, 2015, 06:05:48 pm »
Thank's Jeff but I sure that one would have been way over thair head's. So I did'nt even try to explain. Ron.
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Offline chavez

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Re: 31-33 Avs factory pistons
« Reply #12 on: November 25, 2015, 08:13:13 pm »
Maybe my mis-understanding,  but doesn't target rpm play into the equation?  I understand using the longer rod to slow piston acceleration and increasing dwell time at tdc/bdc. Given intake port velocity as force for cylinder filling, the longer dwell time makes sense.  But, what's ideal for a 7000 rpm engine isn't the same as 5000.  I'm trying to take the fact the stock parts are designed for 36-3700 rpm and optimize for use at 5000.  As Ron stated, maybe I am in over my head, but that's why I'm trying to ask questions in order to better understand.  Yes a different camshaft would be the first place to start, but our rules won't allow it.
Travis Callaway

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Re: 31-33 Avs factory pistons
« Reply #13 on: November 25, 2015, 09:11:36 pm »
cSorry for the confusion on the matter the only eng. I 've ever built with gov. in it went back on a grass cutter  . and the cast pistons in them held up very well at 3600 rpm . wish you luck at 5 grand plus at5 grand plus.
Ronnie McClain
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Offline crazycraftsman

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Re: 31-33 Avs factory pistons
« Reply #14 on: November 26, 2015, 01:20:27 am »
Thanks Jeff. It's nice to know some people are helpful on here!! :woo: :lol3:
owen
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