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Custom Pistons 1725

T

Tom H

Platinum Level Sponsor
Guys, I have ordered my custom pistons from Venolia for my 1725 -soon to be 1820. The pistons will have a compression height about .125 inches shorter than stock. Of course they will also have a shorter overall height to be sure it clears the counterweights on the crank. I suggested an overall height of 3.08 in, compared to stock height of 3.26. In addition they will have an arc (4" rad) at the bottom, to further lighten them. Venolia suggested they normally position the bottom arc to come to 0.180 in from the bottom of the wrist pin. This will result in an overall height of about 2.88 in., about .2 in. shorther than my plan, and about .38 in shorter than stock.

Is there any problem using such short pistons? Lighter is better, of course, but I don't know about other factors like wear surface and wear rate, and added torsional movement (piston rocking on its wrist pin in the cylinder) . Any thoughts?

Thanks,

Tom
 
Nickodell

Nickodell

Donation Time
I assume that you've had the block bored or sleeved to achieve the 5.5% increase in swept volume. Unless you've done so already, you need to calculate the exact CR resulting from this and lowering the piston crown.
 
T

Tom H

Platinum Level Sponsor
Nick, Thanks. I have done all the calculations. I have not yet bored the block. I'll have that done with pistons in hand. But I have all the factors calculated and correct. But what about overall piston height? Any thoughts on that? Any problem with them being as short as I am planning?

Tom
 
R

RootesRacer

Donation Time
Tom H said:
Nick, Thanks. I have done all the calculations. I have not yet bored the block. I'll have that done with pistons in hand. But I have all the factors calculated and correct. But what about overall piston height? Any thoughts on that? Any problem with them being as short as I am planning?

Tom
Click to expand...

The only significant problem is "barreling" of the cylinder liners due to not having
much skirt contact.

Folks have been putting super short pistons in motors for years, and the only real negative is that the motor wont last as long (pistons and cyls will wear faster).
 
T

Tom H

Platinum Level Sponsor
Jarrid, That's what I thought. But do you have a sense of how much I lose? The height is 2.88 compared to 3.08 of my plan, and compared to 3.26 stock. That's about 12% shorter than stock. I'm sure this is not "super short", and I'm hoping that the reduced oscillating weight will result in more life added than I lose in the "barreling" of the cylinder. Do ya think so?

Thanks,


Tom
 
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RootesRacer

Donation Time
Its tough to say, I have pistons in my 6 inch rod motor that has a 1.504 inch compression height, so get you beat big time.

The engine is noisier (more piston slap), but I never really intended it to be a long life engine.
 
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