piston help

[Nucking futs]

I need to measure these pistons. can someone tell me how to measure for rod length and compression hight.
http://www2.***boat.com/image_center/data/520/1638pistons_0030-med.JPG
http://www2.***boat.com/image_center/data/520/1638pistons_0032-med.JPG
http://www2.***boat.com/image_center/data/520/1638pistons_0031-med.JPG
Thanks

[YeLLowBoaT]

compression hieght: take the pin diameter/2 then take the distance from the top of the pin hole to the top of the piston and add those 2 $s toegther.
Ie cent of pin to top of piston
Rod length is the same center of pin to center of the cap end. so half you pin +half the other side + the distance from the edge of each.

[steelcomp]

Make sure you know where the top of the piston is...it's not the top of the dome, it's the flat part here (quench area)
http://www2.***boat.com/image_center/data/520/1729pist.bmp
This is your compression ht.
http://www2.***boat.com/image_center/data/520/1729untitled.bmp
The rod length depends on the stroke and the deck height. Those look like Venolias.

[Nucking futs]

OK, I have the comp. hieght....1.242
Now i need to figure out what rod and stroke they take, any help here?
Scott, these are Venolia gas ported pistons. they are .060 over and I need to get the specs on them.A buddy of mine gave them to me and knows nothing about them. They are for sale.

[Squeezing Spectra]

4.00 stroke 6.535 rod in a standard 9.800 deck block is what i get there could be something else it would do ?

[wsuwrhr]

The gas ports work really well for creating good ring seal with lower tension rings.
However, this causes a significant increase in ring wear, comparatively speaking.
Just in case you were wanting to use them,
Is that help or hurt?
Brian

[steelcomp]

Here's how you do that.
You have a known deck ht of either 9.800 or 10.200 for BBChev. You have stroke lengths of 4.00. 4.25, 4.375, and 4.500, typically. You have a known compression ht of 1.242.
Take your deck ht of 9.800. Subtract the compression ht. Then subtract half the stroke (the distance from the center of the crank mains, to the center of the rod journal) and what's left is the rod length.
9.800-1.242-2.00(4" stroke) gives a rod of 6.558, round off to 6.550.
9.800-1.242-2.125(4.25 stroke)= 6.433...round off to 6.430
9.800-1.242-2.187(4.375 stroke)=6.370
with tall deck:
10.200-1.242-2.00=6.958
10.200-1.242-2.125=6.830
10.2-1.242-2.187=6.771
10.2-1.242-2.25=6.708
I'm looking for a typical combination here, and the only one I come up with is a 467" with a 6.550 rod (4.31X4.00) which is still odd. The only other one would be the 4.31X4.375 (510ci), but only if you had a deck of 9.815, then the 6.385 rod would work (stock + .25) The rest, to me, are completely odd combinations. Are you sure about the c-ht? A 1.29" ch would be what you need for a typical 496, with a 6.385" rod.

[steelcomp]

4.00 stroke 6.535 rod in a standard 9.800 deck block is what i get there couble be something else it would do ?
That would leave it .023 in the hole on a true 9.800 deck. I guess that's possible.

[steelcomp]

That would leave it .023 in the hole on a true 9.800 deck. I guess that's possible.
OK...I just looked at the ch on my JE's for a 496, and they're 1.27, so they're allowing .020 for deck clearance, so Bruce is right. If that's the case, the 510 might work, as well, with a 6.385 rod. That's a small bore for that many cubes, though. It could also be a tall deck 496 with 6.800 rods. That's a nice n/a combination.

[Squeezing Spectra]

Yea if if you probally take into count that most blocks around anymore would not be a true 9.800 unless it was a new one it should be pretty close ?

[Oldsquirt]

I suspect that the 1.242" compression height measurement is incorrect. Venolia lists pistons with a 1.280" compression height for use with 4.250" stroke on a 6.385" rod. That would leave the piston .010" down in a 9.8" deck block.
Venolia Pistons (http://www.venolia.com/catalog2005.pdf#search='venolia piston') Scroll down to the bottom of page 10 and all of page 11

[steelcomp]

There ya go...can't argue with hard info like that.
Thanks Oldsquirt. :D

[Nucking futs]

I suspect that the 1.242" compression height measurement is incorrect. Venolia lists pistons with a 1.280" compression height for use with 4.250" stroke on a 6.385" rod. That would leave the piston .010" down in a 9.8" deck block.
Venolia Pistons (http://www.venolia.com/catalog2005.pdf#search='venolia piston') Scroll down to the bottom of page 10 and all of page 11
We have a winner. After measuring a bit more this all worked out
1.280 ch 13.1 comp. 4.25 stroke 6.385 rod pn 39369. Thanks a bunch for your help.
Bruce said exactly what allen @ bpe said but it did'nt make sence to me.that was a weird combo for sure.

[steelcomp]

We have a winner. After measuring a bit more this all worked out
1.280 ch 13.1 comp. 4.25 stroke 6.385 rod pn 39369. Thanks a bunch for your help.
Bruce said exactly what allen @ bpe said but it did'nt make sence to me.that was a weird combo for sure.
So how much??

[Nucking futs]

300 plus shipping

[steelcomp]

300 plus shippingWith pins? If so, what are they?

[Nucking futs]

No pins. just pistons.