Define compression distance when talking about pistons

[5.0calypso93lx]

I'm looking at purchasing a set of pistons, and have come across a set for a pretty good deal.

I was originally looking at the TRW-L2446F's, and they have a 1.772" compression distance, and give a 9.19 CR with a 60.4cc head, and 8.95 CR with a 63cc head. I soon learned that it was going to be pretty impossible to find a 351w block that wouldn't need bored out .030.

So I found the same set of pistons, but for the .030" overbore. They are part number TRW-L2378F30. They do not list what the compression ratio would be on summits site, but they do have a compression distance of 1.736".

What would the 2nd set of pistons net me with say a 60cc or 61cc head?

The other difference that I see between the two pistons is the Piston Head Volume. The standard bore piston has a +13.20cc volume, while the overbore piston has a +16.90cc volume. What does that refer to?

[Rick93coupe]

Post links to both pistons from summits site and I'll check it out for you.

[kennebellcobra]

http://www.rbracing-rsr.com/compstaticcalc.html This may help. The + on the cc of the pistons raises your compression 1cc is "roughly" .1 compression ratio so a 10:1 with 60cc heads would be 9.5:1 with 65cc heads. Same thing with the compression distance the more it travels the higher the compression. Play with the calculator and you'll figure it out.

The pistons are probably similar because the one with more cc's has less compression heigth but you can figure it on the calculator to see the exact the exact difference.

Think of compression ratio as how much space is between the piston and head at tdc the more space you have the lower the compression ratio the less space the higher it is. A + piston or dome takes up space a - piston or dish adds to it.

The compression distance is the the measurement from the center of the piston pin to the top of it. You need to add stroke, rod length and piston heigth to get your total distance or deck heigth

[5.0calypso93lx]

Post links to both pistons from summits site and I'll check it out for you.

Piston 1: Standard Bore http://store.summitracing.com/partdetail.asp?part=TRW%2DL2446F&autoview=sku

Piston 2: .030 over http://store.summitracing.com/partdetail.asp?part=TRW%2DL2378F30&autoview=sku

[5.0calypso93lx]

http://www.rbracing-rsr.com/compstaticcalc.html This may help. The + on the cc of the pistons raises your compression 1cc is "roughly" .1 compression ratio so a 10:1 with 60cc heads would be 9.5:1 with 65cc heads. Same thing with the compression distance the more it travels the higher the compression. Play with the calculator and you'll figure it out.

The pistons are probably similar because the one with more cc's has less compression heigth but you can figure it on the calculator to see the exact the exact difference.

Think of compression ratio as how much space is between the piston and head at tdc the more space you have the lower the compression ratio the less space the higher it is. A + piston or dome takes up space a - piston or dish adds to it.

The compression distance is the the measurement from the center of the piston pin to the top of it. You need to add stroke, rod length and piston heigth to get your total distance or deck heigth

Excellent info. So since the first piston has a +13.20cc piston head volume, and the 2nd piston has +16.90 piston head volume, that makes the 2nd piston about .3 compression points higher.

Does the shorter compression distance of the 2nd piston(1.736 compared to the 1st pistions 1.772), change how much bigger/smaller the dish is on the top of the piston? That almost seems like it would make the dish a little smaller with 2nd piston, causing even higher compression?

Sounds like I'm getting Twisted Wedges over Victor Jr's ! :lol:

[Rick93coupe]

Thats not the type of piston your looking for. I'll find you something. BRB

[Rick93coupe]

Hmmm, while I was looking, I came across those pistons that are .030 for a good price. They look better in the picture than what is on summit. Don't have much of a dish though, and the summit pictures look like an inverted dome which you can't use.
http://www.nmradigital.com/forums/showthread.php?t=76534

[Rick93coupe]

http://www.probeindustries.com/Pistons/Pistons_SRS/Ford/Ford_351W.htm

You can learn a lot by seeing the different pistons and compression heights, compression ratio.

[Rick93coupe]

These may also be worth looking into, the price is certainly right.
http://store.summitracing.com/partdetail.asp?part=UEM%2DKB364040%2D8&autoview=sku

[5.0calypso93lx]

Hmmm, while I was looking, I came across those pistons that are .030 for a good price. They look better in the picture than what is on summit. Don't have much of a dish though, and the summit pictures look like an inverted dome which you can't use.
http://www.nmradigital.com/forums/showthread.php?t=76534

Those are the ones I'm buying :lol:

I'm basically looking for a forged, dished, low compression piston that will work on stock truck rods for a 351w, with either 60 or 61cc heads. I'd love to have right around 9.0:1 compression.

[5.0calypso93lx]

These may also be worth looking into, the price is certainly right.
http://store.summitracing.com/partdetail.asp?part=UEM%2DKB364040%2D8&autoview=sku

I need a forged piston.

[kennebellcobra]

Excellent info. So since the first piston has a +13.20cc piston head volume, and the 2nd piston has +16.90 piston head volume, that makes the 2nd piston about .3 compression points higher.

Does the shorter compression distance of the 2nd piston(1.736 compared to the 1st pistions 1.772), change how much bigger/smaller the dish is on the top of the piston? That almost seems like it would make the dish a little smaller with 2nd piston, causing even higher compression?

Sounds like I'm getting Twisted Wedges over Victor Jr's ! :lol:

I told you wrong the + dished will lower compression more space a - dome will raise compression. The 1.772 vs the 1.736 means the 2nd piston will sit .036 further down in the hole than the 1st one so if you don't zero deck the block the 2nd one will have even less compression.

[Rick93coupe]

Those are the ones I'm buying :lol:

I'm basically looking for a forged, dished, low compression piston that will work on stock truck rods for a 351w, with either 60 or 61cc heads. I'd love to have right around 9.0:1 compression.

Yeah that was my point. I was looking for another piston, and found a better price on the piston you listed.
The other pistons are listed as hyper pistons for blowers and turbos. I think it would be worth calling them about. I'm not a big fan of the generic looking forgings that TRW puts out.