[thinwhiteduke]

Hay!

Just trying to get piston head volume for TRW L2252A (aka Speedpro 7009P). Short of making a cast of one and then cc-ing it, does anyone know the cc volume of these. They are are common 12.5:1 advertised slug for 350sbc.
Can't find much online and summit has something very similar quoting the displacement as 11cc's.

Anyone know offhand?

Thanks,

Duke

[MouseFink]

The 11 CC volume indicated is the dome displacement. In order to determine the static compression ratio, that amount is subtracted from the combustion chamber volume. The single trough type valve relief volume found on Speed Pro pistons with a dome is a nominal 4 CC and dual valve reliefs found on flat top pistons is 6 CC. The valve relief volume is added to the combustion chamber volume.

[thinwhiteduke]

Originally Posted by MouseFink

The 11 CC volume indicated is the dome displacement. In order to determine the static compression ratio, that amount is subtracted from the combustion chamber volume. The single trough type valve relief volume found on Speed Pro pistons with a dome is a nominal 4 CC and dual valve reliefs found on flat top pistons is 6 CC. The valve relief volume is added to the combustion chamber volume.

Ok , thanks. So when I subtract that amount (11cc) from the combustion chamber, do I still ADD the volume off the dual valve reliefs to the combustion chamber? or what that amount already be factored into the 11cc figure?
I understand how to calculate SCR both old school way, and using the online calculators. So if in fact the quoted dome displacement is,say, 11cc, would I be correct in assuming that both the 'dome' and the 'reliefs' are factored in to the 11cc's ?

Duke

[F-BIRD'88]

The advertised volume is the dome volume - the valve relief volume.
They are both accounted for in the spec.

[thinwhiteduke]

Thanks f,bird....

Duke

Should those pistons actually BE 11cc's ??

[OLNOLAN]

The dome volume varies a bit depending on the oversize.

std- 11.9cc-.240 dome
.030-11.0cc-.220 dome
.040-10.6cc-.213 dome
.060-10.2cc-.200 dome

Also, these are not 12.5:1 pistons, CR ranges from ~10.2:1 to 11.9:1 depending on the head chamber size used and the amount of overbore.

I've got an old catalog if you need more info.

[MouseFink]

You must subtract the dome volume from the combustion chamber volume and enter the remainder where it asks for the "cylinder head volume" . Using the Keith Black website at www.kb-silvolite.com

Example:

57 CC cylinder head volume (68 CC chamber vol. - 11 CC dome vol.)
4 CC piston head volume (valve relief)
.041 gasket thickness
4.20 gasket bore
4.03 cylinder bore
.010 deck clearance
3.48 stroke

11.05:1 compression ratio

[thinwhiteduke]

Thank you mousefink and nolan for your replies!

These are .030"over. The engine measures at:-

Bore: 4.030"
Stroke: 3.48"
Cyl head chamber: 61.5cc
Pistons are the said: 7009P .030 (straight out the box)
Head gasket crushed thickness: .041"
Head gasket dia: 4.166"
Deck clearance: .008"

This is a mates engine thats done a cam, and im helping him rebuild it and maybe improve it some. He was told it was 12.8:1, I got 12.86:1 (basing the piston value on 11cc)
Just trying to get an accurate input on the piston displacement value including the dome and relief, without measuring them.

Thankya!

Duke

[OLNOLAN]

Duke, You may want to recheck your numbers. According to the piston book, your compression should be ~11.26:1 this is based on a 68cc chamber. With a 64cc chamber~ 11.87:1. The spec's on the compression height is 1.56".

I've got company over right now so I'll check back later and see what you figure out.

[thinwhiteduke]

OLNOLAN, thanks for checking. The head chambers are definately 61.5 cc
Does your piston book cover all the variables? deck height etc?

Duke

[cobalt327]

Your best bet is to plug your numbers into a calculator (and continue to use the same calculator so there are no surprises). The one I use is here, there are others- but be sure to enter the dish/dome volume correctly, not all calculators use the same sign (negative or positive) for a dish or dome. The same thing can be said for published volumes- some will give a positive number for a dish, others a negative.

[BigEd36]

Thinwhiteduke, entering your measurements into both the KB-Silvolite and the Pat Kelley dcr calculators I'm getting a static CR of 12.86 (with 61.5cc chambers, .041" head gasket with 4.166" bore, 11cc dome pistons, .008" deck height, 4.030" bore, 3.48" stroke, 5.7" rods).

Using the Fel-Pro/Speed-Pro virtual catalog (that you can download for free), I can't find any Speed-Pro 7009P, but there is a part #L-2252AF 30. It's a forged piston with a .220" dome, 11cc dome.

Download the Del-Pro/Speed-Pro virtual catalog program to your computer here: Federal-Mogul eCatalog Resource Center - Performance Downloads

You can do a "look up" by application or part number online here: Federal-Mogul Resource Center - Performance

Hope this helps,
Ed

[thinwhiteduke]

Thanks Ed and Cobolt
That's what I got 12.86. Yeah, the + and - values can be a bit confusing.
The #L-2252AF 30 is the same piston and thanks to OLNOLAN I've learned that the volume varies a bit with the oversize.
Pretty much established what I wanted to here now so thank y'all for your time and help and links!

Duke

[OLNOLAN]

Just thought I'd let you know I back checked the math on the book listed compression ratios. Its correct BUT, that specific piston is listed as having a .025 deck clearance, so that is what they base the calculation on(along with a note saying all calculations are based on a .038 compressed gasket thickness). When I recalculated at a .008 deck clearance it jumps up over a half a point of compression! Whats pretty crazy is there are some SBC pistons that list a whopping .045 deck clearance. Talk about having to do some serious decking.

Nolan