I just spoke with Matt at Speed Pro and told him of the confusion. He looked through all of his catalogs and said that it should be -23cc. He said that most of the time, the cc is not even listed on the box, and he does not know why the box said 25cc recess.

I have it all put together already or I would measure it.

 

I don't know why I keep forgetting AWilson has to deck his block to "zero-deck"!! I keep thinking he's leaving his block stock. Sorry same mistakes.

Anyway, with the Hyper pistons there's very little growth from heat with this material. That's why skirt clearances are only .001" - .0015". Combine that with his H890CP reverse dome pistons plus valve releifs, he should have no issues. I would suggest less dish, more like -12cc like the pistons I already discribed that would get closer to 10.2:1 (with zero deck and .041" gasket) depending on how hot the cam is going be.

Bottom line is the actual cc of the pistons in the catalog is going to be a little different than the actual part. And with my 15+ years experience working in the test lab at Fel-Pro (later bought out by FM) I can tell you with extreme confidence that the catalog is not the Bible when it comes to specs.

A few tenths on the compression are not going to make a difference in power or detonation limits.

 

gasketDude I agree with you 100% except that I am told by many many people to keep the CR under 10:1. The H859CP gives a 10.2:1, too high. The H890CP gives me 9.23:1. Seems a little low. ones too low ones too high. Don't know what to do. maybe I am splitting hairs? Or spend more money,,,,,,again,, and go with a Weisco -20. It is perfect at 9.5:1. But it's forged and $400 more for the set!

 

Jackson, I agree. I was going to go with a .039 for ideal quench. But the .041 is basically the same thing. The .002 can make all the difference in the world.

 

How much DCR will you have with 10.2 comp and the 230 .050
dur. cam you are going to use. Seems like 9.3.9.5 would be a little
low for a 230 .050 cam.

 

Little Mouse, I appreciate the question but don't know how to answer it.

As you know the cam is a Engle EP-22HYD 230/230 480/480 110LSA

Other info is:
running duration 274
intake opens 8 closes 42
exhaust closes 2 opens 48

UPDATE:
I found a web site that computes DCR. IF I DID IT RIGHT the -23 piston has a DCR of 8.5. The H859CP -13piston has a DCR of 9.6.

SOOO what's more important the CR being around 9.5:1 or the DCR being around 9.5:1? I will also ask this question in a dedicated thread.

 

AWilson:
hope you're not counting on DCR calc at KB / UEM Piston site??? ... it's not right! ... plenty info here on its flaws ... do a search. Your figures seem suspect. Maybe someone else might choose to run them.

Also ... I wouldn't get too caught up in DCR ... search all you want ... I've NEVER found a credible data set regarding DCR limits ... there's too many variables ... I even asked two top PhD Eng at NC's leading Motorsports school (where a much TOO-vaunted Vizard once got his paychecks) ... asked em about DCR ... too many variables. Understand this ... there are lotsa FLOW/FLUID dynamics happening ... NONE of typical DCR calculators take that into account ... if they did (and did it well) they could not be freeware. Also ... up until just a few years ago ... only a very few folks had even heard of a DCR formula ... but most others'd successfully picked a many a cam & static compression. DCR is nice & if you know how to spot trouble ... it can be a handy tool to help guide you ... but it ain't the be-all & end-all ... that's my tail & I'm sittin' on it!

also ... so your deck's at 9.010 ... you seem like you're guessing it might end up 9flat ... but you don't KNOW where it's gonna be ... so don't lock in a gasket unless you know what deck's gonna be. And ... for a STREET car ... NO ... +/- 0.002" gasket thickness really don't mean squat (not to me). Keep this option in mind: GM p/n 10105117 composition gasket 0.028" / 5.8cc. Also ... any good gasket that'll yield 0.035"-0.045" quench will be fine for street.

True, hyper don't grow much ... but things have a way of changing (ie bearing clearance, & as said .. piston ROCK etc) that can effectively tighten quench when running. In this case, I don't sweat valve-piston clearance much ... only crown-to-heads' wedge (quench aka squeeze aka squinch). Promise you ... set quench too tight and then have a rod bearing tear up ... it'll take out at least one piston, rod & bore ... maybe block too.

If I remember to get around to it ... I might call SP & ask em to pull up a drawing for H890CP ... see what the callouts etc tell us about dv. Again ... in the 8.5 to 9.5:1 scr range for THIS STREET sbc combo ... 2cc (-23 v. -25) ... 2cc out of about 90-105 total (chamber+gasket+deck+piston) really don't mean squat to me either.

-edit- your valve events (intake opens 8 closes 42
exhaust closes 2 opens 48) are probably at 0.050" duration ... note: some DCR calcs require SAE/ADV dur events ... some do -- some don't -- some should but don't -- some do but shouldn't, some are so screwed up it really don't matter that much anyway.

 

Jackson, Whats your opinion on whether or not he can run 10/10.2
compression with the 230 .050 cam and his iron heads.
I think maybe you should run the higher compression piston
then do some tailoring.

 

Does he have iron? Is it stated in this thread? Dunno? Has he already got the H890CP30 pistons? Dunno?

But ... if he's got iron 64cc & -12cc pistons & 230* hft cam ... and he's stuck with all 3 ... repeat in this case he's stuck and no option to change ... in this case where no option to change any of 3 ...
... then in this case only I'd say put 383 together w/ good quench at about 10.2:1 scr and keep close company with whoever sells good gas.

Ya know ... if he milled 64cc heads about 0.018"-0.022" ... that'd reduce chamber size about 3 to 3.5cc ... & they'd probably still fit intake OK ... and would raise HIS 383 combo scr about 0.25 to 0.3. With H890CP30 reverse dome, might put him right about where he seems? he wants to be.

 

He has a set 64 cc heads with 194/150 valves that he sent off
had all new seats valves to make them 202/160. I have no
clue if they did any resurfacing they probably did a few thousands
to clean them up.

I thought someone made a -16 piston, if he's talking about a -23
piston ending up at 9.3,9.5 compresson or a -12 making him at 10.2
seems like the 4cc differance would put him a little below 10.0
surely that would work its not like he's going to try and run a L/48
cam.

 

What if???
he has his rebuilt iron heads surfaced to about 60.5cc???
If deck is pretty good shape leave it ... he says it's 9.010" now???

0.026" x 5.4cc victor 5746 or 0.028" x 5.8cc GM 10105117 gasket??

-23cc or -25cc??

calculator
http://www.21cgt.com/FMWebCatalog/frmConversion4.aspx

Depending on -23 or -25 ... I see 9.39:1 to 9.61:1 with 0.036" to 0.038" quench.

I think that's what I'd do if it were mine & I was stuck w/ heads & cam but had not bought pistons.

 

I'm pretty sure from one of his other threads he said the block
was now at 9.010 but the machinest wants to take another
.010 off the block to make it strait. This is why Awilson talks
of using a .039 or .041 gasket.

 

I think KB makes -16cc or thereabouts ... I don't much like KB ... others swear by em.

 

anyone know how many cc's can be added to the head buy unshrouding the valves? adds airflow, cuts cr.
also when i switched to cold air intake, my octane requirements dropped from 91 to 87 with 9.7:1 and iron STR's.
so with cold air, go 10.2
engine air- go <10

 

SRP makes a -16 cc forged piston for a 383.

 

GUYS

I did not buy pistons yet. But I am trying to make a decision now, as I am tired of worrying about it.

Stuck (or happy) with:
numbers matching Block is 9.010 will have to go to 9.00. haven't done it yet, but lets assume thats the number.

Heads 291 double humps just rebuilt. 2.02/1.6 new seats either exhaust or intake, (not sure which) Don't know if it was cut a little or not but they cc'd the heads for me and I am told they are 63's. I questioned why not 64 or 65, they said these heads are notoriously known for being different sizes and the new seats and valves have an effect.

Cam, Engle, as stated above.

my 9.5 ish:1 CR calculations are based on:

63cc heads
9.00 deck height
.039 gasket
3.75 stroke
5.7 rods
-20 dish or reverse dome pistons.
-------------------------------
-23 pistons come out to 9.3 ish:1 CR

This thread is about piston selection so please read the initial post so we can get back to it. It got into DCR a little but I don't think it is an issue anymore.
I am basically trying to get aroung 9.5:1 CR without having to buy the forged Weisco's. At 9.5:1 the actual built CR can go on either side a little and I will be fine.

I really love all the interest and comments. It helps alot. I have learned so much in the last 3 months about SBC engines.

 

If the 890 piston is actually -23, I recommend that one. Are there any shops or parts stores around you that may stock it so that you can actually measure it?

 

"Bite the Bullet" and get the forged pistons.

They run about 475.00/500.00 BUT you get some add'l advantages with respect to some added HP.

The pistons we use on these builds weigh in at 450 grams (nominal), have the 1/16", 1/16", 3/16" ring pack PLUS you get a wrist pin that weighs about 118 grams. And they are NOT dished, they are "reverse- domes", this fact is also a "plus"! We use the -21 cc volume.

All this equates to "free" HP just by the lightweight design. Less loads on the rod brgs, rods, pins, etc. You get about 10 HP from the ring pack alone.

Thanks, Gary in N.Y.

P.S. If you figure what the add'l cost comes out to be, I think you may not be that bad off!! You get to use the R9771 Speed-Pro rings!

 

GOSFAST, what brand and part# is the -21's your talking about?

 

They say 70 percent of friction in an engine is caused by the rings
makes sense, all modern engines are using thinner rings.

The reason I gave you the other part # for the hyper piston of the
same brand, it uses the thinner 1/16 rings the 890 piston uses
the old 5/64 rings.

Speed pro hypereutectic
H137CL30 = 9.6 comp, 64cc chamber, rings 1/16-/1/16-3/16,
lightweight tapered pin, 3.75 stroke, 5.7 rod,
$319.00