I need someone to tell me what I am doing wrong.
Speed Pro hypo piston published data:

Part# H890CP 30

reverse dome: -23
Compression dist. 1.45
Deck clearance .025
head CC. 64cc
CR 8.59

This published compression ratio should be 8.8. I cannot see how they are getting 8.59. Whenever I run other manufacture info I match up to their published CR pretty close. As luck would have it, of all the piston manufacturers I cannot find any contact info for Speed Pro.
Does any one have any ideas? The only thing that works is a head gasket of .052. Is it possible they use this instead of the .039 or .040 that everyone else uses?

 

Try federalmogul.com they have a contact us sect. were u can ask your questions.......Jerrylee///

 

http://www.21cgt.com/FMWebCatalog/default.htm

Here you'll find info and calculators for FM performance parts. In the "Products" tab follow that to Speed Pro, Tech Highlights, Pistons where you'll find how FM "roughly" calculates their advertised values. It doesn't say so but a "as measured" head cc values maybe in use for all the data charts. Example, 65.9 cc gives a 8.59:1 ratio with your above specs.

Bore - 4.030
Stroke - 3.75
Deck - .025 (usually more like .029)
Gasket thick - .041
Bore dia - 4.166
Head volume - 64cc
Dome - -23 (rev. dome in this case)
# Cyl - 8
_____________________________
Comp Ratio = 8.59:1

Swap out the standard head gasket to a shim, .015" gives a better ratio of 9.04:1. Or go with a dished piston, H859P-30 which would give a better 9.49:1 based on info above (standard gasket of .041).

Again, these are rough numbers for calculating, you'll need to measure your parts to get exact values. There will be production tolerences that need to be factored in. This goes for stock O.E. and aftermarket hardware.

Hope this helps,
Later.

 

They maybe using a shorter deck height for the block with a stock nominal height is 9.025".

And the actual compressed height of the piston is needed to estimate c.r.. Lets say TDC piston height is = 1/2 stroke + rod length + compressed height. U subtract this from the the deck height to give u an estimate of the volume above the piston (u are still missing the creave volume between piston and cyl wall - yes its tiny). The "compressed height" is with the mfr piston data - u should verify this.

Let me know if this helps your calcs,
cardo0

 

"quote" Swap out the standard head gasket to a shim

you can't use just the shim in place of the gasket

vc

 

The manufacturer uses the term deck clearance .025. I assume this is interchangeable with the term deck height 9.025. Clearance can be .025 regardless of the deck height just change the piston design height to accomodate a certain deck. But since they state a 1.450 compression distance I can only conclude that the .025 deck clearance means they are .025 in the hole.

 

Vette Crazy -

FP part# 1094, .015", RCM with C.O. of 4.100".

We call the RCM (Rubber Coated Metal) embossed single layer gasket the "shim". This is not a copper repair "shim" nor the O.E. metal gasket "shim" from back in the day that needed half a can of copper coat to seal.

And yes, you can swap this for the performance part# 1003 or equiv. As with any aftermarket part and the almost unlimited number of interchangable parts, care should be taken to ensure the embosses don't fall into a coolant port or C.O. (combustion opening).

GD.

 

I used the H890CP 40 pistons in my build. I ended up with a 9.25CR with the following setup:

3.75 stroke
4.040 bore
.025 piston to deck clearance
.015 gasket (FP 1094)
64 cc heads

Here's a pic:

 

I think your right. FM states that compression ratios are based on "published standard block deck height and the Fel-Pro head gasket volume for each engine." If I use all the numbers I originally stated AND a .051 or .052 gasket instead of a .039, then it hits their CR. SO I think this is the answer. Nice and simple. The good news is that means this piston will work in my application providing a 9.3:1 CR.

 

This is a great help because it does a good cross check on the info.
This plus my opinion they used a .051 0r .052 gasket confirms my opinion that for my set up I will have a 9.32:1 CR;

H890CP 30 piston (-23cc)
3.75 stroke
4.030 bore
9.000 deck
.039 gasket
63 cc heads
1.425 compression distance

The forum never ceases to amaze me. 95% of the time I find the answers.

 

AWilson -

Point was the other parts have tolerence stack ups and the "actual" value FM gets might be based on this. Such as the Head cc is rarely exactly 64cc, same with the piston dish or valve pockets. This can affect values published. The standard FM gasket is between .039" -.041" depending on clamp load, such as use of studs vs bolts and head deck thickness plays into this. FP usually publishes .041" but I have seen as .039" in some cases. Also this simple calc really doesn't include the upper ring volume/bore to piston tolerence, it's just a ball park until you measure - actual parts used.

Second, your still about 8.6:1 with the hardware you first spelled out. Don't change the deck height in your data unless your going to "deck" the block at some point. Either a piston change (H859CP - 30) or the #1094 (.015" thk, 4.100 C.O.) are going to get you into the low 9's. Unless you change the heads, then your talking about a whole different combination.

Remember, dgruenke is using a .040" overbore and the #1094 to get his values. A couple of tenths either way are not a big deal. His 9.25:1 is very close to the calc'd 9.21:1 (not 9.04 I had = forgot to change C.O. size in calc) for your bore size and setup.

Sorry for any confusion.

 

Don't forget 1.5cc's or so for crevice volume of the ring land area.


JIM

 

GasketDude, I think there is a little confusion. The info I originally spelled out was from the FM website. My latest info is my set up. I have to deck the block, it is already at 9.010 and I need to clean it up so 9.00. I calc. 9.32:1. If I allow 1cc for the land area I get a 9.23:1 CR. This -23 piston should get me in the ball park. The otherpiston pushes me over 10:1. Is this sound thinking?

 

Your right, looks like I can't take phone calls etc and try and read/type - my fault. Seems like you got it handled. Have fun with your project.

 

8.6 or 8.8 it ain't gonna matter too much either way

 

Folks:
I have in front of me a brand new set of speedpro H890CP in standard bore size in SP box. A local pal bought em off ebay a few months back. They've obviously never been used & are complete w/ pins & locks. I don't have a handy way to do/post any pics so you'll just have to accept this as I see it.

Rather than being laser etched inside the dish as shown by dgruenke ... these are laser etched on the flat.

-23cc right ... yea I know, I know I've got a hardcopy SP catalog that specifies -23cc dv ... but guess what? ... this box's white end label w/ black print reads "H890CP STD" but also reads "25cc RECESS" ... that's right ... it reads "25cc RECESS" ... twenty-FIVE. Nowhere on/in box or pistons is dv specified otherwise. You do realize that by using "25" when doing the scr calc, result will agree more closely w/ SP's published quotes?

No I have not cc'd these pistons so I do not know what their true dv is. Frankly, for what most folks are doing here ... a 2cc diff ain't squat.

happy & safe thanksgiving to you & yours

-edit- just checked FM web online catalog ... it specifies -23 dv. Box label hasn't changed: "25cc RECESS"

Been a while, but I've called Speed-Pro's Tech line 1-800-325-8886 ... there was a helpful gent named Jim. DoNOT abuse that number or it'll get gone & no one can use it! Capisce?

also ... if dgruenke's pistons are -25cc (instead of -23) ... dgruenke's scr would drop from 9.25:1 to 9.08:1

 

Unless dgruenkes actually measured the actual dish value of the piston there is no way to be sure. He may think he has a 9.25 and really has a 9.08. Boy, it would really be great if you could cc one of those pistons because maybe SP has a typo on their printed spec. Either the box is wrong, the catalog is wrong, or these are custom pistons, or these are not the box the pistons came in. We all have a vested interest in knowing.

 

When I purchased mine, all the catalogs stated -23cc. My box did say -25 recess, like Jackson stated. I did not measure the actual cc.

Has anyone called the SpeedPro number yet?

 

Well this is exactly what I was trying to explain, actual machining tolerences vs the print. Or in this case the catalog/marketing mix up. Your ratio now calcs out to 8.58:1 with the -25cc spec (and all your info from above).

By switching to the #1094 (.015" x 4.1" C.O.) your ratio would be approx 9.04:1. With same gasket and zero deck you'd be at 9.5:1.

Change to the H859CP with catalog spec of -12cc and a "standard" #1003 thickness of .041" you'll be approx 9.5 - 9.6:1 compression. Low 10's (10.28:1) if you then change to the #1094 gasket.

You can call the hotline but your still gonna have to measure the actual parts before/during assembly to know for sure what you have.

My .030" over flat top 327 (4 reliefs, .025" below) with AFR-180E 64cc heads comes in at approx 9.7:1 which is just fine for low grade fuel.

Have fun,
Later

 

If the piston is speced to have 0.025" deck clearance in a stock deck (~9.025") ... but it's installed in a block that has a 9.000" deck height ... it'll have NO deck clearance ... as in "zero-deck".

I do NOT suggest running STREET car w/ zero-deck & FP p/n 1094 gasket ... piston crown will be ~ 0.015" away from head deck at room temp ... less when piston gets hot & grows / rocks. That'd be fantastic quench but ... IMHO ... flirting w/ disaster.

If you have STREET sbc based on 4" bore ... and has zero-deck ... suggest FP p/n 1003 ... about 0.041" x 4.166" = about 9.1cc.