Compression and confusion
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Compression and confusion
Example:
Pistons with -16cc dome are advertized at 9.8:1 with 64cc heads.
That's with a stock deck height block (9.025") ?? What head gasket and thickness ???
I used the CR calculator and assumed a gasket thickness of .040".
How do I know how far the piston is in the hole (before buying the pistons) ???
How much do head gaskets vary (compressed thickness) ?
Pistons with -16cc dome are advertized at 9.8:1 with 64cc heads.
That's with a stock deck height block (9.025") ?? What head gasket and thickness ???
I used the CR calculator and assumed a gasket thickness of .040".
How do I know how far the piston is in the hole (before buying the pistons) ???
How much do head gaskets vary (compressed thickness) ?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Example:
Pistons with -16cc dome are advertized at 9.8:1 with 64cc heads.
That's with a stock deck height block (9.025") ?? What head gasket and thickness ???
I used the CR calculator and assumed a gasket thickness of .040".
How do I know how far the piston is in the hole (before buying the pistons) ???
How much do head gaskets vary (compressed thickness) ?
Pistons with -16cc dome are advertized at 9.8:1 with 64cc heads.
That's with a stock deck height block (9.025") ?? What head gasket and thickness ???
I used the CR calculator and assumed a gasket thickness of .040".
How do I know how far the piston is in the hole (before buying the pistons) ???
How much do head gaskets vary (compressed thickness) ?
You have to know how much (if any) your block has been decked AND pistons' (published) compression height in order to calulate how far down in hole it'll be. If you'll tell us exactly which piston you're talking about (mfg AND p/n) and your block AND stroke specs ... someone can help you.
BTW "-16cc dome" indicates the piston is essentially dished or has "reverse dome) and does not have a "conventional" dome that's pokes above crown. So ... give us more & accurate details.
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Piston manufacturers make varying assumptions ... some assume block is std deck ... some assume block is zero-decked ... some assume something in between. Some assume gasket 0.038" ... some something else. Gaskets range 0.015" - 0.060" ... ALOTTA range!
You have to know how much (if any) your block has been decked AND pistons' (published) compression height in order to calulate how far down in hole it'll be. If you'll tell us exactly which piston you're talking about (mfg AND p/n) and your block AND stroke specs ... someone can help you.
BTW "-16cc dome" indicates the piston is essentially dished or has "reverse dome) and does not have a "conventional" dome that's pokes above crown. So ... give us more & accurate details.
You have to know how much (if any) your block has been decked AND pistons' (published) compression height in order to calulate how far down in hole it'll be. If you'll tell us exactly which piston you're talking about (mfg AND p/n) and your block AND stroke specs ... someone can help you.
BTW "-16cc dome" indicates the piston is essentially dished or has "reverse dome) and does not have a "conventional" dome that's pokes above crown. So ... give us more & accurate details.
In this case I was looking at SRP forged pistons with inv. dome -16cc. This is from Jeg's website:
350 Block Specs: Dome vol. -16cc, 457 grams.
C/R: 58cc - 10.4:1; 64cc - 9.8:1; 70cc - 9.2:1; 76cc - 8.7:1.
1.425'' C/H, 5.7'' Rod, 3.750'' Stroke.
Jeg's part number: 867-139628
I am leaning towards a 383 stroker although a 396 isn't more expensive - the block however is already clearanced for a 3.800" stroke so it's a sure fit with the 3.75" crank. The cam bearings are already installed and I don't really want to grind any more and get all that dirt in there...
It's the new GM stroker clearanced 4bolt main block with a 1piece rms (Summit part number NAL-88962516) Deck height is stock, 9.025"
It seems that I can compensate a lot with the gasket thickness, that's good news....
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
3.75/2 = 1.875 = 1/2 stroke
1.875 + 5.7 rod + 1.425 piston = 9.000"
Piston down in hole 0.025" w/ stock 9.025" deck.
383 implies 4.030" x 3.75" ... I'm calculating CR based on +30 (4.030") bore... CR will be a bit less if 4.000".
If Iron heads ... use FP1094 gasket (0.015" x 3.2cc) for good 0.040" quench.
If Alum heads ... use VR5746 gasket (0.026" x 5.4cc) for fair 0.051" quench ... VR5746 is the thinnest gasket I know of that's truly OK for Alum heads.
I calculate 9.86:1 scr w/ iron 64cc & FP1094 ... w/ Alum 64 & VR5746 I see 9.65:1.
If you get a 3.8" crank (scat has em in cast & forged ... probably eagle too) ... a 5.7" rod w/ 1.425" piston will be zero-decked (not down, not up) ... use FP1003 gasket (0.041" x 9.1cc) good for both iron & alum. I see 9.91:1 scr & good 0.041" quench w/ 64cc head & -16cc SRP.
SpeedPro has same piston but -21cc forged LW2618F+030 ... 388" @ 9.44:1scr ... or ... their -23 cc hyper H890CP+030 makes 388" @ 9.27:1.
1.875 + 5.7 rod + 1.425 piston = 9.000"
Piston down in hole 0.025" w/ stock 9.025" deck.
383 implies 4.030" x 3.75" ... I'm calculating CR based on +30 (4.030") bore... CR will be a bit less if 4.000".
If Iron heads ... use FP1094 gasket (0.015" x 3.2cc) for good 0.040" quench.
If Alum heads ... use VR5746 gasket (0.026" x 5.4cc) for fair 0.051" quench ... VR5746 is the thinnest gasket I know of that's truly OK for Alum heads.
I calculate 9.86:1 scr w/ iron 64cc & FP1094 ... w/ Alum 64 & VR5746 I see 9.65:1.
If you get a 3.8" crank (scat has em in cast & forged ... probably eagle too) ... a 5.7" rod w/ 1.425" piston will be zero-decked (not down, not up) ... use FP1003 gasket (0.041" x 9.1cc) good for both iron & alum. I see 9.91:1 scr & good 0.041" quench w/ 64cc head & -16cc SRP.
SpeedPro has same piston but -21cc forged LW2618F+030 ... 388" @ 9.44:1scr ... or ... their -23 cc hyper H890CP+030 makes 388" @ 9.27:1.
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Thanks, that's great info.
The block is 4.000" bore, so it'll be a 377ci with 3.75" stroke or a 383ci with 3.8" stroke. My heads are aluminum with 64cc chambers.
Mahle (just an example) has a piston with -5cc inv. dome that's advertized at 11.3:1. That piston has a compression height of 1.125" and is for use with a 6" rod. (makes sense as 5.7" rod uses a piston with 1.425"CH)....
Both would be .025" in the hole, sounds like you don't like that too much. What's the big difference between piston in the hole and a thin gasket vs. piston at deck and a thick gasket ?
The block is 4.000" bore, so it'll be a 377ci with 3.75" stroke or a 383ci with 3.8" stroke. My heads are aluminum with 64cc chambers.
Mahle (just an example) has a piston with -5cc inv. dome that's advertized at 11.3:1. That piston has a compression height of 1.125" and is for use with a 6" rod. (makes sense as 5.7" rod uses a piston with 1.425"CH)....
Both would be .025" in the hole, sounds like you don't like that too much. What's the big difference between piston in the hole and a thin gasket vs. piston at deck and a thick gasket ?
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
I dunno what SCR you want? Also, keep in mind ... many performance pistons are not available in std 4.000" bore ... limits choices.
How about this?
SP coated liteweight hyper flat -5cc 1.130" p/n H124CL ... 6" rod ... 3.75 ... 5746gasket ...0.020" down in hole ... 377" @ 10.83:1 ... quench 0.046". This one's available in std.
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
No diff. But I like to see quench in a fresh motor about 0.040"-0.045" ... thin gasket choices for Alum heads are limited ... as before ... 0.026" is thinnest I know of.
I dunno what SCR you want? Also, keep in mind ... many performance pistons are not available in std 4.000" bore ... limits choices.
How about this?
SP coated liteweight hyper flat -5cc 1.130" p/n H124CL ... 6" rod ... 3.75 ... 5746gasket ...0.020" down in hole ... 377" @ 10.83:1 ... quench 0.046". This one's available in std.
I dunno what SCR you want? Also, keep in mind ... many performance pistons are not available in std 4.000" bore ... limits choices.
How about this?
SP coated liteweight hyper flat -5cc 1.130" p/n H124CL ... 6" rod ... 3.75 ... 5746gasket ...0.020" down in hole ... 377" @ 10.83:1 ... quench 0.046". This one's available in std.
I noticed that nobody lists std. 4.000" pistons in their online catalogs - I hoped that they are available but just not listed on the website.
Are there any forged pistons in std size that you know of ?
Now.... if I have to get the block punched out to 4.030" anyways then I might just buy a used block. In that case it has to be cleaned after machining so it doesn't matter if I grid the clearance for the crank....
I hoped I can just order the parts and start assembling without a trip to the machine shop ...
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
There are a few off-the-shelf performance/race forged pistons in std ... that's one of those things it's best to know about early in planning stage
Any of the specialty companies like Ross etc will be glad to make them ...$$$.
You decide exactly which height and volume and SCR you want (narrow this field down quite a bit) ... and reply w/ requirements ... and I'll be glad to look for a match or close match.
Any of the specialty companies like Ross etc will be glad to make them ...$$$.
You decide exactly which height and volume and SCR you want (narrow this field down quite a bit) ... and reply w/ requirements ... and I'll be glad to look for a match or close match.
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Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
I prefer a 5.7" rod so that the pin hole is below the oil ring. That narrows the piston choice down to those with 1.425" compression height. Pistons must be forged and the SCR must be pump gas friendly around 10:1, that narrows the piston choice to those with -16cc inverted dome.....
I guess the one million dollar question is "what pistons are available in std bore size?"
Punching the block to 4.030" is likely the cheaper way to go.
I guess the one million dollar question is "what pistons are available in std bore size?"
Punching the block to 4.030" is likely the cheaper way to go.
Instructor
Joined: Nov 2001
Posts: 101
Likes: 9
From: Paris, FRANCE
I had the same problem and questions before buying my strocker kit. I ended with some SRP flat top -5cc pistons for stock (4.000") bore.
part# : 178676
http://www.jepistons.com/cat/srp/aut...350_flat.shtml
they are available for 5.7" rods too. part# : 231303
I got them as a kit with eagle 3.75" forged crank, h-beam 6.0" eagle rods and rings/bearings from cnc-motorsports.
my block is almost zero-decked (pistons are 0.004" in the hole). with my 68cc AFR heads, CR is at 10.3.
/Vince
part# : 178676
http://www.jepistons.com/cat/srp/aut...350_flat.shtml
they are available for 5.7" rods too. part# : 231303
I got them as a kit with eagle 3.75" forged crank, h-beam 6.0" eagle rods and rings/bearings from cnc-motorsports.
my block is almost zero-decked (pistons are 0.004" in the hole). with my 68cc AFR heads, CR is at 10.3.
/Vince
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Merci, nous avons un gagnant !!!!!
looks like we have a winner - CNCmotorsport lists them on their website
These are awesome...... Jackson, what do you think ??? With a 3.8" stroke crank they're right at the deck (CH is 1.425") when using a stock deck height block - my CR calculator shows 10.6:1 CR with a .060" gasket - too much for pump gas ??
.. might have to get a 3.75" stroke crank instead to lower CR a little.... or more cam ???
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
IMHO, there ain't a dang thing wrong w/ pin X oil ring groove ... so long as o-rings are supported by "oil ring support rails". Some of the KB's don't use supports & I think those are junk.
Following made by www.probeindustries.com 310-784-2977. They're all for STANDARD 4.000 bore, all forged. You'll have to ask probe if you have q's about oil ring etc.
P/N P3832F-STD 1.425" -22.0cc
P/N 12344-STD 1.425" -20.4cc
P/N 12345-STD 1.125" -12.8cc
-----------3.75 & 5746-------3.8 & 1003
P3832F ... 9.00:1 @ 377 ....... 9.23:1 @ 382
12344 ..... 9.13:1 @ 377 ....... 9.37:1 @ 382
12345 ..... 9.84:1 @ 377" ..... 10.11:1 @ 382
Following made by www.probeindustries.com 310-784-2977. They're all for STANDARD 4.000 bore, all forged. You'll have to ask probe if you have q's about oil ring etc.
P/N P3832F-STD 1.425" -22.0cc
P/N 12344-STD 1.425" -20.4cc
P/N 12345-STD 1.125" -12.8cc
-----------3.75 & 5746-------3.8 & 1003
P3832F ... 9.00:1 @ 377 ....... 9.23:1 @ 382
12344 ..... 9.13:1 @ 377 ....... 9.37:1 @ 382
12345 ..... 9.84:1 @ 377" ..... 10.11:1 @ 382
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Merci, nous avons un gagnant !!!!!
looks like we have a winner - CNCmotorsport lists them on their website
These are awesome...... Jackson, what do you think ??? With a 3.8" stroke crank they're right at the deck (CH is 1.425") when using a stock deck height block - my CR calculator shows 10.6:1 CR with a .060" gasket - too much for pump gas ??
.. might have to get a 3.75" stroke crank instead to lower CR a little.... or more cam ???
looks like we have a winner - CNCmotorsport lists them on their website
These are awesome...... Jackson, what do you think ??? With a 3.8" stroke crank they're right at the deck (CH is 1.425") when using a stock deck height block - my CR calculator shows 10.6:1 CR with a .060" gasket - too much for pump gas ??
.. might have to get a 3.75" stroke crank instead to lower CR a little.... or more cam ???
-edit- very simple ... if you want about 10:1 scr in a 377-382 stroker w/ 64cc heads ... you cannot use a -5cc piston.
Last edited by jackson; Dec 27, 2006 at 04:22 PM.
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
JUNK! ... NO BS ... JUNK! ... that 3.8combo would have a quench of about 0.060" ... if 3.75 quench 0.085" ... both junk ... both way too much! You must not make cr adjustment via a big thick gasket!
-edit- very simple ... if you want about 10:1 scr in a 377-382 stroker w/ 64cc heads ... you cannot use a -5cc piston.
-edit- very simple ... if you want about 10:1 scr in a 377-382 stroker w/ 64cc heads ... you cannot use a -5cc piston.
Darn.... those were even on sale
.040" would be an acceptable quench ? With a 3.8 crank that would push the CR to about 11:1 - a little high for pump gas I guess
I'll have to see who sells the probe pistons that you listed.
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Here's something else you'd best take a close look at:
You say you have a fresh, brand new GM block ... can we assume it is finish-honed? Since those motors did not come with forged pistons, can we assume it is finish-honed to fit cast or hyper pistons?
Note:
Most forged pistons require more bore (side) clearance than cast/hyper pistons ... usually about 0.002"-0.005" MORE clearance than a typical cast/hyper.
Salient Question:
Do you KNOW if YOUR bores are finish-honed and do you KNOW what YOUR bores' finished dimensions actually measure? I don't mean what is assumed ... I mean what is verified.
You say you have a fresh, brand new GM block ... can we assume it is finish-honed? Since those motors did not come with forged pistons, can we assume it is finish-honed to fit cast or hyper pistons?
Note:
Most forged pistons require more bore (side) clearance than cast/hyper pistons ... usually about 0.002"-0.005" MORE clearance than a typical cast/hyper.
Salient Question:
Do you KNOW if YOUR bores are finish-honed and do you KNOW what YOUR bores' finished dimensions actually measure? I don't mean what is assumed ... I mean what is verified.
Thread Starter
Le Mans Master
Joined: Oct 2004
Posts: 5,269
Likes: 54
From: Orlando Florida
St. Jude Donor '05
Here's something else you'd best take a close look at:
You say you have a fresh, brand new GM block ... can we assume it is finish-honed? Since those motors did not come with forged pistons, can we assume it is finish-honed to fit cast or hyper pistons?
Note:
Most forged pistons require more bore (side) clearance than cast/hyper pistons ... usually about 0.002"-0.005" MORE clearance than a typical cast/hyper.
Salient Question:
Do you KNOW if YOUR bores are finish-honed and do you KNOW what YOUR bores' finished dimensions actually measure? I don't mean what is assumed ... I mean what is verified.
You say you have a fresh, brand new GM block ... can we assume it is finish-honed? Since those motors did not come with forged pistons, can we assume it is finish-honed to fit cast or hyper pistons?
Note:
Most forged pistons require more bore (side) clearance than cast/hyper pistons ... usually about 0.002"-0.005" MORE clearance than a typical cast/hyper.
Salient Question:
Do you KNOW if YOUR bores are finish-honed and do you KNOW what YOUR bores' finished dimensions actually measure? I don't mean what is assumed ... I mean what is verified.
I am very interessted in one of these new GM blocks (new casting), either the $680 version or the $1000 version that Summit sells. Both have a 1 piece rms and are prepped for hyd roller cams, they also accept a mech fuel pump - these blocks are finish machined to 4.000" and already have the cam bearings installed, that makes me think that you're not supposed to machine them and they're ready for the pistons. They say it's for HD applications but don't say anything about the pistons......
I am more and more leaning towards the cheaper block (the $680 'production version') and have that block machined to fit the 4.030" pistons.... probably less headache
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
Why don't you buy a junk/core vortec 350 ... have the fuel pump flange drilled at MS ... block bored to fit whatever pistons you choose ... it'll have all the lifters & stuff in vortec block for roller cam ... sell its iron vortec heads on ebay.
I have an old vortec 350 block ... got a line on a another complete core 350 vortec motor for around $150. Alotta those motors got changed out because its plastic intake manifold leaked coolant into motor ... most of those don't need much.
I have an old vortec 350 block ... got a line on a another complete core 350 vortec motor for around $150. Alotta those motors got changed out because its plastic intake manifold leaked coolant into motor ... most of those don't need much.
