warning on silvolite pistons - The 1947 - Present Chevrolet & GMC Truck Message Board Network

bigjimzlll · 07-13-2002, 03:31 PM

I just checked my deck hieght on my new engine.... .030 over 350 with silvolite hyper pistons..flat tops with 5cc valve reliefs ..Im at .045. it should of been between .020 and .025..turns out they make a rebuilders piston that has a different compression hieght to allow for block and head milling.. when i ordered the pistons i wanted a C/R of 9.8 to 1 with 64cc heads...well thats what i got...but now the pistons so far down the hole im going to have trouble with detonation....oh well, so much for maybe running a little laughing gas. I have 3 options...tear down the motor, and mill .025 off the deck...replace the pistons...or just build it the way it is.....since i am now poor...i think ill build it the way it is.

Jim

ebfabman · 07-13-2002, 04:11 PM

If the piston is farther down, why would you have detonation problems? Doesn't that mean less compession? Isn't detonation usually a problem associated with higher compression?

Just thought I's ask.........

tom hand · 07-13-2002, 04:46 PM

Can't you compensate for deck height with head gasket thickness?

Super Chevy · 07-13-2002, 04:48 PM

With a compression of 9.8:1 and if you have ping, adding a spacer or in this case the piston sitting lower in the wall,youll have worse probablems then if you had 9.8:1 and proper clearance, here is a good site that explains this...

http://www.speedomotive.com/Building%20Tips.htm

Beast388 · 07-13-2002, 05:15 PM

It all has to do with quench height!!
Check out the info at Keith Black's site: http://www.kb-silvolite.com/page05.htm

Longhorn Man · 07-13-2002, 05:51 PM

While all that is true, the 9.8 to 1 can be thrown out the window. So therefor, he will have lower compression, and LESS likely to detonate...esp if it is more like 9:1 now....025 is quite a bit.

Beast388 · 07-13-2002, 06:22 PM

Not necessarily true......a 10:1 motor with the proper quench will ping less than a 9:1 motor with the pistons too far in the hole.

Here is an excerpt of the info on the KB piston page...... "Excessive cylinder pressure will encourage engine-destroying detonation and no piston is immune to its' effects. An important first step is to set the assembled quench (a.k.a. "squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of the piston that would contact a similar flat area on the cylinder head if you had .000" assembled quench height. In a running engine, the .040" quench decreases to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity through the combustion chamber. This movement tends to cool hot spots, averages the chamber temperature, reduces detonation and increases power. Take note, on the exhaust cycle, some cooling of the piston occurs due to the closeness of the water- cooled head.

Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will create more ping at 9.5:1 than you had at 10:1. The suitable way to lower the compression is to use a KB dish piston. KB dish (reverse combustion chamber) pistons are designed for maximum quench area."

I suggest reading the info on the KB pistons page......good stuff

mikep · 07-13-2002, 07:19 PM

having built quite a few 10:1 compression motors with absolutely no quench area at all ( ported 2V Ford cleveland heads with domed pistons ) I'd call the Keith Black statements a bit of an exageration seeing that with premium gas and loads of timing I never experienced detonation. Yes quench can promote better flame travel but if you are using 92 octane gas which you needed to anyway with that high of a compression ratio then you shouldnt have any problems with detonation as long as you dont get too happy with timing over 34 degrees. Especially dont worry about detonation with nitrous. You get so much extra fuel setup into a standard nitrous setup that detonation isnt much of a worry. I'd be more worried about using nitrous with hypereutectics period. Theyre hard and dimensionally stable but they dont have the
resistance to cracking that forged do and most manufacturers dont reccomend them for extended nitrous or supercharged use.
If it bothers you too much then just use steel shim .018" head gaskets and lose that .020" somewhere else. They work just fine and for $17 a set you cant beat the price. Summit has them part number MRG-1130 .

07-13-2002, 03:31 PM	#1
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	warning on silvolite pistons I just checked my deck hieght on my new engine.... .030 over 350 with silvolite hyper pistons..flat tops with 5cc valve reliefs ..Im at .045. it should of been between .020 and .025..turns out they make a rebuilders piston that has a different compression hieght to allow for block and head milling.. when i ordered the pistons i wanted a C/R of 9.8 to 1 with 64cc heads...well thats what i got...but now the pistons so far down the hole im going to have trouble with detonation....oh well, so much for maybe running a little laughing gas. I have 3 options...tear down the motor, and mill .025 off the deck...replace the pistons...or just build it the way it is.....since i am now poor...i think ill build it the way it is. Jim __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

07-13-2002, 04:46 PM	#3
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Can't you compensate for deck height with head gasket thickness? __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

07-13-2002, 05:15 PM	#5
Beast388 Suburbans RULE! Join Date: Jan 2000 Location: Clinton, IA 52732 Posts: 689	It all has to do with quench height!! Check out the info at Keith Black's site: http://www.kb-silvolite.com/page05.htm __________________ --Ben 71 GMC Suburban 4X4 The "Beast" 388 CID Stroker, TH350, NP205, 8-lug D44, 14BFF w/ Detroit, 4.10:1 gears, 4-Wheel Disks 4" Lift, 35" MT/R's.

07-13-2002, 06:22 PM	#7
Beast388 Suburbans RULE! Join Date: Jan 2000 Location: Clinton, IA 52732 Posts: 689	Not necessarily true......a 10:1 motor with the proper quench will ping less than a 9:1 motor with the pistons too far in the hole. Here is an excerpt of the info on the KB piston page...... "Excessive cylinder pressure will encourage engine-destroying detonation and no piston is immune to its' effects. An important first step is to set the assembled quench (a.k.a. "squish") distance to .040". The quench distance is the compressed thickness of the head gasket plus the deck clearance (the distance your piston is down in the bore). If your piston height (not dome height) is above the block deck, subtract the overage from the gasket thickness to get a true assembled quench distance. The quench area is the flat part of the piston that would contact a similar flat area on the cylinder head if you had .000" assembled quench height. In a running engine, the .040" quench decreases to a close collision between the piston and cylinder head. The shock wave from the close collision drives air at high velocity through the combustion chamber. This movement tends to cool hot spots, averages the chamber temperature, reduces detonation and increases power. Take note, on the exhaust cycle, some cooling of the piston occurs due to the closeness of the water- cooled head. Since it is the close collision between the piston and the cylinder head that reduces the prospect of detonation, never add a shim or head gasket to lower compression on a quench head engine. If you have 10:1 with a proper quench and then add an extra .040" gasket to give 9.5:1 and .080" quench, you will create more ping at 9.5:1 than you had at 10:1. The suitable way to lower the compression is to use a KB dish piston. KB dish (reverse combustion chamber) pistons are designed for maximum quench area." I suggest reading the info on the KB pistons page......good stuff __________________ --Ben 71 GMC Suburban 4X4 The "Beast" 388 CID Stroker, TH350, NP205, 8-lug D44, 14BFF w/ Detroit, 4.10:1 gears, 4-Wheel Disks 4" Lift, 35" MT/R's.

07-13-2002, 07:19 PM	#8
mikep Used to have a truck Join Date: May 2002 Location: port orchard WA Posts: 1,552	having built quite a few 10:1 compression motors with absolutely no quench area at all ( ported 2V Ford cleveland heads with domed pistons ) I'd call the Keith Black statements a bit of an exageration seeing that with premium gas and loads of timing I never experienced detonation. Yes quench can promote better flame travel but if you are using 92 octane gas which you needed to anyway with that high of a compression ratio then you shouldnt have any problems with detonation as long as you dont get too happy with timing over 34 degrees. Especially dont worry about detonation with nitrous. You get so much extra fuel setup into a standard nitrous setup that detonation isnt much of a worry. I'd be more worried about using nitrous with hypereutectics period. Theyre hard and dimensionally stable but they dont have the resistance to cracking that forged do and most manufacturers dont reccomend them for extended nitrous or supercharged use. If it bothers you too much then just use steel shim .018" head gaskets and lose that .020" somewhere else. They work just fine and for $17 a set you cant beat the price. Summit has them part number MRG-1130 . __________________ No truck :-(

07-13-2002, 04:11 PM	#2
ebfabman Registered User Join Date: Nov 2001 Location: Concord, NC Posts: 2,488	If the piston is farther down, why would you have detonation problems? Doesn't that mean less compession? Isn't detonation usually a problem associated with higher compression? Just thought I's ask.........

07-13-2002, 04:48 PM	#4
Super Chevy Registered User Join Date: Feb 2001 Location: Ohio Posts: 1,025	With a compression of 9.8:1 and if you have ping, adding a spacer or in this case the piston sitting lower in the wall,youll have worse probablems then if you had 9.8:1 and proper clearance, here is a good site that explains this... http://www.speedomotive.com/Building%20Tips.htm

07-13-2002, 05:51 PM	#6
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	While all that is true, the 9.8 to 1 can be thrown out the window. So therefor, he will have lower compression, and LESS likely to detonate...esp if it is more like 9:1 now....025 is quite a bit.



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