Go Back   LS1TECH > LS1-LS2-LS3-LS6-LS7 PERFORMANCE > Advanced Engineering Tech
Sign in using an external account
Register Forgot Password?
Search

Advanced Engineering Tech
For the more hardcore LS1TECH residents
Sponsored by
Whipple Super Chargers

Welcome to LS1Tech.com!
Welcome to LS1Tech.com.

You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join LS1Tech.com today!


Reply
 
Thread Tools Search this Thread
Old 05-18-2006, 08:17 PM   #1
LS1 Tech Veteran
Garage is empty, add now
 
Trader Rating: 1
Join Date: Oct 2003
Location: Wichita, Ks
Posts: 1,170
Default Combustion Chamber Size Versus Piston Dish Volume for a Fixed CR

Do you think it is better to have a large combustion chamber and a small piston dish or vice versa while maintaining the same compression ratio?

Let's say that with a .040" gasket you could have a 62 CC combustion chamber with a 20 CC piston dish or a 72 CC combustion chamber with a 10 CC piston dish for a given compression ratio, what do you think are the relative advantages of each? For instance, the bigger piston dish would reduce reciprocating mass and the valves might be less shrouded with the bigger combustion chamber.

Your thoughts please.

Thanks,

Steve
__________________
2000 K2500 Yukon XL, LQ4 Vortec 6000, Custom Comp Cam (200/206 109 LSA), Pro Magnum 1.75 Rockers, Ported Cast Iron Heads, Volant Induction, Commercial EFILive 7.x, PLX M-300, 30 PPH 8.1 L Injectors, Thorley Tri-Y Headers. See my Web Page at community.webshots.com/user/sbryant2100

408 in process - Callies DragonSlayer Crank, CompStar Rods, Wiseco -18 CC pistons, 215 cc Patriot Predator Heads

Last edited by Steve Bryant; 05-18-2006 at 11:09 PM..
Steve Bryant is offline   Reply With Quote
Old 05-18-2006, 08:39 PM   #2
Banned
Garage is empty, add now
 
Trader Rating: 2
Join Date: Mar 2002
Location: NY
Posts: 2,344
Default

Dish and small chamber... well as small as you can get it without hurting the flow. The closer the chamber is to a sphere the better you are.

Bret
SStrokerAce is offline   Reply With Quote
Old 05-18-2006, 10:33 PM   #3
TECH Resident
Garage is empty, add now
 
Trader Rating: 0
Join Date: Dec 2004
Posts: 881
Default

Quote:
Originally Posted by SStrokerAce
Dish and small chamber... well as small as you can get it without hurting the flow. The closer the chamber is to a sphere the better you are.

Bret
The reason for this recommendation is...???

Wouldn't it also be dependent on the shape of the dish and the piston to head clearance?
DavidNJ is offline   Reply With Quote
Old 05-18-2006, 11:28 PM   #4
TECH Veteran
Garage is empty, add now
 
Trader Rating: 21
Join Date: Apr 2003
Location: Shreveport, LA
Posts: 4,050
Default

I was told the same when putting together my parts. The smallest safest combustion chamber will work best. Then fix your CR with the dish.
__________________
02 SS M6:
HKE 454 CI LS2, ET Performance 265cc heads, Harrop 55mm I/R intake, "The Beast" camshaft 243/254 .653"/.644" 110 LSA+0, Full Suspension, External fuel system, Moser 12 bolt.
Beast96Z is offline   Reply With Quote
Old 05-19-2006, 12:19 AM   #5
That's what she said...
Garage is empty, add now
 
TheBlurLS1's Avatar
 
Trader Rating: 8
Join Date: Mar 2004
Location: Nederland Texas
Posts: 7,957
Send a message via AIM to TheBlurLS1
Default

Quote:
Originally Posted by Beast96Z
I was told the same when putting together my parts. The smallest safest combustion chamber will work best. Then fix your CR with the dish.
Any notes about quench in this?

I've been thinking about this issue as well. When a company sells a "-12cc dish piston", is it dished under the valves, or under the flat spot of the head as well? It seems they would like to keep it as flat as possible under the flat part of the head surface (for quench), and have a huge volume under the valves.

This volume under the valves would help with compression and PTV clearance.




BTW - I'm an internal engine n3wb, but at least I have the smarts enough to admit it.
__________________

1998 Camaro Z/28 408ci/N2O ~ 2009 Silverado Z71 6.2L LTZ
TheBlurLS1 is offline   Reply With Quote
Old 05-19-2006, 02:19 AM   #6
Banned
Garage is empty, add now
 
Trader Rating: 2
Join Date: Mar 2002
Location: NY
Posts: 2,344
Default

Quote:
Originally Posted by DavidNJ
The reason for this recommendation is...???

Wouldn't it also be dependent on the shape of the dish and the piston to head clearance?
You've read Larry Widmer's articles on it....
SStrokerAce is offline   Reply With Quote
Old 05-19-2006, 05:02 AM   #7
TECH Regular
Garage is empty, add now
 
Trader Rating: 19
Join Date: Dec 2003
Location: florida
Posts: 463
Default

I've never read Larry Widmer's articles but I think it's better to have a small chamber for a few reasons . I would prefer to have more surface area on the piston versus the head . I know it's a small difference but it's still psi , more area = more force . For a given cylinder head casting , the smaller chambered head would have more material to resist deformation and control heat . Most pistons come from the same forgings to reduce costs and the greater dish volume obviously reduces piston weight which would be great till durability begins to be sacrificed . I know chamber and piston shape also influence power production , and combining these qualitites would help make great power . It was my understanding that a football shaped fuel kernel was ideal , having the edges equal distance from the spark plug . Great thread , and my .02 .
v8pwr is offline   Reply With Quote
Old 05-19-2006, 06:49 AM   #8
TECH Resident
Garage is empty, add now
 
Trader Rating: 0
Join Date: Dec 2004
Posts: 881
Default

And I've talked to Larry on the phone. The dish isn't really dish, its a reverse dome making the as-close-as-possible spherical chamber. Other than unshrouding a deep set valve, the advantage was being able to control the radius at the floor of the chamber, rather than have the opening there to the quench area.

If the quench was tight (you've may have read my question posts asking about sub-.030 quench on 7k CI blocks and sub-.025 on aluminum blocks) and the chamber well shaped the benefit is smaller.

And the pistons are harder to make. Virtually always custom. Some standards, like Yates heads, have reverse domes available. Others were custom. Diamond suggested sending them a head.

And finally, several people and piston companies--with far more experience than me--say that the dished piston adds weight even with lightening machining.

It would seem the benefit would come after beneficial spark plug location, top ring land depth, and overall piston ring sealing.

Diamond and Manley have new for '06 short pin (2.25-2.3") pistons. Diamond will add lightening to a standard piston without a custom surcharge. It seems you would need a pretty extreme engine (competitive racing, everything else done) to justify the cost and time of the reverse dome.
DavidNJ is offline   Reply With Quote
Old 05-19-2006, 10:19 AM   #9
Banned
Garage is empty, add now
 
Trader Rating: 2
Join Date: Mar 2002
Location: NY
Posts: 2,344
Default

David, I'm well aware of revearse concave dome pistons... that's what I was referring too. Hence the Windmer reference.

Bret
SStrokerAce is offline   Reply With Quote
Old 05-19-2006, 03:06 PM   #10
TECH Resident
Garage is empty, add now
 
Trader Rating: 0
Join Date: Dec 2004
Posts: 881
Default

However, the posted said 'dished' piston. LS1 dished pistons look more like this:
Click the image to open in full size. Click the image to open in full size.

than a reverse dome.
Attached Thumbnails
Combustion Chamber Size Versus Piston Dish Volume for a Fixed CR-ls1-dish-piston-1.jpg   Combustion Chamber Size Versus Piston Dish Volume for a Fixed CR-ls1-dish-piston-2.jpg  
DavidNJ is offline   Reply With Quote
Old 05-19-2006, 03:24 PM   #11
TECH Fanatic
1986 Chevrolet Camaro
 
white2001s10's Avatar
 
Trader Rating: 4
Join Date: May 2002
Location: Fairview Heights Illinois
Posts: 1,851
Default

Quote:
Originally Posted by SStrokerAce
Dish and small chamber... well as small as you can get it without hurting the flow. The closer the chamber is to a sphere the better you are.
Bret
I agree with this.
white2001s10 is offline   Reply With Quote
Old 05-19-2006, 07:00 PM   #12
LS1 Tech Veteran
Garage is empty, add now
 
Trader Rating: 1
Join Date: Oct 2003
Location: Wichita, Ks
Posts: 1,170
Default

Although in theory symetrical, mirror image combustion chambers and piston crown topography is worth considering, I'm really wondering about the practical aspects of commonly available production/aftermarket parts. Consider the 243 versus the 317 production heads. They are for all the world variations of the same part except for a few CC's of combustion chamber volume. Now, you are going to buy off the shelf pistons (JE, Diamond, Wiseco, Mahle, anybodies) for a production LS2 block with a 4.000" bore and you have the choice of dished (not reverse dome) pistons in increments of 2 CC's. Which combination would you go for and why?

Steve
__________________
2000 K2500 Yukon XL, LQ4 Vortec 6000, Custom Comp Cam (200/206 109 LSA), Pro Magnum 1.75 Rockers, Ported Cast Iron Heads, Volant Induction, Commercial EFILive 7.x, PLX M-300, 30 PPH 8.1 L Injectors, Thorley Tri-Y Headers. See my Web Page at community.webshots.com/user/sbryant2100

408 in process - Callies DragonSlayer Crank, CompStar Rods, Wiseco -18 CC pistons, 215 cc Patriot Predator Heads
Steve Bryant is offline   Reply With Quote
Old 05-19-2006, 09:39 PM   #13
TECH Regular
Garage is empty, add now
 
Trader Rating: 19
Join Date: Dec 2003
Location: florida
Posts: 463
Default

Which piston manufacturer would you choose to make a set of pistons for heads fairly common like LS6's ? Who would provide good turnaround on a custom set without costing so much . I know it costs money to play , how much would a set of custom pistons run ? Can someone give a breakdown of the initial cost then how much the options such as horizontal gas ports , lightening , custom ring sizes , and whatever else they can do . Is there a company that is better to deal with than others , why ? Any benefit to using one manufacturer over another such as A is affordable but slow , B is expensive but can do it all , C has the best tolerences . Thanks for any info .
v8pwr is offline   Reply With Quote
Old 05-21-2006, 01:29 AM   #14
Staging Lane
Garage is empty, add now
 
Trader Rating: 0
Join Date: Mar 2006
Posts: 50
Default

[quote=v8pwr] I would prefer to have more surface area on the piston versus the head . I know it's a small difference but it's still psi , more area = more force . QUOTE]

This is quite wrong. Even though there is more "surface area" it's not "normal to" the cylinder axis, thus it does nothing to push the piston down, and only forces opposed surfaces apart. If you want a better picture in your head, just imagine a piston with 100 bumps like a golf ball. It won't feel any more pressure in the downward direction than a flat top piston. The ONLY way to get more usable surface area is to increase the bore.

If I were building an engine, I'd go with as flat of a piston as possible, with the lowest mass, and most of the chamber in the head. The flat surface will promote flame travel much better. Not all combustion happens during TDC. The flat design also tends towards lighter pistons.
__________________
- Jeremy -
EFI Engineer - currently in China
Sorry, no LS1,2,6,or 7 in storage with my 89 GTA and 86 Z28
RednGold86Z is offline   Reply With Quote
Old 05-21-2006, 09:43 AM   #15
Restricted User
Garage is empty, add now
 
Trader Rating: 0
Join Date: May 2006
Location: virginia
Posts: 132
Default

Quote:
Originally Posted by SStrokerAce
Dish and small chamber... well as small as you can get it without hurting the flow. The closer the chamber is to a sphere the better you are.

Bret
This is what all the Winston Nextel Sprint Cup engine builders do (Exept for the ones getting lapped)
Jessica is offline   Reply With Quote
Old 05-21-2006, 01:39 PM   #16
Banned
Garage is empty, add now
 
Trader Rating: 2
Join Date: Mar 2002
Location: NY
Posts: 2,344
Default

Quote:
Originally Posted by Steve Bryant
Although in theory symetrical, mirror image combustion chambers and piston crown topography is worth considering, I'm really wondering about the practical aspects of commonly available production/aftermarket parts. Consider the 243 versus the 317 production heads. They are for all the world variations of the same part except for a few CC's of combustion chamber volume. Now, you are going to buy off the shelf pistons (JE, Diamond, Wiseco, Mahle, anybodies) for a production LS2 block with a 4.000" bore and you have the choice of dished (not reverse dome) pistons in increments of 2 CC's. Which combination would you go for and why?

Steve
Steve,

If that's what you are shooting for then the chamber shapes and compression ratios you are looking at are not going to fit into the small chamber dish setup. When you do that, especially on something that doesn't start off with a super small chamber like a 243 casting, you are welding the heads AND making custom pistons.

In that case you are better off going with the best chamber design you can get your hands on. The 243 over the other OEM castings, or something like the Dart chamber and milling that down to size and then running a flat top piston.

Bret
SStrokerAce is offline   Reply With Quote
Old 05-21-2006, 01:43 PM   #17
Banned
Garage is empty, add now
 
Trader Rating: 2
Join Date: Mar 2002
Location: NY
Posts: 2,344
Default

Quote:
Originally Posted by v8pwr
Which piston manufacturer would you choose to make a set of pistons for heads fairly common like LS6's ? Who would provide good turnaround on a custom set without costing so much . I know it costs money to play , how much would a set of custom pistons run ? Can someone give a breakdown of the initial cost then how much the options such as horizontal gas ports , lightening , custom ring sizes , and whatever else they can do . Is there a company that is better to deal with than others , why ? Any benefit to using one manufacturer over another such as A is affordable but slow , B is expensive but can do it all , C has the best tolerences . Thanks for any info .
Diamond does nice custom work, Greg Anderson uses them so they are good enoug for me.

JE can get you anything you want, along with CP as well.

To get the rest of the info you are looking for call up each company OR work with someone who sells those parts and they should be able to get you a quote on what you want.

Bret
SStrokerAce is offline   Reply With Quote
Old 05-21-2006, 01:46 PM   #18
Banned
Garage is empty, add now
 
Trader Rating: 2
Join Date: Mar 2002
Location: NY
Posts: 2,344
Default

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Good examples of the small chamber and reverse dome setup. All of those chambers were welded up to get them that small.

Bret
SStrokerAce is offline   Reply With Quote
Old 05-21-2006, 02:39 PM   #19
NOT BANNED
Garage is empty, add now
 
Richiec77's Avatar
 
Trader Rating: 3
Join Date: Dec 2003
Location: I play with Sand!!
Posts: 1,805
Default

I've also noticed that the Valves are also pretty much unshroaded (sp?). That would help also.

I understand the reason for a spherical chamber is do to the fact that any object that burns goes from solid/liquid to a gasous state. That means there will be a change in pressure and it'll move in an Omni-directional way. Hence the Sphere being the untimate "perfect" idea.

How is the Football shape better? Is it due to the sake of the chamber design due to inline valves?
__________________
Quote:
Only two defining forces have ever offered to die for you, Jesus Christ and the American GI. One died for your soul, the other for your freedom.
Richiec77 is offline   Reply With Quote
Old 05-21-2006, 04:13 PM   #20
Banned
Garage is empty, add now
 
Trader Rating: 2
Join Date: Mar 2002
Location: NY
Posts: 2,344
Default

The football shape is a result of the valve placement, yes.

BTW good quote by the old man in your sig, words to live by!

Bret
SStrokerAce is offline   Reply With Quote
Old 05-21-2006, 04:13 PM
LS1Tech
Pontiac Firebird




Paid Advertisement
Reply

Tags
cc, chamber, combustion, concave, dish, dished, head, ls1tech, lt1, matching, pistons, reduce, size, smaller, volume


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are Off



All times are GMT -5. The time now is 05:21 AM.


Powered by vBulletin® Version 3.7.4
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Advertising - Terms of Service - Privacy Statement - JOBS
Emails & Contact Details