SpeedTalk Store - Opinion Columns

Combustion chamber size

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Combustion chamber size

Postby bigjoe1 » Mon Jan 31, 2011 5:36 pm

Do any of you have a strong opinion about a large chamber and a flat top, as opposed to a smaller chamber and a reverse dome piston ?? Case in point== High performance street and strip 406 or 434 Chevy== Afr heads that come with 80 cc chambers to be used with flat top pistons , or 65 cc heads, to be used with a reverse dome piston. With the same ( or very nearly the same ) compression, will both setups make about the same torque and HP. These both will be in the 650 to 700 HP regime. I will say this. I have used the big chambers with flat tops with great success, but I would like to hear if anyone is doing the other method. These are meant to be run on 91 octane pump gas, by the way.


JOE SHERMAN RACING ENGINES
bigjoe1
Show Guest
Show Guest
 
Posts: 5182
Joined: Thu Aug 24, 2006 7:16 pm
Location: santa ana calif-92703

Re: Combustion chamber size

Postby governor » Mon Jan 31, 2011 5:46 pm

Most of the high dollar 9to1 circle track motors were reverse dome and made some very good HP, but they were swisting the snot out of them and they made a lot of heat.

Arn't a lot of the Cup motors reverse dome?

Gov
a passion for racing
governor
Expert
Expert
 
Posts: 566
Joined: Sat Jan 17, 2009 2:12 pm
Location: Michigan

Re: Combustion chamber size

Postby Rizzle » Mon Jan 31, 2011 5:49 pm

Do the different CC heads have different sized quench pads?

How is the spark plug location changed between the two setups?
Rizzle
Expert
Expert
 
Posts: 572
Joined: Mon Feb 04, 2008 10:34 pm
Location: St. Catharines, Ont

Re: Combustion chamber size

Postby alan johnson » Mon Jan 31, 2011 5:55 pm

if the reverse dome piston weighs less thats my choice.with these modern chamber's i don't think one size would have
anything on another.
alan johnson
 

Re: Combustion chamber size

Postby Orr89rocz » Mon Jan 31, 2011 6:16 pm

Wouldnt the charge be hotter inside the cylinder more with a small combustion chamber head and dish piston? VS the flat top and charge more inside the head's chamber? Thinking you'd beable to get away with more compression with a larger cc head/flattop vs a dish/small cc head because you can cool the charge more in the head since the aluminum disipates heat more to the cooling water than Iron would. OR atleast beable to run abit more timing...whether that makes a difference or not i'm not sure but usually more timing is more power to a point.

Concept is used on blower/nitrous cars..use higher quench heights to get the combustion out of the bore and more into the head side
Orr89rocz
Guru
Guru
 
Posts: 1187
Joined: Sun Sep 28, 2008 8:25 pm

Re: Combustion chamber size

Postby Unkl Ian » Mon Jan 31, 2011 6:21 pm

Would the quench area be the same for both ?
Just because you never studied the Laws of Physics,
doesn't mean they won't try to kick your ass.
Unkl Ian
Guru
Guru
 
Posts: 2849
Joined: Thu Oct 06, 2005 8:23 pm
Location: Just outside Toronto

Re: Combustion chamber size

Postby PackardV8 » Mon Jan 31, 2011 6:57 pm

Would the quench area be the same for both ?


Quench area is usually greater with small chamber/cup in piston.

I note most OEMs are going to a small chamber head. I'm told this is for improving squish/quench, pressure recovery and spark plug location.

Interestingly, back in the day, Gen I Ketterings and Gen II Kettering SBC were pure wedge heads, with flat tops and all the chamber in the head. Next came the Heron head, Westlake head, Chevy 348"-409", Lincoln 430"; all used essentially flat heads with all the combustion chamber in the piston or in the cylinder. Then, the trend went to semi-hemi-twisted-wedge, many using domed pistons and back to the compromise of the LS--style small chamber wedge.

jack vines
Jack Vines
Studebaker-Packard V8 Limited
PackardV8
Guru
Guru
 
Posts: 3540
Joined: Sun Jul 30, 2006 1:03 pm

Re: Combustion chamber size

Postby JoePorting » Mon Jan 31, 2011 7:48 pm

I'd go with the big chamber/flat top piston. I remember flow testing the AFR 227 65cc and 75cc heads. The 75cc heads had about a 3 to 5 CFM improvement which should translate to another 8 to 10 HP. Not alot, but better then nothing. In another story, when I flat milled a set of 65 cc AFR 227 heads .050", I lost around 15 CFM across the board. ouch!!! So I don't think you can lose with big chambers, but can lose alot with ultra small chambers.
Joe Facciano
JoePorting
Guru
Guru
 
Posts: 1932
Joined: Mon Jun 14, 2010 2:16 pm
Location: Burbank, CA

Re: Combustion chamber size

Postby pdq67 » Mon Jan 31, 2011 9:08 pm

I look at it this way and no I don't have any proof!

Imho, the tightest chamber you can use along with a true flat-top piston does well until you run up against the tightest chamber you can run AND a matching chamber outline dished piston to give you the same CR.

And even then, I would go flat-top.

This is way old emissions study stuff here that is driven by octane/timing burn.

If you want to look deep into this, this is why Ed's, (aka, racer1320), BBC ran so good with highly worked over semi-closed -215's.

It's known that the old -206 BB heads with a true "bath-tub" chamber can produce power after being de-shrouded, but they are "dirty" smog-wise. And the power produced is due to timing differences vs the later open chamber heads at a given CR!!

pdq67
pdq67
Guru
Guru
 
Posts: 2792
Joined: Thu Mar 04, 2010 8:05 pm

Re: Combustion chamber size

Postby ClassicComp » Mon Jan 31, 2011 9:30 pm

the $3500+ Ed had into those heads are why they worked well.
results speak for themselves
BobF
ClassicComp
Expert
Expert
 
Posts: 668
Joined: Mon Jan 23, 2006 10:50 pm

Re: Combustion chamber size

Postby JBV-HEADS » Mon Jan 31, 2011 9:37 pm

If the chamber is the only item changed, then the reverse dome (horan) chamber has the most potential. It needs to be cut as close as possible to the shape of the chamber in the head. Any areas that do not match will create, for a lack of a better word, dead areas in the technology. The Horan chamber has been ( around WW-1) and still is the most efficient chamber design known for rpms under 7500-8000 for most applications. In many applications the turbulence in the air/fuel mixture above 6500rpm starts to eat into the squish turbulence, and flame front directional advantages the Horan has. Again on many applications somewhere around 7500rpm there will start to exist an exhaust flushing problem. All of these can be controlled and advanced with centered ignition, centered chambers along the pin, equal area and distance on both sides of the pin and shapes. It’s still used, but controlled improvements are limited, in NASCAR today. For like to like comparisons, the reverse dome cut right, will produce more power if there is a compression rule. And your dyno will pick it up. It’s above dyno error. Good luck,

Joe
JBV-HEADS
Pro
Pro
 
Posts: 347
Joined: Wed Jan 18, 2006 8:06 pm

Re: Combustion chamber size

Postby David Redszus » Mon Jan 31, 2011 9:47 pm

The shortest burn path will produce the smallest burn angle and therefore the highest combustion pressure. The best combustion chamber would be a sphere with the spark source in the center. The next best would be a dished (reverse dome) piston since the flame path is shorter and less chamber surface area is available to quench the flame front.
David Redszus
Guru
Guru
 
Posts: 4483
Joined: Tue Nov 27, 2007 9:27 am
Location: Chicago

Re: Combustion chamber size

Postby torquefan » Mon Jan 31, 2011 10:21 pm

David Redszus wrote:The shortest burn path will produce the smallest burn angle and therefore the highest combustion pressure. The best combustion chamber would be a sphere with the spark source in the center. The next best would be a dished (reverse dome) piston since the flame path is shorter and less chamber surface area is available to quench the flame front.


question for you, david: since we are applying pressure to the top of the piston to turn the crank, wouldn't you want to use the entire piston top since that pressure is expressed as psi? iow; how much combustion pressure would be developed with a 15:1 compression open chamber headed engine with a 4" bore and flat tops where the combustion pattern is evident for approximately 3.9" vs a 15:1 engine with a smaller closed chamber head and a 4" piston with a 3.5 diameter dish and no evidence of burn outside of the dish?

assuming (i know, bad word) no flow irregularities for the closed chamber and adequate combustion for the open chamber.

could that be why the singh grooves work?
torquefan
 

Re: Combustion chamber size

Postby Unkl Ian » Mon Jan 31, 2011 10:40 pm

torquefan wrote:
since we are applying pressure to the top of the piston to turn the crank,
wouldn't you want to use the entire piston top since that pressure is expressed as psi?




The burn lasts long enough that it will act on the full diameter.
Just because you never studied the Laws of Physics,
doesn't mean they won't try to kick your ass.
Unkl Ian
Guru
Guru
 
Posts: 2849
Joined: Thu Oct 06, 2005 8:23 pm
Location: Just outside Toronto

Re: Combustion chamber size

Postby DrillDawg » Mon Jan 31, 2011 11:39 pm

Would it make any sense to use a small pressure recovery type of chamber for better intake flow and position the dish on the exhaust side of the piston to help move the gases closer to the exhaust port?

DD
“Unthinking respect for authority is the greatest enemy of truth.”
Science is the shifting water eroding at the steadfast rock of religion.
One benefit of religion is that you will never know that your wrong. It's the perfect fantasy.
DrillDawg
Guru
Guru
 
Posts: 1159
Joined: Tue Jul 06, 2010 10:03 am

Next

Return to Engine Tech

Who is online

Users browsing this forum: bigmikespec, Brady Planden, mach72, Rizzle, sidestep, suboptimalfit and 23 guests