domed vs. flat tops?
08-08-2010, 12:31 PM
#1
Drifting
Thread Starter
domed vs. flat tops?
Domed pistons using closed chamber heads vs flat top pistons with open chamber heads. Many have said flat tops with open chamber heads produce even combustion. Others state the increased compression of the domed pistons with closed chambers overcomes that deficiency adding a swirl producing more power.
What’s you’re input or experience on this subject.
rustylugnuts
What’s you’re input or experience on this subject.
rustylugnuts
08-08-2010, 01:11 PM
#2
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Domed pistons using closed chamber heads vs flat top pistons with open chamber heads. Many have said flat tops with open chamber heads produce even combustion. Others state the increased compression of the domed pistons with closed chambers overcomes that deficiency adding a swirl producing more power.
What’s you’re input or experience on this subject.
rustylugnuts
What’s you’re input or experience on this subject.
rustylugnuts
The goal is not always peak power using the current technology, as originality trumps power as the ultimate goal for some people.
Are you are seeking an answer, or just throwing out a thread invitation to stir up opinions for a debate (because if you want an answer you should subscribe to SAE.org and search the technical papers on combustion chamber design)?
08-08-2010, 02:14 PM
#4
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I can give you personal experience with all three combos, BUT, UNDERSTAND THIS, I DO NOT have the kind of sophisticated hi-tech equipment to allow me to accomplish a scientific conclusion.
Years ago, when leaded premium, PARTICULARLY the Sonoco 260, was available, the only way to go was domed pistons and small chambers (~64cc for SB heads).
For 34+yrs, one of my 350 engines has 461 heads and flat top pistons and I run 91 octane and everything is just fine.
Although, later engines (SBs) that I've built have either dished pistons with 64cc heads, or flat top pistons with 76cc heads and I run those on 91 octane.
My SB 400s have flat top pistons and 76cc heads and get 91 octane. With 87-88 octane, they WILL knock.
When coming back from the SACC Natls last mo, it was so hot, that the SB400 with FI would ocassionally ping under hard power conditions in 4th gear. Even though the gas I bought was 91 octane, most of the pumps had ethanol.
Tom Parsons
Years ago, when leaded premium, PARTICULARLY the Sonoco 260, was available, the only way to go was domed pistons and small chambers (~64cc for SB heads).
For 34+yrs, one of my 350 engines has 461 heads and flat top pistons and I run 91 octane and everything is just fine.
Although, later engines (SBs) that I've built have either dished pistons with 64cc heads, or flat top pistons with 76cc heads and I run those on 91 octane.
My SB 400s have flat top pistons and 76cc heads and get 91 octane. With 87-88 octane, they WILL knock.
When coming back from the SACC Natls last mo, it was so hot, that the SB400 with FI would ocassionally ping under hard power conditions in 4th gear. Even though the gas I bought was 91 octane, most of the pumps had ethanol.
Tom Parsons
08-08-2010, 02:15 PM
#5
Tech Contributor
08-08-2010, 07:05 PM
#7
Le Mans Master
2 cents worth, I have a friend, Russ, one of the most respected piston design engineer's in the world.
Russ has helped Ford, GM, Chrysler, Toyota, Mercury Marine and most other manufacturers at one point or another. He has also worked with all the major engine rebuilders to find combinations that work. Did I mention worked to redesign many of the original TRW forged pistons for Federal-Mogul at the Malden Mo Piston plant. Since moved to India.
Russ shared that in combustion chambers he could make more power every time if he could have a dished piston to work with. That being said the compression ratio is still important. Russ say's he could give up a half point of compression and make more power with a dished piston compared to a flat top or dome because it helped the flame front form a ball which created a more complete burn, good for power and emissions. This is the reason many OEM designs for the past several years have used a silver dollar shaped dish in pistons. He claims the dish allowed more timing advance. Rather than seat of the pants he backed this up with Dyno results and real world feedback from customers.
All that said if you are running old heads, the engine will pop better with 11.0:1 than with 9.0:1. If building a new engine you have more options.
Russ has helped Ford, GM, Chrysler, Toyota, Mercury Marine and most other manufacturers at one point or another. He has also worked with all the major engine rebuilders to find combinations that work. Did I mention worked to redesign many of the original TRW forged pistons for Federal-Mogul at the Malden Mo Piston plant. Since moved to India.
Russ shared that in combustion chambers he could make more power every time if he could have a dished piston to work with. That being said the compression ratio is still important. Russ say's he could give up a half point of compression and make more power with a dished piston compared to a flat top or dome because it helped the flame front form a ball which created a more complete burn, good for power and emissions. This is the reason many OEM designs for the past several years have used a silver dollar shaped dish in pistons. He claims the dish allowed more timing advance. Rather than seat of the pants he backed this up with Dyno results and real world feedback from customers.
All that said if you are running old heads, the engine will pop better with 11.0:1 than with 9.0:1. If building a new engine you have more options.
08-08-2010, 07:10 PM
#8
Drifting
Thread Starter
I agree, when octane was over a hundred and ethanol was not available the compression of high performance factory engines ran 11:01 up to 12 & 13 compression ratios in some rare cases. Not really sure what octane I'm running in the 61 FI @ 11.0:1 mixing 92 @ 50% with aviation fuel, but she runs great as you stated up to 96 to 98 degrees. Then she pings and pre-Ignition after a shut down. So when it's that hot out, I rarely use my 61 and drive something newer with air-condition mostly for my wife’s pleasures.
I was wondering if flat tops with 76cc heads like 9.5 to 10:01 might run better on the straight 91wheezel **** that is available today. Also the performance of this type of build would be a depletion of how many horses, in percentage (ball park) figures of course.
rustylugnuts
I was wondering if flat tops with 76cc heads like 9.5 to 10:01 might run better on the straight 91wheezel **** that is available today. Also the performance of this type of build would be a depletion of how many horses, in percentage (ball park) figures of course.
rustylugnuts
Last edited by rustylugnuts; 08-08-2010 at 07:13 PM.
08-08-2010, 07:19 PM
#9
Drifting
Thread Starter
2 cents worth, I have a friend, Russ, one of the most respected piston design engineer's in the world.
Russ has helped Ford, GM, Chrysler, Toyota, Mercury Marine and most other manufacturers at one point or another. He has also worked with all the major engine rebuilders to find combinations that work. Did I mention worked to redesign many of the original TRW forged pistons for Federal-Mogul at the Malden Mo Piston plant. Since moved to India.
Russ shared that in combustion chambers he could make more power every time if he could have a dished piston to work with. That being said the compression ratio is still important. Russ say's he could give up a half point of compression and make more power with a dished piston compared to a flat top or dome because it helped the flame front form a ball which created a more complete burn, good for power and emissions. This is the reason many OEM designs for the past several years have used a silver dollar shaped dish in pistons. He claims the dish allowed more timing advance. Rather than seat of the pants he backed this up with Dyno results and real world feedback from customers.
All that said if you are running old heads, the engine will pop better with 11.0:1 than with 9.0:1. If building a new engine you have more options.
Russ has helped Ford, GM, Chrysler, Toyota, Mercury Marine and most other manufacturers at one point or another. He has also worked with all the major engine rebuilders to find combinations that work. Did I mention worked to redesign many of the original TRW forged pistons for Federal-Mogul at the Malden Mo Piston plant. Since moved to India.
Russ shared that in combustion chambers he could make more power every time if he could have a dished piston to work with. That being said the compression ratio is still important. Russ say's he could give up a half point of compression and make more power with a dished piston compared to a flat top or dome because it helped the flame front form a ball which created a more complete burn, good for power and emissions. This is the reason many OEM designs for the past several years have used a silver dollar shaped dish in pistons. He claims the dish allowed more timing advance. Rather than seat of the pants he backed this up with Dyno results and real world feedback from customers.
All that said if you are running old heads, the engine will pop better with 11.0:1 than with 9.0:1. If building a new engine you have more options.
Thanks, rustylugnuts
08-08-2010, 08:15 PM
#10
Safety Car
Domed pistons using closed chamber heads vs flat top pistons with open chamber heads. Many have said flat tops with open chamber heads produce even combustion. Others state the increased compression of the domed pistons with closed chambers overcomes that deficiency adding a swirl producing more power.
What’s you’re input or experience on this subject.
rustylugnuts
What’s you’re input or experience on this subject.
rustylugnuts
08-09-2010, 12:12 PM
#11
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Modern 3D chamber shapes are optimized with piston designs that are not limited by only flat-top and domed piston crowns. Westlotorn's post starts you on the right path, but even when you take it all in there is always something that demands a compromise, like working with an original head (etc.) and a need to focus on the goal (peak average power at xxxx->-xxxx rpm, detonation resistance, emissions quality...).
Rather than toss out a debate topic, why not simply state the problem you want to resolve (detonation on xx grade fuel with my 61' FI)?
08-09-2010, 01:27 PM
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Last edited by MikeM; 08-09-2010 at 01:31 PM.
08-09-2010, 06:41 PM
#13
Drifting
Thread Starter
Modern 3D chamber shapes are optimized with piston designs that are not limited by only flat-top and domed piston crowns. Westlotorn's post starts you on the right path, but even when you take it all in there is always something that demands a compromise, like working with an original head (etc.) and a need to focus on the goal (peak average power at xxxx->-xxxx rpm, detonation resistance, emissions quality...).
Rather than toss out a debate topic, why not simply state the problem you want to resolve (detonation on xx grade fuel with my 61' FI)?
rustylugnuts
08-09-2010, 06:56 PM
#14
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You might be better served if you changed your user name. I think this one is tainted.
Why spend thousands on a 283 changing combustion chamber shape when you can enlarge cubic inches for hundreds and get the same thing?
Silly question you asked. You coulda' asked yer buddy at MIT for an answer to your question and not exposed yourself.
Why spend thousands on a 283 changing combustion chamber shape when you can enlarge cubic inches for hundreds and get the same thing?
Silly question you asked. You coulda' asked yer buddy at MIT for an answer to your question and not exposed yourself.
08-09-2010, 07:32 PM
#15
Drifting
Thread Starter
ha ha ha!!!..... The MIT thing was funny a few times, but it’s getting old, no pun intended. I see you’re always going to answer because your (pass aggressive), no problem, but find something new and interesting to say.
rustylugnuts
rustylugnuts
08-09-2010, 08:55 PM
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I did have something new to say. Maybe you missed it.
08-10-2010, 07:52 PM
#17
Drifting
Thread Starter
On SAE.org found a few interesting articles/papers on ten chamber configurations of three types of pistons: wedge, hemispherical, and Heron. With a compression ratio of 11.5 and a swirl ratio of 3 etc.
I appreciate the great advice, I see there is a ton of reading.
Thanks, rustylugnuts
I appreciate the great advice, I see there is a ton of reading.
Thanks, rustylugnuts
