5sfe Combustion Chamber - Why the Humps

wesnemo · 02-07-2007, 09:46 PM

5sfe Combustion Chamber - Why the Humps

I'm perplexed. Any idea why the 5sfe combustion chamber has the "humps" between each of the intake valves and each of the exhaust valves? The 3sgte combustion chamber has no similar humps. Are they just to raise compression? Do they serve a swirl function?

Has anybody hogged out the humps to see how flow is affected statically?

Has anybody hogged out the humps and done any dynamic testing?

Does anybody care? Does anybody wish to speculate? Mr. Spock?

mrturrari · 02-08-2007, 06:30 PM

I'm paraphrasing from my other post.

The humps are quench zones. Because the valves are at a lower angle and therefore take up more space in the chamber, if they would have built them like the 3sgte and just put them beside the valves they wouldn't have as much area. So they made it stick out between the valves.

Quench zones push the burning fuel mixture towards the center and away from the edge of the pistons as well as push the air fuel mix towards the flame front during combustion. That keeps heat away from edges that could get hot and cause pre-ignition and makes for a faster more complete burn.

The only reason I would ever mess with them is if you are installing 2mm oversized valves and cut them back a little to give enough room for the air to get by the larger valve.

wesnemo · 02-08-2007, 09:46 PM

I was thinking they were quench zones but with the JE pistons most of the hump would be out over the piston dish so that there would be no effective squish in that area. A mystery.

Mystery solved. I checked the stock pistons. The stock pistons have a corresponding hump on each side of the dish. A small expensive irony here. Higher dollar aftermarkets may be inferior in an important respect to stock pistons. Especially if you are looking to crank up the compression ratio a notch. So much for custom 5sfe pistons. Another kink to work out in an NA build.

Nil Desperandum.

mrturrari · 02-09-2007, 01:40 AM

Yes, I noticed that with my forged pistons as well and I have been running mine for almost a year with no problems. I had forgotten about that. One thought that comes to mind is that forged pistons can take more heat so not as much quench would be required. Also I am pretty sure the quench areas around the outside are in the end more important then the humps in the middle to keep heat away from the ring lands.

So maybe it won't kill you if they're not there but they help the combustion pattern in a stock engine when you have the stock pistons. If you think about it the stock quench zones create a butterfly shaped pattern and without them you would have a more circular pattern of combustion.

Here is a pic of my Atomic Speedware (Arias) pistons before they went in:
http://warp.scl.utah.edu/mr2/5sfeReb...gedPiston2.jpg

Also if you are raising compression then your pistons should have more of a flat top which may line up to part of the humps. If you feel that it is really important to keep all of your quench zones I'll bet Atomic Speedware would make some custom ones for you for not too much more.

Removing the humps will also increase your combustion chamber volume which decreases compression.

02-07-2007, 09:46 PM	#1 (permalink)
wesnemo wesnemo Join Date: Feb 2007 Location: Northeast PA Posts: 274 Thanks: 11 Thanked 15 Times in 9 Posts iTrader Rating: (2/100% )	5sfe Combustion Chamber - Why the Humps 5sfe Combustion Chamber - Why the Humps I'm perplexed. Any idea why the 5sfe combustion chamber has the "humps" between each of the intake valves and each of the exhaust valves? The 3sgte combustion chamber has no similar humps. Are they just to raise compression? Do they serve a swirl function? Has anybody hogged out the humps to see how flow is affected statically? Has anybody hogged out the humps and done any dynamic testing? Does anybody care? Does anybody wish to speculate? Mr. Spock?

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02-08-2007, 06:30 PM	#2 (permalink)
mrturrari I <3 my 5sfe Join Date: Mar 2005 Posts: 418 Thanks: 2 Thanked 93 Times in 60 Posts iTrader Rating: (0/0% )	I'm paraphrasing from my other post. The humps are quench zones. Because the valves are at a lower angle and therefore take up more space in the chamber, if they would have built them like the 3sgte and just put them beside the valves they wouldn't have as much area. So they made it stick out between the valves. Quench zones push the burning fuel mixture towards the center and away from the edge of the pistons as well as push the air fuel mix towards the flame front during combustion. That keeps heat away from edges that could get hot and cause pre-ignition and makes for a faster more complete burn. The only reason I would ever mess with them is if you are installing 2mm oversized valves and cut them back a little to give enough room for the air to get by the larger valve.

02-08-2007, 09:46 PM	#3 (permalink)
wesnemo wesnemo Join Date: Feb 2007 Location: Northeast PA Posts: 274 Thanks: 11 Thanked 15 Times in 9 Posts iTrader Rating: (2/100% )	I was thinking they were quench zones but with the JE pistons most of the hump would be out over the piston dish so that there would be no effective squish in that area. A mystery. Mystery solved. I checked the stock pistons. The stock pistons have a corresponding hump on each side of the dish. A small expensive irony here. Higher dollar aftermarkets may be inferior in an important respect to stock pistons. Especially if you are looking to crank up the compression ratio a notch. So much for custom 5sfe pistons. Another kink to work out in an NA build. Nil Desperandum.

02-09-2007, 01:40 AM	#4 (permalink)
mrturrari I <3 my 5sfe Join Date: Mar 2005 Posts: 418 Thanks: 2 Thanked 93 Times in 60 Posts iTrader Rating: (0/0% )	Yes, I noticed that with my forged pistons as well and I have been running mine for almost a year with no problems. I had forgotten about that. One thought that comes to mind is that forged pistons can take more heat so not as much quench would be required. Also I am pretty sure the quench areas around the outside are in the end more important then the humps in the middle to keep heat away from the ring lands. So maybe it won't kill you if they're not there but they help the combustion pattern in a stock engine when you have the stock pistons. If you think about it the stock quench zones create a butterfly shaped pattern and without them you would have a more circular pattern of combustion. Here is a pic of my Atomic Speedware (Arias) pistons before they went in: http://warp.scl.utah.edu/mr2/5sfeReb...gedPiston2.jpg Also if you are raising compression then your pistons should have more of a flat top which may line up to part of the humps. If you feel that it is really important to keep all of your quench zones I'll bet Atomic Speedware would make some custom ones for you for not too much more. Removing the humps will also increase your combustion chamber volume which decreases compression.