Okay, here we go.
As everyone here knows... I design engine parts. I have finished up my new line of pistons, and during this process, some truth has been shed on the compression ratio numbers game. I use the only manufacturer that I could find that uses 3-D chamber and dome scanning. This scanning, along with "proper" math has brought me to the following conclusion; There is no such thing as a true 14:1 piston in a stock bore 700! I will explain how I got to that bold statement, and let the games begin!!
I designed 3 different domes;
11:1 uses a -.9cc effective dome
12.5 uses a 7.9cc effective dome
14? uses a 9cc effective dome, which is the largest effective dome that will fit into the chamber. When I say "effective" dome, I am referring to the actual dome size after valve reliefs have been machined.
Notice the jump from 11:1 to 12.5:1 requires a dome size increase of 8.8cc's. That is what is required to increase the compression ratio 1.5 points. I could possibly gain 1 more cc by not using a trough style valve relief on the exhaust. Now you must realize that as the dome gets larger, valve reliefs remove more material. The dome also has to become progressively narrower at the top to fit the chamber, making it even harder to gain dome volume. Notice the piston with a claimed 14:1 only has a net increase of 1.1cc....... I do have very large valve reliefs for use with .550"+ lift cams, but the piston company I use actually has a dome shape that fits the whole chamber.
Okay, now add in the fact that I have the only off the shelf piston that sits .015 "in the hole", while most sit in the hole .050-.065". This gives me the ability to have the highest compression with the smallest domes. There are some custom pistons out to compensate, but the math stays the same. The valve pockets have to be machined deeper to retain clearance, and the dome only goes into the middle of the valve pockets..... Again, not happening. Now we can add in the fact that most manufacturers conveniently forget to add the 1.2 or so cc void around the piston head to the top ring...... You can see how quickly this becomes a "theoretical compression" numbers game.
Now to the defense of dealers and engine builders..... most do not have the equipment to measure actual net dome volume. This is a very difficult task. So they have to trust what the manufacturer tells them. The manufacturers give a "theoretical" number that often assumes "0" deck, or sometimes doesn't account for valve reliefs, and the truth gets lost in the wash.
I will be posting this on all the forums that I frequent, and will be more than happy to go "in depth" about the math I use for my conclusions. The obvious question would be; What is the highest compression I have seen in a stock displacement engine? 12.8:1. Please do not ask questions about dome shapes if you do not want an honest answer. Lipstick on a pig? (that phrase cracks me up) :grin_nod:
So what would the compression be on a 14:1 piston?
I knew that 18:1 piston I bought off of Ebay was too good to be true :confused:
Quote from: Socalrappy700 on September 11, 2008, 08:34:53 AM
So what would the compression be on a 14:1 piston?
Usually a tick over 12.5, some are less. 12.5 and 11:1's rarely meet their ratings as well 8)
Quote from: troywcc on September 11, 2008, 08:38:59 AM
I knew that 18:1 piston I bought off of Ebay was too good to be true :confused:
No that one really is 18:1 :thumbs:
Quote from: Kenny on September 11, 2008, 08:54:40 AM
Quote from: Socalrappy700 on September 11, 2008, 08:34:53 AM
So what would the compression be on a 14:1 piston?
Usually a tick over 12.5, some are less. 12.5 and 11:1's rarely meet their ratings as well 8)Quote from: troywcc on September 11, 2008, 08:38:59 AM
I knew that 18:1 piston I bought off of Ebay was too good to be true :confused:
No that one really is 18:1 :thumbs:
Not to sound like a dumb ass but based on that would there be any performance difference between the 12.5 and the 14?
So you're saying. "Theoretically" the jump from 12.5 to 14 they'd have to be using at the least a 17.6 cc effective dome?
So.. Really. it shouldn't/isn't over 13:1 is it.
Any gains made would be MINISUCLE
Good stuff Kenny :thumbs:
What about the effects just beyond TDC of a "14-1" vs a true 12.5-1 for quench?
Quote from: Colorado700R on September 11, 2008, 09:08:30 AM
Good stuff Kenny :thumbs:
What about the effects just beyond TDC of a "14-1" vs a true 12.5-1 for quench?
Coming from a laymens point of view here. Lookin at the done on the 12.5 piston Vs. a 14.1 piston the difference is HUGE. how does that not dirrectly translate to more compression?
Quote from: Socalrappy700 on September 11, 2008, 08:57:35 AM
Quote from: Kenny on September 11, 2008, 08:54:40 AM
Quote from: Socalrappy700 on September 11, 2008, 08:34:53 AM
So what would the compression be on a 14:1 piston?
Usually a tick over 12.5, some are less. 12.5 and 11:1's rarely meet their ratings as well 8)Quote from: troywcc on September 11, 2008, 08:38:59 AM
I knew that 18:1 piston I bought off of Ebay was too good to be true :confused:
No that one really is 18:1 :thumbs:
Not to sound like a dumb ass but based on that would there be any performance difference between the 12.5 and the 14?
It is a perfect question! Depending on your previous setup, by the numbers it can see some gain. That is assuming that your 12.5:1 was calculated incorrectly as well. If your 12.5:1 was from a different manufacturer that had a more accurate measuring technique, there would be none. If you have a piston that sits farther in the hole, but uses a more aggressive dome design to keep the compression up, the likely outcome is a power loss due to flame obstruction. ::)
Quote from: Krandall on September 11, 2008, 08:58:50 AM
So you're saying. "Theoretically" the jump from 12.5 to 14 they'd have to be using at the least a 17.6 cc effective dome?
So.. Really. it shouldn't/isn't over 13:1 is it.
Any gains made would be MINISUCLE
CORRECT! :clap:
Quote from: Colorado700R on September 11, 2008, 09:08:30 AM
Good stuff Kenny :thumbs:
What about the effects just beyond TDC of a "14-1" vs a true 12.5-1 for quench?
There are definite flame propagation penalties to be paid :thumbs:
Quote from: preddy08 on September 11, 2008, 09:32:32 AM
Quote from: Colorado700R on September 11, 2008, 09:08:30 AM
Good stuff Kenny :thumbs:
What about the effects just beyond TDC of a "14-1" vs a true 12.5-1 for quench?
Coming from a laymens point of view here. Lookin at the done on the 12.5 piston Vs. a 14.1 piston the difference is HUGE. how does that not dirrectly translate to more compression?
Only the dome height difference is huge. Once you start measuring how much extra material is removed for valve reliefs, and the fact that the dome narrows as it gets taller. Keep in mind that my 11:1 has about 3cc's of total valve relief, and my 12.5 has a shade over 6cc's removed to get the same valve to piston clearance, which means I had to increase the dome 12cc's to net 7.9cc's. Another thing to remember, is that my domes fit the
entire chamber shape. Most piston domes start halfway through the valve relief, which makes their claims even more outrageous. ;)
"Have you ever seen that scene in Scanners where that dude's head exploded?"
:lol:
I just learned more about engines with one post, than I have my whole life! :lol: :help:
Very intersting! :thumbs:
I'm still not sure what the hell he is talking about! Where's RaptorNut when you need him? :lol:
Kenny, have you ever measured a stock piston Yamaha claims @ 9.2/1
Oh GERD, don't say "pig with lipstick" it gets peels all riled up :humper: :humper: :humper: :humper: :humper:
Quote from: preddy08 on September 11, 2008, 05:44:02 PM
Oh GERD, don't say "pig with lipstick" it gets ME all riled up :humper: :humper: :humper: :humper: :humper:
nyuk nyuk nyuk :P
Quote from: Bert on September 11, 2008, 01:10:28 PM
Kenny, have you ever measured a stock piston Yamaha claims @ 9.2/1
Yes. The factory piston has a 9cc dish, it sits .050" below deck and when combined with a head gasket .028" thick, comes up to
EXACTLY 9.2:1 :thumbs: I will give you an example of piston differences. The first piston is a Wiseco. Notice how the valve reliefs negate some of the dome, which obviously doesn't fit the shape of the chamber. This piston sits .050" in the hole just like stock.
(http://i233.photobucket.com/albums/ee157/kennybasham/Wiseco11to1P2.jpg)
Notice my 11:1 piston (on the right), even though the valve reliefs are much larger than the Wiseco, the corrected deck height requires much less dome for
MORE compression :thumbs:
(http://i233.photobucket.com/albums/ee157/kennybasham/100_0472-1.jpg)
Good talking to you again Kenny :thumbs:
Per the manual the stock 9.2-1 equates to a standard sea-level pressure of 450 kPa (4.5 kg/cm2, 64.0 psi), so I think we could use that as a baseline when we get your pistons installed to create a PSI graph so the average joe can test their PSI and compare results and approximate their "true" compression ratio.
Aaron
Like we discussed, the cam, valve lash, and piston ring conditions may very the results, but at a minimum cylinder pressure should be a helper guide fuel octane considerations correct?
Here's a calculator :thumbs:
http://rapidshare.com/files/145622362/KDS_Racing_compression_calculator.xls
Kenny, so does that mean us guys with the "14:1" pistons could get away with a half and half mix of race gas since they are only 12.8:1?
wow ??? my freakin brain hurts now...
lol i think i get some of this but not really :lol:
Quote from: preddy08 on September 15, 2008, 06:42:50 PM
Kenny, so does that mean us guys with the "14:1" pistons could get away with a half and half mix of race gas since they are only 12.8:1?
Not necessarily.... Look what happens as you tighten up the quench .010" and shave the head .040". This is a 12.5:1 example:(http://i233.photobucket.com/albums/ee157/kennybasham/img028.jpg)
(http://i233.photobucket.com/albums/ee157/kennybasham/img027.jpg)
Ok, now I'm really lost.
Great info Kenny! :thumbs: I feel like Kelly Bundy where I need to forget something in order to learn something new! ;)
Quote from: NaturalRaptor on September 16, 2008, 08:49:35 AM
Great info Kenny! :thumbs: I feel like Kelly Bundy where I need to forget something in order to learn soemthing new! ;)
:lol: great analogy :thumbs: I still feel like "the guy in scanners when his head blew up" :rofl:
I don't think I have done a very good job of turning this into digestible bites. I promise it isn't as hard as I make it look. Just hang with me, and as soon as I can get my sick ass off the couch and think clearly, I will get you guys some "good" understandable info :thumbs:
Other than the obvious difference being 4 valves vs 5, are the pin heights and ring lands the same between a 660 and 700? Would it be posible to take a 700 uncut piston and make a 5 valve 660 piston out of it? I have a friend that owns Issco Man. which does nothing but CNC out airplane parts all day? I really need a 15+:1 piston. Do you have any sudgestions?
Quote from: Kenny on September 16, 2008, 08:10:42 PM
I don't think I have done a very good job of turning this into digestible bites. I promise it isn't as hard as I make it look. Just hang with me, and as soon as I can get my sick ass off the couch and think clearly, I will get you guys some "good" understandable info :thumbs:
We want more little neat parts to put on to go along with the info.
Actually the Wiseco dome fits better than any piston Ive used, dont have to clearance the chamber sides to keep the dome from hitting when milling the cylinder. :)
Quote from: VelociRaptor on September 18, 2008, 06:55:17 PM
Actually the Wiseco dome fits better than any piston Ive used, dont have to clearance the chamber sides to keep the dome from hitting when milling the cylinder. :)
I think the Wiseco piston is a good budget piston, but the dome sucks. I haven't had any issues at all when milling the cylinder for correct deck height. But it is definitely preferable to have a piston that is designed correctly from the start. The price of milling the cylinder and flycutting for valve clearance make my piston seem a lot less expensive. Especially when you consider the Wiseco is made from 4032 material, and my piston is 2618 which is far stronger. I don't think the Wiseco is gonna stand up to squeezing things real tight. You really need to pay close attention to the wall clearance when you are running a motor hard. :thumbs:
Quote from: Kenny on September 16, 2008, 06:25:13 AM
Quote from: preddy08 on September 15, 2008, 06:42:50 PM
Kenny, so does that mean us guys with the "14:1" pistons could get away with a half and half mix of race gas since they are only 12.8:1?
Not necessarily.... Look what happens as you tighten up the quench .010" and shave the head .040". This is a 12.5:1 example:
(http://i233.photobucket.com/albums/ee157/kennybasham/img028.jpg)
(http://i233.photobucket.com/albums/ee157/kennybasham/img027.jpg)
Ya lost me on that one. Kenny, go easy on my little mind! :lol:
I'm wondering the same thing Preddy is. It really sounds as though going with a 14:1 off the shelf piston will not require 110 octane as we are told since the compression is only around 12.5. This is for the guys who just dropped in a 14:1 piston. No shaving done on the piston or jug. Am I understanding this correctly, or am I still not getting this. ???