So, I just realized after building up my head with over-sized valves that the shape of the valve face may affect the compression. I figured this out after noticing that the Eco stock valves have quite a large dish to them. After noticing this I decided "hey, I guess I should measure the dish and see how this would affect compression. Well, it turns out that the combined dish of all four stock ecotec valves is equal to 7.392 CC per cylinder. The flat faced GM racing valves only have a slight dish, actually hardly any. They came out to around 2.2ccs combined.
Basicly it looks like the new valves I installed resulted in about 5cc's less of area in the cylinder.
So my question is this:
What does 5 cc's less of area per cylinder do to gross compression?
I am already at 11:1 so what will this do? Like a 1/4 point?
Ill include some pics but it doesnt seem like you can really see the difference................(the stock valves have more of a dish than what appears in the pics)
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Well, I guess I'll answer my own question since no-one wants to do math on a monday night........ b!chez!
After dusting off my automotive math books I discovered this formula:
CR= cylinder volume + chamber volume / chamber volume
So a stock eco looks like this: 546.98 + 60.78 / 60.78 = 9.99934 (10:1 compression)
I am reducing the chamber volume by 5cc's so: 546.98+55.78/ 55.78 = 10.806 ( 10.8:1 compression)
But wait! .............. I have 11:1 comp pistons, so where would these flat faced valves put me?
546.98+49.70/49.70= 12.01 (12:1 compression!!!!!!!!!!!!)
So a 5cc decreace in volume due to the flat faced valves results in a whole point up on compression when your already at 11:1.
Stock compression we are looking at .8 of a point increase.
I guess the moral of the story is: Eco guys, compare the valves you order to the stockers..... the shape of the valves will affect your compression. I am now running roughly 12:1 comp on my eco build due to these valves. I cant wait till spring so I can tune this monster.
Edited 1 time(s). Last edited Monday, January 07, 2008 6:33 PM
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I want to see dyno numbers
Edited 1 time(s). Last edited Monday, January 07, 2008 7:26 PM
did you cc the head?
its hard to guess without an actual measurement of each combustion chamber actual cubic centimeter displacement
but if thats the case.. thats great news =D
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did you cc the head?
No I didnt cc the head, what I did was use the stock cylinder volume which is known and the stock compression value which is also known. Then I solved for the only missing value .... the cc of the head. Then I cc'd the valves to calculate the difference.
My point of making this post is to give people the heads up that the GM racing valves which are decreasing the combustion chamber volume by 5cc's are sold as stock replacements. I dont know if anyone is taking into consideration that these valves will affect your final compression ratio. For me its fine.... but what about people who are going turbo? They just unknowingly increased thier compression from anywhere between .5 to .8 and most likely dont realize it.
The guy who buys wiesco 10:1's and then decides "hey I need stainless valves to handle the high EGT's of a turbo motor.... I'll buy the GM racing valves" just unknowingly turned his 10:1's into 10.8:1's...... thats a big jump!
Im happy about it though, 12:1 is closer to what I wantt for some N/A powa!
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Oh yeah,
Another thing..... to all you people that are trying to boost compression by shaving thier head down........and thus screwing up thier timimg chian from overextending thier tensioner.......... why not buy flat faced valved instead? You could grab a half point by picking up some stock stainless replacements from GM racing through Karo.
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There are 2 types of valves which I offer for the Ecotec engines.
Set One:
Stainless Intake / Exhaust Stock Size or 1mm Oversize OEM Keeper Setup(more for NA people or SC people)
Set Two:
Stainless Intake / Inconel Exhaust .5mm Oversize Single Groove Setup (High HP, High Heat, Big Boost Applications)
The second set of valves seem to have a deeper pocket than the first set of valves. When I was looking at them both side by side Set 2 vs OEM seemed to be dead on the pocket size. Set 1 does have a smaller pocket vs stock valves.
so if i put these valves in my car would i see an increase
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so if i put these valves in my car would i see an increase
If you mill the head slightly (which is necessary for a clean gasket surface anyway) for a .25 point + the valves .5-.8, you would have to notice a difference in my opinion.................
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Hmm, definitely interesting. What exactly did you do to determine the CC's of each type of valve though? Just curious as I've seen several different methods.
Arrival Blue 04 LS Sport
Eco
Turbo
Megasquirt
'Nuff said
Quote:
Hmm, definitely interesting. What exactly did you do to determine the CC's of each type of valve though? Just curious as I've seen several different methods.
I went old school on this one. I used some alcohol, a syringe, and a measuring "test tube" device for cc's. The exhaust valves have a pretty big cup in them so it was really easy. I also underfilled the valve slightly to take into account surface tension of liquids.
The method was not perfect but 5cc's is a conservative estimate.
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to find the compression , you have to know the actual CC of the combustion chamber , before and after
also cylinder head gasket thickness provides more CC's , so you need the compressed gasket rating
then piston to block height , with a zero deck , the piston and lip of the block are same height , then you have 1s that stick out and some that are below the deck height
if your below the deck you need to check that CC also to determine the compression ratio
then there is dynamic and static compression ratios , how much over lap the cam has , so your basic math can be giving you alot of bad information
Quote:
to find the compression , you have to know the actual CC of the combustion chamber , before and after
also cylinder head gasket thickness provides more CC's , so you need the compressed gasket rating
then piston to block height , with a zero deck , the piston and lip of the block are same height , then you have 1s that stick out and some that are below the deck height
if your below the deck you need to check that CC also to determine the compression ratio
then there is dynamic and static compression ratios , how much over lap the cam has , so your basic math can be giving you alot of bad information
Yeah, I wasnt really out to calculate the exact compression, what I was out to do is
estimate how 5cc's change in volume would raise compression. The volume change based on the valves is easy to arrive at, I wont know my true compression until the motor is together.
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And yet people still ask "when am I ever going to use this", lol.
_________________________
Quote:
Another thing..... to all you people that are trying to boost compression by shaving thier head down........and thus screwing up thier timimg chian from overextending thier tensioner.......... why not buy flat faced valved instead? You could grab a half point by picking up some stock stainless replacements from GM racing through Karo.
is it possiable to just use a shorter belt to take up the travel? or is it the actual angle change of the tensioner itself?
"
boobs now with Riboflabin"
So . . . . what happens when you have 12:5 : 1 wiseco pistons and Karo's valves and GM cnc machined head and Comp Cams stage 3 camshafts and 100 oct unleaded fuel = guesstimating 40 whp
-Ben
I'm going to call a local machine shop and take all 3 valves I have here to have them CCed to find out exactly what the differance between the 3 are. Soon as I get any results I will post it up for everyone to know.
Jcavi wrote:Quote:
Another thing..... to all you people that are trying to boost compression by shaving thier head down........and thus screwing up thier timimg chian from overextending thier tensioner.......... why not buy flat faced valved instead? You could grab a half point by picking up some stock stainless replacements from GM racing through Karo.
is it possiable to just use a shorter belt to take up the travel? or is it the actual angle change of the tensioner itself?
Lol, forgive me for pointing out your brain fart, but you'd need a shorter CHAIN...
He's talking about the timing chain due to the shorter overall height which results from shaving the head. Not to mention I seem to recall reading many moons ago that shaving the head also advances your cam timing by default (oh look! another possible use for those "useless" adj. cam gears we keep hearing about!).
Arrival Blue 04 LS Sport
Eco
Turbo
Megasquirt
'Nuff said
I was talking to a few different valve manufactures and they were saying how almost any aftermarket valve you buy will not have as much of a "dip" or a "dish" on the valve simpley because for max performance you dont want to have such a big dish in it. Something to do with the design.
Either way, soon as I find a machine shop to do the work for me I will post up the information unless Ben / Ben's Dad beat me to it.
^^ I'm not sure if there was an engine issue or not (something about a wet #4 cylinder) but ben's clutch ended up shearing itself clean off of the flywheel.
I'm not sure if it ended up happening during our race in the final, or at some point during the day because ben was having trouble catching second gear all day.
I have pictures tom, drop me an IM if you want to see them (ben sent them to me about a week after the bash)
Karo (Car Customs) wrote:I was talking to a few different valve manufactures and they were saying how almost any aftermarket valve you buy will not have as much of a "dip" or a "dish" on the valve simpley because for max performance you dont want to have such a big dish in it. Something to do with the design.
Either way, soon as I find a machine shop to do the work for me I will post up the information unless Ben / Ben's Dad beat me to it.
Well, I can understand that completely... At least from my completely layman understanding of airflow, a really dished exhaust valve is going to tend to deflect the exhaust gasses back into the chamber instead of cleanly out past the valve....
Arrival Blue 04 LS Sport
Eco
Turbo
Megasquirt
'Nuff said
