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Old 04-08-2009, 06:02 PM   #1
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Default Decking Heads / compression ratio

A Couple related questions:
What is the stock compression ratio on 1.6? (9:1 ish?)

On stock components...
How much clearance do I have on the heads before the valves and pistons become kissing cousins, (even if a timing belt snaps)?

And, how far do you have to machine the head to achieve a 9.5:1 and a 10:1 compression ratio respectively?

If anyone knows, or could point me in the right direction I'd appreciate it.
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Old 04-08-2009, 06:59 PM   #2
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this is a turbo forum.
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Old 04-08-2009, 07:36 PM   #3
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Originally Posted by Smurf'n View Post
A Couple related questions:
And, how far do you have to machine the head to achieve a 9.5:1 and a 10:1 compression ratio respectively?
WOAAAAH!









(none of them fit )



You lookin for an all motor build?
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Old 04-08-2009, 07:38 PM   #4
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this is a turbo forum.



Yessssss!!!




Quote:
94-95.5 have 8.8:1
95.5-97 have 9.0:1
99-00 & MSMs have 9.5:1
01-05 have 10.0:1
(from a "compression" search on "search")
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Old 04-08-2009, 07:58 PM   #5
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let me point you in the right direction:
low compression: lots of spark advance
high comp: lots of slow gayness and detonation

I'm making a substantially more torque on my 8.6:1 motor with a gt2860rs than about anyone on a 9.0:1 static motor. So much that I was surprised. Take a look through my build and dyno threads...the #'s speak for themselves. My car isn't sluggish off boost either, I wouldn't change a thing if I had to do it again.

Now, flame away and tell me about how my turbine-housing is too big, my compression is too low, and how I constantly pull the wool and how you've never seen a naked chick in your life, bro. Bubble hard in the BRG, flex the roll, with the top dropped, holler back...
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Old 04-08-2009, 09:05 PM   #6
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So i can ask it a different way.
I would like to run 8 lbs of boost. I'm running a Greddy system (not the greatest) with a piggy-back (not the greatest^2) and don't feel like tuning a high boost car with just fuel pressure or getting a piggy-back fuel management system. High power is not my goal with this build. Nor am i trying to make more than 180 horse on this car.
Usually the recommendation would be to drop the compression, add thicker head gasket for instance, then add boost to make power. I personally don't want to tune above 10 lbs w/o a stand alone, nor am I going to buy one because of my financial situation.

I have my motor apart right now and am just going to use stock components putting it back together b/c I don't have any $$ for forged components or lots of machine work. In fact, I'm taking out a loan just to fix the car because I have to have it running. What I can do is deck my heads for free. My plan is to push up the compression a tad and run mid-to-low boost.

What is the optimal compression ratio on stock components without running into heat and detonation problems?

I would imagine like 9.5:1 or maybe 10:1; even though that's pushing it.

Next question is how to achieve that ratio with just decking the heads.

... closer to a 'turbo forum' question now or does 'head work with boost application' fall under a separate category? It sounded like an "engine building question" to me, but I could be mistaken.

It is interesting to correlate 'high compression' with 'slow gayness and detonation.' If i wanted to run 11:1... I'd say that's just an N/A build or a bit ridiculous if you wanted to add boost.

My question is; given 8 lbs of boost, what is the highest compression ratio you can safely run; and how to achieve it. I assumed I had a good idea what that ratio would be and wanted to ask a simple question.

It is also interesting to correlate intent with a technical question. I'm not here to compare my nuts to anyone. I just want to try and upgrade my car within the means of time and resources I have available to me and hoped someone would know.
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Old 04-08-2009, 09:37 PM   #7
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I think y8s has been running boost on his 10:1 stock pistons for a while now so its clearly possible (I'm not sure if the 10:1 pistons still clear the valves in the event of a cambelt snap, anyone care to comment?)

You have the engine apart so the easiest way will be to measure your engine. I wouldn't feel safe machining bits based on information from someone else's motor.

Also there is no way in hell you are going to raise your compression from 8.8:1 to 10:1 by having your head skimmed. Only way is to use domed pistons with recesses cut for the valves if you are worried about cambelt snapage. Unfortunately you are out of luck for drop in replacements because all of the higher comp pistons are for 1.8's so its going to be an expensive experiment.

If you have a really good buddy who does **** hot welding you could try adding material to the combustion chambers between the valves, thought this will require you to do a lot of grinding and polishing so that all of the cylinders are "cc'd". But it's a good excuse to port the **** out of the head while you are there.

Some people I know have tried adding material to their pistons, they also then had some interesting crankcase ventilation so I wouldn't advise it.

Let us know how you get on.
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Old 04-08-2009, 09:37 PM   #8
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Originally Posted by hustler View Post
let me point you in the right direction:
low compression: lots of spark advance
high comp: lots of slow gayness and detonation

I'm making a substantially more torque on my 8.6:1 motor with a gt2860rs than about anyone on a 9.0:1 static motor. So much that I was surprised. Take a look through my build and dyno threads...the #'s speak for themselves. My car isn't sluggish off boost either, I wouldn't change a thing if I had to do it again.

Now, flame away and tell me about how my turbine-housing is too big, my compression is too low, and how I constantly pull the wool and how you've never seen a naked chick in your life, bro. Bubble hard in the BRG, flex the roll, with the top dropped, holler back...
HAH wow i never thought i could find someone soooooo gay, do you know anything about your engine at all. Or did you just buy everything you see that you want and slap it together. Let me guess you bought a kit or parts that someone said will work b/c they put a lot of time and energy researching and making custom so you can ***** it out and say you are fast?
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Old 04-08-2009, 09:40 PM   #9
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I think y8s has been running boost on his 10:1 stock pistons for a while now so its clearly possible.

You have the engine apart so the easiest way will be to measure your engine. I wouldn't feel safe machining bits based on information from someone else's motor.

Also there is no way in hell you are going to raise your compression from 8.8:1 to 10:1 by having your head skimmed. Only way is to use domed pistons with recesses cut for the valves if you are worried about cambelt snapage. Unfortunately you are out of luck for drop in replacements because all of the higher comp pistons are for 1.8's so its going to be an expensive experiment.

If you have a really good buddy who does **** hot welding you could try adding material to the combustion chambers between the valves, thought this will require you to do a lot of grinding and polishing so that all of the cylinders are "cc'd". But it's a good excuse to port the **** out of the head while you are there.

Some people I know have tried adding material to their pistons, they also then had some interesting crankcase ventilation so I wouldn't advise it.

Let us know how you get on.
The head was finished being ported today. Also was free, along with dyno tuning, decking, valve job, laping, and porting the chambers.
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Old 04-08-2009, 09:46 PM   #10
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Free is good......Gimme
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Old 04-08-2009, 10:00 PM   #11
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.... so 8.8:1 is the stock compression ratio on a 1.6L...

that's all I really wanted.

Thanks
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Old 04-08-2009, 10:31 PM   #12
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Default Intake ports mild port job

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just a pic of the head i ported going on this car, exhaust pics to come. Still needed to be polished when this was taken
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Old 04-08-2009, 10:48 PM   #13
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The thing you might not fully appreciate is that 0.5psi will give you more return on investment than going from 9:1 to 10:1 in your compression ratio. And your increased ratio will preclude further gains that can be achieved when you are in a better financial situation. It is a foolish move by any measure for an automobile that will be used on pump gas.

You and the raven fellow are obviously in need of a book or two in your private libraries regarding turbocharging gasoline engines. I would recommend "Maximum Boost" by Corky Bell as a point of embarkation.

Raven: Don't be so foolish as to mock The Hustler when he is offering wise advice. There is nothing unsound in his statement except the holler back part.
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Old 04-08-2009, 10:54 PM   #14
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The thing you might not fully appreciate is that 0.5psi will give you more return on investment than going from 9:1 to 10:1 in your compression ratio. And your increased ratio will preclude further gains that can be achieved when you are in a better financial situation. It is a foolish move by any measure for an automobile that will be used on pump gas.

You and the raven fellow are obviously in need of a book or two in your private libraries regarding turbocharging gasoline engines. I would recommend "Maximum Boost" by Corky Bell as a point of embarkation.

Raven: Don't be so foolish as to mock The Hustler when he is offering wise advice. There is nothing unsound in his statement except the holler back part.
And he never said he wanted to go to 10:1 all he wanted was to know what the stock compression was, nothing more. He does not want to run more than 8 psi b/c he is not going to upgrade the fuel system, so he is going to pull a little more compression to give mabye only 3 more hp but 3 more is better than 8.5 psi and a blown engine. And i have built quite a few forced induction engines, last one put down 731 to the tire.
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Old 04-08-2009, 11:05 PM   #15
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And i have built quite a few forced induction engines, last one put down 731 to the tire.
Should have used a limited slip diff.
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Old 04-08-2009, 11:06 PM   #16
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Should have used a limited slip diff.
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Old 04-09-2009, 12:25 AM   #17
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Quote:
Originally Posted by Smurf'n View Post
So i can ask it a different way.
I would like to run 8 lbs of boost. I'm running a Greddy system (not the greatest) with a piggy-back (not the greatest^2) and don't feel like tuning a high boost car with just fuel pressure or getting a piggy-back fuel management system. High power is not my goal with this build. Nor am i trying to make more than 180 horse on this car.
Usually the recommendation would be to drop the compression, add thicker head gasket for instance, then add boost to make power. I personally don't want to tune above 10 lbs w/o a stand alone, nor am I going to buy one because of my financial situation.

I have my motor apart right now and am just going to use stock components putting it back together b/c I don't have any $$ for forged components or lots of machine work. In fact, I'm taking out a loan just to fix the car because I have to have it running. What I can do is deck my heads for free. My plan is to push up the compression a tad and run mid-to-low boost.

What is the optimal compression ratio on stock components without running into heat and detonation problems?

I would imagine like 9.5:1 or maybe 10:1; even though that's pushing it.

Next question is how to achieve that ratio with just decking the heads.

... closer to a 'turbo forum' question now or does 'head work with boost application' fall under a separate category? It sounded like an "engine building question" to me, but I could be mistaken.

It is interesting to correlate 'high compression' with 'slow gayness and detonation.' If i wanted to run 11:1... I'd say that's just an N/A build or a bit ridiculous if you wanted to add boost.

My question is; given 8 lbs of boost, what is the highest compression ratio you can safely run; and how to achieve it. I assumed I had a good idea what that ratio would be and wanted to ask a simple question.

It is also interesting to correlate intent with a technical question. I'm not here to compare my nuts to anyone. I just want to try and upgrade my car within the means of time and resources I have available to me and hoped someone would know.
then, at your gay-lower power goals, stick with a stock motor. Spark advance manifold pressure, and fuel ratio are fun variables to play with. Read my threads, read other's then see what you want to do.

The sad truth is that you're a ******* moron and don't understand that 8psi from a 2554 is different from 8psi with a 2871...so leave the motor in stock form, buy a 2554, and check out my tail lights while your girlfriend is ******* my sphincter on the way home from the chili-cook-off. She's a *****.
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Old 04-09-2009, 12:59 AM   #18
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If you registered in 2009 and posted in this thread, you have absolutely no ******* clue what you're talking about.
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Old 04-09-2009, 05:27 AM   #19
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This thread sucks, so does the idea. If there is nothing wrong with the stock engine, why open it to machine the head to raise the compression .5, which will only increase the chance for detonation and yield little to no gains. I machined my head when I rebuilt as well, and wish I could undo it. I'm probably at around 9.6-9.8:1
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Old 04-09-2009, 10:56 AM   #20
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If you registered in 2009 and posted in this thread, you have absolutely no ******* clue what you're talking about.
i saw the reported post. he's got some more bruises to take first.
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