Vitara pistons.... compression check... 90psi across the board????
03-03-2005, 06:58 PM
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Vitara pistons.... compression check... 90psi across the board????
I have vitara pistons in a A6 block, y8 hg, and z6 head... NA
i changed the oil today and i figured id do a comp test since its been just about 3k since the build, well i got ~90psi in all 4 cyc. , now i know the comp is like reaaaal like 7.9-8.2, whatever its real low... are these good numbers for a c/r that low? I remember reading as long as all 4 are about 5psi within each other you are fine, which they are. It runs reallllll strong so i dont think i have any blow by. Let me know what you guys think.
i changed the oil today and i figured id do a comp test since its been just about 3k since the build, well i got ~90psi in all 4 cyc. , now i know the comp is like reaaaal like 7.9-8.2, whatever its real low... are these good numbers for a c/r that low? I remember reading as long as all 4 are about 5psi within each other you are fine, which they are. It runs reallllll strong so i dont think i have any blow by. Let me know what you guys think.
03-04-2005, 06:40 AM
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Re: Vitara pistons.... compression check... 90psi across the board???? (shaun311)
90 psi sound low but it all depends on your guage and how you did some guages read different that other main concern is to make sure they are level across the board. if the car runns good doesnt burn any oil then keep driving it
03-04-2005, 06:53 AM
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Re: Vitara pistons.... compression check... 90psi across the board???? (b18bturbo)
That does seem kinda low. but you do have to factor in the c/r that them pistons are known for 
03-04-2005, 07:30 AM
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wow, thats some low compression. Check the stock compression readings online for like an SRT4 or an old Mitsu Starion, both of those motors have around 8:1 compression.
03-04-2005, 07:35 AM
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Re: Vitara pistons.... compression check... 90psi across the board???? (shaun311)
Are you sure you checked the compression correctly? Are the valves adjusted? Were you holding the throttle body all the way open?
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03-04-2005, 05:51 PM
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Re: (fjt)
no, i just put it in there and tried starting it a few times didnt give it barley any gas... you are supposed to do it wot????? really now? huh
03-04-2005, 06:16 PM
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Re: (shaun311)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by shaun311 »</TD></TR><TR><TD CLASS="quote">no, i just put it in there and tried starting it a few times didnt give it barley any gas... you are supposed to do it wot????? really now? huh</TD></TR></TABLE>
Yeppers, that's a roger there captain! Think about it like this --> if you crank the engine over with the throttle closed, it's just sucking on a closed container. At idle it's a big enough restriction to bring your 125hp engine down to about...2. Put an empty milk jug over your mouth and try to inhale. Same difference
Yeppers, that's a roger there captain! Think about it like this --> if you crank the engine over with the throttle closed, it's just sucking on a closed container. At idle it's a big enough restriction to bring your 125hp engine down to about...2. Put an empty milk jug over your mouth and try to inhale. Same difference
03-05-2005, 03:15 PM
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Re: (shaun311)
You do have all the plugs out and the ECU fuse pulled right? If you are doing it by yourself crank it about 7 times to give the reading a chance to stabilize and youll probably get higher numbers. Sounds like its fine either way.
03-07-2005, 02:41 AM
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There is a really good thread on http://www.homemadeturbo.com about these pistons and how low they sit in the hole. I would pm bamboo7 on hmt (i think thats his username) that or make a post about it. They came up with some pretty usefull information.
-Josh
-Josh
03-07-2005, 12:42 PM
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Re: (shaun311)
Here is a quote from PumaRacing....
"You can expect the cranking pressure in psi for a road engine with a standard cam to be about 17 to 20 times the value of the compression ratio. So our engine with a CR of 10:1 should generate between 170 and 200 psi. The better the condition of the engine the closer the figure will be towards the top end of this range. If the engine has been modified by fitting a different cam then you need to make some allowances."
Given their simple formula, your lower compression ration of 7.9:1 would calculate to 134 PSI. (7.9 * 17 = 134)
Craig @ Tuner Toys
"You can expect the cranking pressure in psi for a road engine with a standard cam to be about 17 to 20 times the value of the compression ratio. So our engine with a CR of 10:1 should generate between 170 and 200 psi. The better the condition of the engine the closer the figure will be towards the top end of this range. If the engine has been modified by fitting a different cam then you need to make some allowances."
Given their simple formula, your lower compression ration of 7.9:1 would calculate to 134 PSI. (7.9 * 17 = 134)
Craig @ Tuner Toys
03-07-2005, 01:26 PM
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Re: (TunerToys)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TunerToys »</TD></TR><TR><TD CLASS="quote">
Given their simple formula, your lower compression ration of 7.9:1 would calculate to 134 PSI. (7.9 * 17 = 134)
</TD></TR></TABLE>
Close, very close it was between 140-145 accross, better than 90 psi
Given their simple formula, your lower compression ration of 7.9:1 would calculate to 134 PSI. (7.9 * 17 = 134)
</TD></TR></TABLE>
Close, very close it was between 140-145 accross, better than 90 psi
03-07-2005, 01:35 PM
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Re: (shaun311)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by shaun311 »</TD></TR><TR><TD CLASS="quote">
Close, very close it was between 140-145 accross, better than 90 psi</TD></TR></TABLE>
glad you got it right .
Close, very close it was between 140-145 accross, better than 90 psi
</TD></TR></TABLE>glad you got it right .
03-07-2005, 01:52 PM
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Re: (shaun311)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by shaun311 »</TD></TR><TR><TD CLASS="quote">Close, very close it was between 140-145 accross, better than 90 psi </TD></TR></TABLE>
Glad to hear the compression came up
I'm sure you are too!
</TD></TR></TABLE>Glad to hear the compression came up
I'm sure you are too!
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