I'm amazed that some people don't know how many valves they have
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| Differences 8 valve vs 12 valve head http://4g61t.org/forum/viewtopic.php?f=17&t=5147 |
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| Author: | pumaproton [ Sun Sep 07, 2003 5:45 pm ] |
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I'm amazed that some people don't know how many valves they have
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| Author: | T__K__A [ Sun Sep 07, 2003 5:47 pm ] |
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So i have a 12 valve? I never could figure out how a motor could have only 12 valves but that fixed that up, i never thought that 3 valves per cylinder was used |
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| Author: | socrateez [ Sun Sep 07, 2003 9:25 pm ] |
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I think Toyota did it too. Might be wrong but i know for sure that Mitsubishi wasnt the only one. |
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| Author: | HondaHunter [ Mon Sep 08, 2003 2:39 am ] |
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i belive the toyota 1.8L in the carollas used 12 valves i could be wrong....but i do know the toyota 1.6's and 1.8's fit into geo metros....seen it first hand 
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| Author: | The Ethereal [ Mon Sep 08, 2003 5:53 am ] |
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Quote: Last night I did my valve lash on my engine, im curious, on the intake rockers there is the normal sized valve, but there is a smaller valve. What the h*ll are those for? Im guessin I have a 12v head
That smaller valve on the intake side is probably the jet-valve, if you have a carburetted engine. If you have an EFI it's probably the 12 valve head.
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| Author: | T__K__A [ Mon Sep 08, 2003 8:06 am ] |
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Its a carby, so whats this jet valve for? Is it like fuel injection? |
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| Author: | xlr8 [ Mon Sep 08, 2003 9:57 pm ] |
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hmm, possibly the third valve could be what is called a "jet-valve" which is found on some 8v heads. Dont get too excited though since its only an emmissions device. 
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| Author: | T__K__A [ Mon Sep 08, 2003 11:34 pm ] |
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Thats what I thought, d*mn 4g15 and all there "emission saving" sh*t. F*ck the environment, put big noisy exuast systems on, get rid of all the environmental toys on engine and let them breath out what they were suppost to. jk 
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| Author: | The Ethereal [ Tue Sep 09, 2003 5:16 am ] |
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Disabling the jet-valve on the 4G15 is exactly the same as on the G32B or 4G63BT (starquest engine). Please look at G32 talk, because I forgot how to disable them. I think it was just loosening the rocker arm or something that easy... BTW has someone info on the JDM 4G15 DOHC? I'm trying to gather info on that beast, too. I already know it exists and should bolt straight on.
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| Author: | HondaHunter [ Tue Sep 09, 2003 1:52 pm ] |
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doesnt it put out about the same HP as the 12v? |
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| Author: | The Ethereal [ Tue Sep 09, 2003 5:10 pm ] |
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The DOHC puts out 110 HP. I got the torque written down somewhere, too. I don't know if it fits a 8V, 12V or both heads, but it is supposed to bolt on both. |
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| Author: | xlr8 [ Tue Sep 09, 2003 8:39 pm ] |
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I dont think disabling the jet valve will do anything for performance gains considering how it works (injects air into the exhaust gas to burn any excess fuel). If you swapped to a non-jet valve head there might be some gains as the combustion chamber will flow a little better. The DOHC 4G15 heads aren't suitable for the early 4G15s unfortunately. RPW has a bunch of these ATM and I was all set to buy one for my X2 Excel until I found out that they only work with the new 4G15 engines that have the motor mounted on the other side of the engine bay.
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| Author: | The Ethereal [ Wed Sep 10, 2003 6:54 am ] |
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Quote: I dont think disabling the jet valve will do anything for performance gains considering how it works (injects air into the exhaust gas to burn any excess fuel). If you swapped to a non-jet valve head there might be some gains as the combustion chamber will flow a little better.
I meant welding the jet-valves shut to strengthen the head or just to disable them so they won't stick open. Although, this may be not as important in a NA car than in a turbo car.The DOHC 4G15 heads aren't suitable for the early 4G15s unfortunately. RPW has a bunch of these ATM and I was all set to buy one for my X2 Excel until I found out that they only work with the new 4G15 engines that have the motor mounted on the other side of the engine bay. Looks like we're out of luck with a DOHC upgrade. Aren't there any other DOHC heads that may fit? 4G61 head perhaps? 
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| Author: | xlr8 [ Wed Sep 10, 2003 8:41 pm ] |
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The 4G61 head has no chance of fitting the 4G15. One look at a 4G15 block next to a 4G6x block and you will see what I mean. The 4G6x blocks are alot bigger and have very different bore spacing. Also, its debatable how much of a gain a 16v head would give the 4G15 given you would loose all-important mid-range torque. Peak figures ultimately mean very little. |
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| Author: | The Ethereal [ Thu Sep 11, 2003 5:15 am ] |
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Okay, it was just a quick thought.  Indeed, the 4G15 has not much torque to begin with. Loosing midrange torque will make the car undrivable as a daily driver. BTW has anyone noticed drivability issues when reatarding the cam 5 degrees?
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