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Differences 8 valve vs 12 valve head http://4g61t.org/forum/viewtopic.php?f=17&t=5147	Page 1 of 4

Author:	The Ethereal [ Tue Sep 02, 2003 6:21 am ]
Post subject:	Differences 8 valve vs 12 valve head
Hi! Recently so many of us tried to elaborate some differences between the 8 valve and the 12 valve 4G15 heads, either to find out if they're non-interference or how retarding the cam will give more horses or doing a swap. How about a joint effort in covering all those differences? I.e. it's known the 8v head is non-interference, while it is unknown if the 12v is. This may be important when retarding the cam timing. The (German) 8v engine have a CR of 9.4, the (German) 12v have 9.2 but yet higher torque and more power. Is the CR reduced due to head construction or in the pistons? Common guys let the research begin!

Author:	pumaproton [ Tue Sep 02, 2003 5:58 pm ]
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This is what I've picked up, so it may not be accurate. 12 valves have flat top pistons, 8 valves have little dent bits for the valves. 12 valve carb and injection heads are identical in design. Not sure about 8 valve, never seen an injection 8 valve. Putting an 8 valve head onto a 12 valve block with its flat top pistons is supposed to bump up the CR nicely. I have these figures for the injection 8 valves and 12 valves (also have carb info if interestted) 12 Valve 91PS (6000rpm) 121.6Nm (3000rpm) 8 Valve 82 PS (5500rpm) 123.56Nm (3000rpm)

Author:	xlr8 [ Tue Sep 02, 2003 10:15 pm ]
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The 8v EFI head is very different to the 8v carby head. The EFI head has larger inlet ports spaced differently although the exhaust ports are the same. Plus the EFI head has no provision for a mechanical fuel pump although there is a still a lobe on the camshaft for it. The 8v carby 4G15 block uses flat-top pistons and the head has hemispherical combustion chambers. The EFI 8v 4G15 block has dished pistons, the head combustion chambers are smaller and kidney shaped - the combination of which maintains the same CR as the carby engine.

Author:	The Ethereal [ Wed Sep 03, 2003 5:09 am ]
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Thanks guys! I'm gonna type up my comprehensive list about that now.... I'll post it when it is all typed in.

Author:	The Ethereal [ Wed Sep 03, 2003 5:52 am ]
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EDIT: Thanks to Jason, that stuff is now here: http://www.4g61t.com/howtos/4g15.html I think I will post more Code: code here when I have actualized everything. Right now I cut it out to save some space on Jason's HDD.

Author:	pumaproton [ Wed Sep 03, 2003 5:57 am ]
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I own a 12 valve carb, its got a lot more power than that, but maybe its because mine is a Proton engine (not available in USA). I thought it was identical to the mitsubishi 12 valve carb.

Author:	The Ethereal [ Wed Sep 03, 2003 6:07 am ]
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Most of this info is from a German book about European engines. That's what is making things really weird sometimes. This is also the cause why I wanted to include RON and MON ratings, as RON is used in Europe and MON in America. How much power and torque does your Proton engine have? DIN HP/SAE HP/kW? I'm afraid we will only find out the differences in international 4G15s here, nothing more...

Author:	Guest [ Wed Sep 03, 2003 7:09 am ]
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http://www.4g61t.com/howtos/4g15.html

Author:	pumaproton [ Wed Sep 03, 2003 9:32 am ]
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From the back of my Proton Manual for 12v carb. What carb did mitsubishi use? Mine is an Aisan variable venturi (listed on www.nardek.com.au) Mine has CR of 9.2:1 64Kw@6000rpm and 118Nm@4000rpm. I'm quite sure this engine is identical to a Mitsubishi, everything is stamped with mitsubishi part numbers.

Author:	The Ethereal [ Wed Sep 03, 2003 12:16 pm ]
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Strange. The torque indicates a carbed 4G15. But the rest doesn't fit. How can one get more power with less compression? 64 kW equals 87 HP DIN or 86 HP SAE. Maybe they use a different carb. AFAIK Mitsu used Mikuni Solex carbs, type 32-20 I think. Or was that the FBC used in G15B?

Author:	The Ethereal [ Wed Sep 03, 2003 12:27 pm ]
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Quote: Putting an 8 valve head onto a 12 valve block with its flat top pistons is supposed to bump up the CR nicely. Will this really fit w/o damaging anything? How much would CR increase? If this will work out we had an instant upgrade for all 12 valve engines. And never worrying about a broken timing belt again...

Author:	stealthpony [ Thu Sep 04, 2003 2:30 pm ]
Post subject:	8vs12 valve head
i have two spair 8 valve heads and one 12 valve. I notice that the oil galleys are different and so are the water jackets. You can see the difference if you compare the head gaskets. If for some reason it does work you would have to use the 8 valve intake manifold which means no TB upgrade off the 1.8 and the TPS sensor is different between the two intakes also. However you can swap the sensors by doing a few things. Swap the shaft from your 12 valve TB into the TB on the 8 valve. Putting the TB back together can be a pain in the @$$ but it works. I'm currently working on an adapter plate for an 8 valve intake manifold so that you can do the 1.8 TB upgrade. '89 Colt 1.5 8 valve port & polish 8mil excel wires custom cold air intake

Author:	The Ethereal [ Thu Sep 04, 2003 3:25 pm ]
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Hey thanks for the info! Guys please be patient, I'll update that list very soon.

Author:	The Ethereal [ Thu Sep 04, 2003 3:59 pm ]
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Just a short thought: when putting a 8V head on a 12V block, CR increases. When doing vice versa, will CR drop enough to bolt on a turbo and run behind-kicking high boost?

Author:	T__K__A [ Sun Sep 07, 2003 4:48 pm ]
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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

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