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How to distinguish 7 bolt head, 6 bolt non-turbo head, & 6 bolt turbo head

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Lambiablo

15+ Year Contributor
91
4
Apr 8, 2008
Elon, North_Carolina
I have had difficulty finding details on this particular topic, but I am trying to figure out how to tell these heads apart.

I know the 6 bolt heads have much larger ports, but does this apply for the turbo AND non-turbo 6 bolt heads? Or do the non-turbo heads have smaller ports?

In addition, are there any other good ways to tell all three different types of heads apart?

I have a couple different heads right now, one I know for a fact is a 6 bolt turbo head and has very large ports. Then I have another that is supposedly a 6 bolt head, but I am really not sure if it is a turbo or non-turbo 6 bolt head or even a 7 bolt head. The ports are somewhat smaller than the one I know to be a 6 bolt turbo head.

Just trying to make heads and tails of the parts I am working with before proceeding with my build.

Thanks in advance.
 
If you had a bare 6-bolt turbo and 6-bolt non-turbo head sitting right next to each other, you would not be able to tell a difference. The same goes for a 1G 7-bolt turbo head and 1G 7-bolt non-turbo head. Between the two (6-bolt and 1G 7-bolt), there is very little difference visually. There are two "giveaways". First, the 1G 7-bolt head uses two different sizes of exhaust manifold studs -- seven of which are M8 and the other/outermost two are M10. Second -- and I don't have exact measurements on me at the moment, though I can get some tomorrow if need be -- you will have a difficult time fitting an original 12mm diameter 6-bolt head bolt through the bolt holes on the (any really, 1G or 2G) 7-bolt head; the original 7-bolt head bolt is 11mm in diameter.

If you are talking 2G 7-bolt heads, there is a bit more that differentiate them from 1G heads. The thermostat housings use different bolt patterns: the 1G in a triangular shape (three fasteners) and the 2G in a more rectangular shape (four fasteners). See pic 1 below for a visual: 2G on top, 1G on bottom. A second, easy identifier of a 2G head vs. a 1G head is the location of the hole on the exhaust side of the head, seen here: Is this a 2nd gen or 1st Gen head. Third, a 2G head is differentiated from a 1G head because of the size of its intake runners. See pic 2 below: the top head is a 2G, the bottom is a 1G. Finally, 2G heads normally have a code "G6S" or "G6K" on the thermostat side where the 1G heads will have "2.0" (also pictured in pic 1 below) or simply "G6" with some numbers underneath it.

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You caught me in the middle of a ninja edit, Bud. I have gone back and entered "intake" runners for the second picture. Anyway, you can clearly see the cam sprockets on the left side of the picture for the 2G head and the plots for the fuel rail spacers and holes for the injectors so it is obviously the intake side. ;)

Check the link in my 2nd paragraph for a comparison of the exhaust sides.
 
Are those your heads in pic number 2? If so will you show me the difference between the runners as they are commenly called, between both of the heads please? I should be able to decifer on my own which head is which..

Everyone always says the runners in the 2g head flow better, than the stock 1g..I just want to see for myself..cause what Im seeing right now is the 1g intake side flows better, and the exhaust side look about the same..
 
Are those your heads in pic number 2? If so will you show me the difference between the runners as they are commenly called, between both of the heads please? I should be able to decifer on my own which head is which..

The difference I'm alluding to is a simple visual difference, the difference in size of the head's intake runners, or ports if you like. Are you wanting a picture inside the intake ports or do I misunderstand you? :confused:

Everyone always says the runners in the 2g head flow better, than the stock 1g..I just want to see for myself..cause what Im seeing right now is the 1g intake side flows better, and the exhaust side look about the same..

The idea behind the 2G head flowing better than a 1G has more to do with how the air flows (its floor height and associated port angle, velocity, overall efficiency, etc.) rather than how much air you can flow in the ports. I don't know enough about it myself to be sold one way or the other (though I do tend to agree with some of the more reputable folks this site has seen in the past), I just report what the general consensus is and that it is the general consensus.
 
And that's why I wanted a visual comparison as well..Because they say the 2g head is designed better for better flow..And I know is what the good folks have said in the discussions about the 2g vs 1g head just like you..So I'll have to take peoples word for it tha the 2g head flows better, cause I've never seen the difference..And also the dyno numbers between the two on both the 1g and 2g..Not just the rated hp,, but the actual dyno info on a 1g with 2g head, how much hp it picks up, or a 2g with a 1g head and see how much hp the 2g looses..

But like you said all I have to go on is what the wisemen say that the 2g just flows better..
 
Thanks again Brian! That is all very helpful.

And to help answer the flow comparison:

The way the 2g is designed creates a greater airflow through greater velocity. It all comes down to fluid mechanics, but basically the path that the air takes in a 2g head is exposed to less restriction due to a more direct path, BUT in a smaller area. Similar to when you plug part of the end of a water hose, the water comes out at a higher speed and pressure.

All in all this results in better lower end response for the 2g, but greater power at the higher rpm ranges for the large 1g ports.
 
But the 2g higher compression also helps on the low end as well..

So really if your going to have a ported head it makes no difference which head your going with.That makes alot more sense now..Even tho I have never seen the inside of either head..
 
thanks for this thread, it prevented me creating a thread asking the same question!!!
 
Goodness! 3 days in this site, and i learned a ton more than my 2 years of working on my evo engine and vr4, and going thru in and outs on some diy vids...thanks a ton of lots guys! :applause:
 
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