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Thread: +2 -2 Head

  1. #1
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    +2 -2 Head

    Anyone have any info on this head and why it performed so well? I have been looking and researching and cannot find anyting outside of The DDG with info. Any insight of why it performed so well.

    Paul
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  3. #3
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    Doesn't really tell me too much as far as what was done. And they all thought it was smaller exhaust valves as far as stock when in reality it was stock exhaust valves and the 44mm intakes
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  4. #4
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    Re: +2 -2 Head

    The head is a completely different casting. Considering it's a prototype and there are two units, the info is as good as it gets. You won't get cut-open pictures of it.


  5. #5
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    Re: +2 -2 Head

    Reportedly, the exhaust ports were smaller and taller, making this head very difficult to duplicate. Also, it was used in N/A testing, so you won't know how well it did on turbo models.

  6. #6
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    Interesting enough how it was done off of a swirl chamber. Wish there were pictures of the ports to compare. I wonder how different the ports were. And I imagine it can't be to different from our heads considering it uses the same valves as ours.
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  7. #7
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    Re: +2 -2 Head

    These were slightly misunderstood cylinder heads and there's a few reasons for this - its existence and purpose was slightly less intense than a plan for a new performance head.
    The head is better and more accurately defined as a second generation head for the 2.2/2.5 if they had lived beyond the 2.4L.
    The casting was primarily changed to support the seat diameter reduction on the exhaust and seat diameter increase on the intake and therefore result in a production-like un-ported head for accurate test comparisons.
    The exhaust size was reduced at the seat ID and the valve OD to maintain the proper ratios while generating improved low lift flow numbers and slightly improved flow throughout the remaining lift range.
    The intake valve OD and seat ID was enlarged in an attempt to re-gain flows closer to the old stock 'G' head while still supporting adequate swirl, for idle and emission purposes.
    The result was mildly improved exhaust gas flow/velocity through the port and acceptable increases in flow volume on the intake side without sacrificing swirl and charge motion, when compared to a stock Fast-Burn.
    Nearly all that was done on the +2/-2 can be implemented on a standard head but considering the time and effort required to duplicate a production planned arrangement, a higher flowing big valve ported arrangement can be made.
    In short, it accomplished the the task of improve flow over a standard fast-burn head but like any standard fast-burn or 'G' head a fair amount of work is needed for it to support higher performance levels.

    Hope this helps.

  8. #8
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    Yes it definitely does. Thanks. Do you have any insight on what was exactly done to the ports.
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    Re: +2 -2 Head

    Quote Originally Posted by 85boostbox View Post
    Yes it definitely does. Thanks. Do you have any insight on what was exactly done to the ports.
    Minor work in the bowl area(s) - primarily to properly blend in the change in seat diameters and the intake port volume may have went up slightly, while the exhaust ceiling near and slightly beyond the guide received more 'arc'.

  10. #10
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    Re: +2 -2 Head

    Interesting factual info on a part that not many really know about or understand. Thanks again, Ken!

  11. #11
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    Hmm that is very interesting. Thanks again Ken. Very much appreciated.
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  12. #12
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    Re: +2 -2 Head

    Has it been clearly determined that a larger exhaust valve will not help on an 8V?
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    Re: +2 -2 Head

    Quote Originally Posted by John B View Post
    Has it been clearly determined that a larger exhaust valve will not help on an 8V?
    Not at all but in the case of the cylinder head being discussed, it was an improvement to the production head at minimal cost.
    Last edited by 5DIGITS; 02-23-2013 at 12:54 AM.

  14. #14
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    I guess it makes sense for the smaller exhaust valve. Of course the more air you cram through the intake, it is going to move quicker coming out of the exhaust. Would explain the flow characteristics if you have the exhaust port ported correctly. I would imagine that the spool of the turbo would be awesome because the air is trying to escape out of the exhaust port so quickly.
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  15. #15
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    Re: +2 -2 Head

    So i came across this post and wanted to bring it back from the dead. I have been doing alot of research lately on head porting and valve sizing. Ive purchased David Vizards porting book, watching his videos, and reading alot of info from Darin Morgan.

    My understanding is that you want 51% of bore size for intake and 40% for exhaust, that equates to 44mm and 35mm, so stock exhaust and oversized intake.

    The science behind it is port velocity, keeping the exhaust gasses flowing faster will help pull fresh air in as well as spool the turbo faster. It is said that an increase of 5-10 cfm on the intake will net a larger gain of hp than a 15-20 cfm increase on the exhaust side.


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    Re: +2 -2 Head

    Lots of good info here. Too bad 5Digits isn't here anymore to respond (RIP). I did some reading 20-30 years ago on David Vizard's theories and application about turbo camshaft timing events. IMO, it seemed like the one flaw to all of his logic was assuming the old 2:1 exhaust/boost ratio was a fixed ratio and couldn't be improved upon much. Twenty+ years ago a few smart TD enthusiasts found their engines performed way better at the track and the dyno with camshafts with tighter LSA's if they lowered that 2:1 ratio with more efficient manifolds and turbos with bigger turbines. Camshaft selection ended up not much different than N/A applications. So much for avoiding overlap and delaying intake opening with modified engines... The engines just had way more power with area under the curve with a tighter LSA than with a wide LSA. Today's turbochargers are a completely different animal than say 30-35 years ago when some of David Vizards articles were published.
    Todd
    Last edited by 4 l-bodies; 09-08-2021 at 10:55 PM.

  17. #17
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    Re: +2 -2 Head

    I havent touched on his camshaft theory, but to think the pressure differential is set is definitely a flaw. As you said more efficient turbos and more efficient headers can get the pressure differential down to 1:1 and sometimes even lower. I come from the LS world and most of the turbo cams look nothing like the ones for the Turbo Dodge motors. I have learned tho that overlap in any motor makes more power. People tend to think that because the boost is lower with more overlap that you wont make more power but they forget that boost numbers mean nothing other than how restrictive your intake tract is. If you havent looked into Darin Morgan look him up and read some of his stuff, he's a very smart dude as well..

  18. #18
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    Re: +2 -2 Head

    Wow, I had never seen this thread on here, even when I had previously picked Ken's brain about it.

    I read Gary's page on it way back. Probably around 2001 I had +4 intake valves put in a swirl head and left the stock exhaust valves. Was just something I wanted to try after reading about th +2/-2. I changed and messed up too many other things with the setup when I ran it.

    I'll look through my PM's and share what Ken said. I thought there was more difference to the chambers

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    Re: +2 -2 Head

    That would be phenomenal Dan. If you could post some of that info, I would really appreciate it. I think we all would.

  20. #20
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    Re: +2 -2 Head

    Quote Originally Posted by Dan H View Post
    Wow, I had never seen this thread on here, even when I had previously picked Ken's brain about it.

    I read Gary's page on it way back. Probably around 2001 I had +4 intake valves put in a swirl head and left the stock exhaust valves. Was just something I wanted to try after reading about th +2/-2. I changed and messed up too many other things with the setup when I ran it.

    I'll look through my PM's and share what Ken said. I thought there was more difference to the chambers
    So you never got to find out if the bigger intake valves worked better?


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