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  • Discussion: Oversized Valves

    As this sounds like a wish list, start with the basic engine and build on it. If you really plan to get to 600HP, I would put in the Z32 crank, rods and forged pistons. Spend some money on the heads, send them across country if you need to, in order to find someone that can effectively port them. You are limited on valve size, 1mm over on intake and 2mm on exhaust is what you can get. Good heads will allow you to get where your going with a smaller turbo. You will need to fabricate a better turbo location. Much like Hybird88's, look on Jason's site, many choices. The turbo you need will probably not fit in the stock location.

    Getting to here will take a lot of money and even more time. It can be very frustrating waiting to get things done even though you have the cash and the desire. You don't need to buy all the other crap right away. High HP and quick spool are not likely. Your power band will shrink and go to higher rev's. Again to help with this, you need very good heads and more displacement (VG 33).

    Build it for endurance. If you check, most of the folks with high HP (400+)are always breaking something. Half shafts seem to go first. Once you get to 600+ HP you will find all the weak points on this engine. Especially if you run it hard. While you waiting for someone to take your money, you will have plenty of time to research.

  • #2
    JK wrote:
    What kind of HP do you make with your T70, and your TO4R?

    Why do you believe that oversize valves are a waste of money?
    440whp/495ft-lbs with the T04R on a stock motor and modest Fuel System
    The Setup that I was building with the T70 I ended up ditching in favor of a motor built around a 102mm GT42 (what im doing now)

    Oversized valves are a waste on all but the most extreme setups because the amount of airflow gained is insignificant and the money spent on machining to make them work to thier full potential can be spent better elsewhere in the Cylinder Heads.
    2005 whore magnet

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    • #3
      [quote]SteveZ31 wrote:
      Originally posted by JK
      What kind of HP do you make with your T70, and your TO4R?

      Why do you believe that oversize valves are a waste of money?
      440whp/495ft-lbs with the T04R on a stock motor and modest Fuel System
      The Setup that I was building with the T70 I ended up ditching in favor of a motor built around a 102mm GT42 (what im doing now)

      Oversized valves are a waste on all but the most extreme setups because the amount of airflow gained is insignificant and the money spent on machining to make them work to thier full potential can be spent better elsewhere in the Cylinder Heads.
      Well 440 HP is nothing to sneeze at, but its 160 HP away from this guys goal. That's a bit of a jump. 500rwhp is the most I have seen from the stock turbo location. But I haven't seen it all. On purpose built cars, turbo's seem to require tweeking a bit. The fabrication necessary to facilitate a more friendly location, for me, would be time well spent.

      The Nissan valves are two piece spun weld steel. While They are ok for mild HP, I think an upgrade is required especially for a 600HP endeavor. As any misstep in timing or fuel will fry these valves at these cylinder pressures. Stock or oversize, price is about the same. 1mm over same valve seat. Just a different cut. On Blown VG heads or NA, once the valves close, only cylinder pressure expells the gases. The exhaust port is woefully inadequate. Go back and read what Jason found out about these heads.

      It has always been of interest to me that the rest of the automotive world refers to the heads as the heart of the engine. For example, check out the number of high performance heads available for small block Ford's and Chevy's. My assumption is that this goes to the importance of good heads. Yet the collective conventional wisdom for Z31's puts the emphasis on the turbo. A back yard 'do it yourself' porting job is deemed sufficient. So I can understand why you would feel that oversize valves are a waste of money. 6 valves seats on the exhaust, maybe $200. Seems cheap to me. Also, the biggest restriction of airflow in the heads are the valves. So where can you spend your money better to affect airflow? A better head porting job? Whats the first thing a good head porter looks at?
      Attached Files

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      • #4
        JK wrote: well 440 HP is nothing to sneeze at, but its 160 HP away from this guys goal. That's a bit of a jump. 500rwhp is the most I have seen from the stock turbo location. But I haven't seen it all. On purpose built cars, turbo's seem to require tweeking a bit. The fabrication necessary to facilitate a more friendly location, for me, would be time well spent.
        Yea I made 440 but the T04R can easily support over 600 I just didnt have the Fuel or the motor to support that at the time.


        JK wrote: he Nissan valves are two piece spun weld steel. While They are ok for mild HP, I think an upgrade is required especially for a 600HP endeavor. As any misstep in timing or fuel will fry these valves at these cylinder pressures. Stock or oversize, price is about the same. 1mm over same valve seat. Just a different cut. On Blown VG heads or NA, once the valves close, only cylinder pressure expells the gases. The exhaust port is woefully inadequate. Go back and read what Jason found out about these heads.
        Ive probably ported and polished 10 sets of SOHC VG heads, I know exactly how inadequate the Exhaust ports are. Im all for a set of Ferrea(or the like) SS replacements for added durability

        JK wrote:
        It has always been of interest to me that the rest of the automotive world refers to the heads as the heart of the engine. For example, check out the number of high performance heads available for small block Ford's and Chevy's. My assumption is that this goes to the importance of good heads. Yet the collective conventional wisdom for Z31's puts the emphasis on the turbo. A back yard 'do it yourself' porting job is deemed sufficient. So I can understand why you would feel that oversize valves are a waste of money. 6 valves seats on the exhaust, maybe $200. Seems cheap to me. Also, the biggest restriction of airflow in the heads are the valves. So where can you spend your money better to affect airflow? A better head porting job? Whats the first thing a good head porter looks at?
        I definitly agree that the heads are really the heart of the Engine. Alot of power can be gained (or bottled up) in the Cylinder heads. In my opinion the best money spent for Cylinder Head modification is for a good Valve Seat Grind. Like I said before Oversized Valves are a good choice for the most extreme setups but there far from required to make some serious power. I have put around 40hours into my Cylinder heads and probably have another 5-10 to go and I am using Ferrea OEM spec valves. I will let you know how that works out.
        2005 whore magnet

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        • #5
          Cylinder heads must be able to make a huge difference.

          In the engine shop that I worked at, the stock car guys couldn't touch the heads that were required in there class. I am pretty sure this is because you can gain alot of HP with some good porting....


          Can't you buy those heads they used on the electromotive car? Like 2 grand or something....

          Terrible idea putting those wheels on...

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          • #6
            MrwassmanNA2T wrote: Cylinder heads must be able to make a huge difference.

            In the engine shop that I worked at, the stock car guys couldn't touch the heads that were required in there class. I am pretty sure this is because you can gain alot of HP with some good porting....


            Can't you buy those heads they used on the electromotive car? Like 2 grand or something....
            He bro, Yeah those are the magical Nismo Heads that everyone talks about but that I've never actually seen. They probably cost even more then two grand and they'd surely require tons of machining work but could proabbly support 1200+HP on a vg. The Nissan race car was claimed to use *Stock* heads though.

            The power band is so crappy(for my tastes) when you get to 800+ HP on a boosted engine like the Zjz, RB or VG that I'd say funk it and spend the insane money on a different engine like a sleeved and bored VQ. Not to mention the clutch setup required to hold 800HP reliably is a headache on anything other then the race track but all the crazy kids here like to drive their 1000HP Supras with race gas on the street and smoke 600cc crouch rockets..lmfao but it's true.

            So, 600+ hp would be a really fun and doable project with wise investment of time and money as mentioned above.

            IMVHO going with 1mm Oversized Ferrea vales is a wise investment for the entire engine in the long run. The valves in themself will reduce heat substantially and theirfor decrease engine wear and time between rebuilds. Yeah the Nissan valves are very kick ass but they just don't comapre to the Ferrea's(they're laughing all the way to the bank aren't they).

            We all have to keep in mind that running boost is compensating for a smaller engine and running 28psi on a perfectly built VG is still goint to wear the engine out faster then a V10 with the same power from compression and displacement. I hate replacing bearings...arrrr time for cryo.

            Great thread.

            Peace
            Ucked Fup!!!

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            • #7
              Everyone does know that SI valves have oversize valves cheaper than stock right?

              They are only .5mm oversize. But at only $12 a piece i don't see why everyone doesn't have them fluttering in their heads.
              KILL HADJI

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              • #8
                Alex86na2t wrote: Everyone does know that SI valves have oversize valves cheaper than stock right?

                They are only .5mm oversize. But at only $12 a piece i don't see why everyone doesn't have them fluttering in their heads.
                i don't think that SI valves are stainless , which IMO ss ferrea valves would yield a better upgrade than .5mm oversize valves.. even if they are alot more money.

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                • #9
                  Their racing valves are all 304 stainless. Their street valves are carbon steel for intake, and a low grade stainless for exhaust.
                  KILL HADJI

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                  • #10
                    Alex86na2t wrote: Everyone does know that SI valves have oversize valves cheaper than stock right?

                    They are only .5mm oversize. But at only $12 a piece i don't see why everyone doesn't have them fluttering in their heads.
                    SI? Am I just being lame right now?
                    http://z31performance.com/forum/viewtopic.php?f=5&t=147

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                    • #11
                      Alex86na2t wrote: Their racing valves are all 304 stainless. Their street valves are carbon steel for intake, and a low grade stainless for exhaust.
                      i couldn't find any of the racing valves for the vg on their site . and im thinking maybe ss valves can withstand heat better? if so then doing modifications to the head like cutting guide bosses off (some people argue that its needed for heat dissipation)would yield very good gains for flow.

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                      • #12
                        2+2turbo wrote: i couldn't find any of the racing valves for the vg on their site . and im thinking maybe ss valves can withstand heat better?
                        You have to call about them. But really if you are trying to get performance then why would you even bother with their shitty street valves. With that aside i don't see how one valve could dissipate heat better than the other if they are both made of the same SS. Really the only way to find out which is better is to put them both on a flowbench for flow comparisons. I would be suprised if the stock diameter valves won on that one though. It would mean some premium products.
                        KILL HADJI

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                        • #13
                          What about using the Z32 crank in order to use a Z32 flywheel. This would open up the door to some bitchin possibilities. Triple disc carbon clutch anyone??
                          ""You gota watch out in this weather. Its when them white boys with their turbos come out to play" Mr. Rimpson - UTI Instructor, refering to a slightly damp 50 degree day.

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                          • #14
                            you guys check these out?

                            http://www.revvalves.com/home.php?cat=135
                            Gone - 1988 Shiro
                            2004 BMW 330Ci
                            2005 BMW 330i
                            1991 Twin Turbo Z's (Red and Black)
                            http://www.E46Turbo330Ci.com

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                            • #15
                              these for our motors or the dohc ??
                              http://www.revvalves.com/home.php?cat=197
                              i cant seem to figure it out , also do any of you guys find an address of where they are located?

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