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Rb26 Head Flow Figures

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    #1

    Rb26 Head Flow Figures

    Hi everyone.

    Well recently i had an rb26 cylinder head flowed to see what it flowed intake verse exhaust. To say i was supprised how poorly the exhaust flowed compared to the intake would be an understatment.



    Now the specs on the head in question are as follows, and theres a few pics of the ports/chambers too:

    Tomei Cams - 270deg 10.8mm inlet 280deg 10.8mm exhaust
    Tomei cam gears
    Tomei cam cap studs
    Supertech manganese guides
    Supertech Valves - 1mm in 1mm ex
    Supertech dual springs and titanium retainers
    JHH labour - port & polish, clean & assemble
    JHH custom shims (for smaller base circle cams)
    JHH custom inner spring seat



    The entire head work was performed by John Hill Engineering in brisbane.

    The point of this thread is to have a discussion on what these figures mean in terms of i spose power delivery & boost response etc, to discuss how the head could be optimised to get more even flow between the 2 sides by either more/different port work, different valve combo etc, and how different cam profiles will affect the real life power delivery and boost response.

    Also for those of you who have done some back to back flow testing with different head specs, if you could shed some light of your finidings that would be fantastic.

    Shane
    Tags: None
    #2
    Yes, well, exhausts flowing 65% of intakes is a bit low. Looks like they could do with some rework. Someone like TK here would probably be able to make some changes to the seats and bowls to get the exhausts up a few more %.
    Originally posted by bugle
    The non GTS's were gay

    Comment

      #3
      Yeh its a 6.1k head so i was expecting it to be near perfect. Now im a bit concerned its not going to be optimum for the setup.

      The bottom end is being screwed together now so time left isnt all that great, but i'll wait to see what TK has to say and if/what services he can offer.

      Bottom line is we want this motor to make as close to 750bhp as possible on pump fuel

      Comment

        #4
        I know you can get 300cfm out the intakes & over 200cfm out the exhausts with 1mm oversize valves.
        The way the intake flow rises quite well through the mid lift tends to indicate that the intake seats are ok - I suspect they are not quite wide enough through the short turns & that perhaps the intake runners should be raised in the roof more.

        The poor (ish) exhaust flow is more than likely due to the ex short turns not being cut back enough - not many shops have done enough work on multi-valve heads to know how to do ex short turns, a relatively small amount of metal taken off the right spot can make a big difference to flow.

        6.1k - fully assembled, with cams, springs, 1mm os valves etc - or just headwork?

        Comment

          #5
          6.1k fully assembled ready to bolt on

          Are you able to give a ballpark as to what it'd cost for you to 'fix it up'?

          Comment

            #6
            I'd have to have a look - & you'd have to be in no hurry!, I couldn't do anything before Feb next year....

            You can make the power with it as is no probs - it may just not be quite as quick on the spool as it could be & may take a little more boost to get there.

            I gotta do an RB25 head in the next week or 2 for an RB25/30 - I'll post some figure on that when it's done.

            Comment

              #7
              Have you questioned the results with JHH?

              JHH are considered to be one of the best in qld for multivalve heads fwiw.
              (for the benefit of others, shanef obviosly knows this).

              When I last spoke with them I got the impression that JH was no longer running the show though. Could be a case of less porting, more polishing.
              David Fraser - Automotive Historian!

              Originally posted by bigmuz
              You can't polish a turd but you can put 600hp in it and laugh your fucking arse off coming past someone sideways at Powercruise.

              Comment

                #8
                Originally posted by JZK25 View Post
                Have you questioned the results with JHH?

                JHH are considered to be one of the best in qld for multivalve heads fwiw.
                (for the benefit of others, shanef obviosly knows this).

                .....................................
                Yeh I'm not sure why they have such a reputation though, I'm not going to knock them but would suggest a talk with Alex Cowie 3208 5539 may be useful.
                Richard's DatsunZ lappin LakesidZ http://www.youtube.com/watch?v=47OSh...&feature=g-upl

                “Freedom of speech does not protect you from the consequences of saying stupid shit.”
                ― Jim C. Hines

                “Everyone is entitled to his own opinion, but not to his own facts.”
                ― Daniel Patrick Moynihan

                “Four hostile newspapers are more to be feared than a thousand bayonets..”
                ― Napoleon Bonaparte

                Comment

                  #9
                  Originally posted by TK View Post
                  I'd have to have a look - & you'd have to be in no hurry!, I couldn't do anything before Feb next year....

                  You can make the power with it as is no probs - it may just not be quite as quick on the spool as it could be & may take a little more boost to get there.

                  I gotta do an RB25 head in the next week or 2 for an RB25/30 - I'll post some figure on that when it's done.
                  next feb would be too late unfortunately.

                  the extra spool would be nice but i guess i'll keep all of this in mind come next time.

                  thatd be good to make a comparison against

                  Originally posted by JZK25 View Post
                  Have you questioned the results with JHH?

                  JHH are considered to be one of the best in qld for multivalve heads fwiw.
                  (for the benefit of others, shanef obviosly knows this).

                  When I last spoke with them I got the impression that JH was no longer running the show though. Could be a case of less porting, more polishing.
                  i havnt yet, i do know jhh dont believe in using a flow bench, so i'll see how i go.

                  they certainly have done some heads for some cars that have made quite remarkable power and response, i've also had 2nd hand experience with their rb prepared heads that have done very well.

                  will runs the show there now as john is semi retired

                  Originally posted by 260DET View Post
                  Yeh I'm not sure why they have such a reputation though, I'm not going to knock them but would suggest a talk with Alex Cowie 3208 5539 may be useful.
                  what's his background/wheres he work?

                  Comment

                    #10
                    AC is at Slacks Creek, all he does is head jobs, errr, head work.
                    Richard's DatsunZ lappin LakesidZ http://www.youtube.com/watch?v=47OSh...&feature=g-upl

                    “Freedom of speech does not protect you from the consequences of saying stupid shit.”
                    ― Jim C. Hines

                    “Everyone is entitled to his own opinion, but not to his own facts.”
                    ― Daniel Patrick Moynihan

                    “Four hostile newspapers are more to be feared than a thousand bayonets..”
                    ― Napoleon Bonaparte

                    Comment

                      #11
                      rob's head was meant to be one of the best in the country, flowed around 210 and 300 respectively.

                      was for sale for 8k, full jun top end included.

                      Comment

                        #12
                        Tony, i have been susing prices for my 26 head

                        i can get ferra 1mm over for 1140 from AUS and 300 for some valve springs

                        or i can go supertech 1mm over, titanium retainers, dual valve springs, guides etc from usa at current exchange rate for 2000

                        Or i keep std valves and u port the fuck out of it, what should i do?

                        Also February is good time for me maby even bit later then that.
                        3D scanning
                        3D modelling
                        Structural certification
                        3 and 5 axis milling

                        Comment

                          #13
                          Supertech are good - I've been using em in some WR heads lately with good results.

                          If you've got the coin then go for the supertech valves, dual springs & tit retainers - don't worry about the guides tho.

                          Feb should be ok.

                          Comment

                            #14
                            LOL, no time now, but I'll be back later tonight - got flow figures on the RB25 head with stock valves I just did.
                            Damn near matches the above RB26 with 1mm os valves.....

                            Comment

                              #15
                              I was at my engine tuners yesterday and he had a RB26head/rb30 block on the dyno andhe was saying the same the RB25 head is a better thing. It still made 720hp/650ft/lb though . should go okay in a streeter
                              SA IPRA cars 15, 51, 77 and 25
                              (Sharperto Racing)

                              http://www.iprasa.mx.com.au/

                              Comment

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