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Doing some stupid shit to an old datsun head

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    Originally posted by TK View Post
    Ok, just flowed the revised intake port & the 1/2 shafted TB's:

    Bare head:

    .1 - 57
    .2 - 115
    .3 - 150
    .4 - 181
    .5 - 214
    .55 - 224
    .6 - 234
    .65 - 236
    .7 - 238

    Above .700" it goes turbulent again, but not as bad, only backs up 5cfm or so - calling it good.

    1/2 shafted TB's have improved matters with the intake on - tops out at 227cfm now, which is enough.

    Out of interest I moved the head over on the bore adaptor to see what a larger bore would do - saw 245cfm @ .700" lift, with the chamber optimised for the larger bore I reckon we'd see closer to 250cfm - enough to make 290+hp.

    I can see a big bore short stroke short motor in the future........
    Love your work Tony, out of interest, do you have flow figures for a stocker l20?

    Comment


      Nope, never saw the need to flow one!

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        Originally posted by Guido View Post
        Please video it on the engine dyno.
        The amount of dort this engine will have can be measured in the tens of thousands.
        Originally posted by Dimi
        80mm of penetration isn't bad, i wish i had that much.
        Originally posted by schnitzelburger
        My entire working career pretty much consists of suckin dick and takin names.

        Sometimes im too busy to take names.

        Comment


          Going through the short motor while I'm waiting on cam & a few other bits.

          She had hurt a rod bearing when it came apart, so I went looking a little closer - turns out the rod big ends varied in size by .0003" & bearing clearances were .0015-.0018" - too tight, there's the problem.
          So I sized the rods within .0001" & opened them up .0004" so now we have .0022" clearance - that'll work better.

          Pistons were also sitting .018- .024" down from the deck face at TDC - not cool for a race engine, so I milled .020" off the block to get them as close a possible to zero deck.

          I'll get it all washed up & short motor together this arvo.

          Comment


            Any updates TK?

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              Is this for orange 1600?
              3D scanning
              3D modelling
              Structural certification
              3 and 5 axis milling

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                Owner lurks here, he can post if he wants it known whose engine it is!

                No real updates, waiting on valves & cam, short motor is all done, can't do a bunch more till I get cam etc.
                Been bustin my ass getting some RB, subi & 308 stuff out the door.

                Comment


                  Tony,

                  Great thread! I shared this on Larry Meaux's forum and he really loved it.

                  A few questions:

                  What are the valve sizes you have chosen? Seat angles?

                  In an application like this, with the poor SSR on the exhaust, do you like a very tuliped exhaust valve? I know you'll be using a nailhead type intake valve. I would imagine with an exhaust port like this, you would want to increase low-mid flow on the exhaust port to get it to blowdown ASAP.

                  Your MCSA, what rpm band did you size this for (I'm not sure what displacement you'll be using). Why did you place it where you did? With a stock type chamber, would you have moved placed it elsewhere in the port?

                  Thanks,
                  Bob

                  Comment


                    Valve sizing is 45mm & 38mm.
                    Valve job is 35 deg top cut (fairly small), 1mm 45 deg seat, 65 bottom cut, 75 throat cut.
                    Exhaust is 35 deg top cut, 45 deg seat, radius, 80 deg throat cut.
                    Throat cuts for both intake & exhaust are not left 'as cut' - the angle is changed by hand with the grinder depending on position around the bowl - on the short turn it's laid back, on the long turn it's left near 'as cut' on the bore centre side it's also almost as cut & on the bore wall side it's cut closer to 85 deg.
                    I've got tulip exhaust valves - I'd like a larger tulip, but with these things you take what you can get, choices are somewhat limited in 38mm Datsun exhaust valves!
                    I've sized for 8000-8300rpm peak.
                    MCSA is about 3/4" before the short turn, runners taper down to the MCSA - to achieve max velocity (for velocity ram) as close to the valve as possible without being so close as to choke the short turn & cause turbulence.
                    With a stock chamber I'd run the MCSA in the same spot, but I'd use a slightly different valve job (longer 65 deg cut) & slightly smaller throat.

                    Comment


                      Thanks, Tony.

                      Have you looked into getting custom valves made? I know in the states, custom Ferreas aren't really all that bad when you buy it from someone with a dealer account.

                      These are the valve profiles my porter (Nick Smithberg in the US) settled on for my head (2 valve, Hemi) after testing a bunch of different profiles:


                      They were right around $35 a piece. I haven't looked at the exchange rate recently to know how they are for you guys. The exhaust valve is 37.5mm (the intake is 48.25mm (1.900") for reference). My ports are shallow enough that he had to clearance the guides on the valve sides due to the tulips.

                      Have you ever tried offsetting the throat on the exhaust port away from the short side to help out with it? Do you think moving the MCSA back a little further would have helped a bit with the flow backing up?

                      Cheers,
                      Bob

                      Comment


                        I did move the MCSA back a little bit & it did help with the backing up!
                        I could get it flowing more at higher lift, but I'd be moving the MCSA further upstream than I'd like, that'd hurt fill ABDC, given unlimited time I may be able to find a better compromise, but I'm on a time frame here & time = $!
                        As it sits cross section is good, taper is good, stability is good enough & flow is good enough, that will have to do.

                        With a sharp sharp exhaust short turn I often find you need to get into the seat insert & lay it back quite a lot more, throat needs to be close to the seat through there - you don't want that gas coming past the valve as the valve cracks open on blowdown to shoot back into the middle of the throat & screw up the blowdown around the rest of the valve circumference. That's something that won't show on a flow bench, you cannot simulate the near sonic (some say supersonic) blowdown on a steady state bench, even testing at higher pressures won't show you anything much, you just have to picture it & think about it.
                        So yeah, you lay back the turn quite hard to allow the rest of the valve to work nice at blowdown, sure it hurts low lift flow at 28" testing pressure, but that don't apply!

                        With the turn laid back you can get a better transition into the port floor as well, less abrupt, that helps stability a lot.

                        Another little point with alcohol fuels & high comp ratios - you will have a much higher pressure differential at blowdown than with petrol type fuels, so that gas is leaving one way or another, best to just let it leave in an orderly manner - that means stability & cross section come before flow at 28", keep the flow smooth & give it room & it'll get gone.

                        I was going to get custom valves for this, but anyone here that can do it likes to take their time - last set I got for a datto took 3 months, this has to be on the dyno on Friday or Monday, race meet the weekend after next, we don't have the time luxury of getting in custom valves.

                        Same goes for cam, I'd like another 6-8deg duration & some more lift, but can't get it in this country, need to get a cam out of the US to get what I'd really like, as it sits the cam will have 2 of the largest lobe profiles available over here.

                        We'll see how we go, if this turns out good then I may well get the chance to do a big bore short stroke engine & have time to organise a more ideal cam.

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                          double post

                          Comment


                            Great info, Tony. Thank you!

                            Nick worked really hard on both of my ports to get them to be as rock steady as possible. Compared to what I've seen with other heads of the same make/model, I think the head will punch above others with similar flow volume for that very reason (velocity management is another).

                            I've seen more than a few top guys now say they don't pay much attention to cfm on the exhaust side. CSA, velocity, and port stability are the big players there. Darin Morgan was the first person I heard say that, but I've seen it also from guys like Curtis Boggs, another person a friend used that has worked with Darin, Nick, etc. The conversation gets even more interesting when you start talking to guys like Calvin Elston (http://www.elstonheaders.com/). He's posted some fantastic stuff and I haven't had a phone conversation with him that was less than 40 minutes. He started a blog here: http://www.exhausting101.com/

                            Looking at pictures of other Datsun heads, I always felt the exhaust ports were too big on those heads. Of course, I've never seen measurements or flowed any to know.

                            That said, it's fantastic to see this kind of data, level of work performed on an oddball head. You can find posts like this by guys like Larry Meaux, Darin Morgan, and Chad Speier on the V8 stuff, but nothing of this sort for the oddball stuff. My bet is most that work on this type of stuff would look at you weird if you asked what they sized the MCSA to.

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                              Just out of interest I pulled up the flow sheet on Robs beamer M20 (IP engine I helped with last year), we made around 390hp from 2.8L (6 banger) from that thing - around 140hp/l.
                              This Datsun head flows a good 10cfm clear of that one at .600" lift & has a bit more MCSA, Datsun exhaust is 8cfm short.
                              From memory I cammed that one with minimal forward split & tight lobe centres (105), duration was late 260's/early 270's & lift was around .600"
                              So we're in the ballpark, datto cam is early 260's, just short of .600" lift & 105 centres.

                              Knocking 2 cyl off the BMW engine we'd be at 260hp & 1.86L, datto has another .14L to help matters, a little more forward split & larger exhaust valve (same size intake I think).
                              The datto is disadvantaged in being an inline while the BMW is sorta hemi - all in all they are pretty close in spec.

                              Comment


                                Originally posted by TK View Post
                                Just out of interest I pulled up the flow sheet on Robs beamer M20 (IP engine I helped with last year), we made around 390hp from 2.8L (6 banger) from that thing - around 140hp/l.
                                This Datsun head flows a good 10cfm clear of that one at .600" lift & has a bit more MCSA, Datsun exhaust is 8cfm short.
                                From memory I cammed that one with minimal forward split & tight lobe centres (105), duration was late 260's/early 270's & lift was around .600"
                                So we're in the ballpark, datto cam is early 260's, just short of .600" lift & 105 centres.

                                Knocking 2 cyl off the BMW engine we'd be at 260hp & 1.86L, datto has another .14L to help matters, a little more forward split & larger exhaust valve (same size intake I think).
                                The datto is disadvantaged in being an inline while the BMW is sorta hemi - all in all they are pretty close in spec.
                                The cam looks similar to what I've seen on other engines of similar power potential and limitations (duration vs. flow / displacement / rpm range).

                                My guess in an ideal scenario, you would want about 8-12* more exhaust duration? I would imagine you would want a bit of overlap (vs a more efficient head) to aid in getting that exhaust port moving, hence the tighter lobe center.

                                What do you guys use for headers? I feel like this is the kind of package that would really benefit from a really well designed and constructed exhaust.

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