Here is another option not as oldskool but still sort of period and cheaper than buying/rebuilding a 2 inch SU these days.

Attach file:

---

  z+maxflow_twinstack+velocity_stack.jpg (74.47 KB)

Ill start by saying Lemonhead never stated why he is no longer completing the big block 82mm bore setup he had made - The valve and port sizes I believe are big enough compared to other 1800cc 8v engines like a J18 Mg 1.8L or even some Honda 8v engine from older accords etc. However it must be about chamber mis-alignment for 1 and 4 are offset quite a bit.

The reason for slightly better rod stroke ratio was to reduce a tad the force on the sleeves, I was only chasing a few points higher and thought it wouldnt be that significant an increase to cause major issues with valves especially with macthing flycuts on the pistons to help with clearance.

The SU is only temporary there is a way to go from 50.1mm to 56mm with this unit but I remember something along the lines of 48-50mm will allow enough to flow up to 180-200hp yet I only expect to make 60% of that. I really wanted to take steps by running it in and going in stages but more importantly getting started on the most important part the block.

edit: mazda head conversion is better than any oval port head mods so no longer worried about modding an A head.

Let me be clearer here David - even if you aren't looking for hp records, I'm trying to tell you you need to do a #OOPS#load to an a series head to support that sort of capacity. Contrast that with, for example, the sr20ve head. Decent porters have gotten them to flow enough to support close to 300bhp (to be honest I don't have the current state of this, that's a few years ago now!) without the sort of 'commando' porting that might be necessary on others. Those heads will support massive flow and supply a 2 litre engine very well, and over a broad rpm range.

With respect to the head you are talking about for the future, if you are getting major welding done, if they don't take out all the guides and seats and studs first, you may as well not bother. With significant welding like this, EVERYTHING moves around, and having anything 'stuck' in there will affect it. You'll need to weld it, heat treat it (maybe) and straighten if necessary, then re-machine practically everything. If they are asking less than around 3-4 grand for the whole job, I can't see how the hell they are going to do it. And keep in mind, if you wanted torque, a supercharged a14 (or 15) will poo on it from a great height, for about 1/5th the overall cost.

Another thing I'd bring up, which I was going to with the previous post, but honestly just forgot. And ironically you have mentioned it again. You seem (and I mean this a bit tongue in cheek, don't take this one to heart) a bit obsessed with rod: stroke ratio. GRanted, if it is really 'bad' in an engine - perhaps 1.4ish or less, then the side thrust and friction is a bad thing. BUT there's a situation called the case of diminishing returns, where if some does X% improvement, then double that feature might only do 1.25 as much improvement, instead of twice the improvement, and you can eventually get to the point where it COSTS power.

You see the issue is two fold. The longer the rod, the longer (in crank degrees) the piston will dwell around TDC. This slower 'turnaround' can help save breaking a piston or a rod at high rpm. BUT if the engine doesn't have a problem throwing rods or otherwise letting go at big rpms, then this is not a good thing. But the other thing is that the quicker the piston moves away from TDC, at more modest rpm ranges (the precise range you are aiming for with the desire for big torque figures) then the quicker and stronger the pressure drop and signal or 'pull' on the intake port. ANd basically at lower rpms it gets teh intake flowing quicker, which leads to more mid range torque. In engines built to make power at more modest rpms (and if you look at the enginemasters challenges that were done a few years ago, maybe still going, they change the capacity etc each year to try and get new combos entered but the general 'winner' is the motor with the most average power from 2500-6500rpm, rather than any peak power figure. Now whilst you might find 1.75:1 or longer rod ratios for higher revving circuit racers, engines built for this situation often had ratios 1.6:1 or lower, and performed better for it).

If that wasn't a good enough reason, antother point is relatively long stroke engines (and even the stock stroke a15 qualifies for this imo) tend to want slightly closer lobe separation angles. This closes the exhaust valve a little later, and opens the intake valve a little sooner. Now the problem here is that if the piston is hanging around a lot longer at TDC, you can't close the exhaust valve as late, as it will still be hanging open and the piston will hit it on the upstroke, and the piston will still be there, so you can't open the intake valve as early as ideal, or it will hit the piston too. Now you are stuck with a wider lobe separation (potentially speaking) for any given duration and it will work less effectively for a big a-series in general, and if anything, it will kill off some mid range torque, and give a small gain (but not as much as it loses down in the mid range) up top. Which is close to the exact opposite of the stated goal.

Another issue I'd mention is carb size. In the past you've often (that I can recall, I don't stalk you so I don't read every post!) suggested a 1 3/4" SU as being adequate for a drawthrough, but here you are considering a >2" SU for an NA engine. Here's teh thing, yes the turbo can force feed air/fuel into the engine well above it's ability to draw it in normally aspirated. BUT in a drawthrough, even though the turbo compressor wheel can create a massive pressure drop behind the carby, it is still up to atmospheric pressure to push the air in through the carb. So in a drawthrough, much like an NA engine, you'll actually find that the size of carb that can supply X bhp for an NA engine of some type is about the size you want to attain X bhp for a drawthrough turbo. SO if an NA 1800cc engine will 'like' a big SU, it should become fairly obvious that even a modest boost drawthrough a15 will too. Since that turbo can produce a larger and constant pressure drop behind the carb, it WILL still make good power with a 1 3/4 SU, so for a streeter it's not a huge concern really, but for something more serious it's fairly easy to make a good case for either a 2inch SU or perhaps twin 1 3/4" SUs for a drawthrough. Knowing from experience (and I bashed my head against brick walls for a long time with this sort of stuff back in the late 80s and early 90s when it was impossible to get any exhaust shop to put a 3 inch exhaust on a turbo 6 for example) anyhoo, it became clear that for around 200bhp twin 1 3/4" SUs on a drawthrough wasn't a bad option. You'd 'get' it with a single, but there'd be so much more back pressure as the turbo has to work that much harder to manage to get sufficient air in through that carb to produce the same boost levels (and create more heat in the process, putting one closer to detonation)

Seriously there's almost nothing in engine building where 'if some is good, more is better'. It's almost always a case of 'what's the best set of compromises that gives the best overall result' Certainly there is out of the box thinking, but there's still this catch called 'the laws of physics' Certainly, it's still down to massive trial and error but there's going to be general trends in what works and what doesn't and the underlying reasons why.

If you are wondering where I'm going with all this - here it is: If you want big torque, and decent hp (you may not want 'record' hp levels, but you will definitely be able to outpower ANY NA a-series, on pump fuel, and that's just a fact) - well the truth is NOTHING works like forced induction. You can pick up a supercharger or turbo for pocket money, a big enough SU, an oval port head, a mild cam and std (albeit freshened up) bottom end, and maybe water injection. You'll snot any NA a series, and do it with rpm levels that will mean it will last as long as a stock a15 will.

I strongly urge you to consider it David, it'll cost you way less, last way longer, and if it eventually did wear out or break, you aren't 'destroying' a head worth more than 90% of the complete cars on the road of this type.

Cuz thats right on! Rarer than the endangered Kakapo
and wild Kea tinkering out of the box thinking!

This one D?

Attach file:

---

  downport 1.JPG (36.88 KB)

This is an idea for the head Ive posted before, I cant find the pics of the kiwi one but it looked very promising also.

Attach file:

---

  A serious head kamikaze.jpg (51.78 KB)


  A series high flow head.jpg (195.00 KB)

There is some confusion in that Im not wanting to break any records in hp, Im sure the big A series has been done and not informed on this forum where opinions fly before asking questions or often disrespecting others undisclosed intentions. I did mention earlier between all the dramas that the stockish head is just until the extreme one is finished (extreme for me much like the New Zealand one that was disclosed recently) as with all things Datsun or DIY builds if you dont learn to do the work yourself then you are on the waiting list or the mercy of others. Im still not sure the head will be after all the welding usable or able to be straightened enough, Im hoping the welding is done right rather than been rushed. Welding up/redrilling and tapping for new guides to suit bigger valves than usual 44mm in/ 35mm ex is a big task and hopefully the 83mm bores help. My modded head is a side job as the the big rigs and boat engine have priority.

Ive accepted that the A series looks best in a small 1000 and would like to get started on something thats been daunting and with a few big sighs on first attempts. The fall back and maybe not a good one as Im unsure whether it will leak like crazy but is fascinating is the recent Mazda B head conversion but would prefer pushrods here rather than a low torque Mazda head that would be happier with revvs.

Im after plenty of useable torque rather than hp and the rod stroke ratio should help the valve sizes as well by been around the 1.6 or below that for increased air speed at lower rpm and hopefully high compression enough to be useful up to 7000rpm. More of an A series compact grunter with just enough revvs to be fun with a 3.5 or 3.7 final ratio.

for whatever it's worth, and I make this comment within the specific context of the fact that I consider David a friend, having spent a bit of time with him over the years in person, since he lives not too far from me, and I've had arguments on here with Harry (but I'll note I still respect his knowledge and opinions) - in all fairness I think you are over-reacting to Harry's posts. None of us is Shakespeare, and in all sincerity, David, you do come up with a lot of ideas, some of them are more 'doable' or ideal in the real world, others are not so much. That doesn't mean you are an idiot or anything like that, but someimes if we don't bring forward legitimate concerns or forseeable problems, it could end up costing the original poster (or anyone else reading it and considering the same) time and money for a less than ideal result.

Once you start stretching the capacity of the A-series (and within the context of this discussion) to well beyond 1600cc, the biggest hurdle, almost to the complete exclusion of all other concerns, is how much even a very well ported head will be able to support the necessary intake and exhaust flow to keep that engine happy, even at more modest street rpms.

As an example, though the info is certainly well more than 10 years old, NASCAR were running 'basically' the same rules on their superspeedways, save for the fact that the engines had to run a restrictor plate under the carb (I forget if the carb size itself was different too, but that's somewhat irrelevant if the restrictor plate was fitted, and it cuts a hell of a lot of power). It got to the stage that the engines were just starving for air at higher and higher sustained rpms, and they weren't making good volumetric efficiency and the actual 'running' compression ratio was much lower too. And what a few engine builders played with was the fact that engine size was limited, but there was no set minimum. So instead of running the 355ci engines (I think 355 was the limit) they were running shorter stroke engines of maybe 300-330 ci, and due to them being able to get a full cylinder of air/fuel at higher rpm (compared with the larger engine) they actually made more power, and used less fuel to make the same power. It basically made them quicker and also able to go a few more laps (for any given similar run, of course they all still draft other car's slipstreams etc) and it was a winning move. And not too long after that, Nascar then mandated not only a max capacity but also a minimum capacity.

What you are doing with this proposed combination, in a sense, is running a restrictor plate engine (by virtue of a stock head, and remember that even in ported form it'll struggle to feed a decent a15 as well as we'd like, let alone a much bigger one). Ah, but you won't be spinning it as high. That necessarily limits cam duration, which then gives the motor less time to get air in and out for every revolution, but at the same time, as you reduce the duration, due to max safe opening and closing rates of the cams (mostly dictated by lifter footprint size and cam base circle diameter, which aren't too easy to change!) then you are limited much more in terms of lift, not just peak lift, but how long it'll stay at any point beyond mid range lifts (relative term of course). So in practice, there's a hell of a lot of stuff 'choking' the life out of a big engine capacity through an A series head, and even more so an unported one. Ask any historic touring car racer, and as far as engines themselves go (in determining overall performance) 'it's all in the head' so to speak.

I assure you David, and I say this as respectfully as possible without this forum becoming a hug fest, if you put together such a combination, if you added up the costs of going to such large capacity, but stuck with a stock head, a similar amount of money, but priority given to headwork (and you can get gains out of em without needing a full race spec cam mind you, there's lots of room for improvement in the valve guide/bowl/valve seat area before you have to start getting exotic). Anyhoo, that same budget (or even a more modest one) prioritised for the head (and careful cam selection) will in fact get you a much better result.

If you were instead talking of something like an L series, you'd still do head work of course, but it's more than possible to get a very wide powerband and decent top end, basically the whole nine yards, and running a stroked crank combo up to 2.3litres or so. But that is because the heads, esp with some work, are capable of actually feeding a >2 litre engine.

Very generally, esp for a streeter, more capacity pays off, but you have to ensure that the head is actually capable of catering to its needs.

On the carb issue, the wider powerband and better throttle response, i.e. a more flexible all round engine will come from 1 carb throat per intake port, and would be the way I'd lean towards. It would have to be a case of finding the right sized carb (or in the case of dcoe webers or similar, the right choke size) so that it meets it's peak flow demands, but not much more, as any further beyond that and you lose signal strength and velocity, and the mid range becomes less and less crisp, and the overall performance on road is hit hard.

If there happened to be a decent intake manifold (and arguably there are some for mini a series engines, but none that I know of for the datsun a series engine) a largish single SU type carb can produce the goods. But there isn't, so you'd have to make a custom one, and good luck getting it right.

I mentioned in the past the idea of a 4 runner curved intake (inspired by but not 100% identical to toyota k series intakes) and a holley 2 barrel. I'll stand by that option over any modded stock downdraught carb intake manifold that has a single front and rear runner and only branches out right before the ports in a Y shape . I'm not suggesting it'll outgun a twin weber intake, but if done right it'll be about the best you could do as far as a single (but 2 barreled or more) central downdraught carb would. I'd put that above a custom single SU intake, but that's just me. If I find time this summer, I'll do my best to make one (using bits from : http://www.sonicperformance.com.au/Al ... minium-Half-Donuts/pl.php ) but it's just as likely I'll end up working through!

TO try and put it in simple terms, the idea of a really big motor with a std head, it's a bit like cloning Pharlap (or Seabiscuit for folks in the US) then cutting off one of its legs and being surprised that it doesn't win any races. These aren't personal attacks on you David, it's more a case of pointing out the issues. I can't claim to have done it to datto a series engines, but I've done a fair bit on 'stretched' engines with limited flowing heads (even with porting) and it cost me a fortune to find out that either the whole combo can work with one another optimally, or it won't run half as well as a non stretched engine with money/time focussed on what will really deliver the results.

Chris, i was trying to start my build diary again but again you have to have your high pony chimp squeal.

You have polluted mine and other peoples diary and for sale threads for so long with your primitive minded opinions that its time you change your repulsive disrespect.

Dave, has it ever struck you that your attitude may be the cause of such animosity!

You have an ego problem that has warped and grossly amplified your sense of self worth.

What has been the progress on this build in four pages apart from being an entertaining read for all the wrong reasons!