Is that an IDA manifold? Not a DCOE manifold?

I'll keep an eye out for the LZ head D, never really watch that stuff until now.

Doh! DCOE is side-draft, and this manifold definitely isnt:

Yeah see if you can get a bundle or halve a dozen of them Lz heads. Ill just take one you can have the others
Being asking an american engine designer if he can supply a rotary valve design for the a-series but his involved in supplying one for the popular k-series engine in the UK, this rotary valve head is used on some small capacity jap bikes, rc cars and go carts and can get 270% more air capacity than a formula one engine. Back to reality those manifolds would be a nice addition with some kind of filters like downdraft racing beat ones sticking out of the bonnet and protected from rain.

The reason I asked about single vrs. dual DCOE's is that,in left hand drive datsuns,there is a problem with the duals and the brake booster,so unless you want to go through the whole workout of leaning your engine and then have to work out the consequences of this leaning on the springs and the rest of the suspension, a single might be a alternative to buying a dual set up and keep it in a box forever.(right hand drive cars do not have this prerogative) I personally would prefer duals,but unless you are going to floor the pedal full throtle,somebody driving in a city,street fast,might not enjoy the full benefit of a dual set up,in that case,a single will give you more torque,quicker takeoffs,higher rpm(faster),while the duals enter into the picture at higher RPM,so,2 are more complete,but a single is fine too.One is better than using the stock carbie.
Jaime

In a rotary engine the long manifold 45mm sidedraft weber setup shines in overall performance for racing giving better torque to the low torque characteristics of the rotaries. But they are like comparing oranges to apples with piston engines. However the same goes for long manifold 6 cylinder engines such as jags and fords almost 1 metre runners! in their optimal torque prototypes.
The only thing I know is that the longer the intake manifold the better the torque. Eg e15 has a very long manifold and those engines produce much better torque down low (beautiful drivability) than an a15 they also rev better even though they have a more restricted exhaust but I guess you cant beat OHC for ease of revving. In most cases the overall thing is that a single big carb manifold as for the a-series lynx Ive seen they usually have a more complex tunnel passage which could create more torque than short runners by letting the mixture travel and mix more thoroughly making a slight ram effect. Also met some rally guys who preferred the single for better torque delivery due to the length of the tunnel runners in those manifold setups. The classic example is the old vw manifolds for the flat four bettles. They had beautiful torque characteristics but thats prob the flat four design. As for high rev performance engines the higher the power peak the shorter the runners needed. Street engines do better obviously with torque rather than high rpm. Anyone else that can teach us or shed better light on the differences??
Anyone driven a volksy before?? I am still surprised how smooth those old things are. Silky smooth delivery and crisp gear changes with beaut torque pulling you from very low engine speeds.

Could this be an alternative for LHD A series owners?

Down draft manifold

I'd think it would end up being too tall but I don't know for sure.

They look awesome and yes they would be too tall but you could run a shaker like in mad max and twin downdraft alfa 33 carbs like the 36, 38, 40 or 42mm downdrafts.
These are really weird I didnt know anyone made these for the A-series! good find!

You ever seen the japanese LZ twin cam heads for the L14 or the Os giken twin cam heads for the L16,l18 and l20? they would be a nice auction item! check out ferals website for reference
http://www.datrats.com.au/PICTURES.html

With all this talk about "low speed torque" ... let's just boil it down to this: A smaller intake, carb and exhaust gives better low speed torque.

this is what makes efi so good.
what happens with intakes, is that there is a pressure wave. The air enters the runners and goes into the engine. when the intake valve closes the air hits the closed valve. This causes a pressure wave to travel backwards up the runner. when it gets to the end of the runner, the wave turns around, and starts heading back toward the intake. If one tunes the runners, so that this returning pressure wave, arrives at the valve just as in opens,
you get extra cylinder filling. to get this affect at low revs, you need a long intake, to get the effect at high rpm you need a short intake.
Carby engines can't have long intakes because the fuel begins to stick to the walls.
If you don't understand my explanaition, the intake runners work on the same principle as extractors.
with extractors you want a low pressure zone when the exhaust valve opnes, on the intake u want a high pressure. If u need some general lengths, ask.

Nice old thread.

Have a question I'd like to put foreward. For the purpose of achieving a certain tune for your motor say high end power, would you cut a sectoin out of a twin sidedraft manifold and weld the flange back on? or would you just take a different approach to it?

Getting an engine to perform better mostly about getting more air and fuel misture into the engine. A standard A14 with standard carby might get about 85% volumetric efficieny, which mean it gets about less than 300cc of air into each 350cc cylinder. A well tuned road engine might get around 95% and a top race engines can have up to 110%.

They do this buy TUNING the engine. I emphasisd tuning because its best way of looking at it. Bigger is not always better.

When the inlet valve is openned, the air fuel mix travels at speed through your ports toward the chamber. At some point the chamber will overfill and then the flow will turn around and start heading back out. If your intake timing is good, the valve will close just as the cylinder reaches its maximum pressure.

Using port size and carby throat sizes that are too big will slow the inlet port flow and hence reduce the amount of 'overfilling' that might have otherwise happened. Using ports and throats that are too small will result in high port speed (which is good) but will take too long to fill the cylinder, so the engine will not want to rev hard. So you see there is an optimum port and throat size for your engine!

Next, when the inlet valve closes, a high pressure pulse travels up the port and manifold toward your carby until it reaches an opening to atmosphere or a change in manifold area like entering a plenum chamber. When it does this, the pulse is reflected back toward the engine. If the pulse is timed correctly it will arrive at the inlet valve just after it starts to open. This will give the charge a head start at filling up the cylinder. You change the timing of this return pulse by changing the length of your ports (which in practical sense includes the manifold, carby throats and any extensions you have bolted to it).

Throat-per-cylinder setups are the most simple system to tune and work very well in all conditions. There are some advantages of plenum chambers, especially for standard road cars. They get a bit of a bad rap because alot of people end up over-carbureting their engine. A pair of DCOE32's would be great in a streetable A14/15.

The two-cylinder-per-throat system sucks a-hole in my opinion. You loose most of your ability to tune the engine. And the setup pictured above suck unevenly. The first throat sucks twice, then the other throat sucks twice. Try tuning that to a particular rpm!! But it works well enough for a road car and has the advantages of being cheaper to buy and easier to tune. It will probably idle a butt load better too because the fuel isn't forming large drops in the manifold because the charge is moving too slowly at idle.

SU's have a throat which has variable port area. Its a pretty simple setup with a plunger operating on vacuum, but it works. It closes the throat at low throttle to increase the flow velocity and opens up at high throttle to let it breath better. Great setup for road cars in theory! I had a Cooper S with twin su's once....I will never go back to SU's due to reliability issues.

If I'm not mistaken, you have a 120Y. I have a friend who has duals on his A-14 in a 120Y. What he did was shift the engine in the opposite direction to gain the needed clearance. I have also, personally, installed a single on a B-210 and ran the same style Piper Cross filter as the Chickenhawk. The brake bleeders poked into the filter right in the center of the air horns but everything seemed ok.
As for the torque versus horsepower argument, conventional wisdom says the single will make more torque while the duals will make more top end. Of course with an A-series, you can pretty much write off torque since they are such wee litle engines. That's just my opinion though.

i would love to hear a good technical description of how in any way a single side draught weber could be better than two other than with regard to fuel consuption, its a bit like whoever told another guy that SU's where better cause they had more low down torque, surely theres no factually reasoning i hate to say it but i reckon people are just trying to justify running inferior setups (sorry if this insults anyone, i just cant see there being any truth in these particular agrguments and would hate to see someone looking to build an ultimate car being mislead by bullshit)

The argument I have always heard for SU carbs is that they are a continuously variable venturi design. This type of carb only allows as much air as the engine can use through at any time. Therefore, it SHOULD be more efficient and produce more torque. Yes, a throat for each cylinder will make more top end power. I think that the individual throat setup tricks people into thinking there is more bottom end by having so much more topend and therefore the revs are kept up higher. I contend that if two nearly identical cars, one with CV carbs and one with individual throats but all else the same, were to drag race starting in third gear, the CV carbs would win. I have never tested this theory so it is just speculation.