now your stretching it, i can never remember which ones have water passages, i think the a-12 gx does but not sure

ive been told bout a-14 round port though dont remember seeing one im fairly certain they exist, not in an a-15 head though

1200RC
What am i stretching? [dont be rude]

I have seen one or two of the A14, oval port heads without the water holes, but this can easily be remedied, if necessary, with a gasket as a template & a hand held drill.
Generally speaking, pretty much all of the oval port heads that i remember looking at had the water passages.
These are important if you live in a cold climate to provide manifold heeeeeet, as those Hitachis don't like being cold. [neither do i]

None of the round port A10 / A12 heads had the water holes as their single carb manifolds were "hot spot" heated direct from the single outlet exhaust manifold.
Chris

Dodgeman
I might well be wrong, because the two twin SU manifolds I have seen are (were) on 1200's and could have been aftermarket ones for the round port head, hence the bolt holes "in the middle".
On the other hand, the twin Weber manifold that we use has oval ports, but has the A12 bolt pattern, which meant that we had to drill and tap the two extra holes in the A14 head to fit it. Its not terribly satisfactory, but it seems to work ok.
I'm just diving down to the Deli to order my humble pie if required.
StewMck.

Dodgeman.
If you want to be warm, turn the heater up, but us performance minded ricers want that charge going into the combustion chamber to be as cold as we can get it. This is why we use cold air boxes, intercoolers etc. A cold charge is cool. At least as cold as a mother in law's kiss-colder if possible.
Warmer charge means it is less dense, that is less air and therefore lower volumetric efficiency. Lower volumetric efficiency equals less power, if I remember any thermodynamics at all.

89mm
You are absolutely right in your comments about air density & volumetric efficiency, & if i were driving a racer at full throttle & near to full revs, all the time, then the comment that "cold is good" would apply, but i don't. My car lives on the street, with speed limits, & traffic, & cops, & corners, & intersections & lights, etc.

Can you estimate what percentace of your LEGAL street driving time is done at full throttle & near full revs? Be serious, actually tally up the total time in any normal urban journey that you spend at full throttle where the cold air intake would ACTUALLY provide a benefit. If it was ONE PERCENT, i'd say you were a skite [braggart]

At lower speeds, & at lower throttle settings two interesting refrigeration principals come into play. Simple pressure drop behind the throttle plate causes a serious drop in temperature.
How do i illustrate this,....umm, ok, think back to the last time you used a compressor, & after a while you shut it down & bleed the tank down to remove the pressure. Did the drain valve frezze over? As the air expands, it takes a lot of heat with it.That is going on in your carb ALL the time that there is vacuum in the manifold.

The next principal is called "Latent heat of evaporation" When a liquid changes to a gas it draws off a huge amount of heat with it. The example? Dip some fingers into some petrol / gasoline & hold them up into the breeze. Feel cold? [This works best in winter] This is because the fuel that is evaporating in the breeze is sucking the heat right out of your fingers righ down to the bone. This is going on in your induction system ALL the time that there is airflow in your intake.

Next. The boiling point of a liquid is REDUCED as the ambient pressure is reduced. Water boils at a much lower temp on top of Mt Everest than at the bottom of Death Valley. The reverse is also true, which is why cars have pressurised cooling systems.

Fuel Boils [changes to gas] in the [partial] vacuum of the inlet manifold, resulting in a great reduction in temperature. The now cold manifold allows fuel to condense on the walls, robbing the airflow of combustible gas [remember the fuel needs to be a gas before it will burn] & in so doing, leaning out the mixture & allowing raw fuel to enter the cylinders & do a very nice job of washing oil from the cylinder walls. This of course accelerates bore & ring wear. The lean mixture means power & driveability is reduced.

Now, on the other hand, if we HEAT the incoming mixture a little, we VAPORISE the fuel, which burns completely providing full power & economy from every drop. The volumetric efficiency thing is of no consequence because we are operating at part throttle anyway, so the throttle position determines the level of V.E.

I knew all of these principals from my science classes by the time i left in 4th form [Yr 10] so surely you did too.

So here is the deal. You reap the benefit of a little extra V.E. at the very top end of the operating range for, say 1% of your LEGAL street driving life, while i am prepared to sacrifice this & reap the benefit of easy starting, smooth running, good mileage & long engine life for the other 99%.
Thats why the factory engineers do it this way. They not as stoopid as you think.

This is why i have run the stock GX setup for so long that i wore the motor out twice [about 100,000 miles each] & loved every mile of it. Sure, there were faster cars, more powerfull cars, cars that could blow my doors off, but i outlived them all & i will be using the same engine [& g/box] all over again in another Datsun. No trail of busted parts at my place, & i don't need to prove anything to anyone.

Oh let the good times roll. [again]
Chris

P.S. The amount of heat absorbed by the incoming fuel / air mixture from the heated manifold at full throttle & at full revs is a LOT less than you seem to think, but if i was selling carbs & manifolds, perhaps i wouldn't mention that either.

P.P.S. I appologise to one & all for becoming so involved in a "non EXHAUST manifold" subject, but i just couldn't let this silliness pass

just talking bout stretching my memory man,

good points in your argument, very interesting read, but yeah as you sort of said it depends on your driving style, me i sacrafice drivability for top end to a point

Quote:

was that neccesary, i mean you put a good agument forward, then attempt to start a new bitch sesion??

Hey Dodgeman!
There's a couple of details that you may have overlooked.
(1) The pressure drop across the butterfly in a carb is measured in Pascals or when I was a stude, inches of water gauge. This is hardly enough to have any material effect on the heat dragged in in the process of isothermal (adiabatic) expansion. No way! (Hint: look at the very small orders of energy involved- please don't be offended when I suggest that you dust off your copy of Wrangham's "Heat Engines" or equivalent and refresh your memory, because some of what you say is pretty woolly from a scientific viewpoint)
(2) I can still remember when cars had a "hot spot", utterly ineffective after a short time because of the insulating effect of the gas carbon that clogged it up, OR had no manifold heating at all. My recollection is that these cars ran well and delivered their power smoothly without flat spots etc. The only time that fuel vaporisation was a problem was on days of extreme temperature and it boiled (=vaporised in the carb or upstream of the petrol pump). It seems to me that the principle reason for manifold heating is to provide the replacement heat for the fuels latent heat of evaporation. Given that all modern U/L fuels are a cocktail of pretty horrible ingredients (MTBE being a contributor), to get them to be effective (i.e. small enough droplets) probably requires rather more heat than in the past.
(3) Having driven cars with and without manifold heating, I can say
that if the carb(s) and ignition system are tuned correctly there is no particular problem.
(4) You don't have to be defensive about your driving habits, to each his own. Me, I like my car to have the acceleration, handling and stopping to cope with modern traffic conditions where mid range torque is the parameter that counts.
(5) Also, no apology is required for diverting the thread. What is most important is the interchange of ideas and experience that this Club thrives on. To be able to express an opinion, have it praised or criticised without taking offence is the most important thing. That way, we all benefit ;-

Therein lie the strengths of 1200.com

89mm
Huzzah, someone i can talk with, & i thank you for your informed response.

You are correct when you state that the cooling effect of the pressure drop across the throttle plate is not great in itself, but it is a great contributor to the latent heat part by allowing the fuel to readily convert to a gas. Most of my driving was, & to a degree still is, long distance cruising & i always tried to lift the vacuum guage needle to as near as possible to 18" of Hg [or more] which is what all good vacuum guages should be reading in. This level of vacuum in highway cruise mode is VERY efficient at converting liquid fuel to gas. I have had the butterflies freeze in my Datsun one cold winters morning when driving to work in Goulburn. The shafts froze in the carb housings, as it was running real good, but wouldn't slow down when i lifted the foot. Natural cruise control. The carbs didnt receive heated air, but the manifold is heated. These throttle shafts are downstream of the variable venturi & are in the fuel stream, so ice built up on the outside of the carb housing, freezing the shafts.

The hot spot system usually works really well when it is in servicable condition with a fully functional thermo & pressure operated flapper valve. By the time the engine has enough miles on it to have a heavy carbon buildup under the hot spot, it is usually well into it's service life & burning a little oil, which is often the source of the carbon, & the flapper valve is usually stuck, often in the part open position. This means that the hot spot is getting at least some, & possibly a lot, of the exhaust flow ALL THE TIME, so it is not innefective, it is often overeffective. Combine this with the aforementioned part-worn engine with low [ish] vacuum & like you said, no problem. If the hot spot was innefective, one would usually know about it pretty soon in a low milage car.

Untill the advent of heated air intakes [flex hose fron air filter to the exhaust manifold] in cars in the late 70's, the easiest problem to fix for the night time NRMA men around here in winter was carburettor ice. The better the state of tune of the engine, the worse the problem. The fix? There was no fix, by the time he got there, the carb had soaked up some heat, the ice in the air passages of the carb had melted, the engine usually started straight up & the driver often left feeling sheepish.

I am the former Telecom Fleet manager for an area that finally extended from Cambelltown to the other side of the Vic border & out west to Young, I ran both the Canberra workshop as well as the Goulburn one & maintained about 600 fleet units of all types. I remember driving my Valiant six [company car] for about a year [1981] with extractors after the exhaust manifold broke. I had it dyno tuned to perfection & the further i drove it in cruise mode, the worse it got. I eventually refitted a new exhaust manifold & it was perfect after that, so from that experience [& others] my observations are diametricaly opposed to yours in point 3. The better the state of tune, the bigger the problem due to the higher vacuum in well tuned engines.

As i had writen before, you are right in your assessment about cold, dense air providing more oxygen, which can burn more fuel, but it needs high gas velocitys to maintain fuel mix stability & usually richer mixtures to compensate for the fuel not converted to gas on the way from carb to combustion chamber.
Now tell me, if you need all this cold air induction with high flow carbs etc to keep up with modern traffic, where are you driving? Taladega Speedway? [NASCAR]... [infantile chuckle ]
I just drove from here to the other side of Taree,... & back,... on Friday, in my near stock 200B, & i kept up OK. Got great mileage & gave the finger to 7 roadside radar Nazi's on the trip.
I think, like you, that the best place for the best torque figure to be, is where you need it most, usually at the engine speed used when passing & for me, that is a lot closer to 3,000rpm than the stocker ever was.

Anyway, what i have learned after more than 35 years in the game, after building & running a variety of hotties, & making the odd error or two, is that factory engineers are not stupid & that if it was possible to make a car that didn't have this feature or that feature [like t/stats & heated intakes] & still have these cars perform to specs, then these things would not exist. The trick is to try to fully understand why a certain design element exists, what benefits it provided & what it blocks, then honestly asess wether changing it will provide a real benefit to you in YOUR APPLICATION, for your driving regime. The stock 1200GX setup served my purposes perfectly, but some of my mates had Datsuns with 45 DCOE Webbers that went faster than my car, but none ever went as well, or for as long. Think twice [even thrice] act once.

Dif'rent strokes.......

GX RULES [does that sound provocative, do you think?]
Chris
P.S.
GX exhaust manifolds are real good too.

Fantastic input Fellas.
I do like to try and understand the hows & whys of the workings.
Should be more of this , much better than those silly bickerings that go on occasionally.
"GO Datsun1200.com"