righto turbo veterans. need help with water lines where should i be running the water from out of the block to the radiator i assume. any pictures regarding water plumbing would be good im using a turbo from an RB20 so basicly a big non BB T28 with the ceramic wheel and iv got a single 40 webber for my carb just wondering how i would go about cooling the snail

good info john!!

On the SU vs CD Stromberg carbs - if set up right, the result will be identical. Here's the funny thing - I've been exposed to both types (which are as close as webers and dellortos - same principles and similar designs - in all seriousness probably they only changed those various things so that it wasn't a close enough match (in principle, not in practice) that patent issues might arise,

Anyway - I've been exposed/around both types since I was an apprentice. It's no big secret mini's came out with SUs (various sizes, and twins in some models). If you asked a mini owner, many would say they are best. Early toranas (i.e. the XU-1 models) had triple strombergs from the factory, so you'll find a lot of xu-1 or holden fans in general who would say that they are best (and interestingly factory setups go for as much as triple the price of a set of SUs on a lynx manifold (basically they are identical in potential).

So really speaking - there's not much in it at all.

Having said that, although they'd be near identical to optimise, there seem to be a hell of a lot more SUs floating around, popping up in cars in wrecking yards or whatver. So the parts (or the initial carb itself as the first step in getting/optimising said car) seem to be a little bit easier to come by.

On a related note, the SUs have a piston inside that bell shaped cover, and there's just enough clearance to allow it to rise and fall without it sticking due to air being trapped above it or whatever. Pretty simple, and if they suffer any trace amt of corosion, kerosene and a length of scotchbrite can usually clean them up enough to move as freely as required (or worse case - transmission fluid as a lubricant and very fine - 800 or finer wet n dry or similar sandpaper.

the strombergs have a rubber diaphragm inside it, essentially they are (in that specific instance) like the impco mixers which have diaphragms. (and incidentally the ohg x450 mixer, designed by the bloke reponsible for the impco mixer, goes away with teh diaphragm too, though to be fair, they are fine on most impco's, it's anecdotaly usually only the 300A that can see inconsitent meterng due to the diaphragm wearing, and also ballooning after any backfires)

Any way this diaphragm can crack. I dunno what the situation is for replacements - if all else failed, I'd even suggest trying a volvo dealer/workshop, might have some old stock as some of the volvo's had strommies iirc - though obviously not too many customers would bring pre 1990 volvos in for an authorised dealership service (might cost more than the resale value) but worth a try.

The SUs mixture adjustment is either via a screw on hif types or a nut on HS types - both 'work' by raising or lowering the jet so it's more blocked, or less blocked and leans or richens the mixture respectively. Easy enough stuff.

The strombergs (well teh ones I've had at least) instead of mving the jet, you actually use special tools inserted into the 'sleeve' that the damper oil/shock absorber like valve goes, and it raises or lowers the needle. So you'd have to have a special tool for that. It won't be horrendously expensive, or ought not be at any rate. Additionally, the sus can be adjusted whilst running. Technically the stromberg could too, but pushing down whilst adjusting it (to make sure the tool didn't slip out, like a damaged screwdriver popping out of the screw ) can lead to it stalling.

Early SUs had a manual choke, no big deal. The Hif type has an interesting addition. The jet isn't held solid (well not completely) it is held in place by a lever arm (adjut the mixture screw and it raises or lowers this lever arm, like a see saw. But this arm isn't 'normal' - it is bimetalling - it's like two icy pole sticks sandwiched together (alveit very thin ones) - and the two types of metal are different, and have different expansion rates for any given temperature. So as it cools, one side shrinks mre than the other, which causes it to 'warp' and move the jet down, richening the mixture. As the car gets up to operating temps, this lever arm warms up, and it expands one side more than the other, so it curves the opposite way, raising the jet, and leaning it out.

It's only meant to be a small change, but it basically alters the mixture richer for startup and initial cold running, then leans it out to 'normal' for proper warm running mixtures. This is all well and good, but in the mini blowthrough setups, they found that the radiated heat from the turbo, a very tight fit between engine and firewall - well it could cause the thing to lean out the mixtures at high temps, just where you'd need richer and richer mixtures for safe full boost running.

so that is a tiny but potential drawback. Some people have made their own lever arm to address it, in a drawthrough, assuming it's reasonably positioned, you'll likely never run into that problem. But if you did see a/f being inconsistent (but seeming to co-incide with running it hard with boost, but lower speeds (like on a dyno, on a hillclimb, or whatever, as opposed to a circuit where you'll have enough road speed to put enough air through and out of the engine bay so as not to over heat it.

Anyway - the strombergs don't have that. Instead they have a bimetallic spring (same idea as the hif) but instead of moving the jet, this spring curves when warm, and pops open a small valve (a bit like a wastegate flap) and lets a little bit of air bypass the main throat. So with it closed, a little richer for starting and initial cold running, and then it opens when warm, for 'optimal' idle mixtures. It can be fairly easily plugged, but it's only a small passage, and it's effects will mstly only show at idle, because when you go past idle and into cruise, that small hole doesn't constitute a big percentage of the total airflow. In contrast the HIF su moves the jet, so it will affect it across the entire rev range more broadly.

So in a nutshell, there's some minor gains/losses with either carb, but none of them are deal breakers.

If it was me, I'd personally go for an SU because I've got enough parts, or can get them a little easier. but if the question was hypothetically 'which one will be a better result once tuned/optimised?" - well honestly it'd be either one, flip a coin whatever - there just isn't much between them at all. If you set up two datsuns with identical engines, turbos and one with a cd stromberg (aka zenith stromberg, etc) and one with an SU (both of them being 1 3/4") and then kept the bonnets shut and got a race driver to do some laps, or a hillclimb in each car - no way known would a professional be able to figure out which car had which carb.

Keep it simple and go with what jmac says 1 3/4 is all you need
2 inch is only from rover 2ltr not v8 and Jaguars.

The simpler the setup the better and to make it a little more
reliable go for water inj.

me me john pics please
and 1 3/4 is big enough thats what i hot its called a hs6 1 3/4 su
but ive been told that cd175 are more tuneable

fwiw they used to run single 1 3/4 SUs on drawthrough holdens. they were definitely restrictive in that guise, but in all seriousness, a single 1 3/4 should be enough for practically any boost level you'll be likely to try on an a series - even an a15. People have managed about 220bhp from a single SU in drawthrough (defiitely that much in blowthrough) but the combo producing that much power in a drawthrough would probably jump 20-30 bhp just from a less restrictive carb at the same boost level.

But for an A series 1.5 litres, a single SU is enough. The 'trick' that happens when comparing carb size - i.e. 2 of them on a 1.8 litre motor - well if you actually separate each intake event, you'll see that with cams around std duration, there's very little overlap of each intake even on a 4cylinder, so a single SU feeding all 4 would still do the same as twin SUs split up that only feed 1/2 and 3/4. For each of those carbs, about 50% of the time, they are 'technically' not flowing all the time. Whereas with the turbo, it's flowing through the carb all the time.

Another example of this is comparing carb flow on an inline 6. believe it or not, the sort of carb cfm you'd need to feed a twin carbed six (with 123 fed by one carb and 456 fed by a second) would actually be the same sizing Per carb, as if you ran a single carb (or carb throat) on each individual cylinder. Since on there's no real intake overlap of those cylinders..Not that too many people bother looking at it that way, since there's other advantages of one carb throat per cylinder in NA setups.

Anyway point being - 1 3/4 will do the job, for sure. Not that anyone here (afaik) is trying this, but hypothetically if anyone wanted to run methanol, you can actually fairly easily adapt a holley fuel bowl and float (and they have off the shelf needle and seats that flow enough for alcohol, made specfically for them in fact) to cope with the amount of flow rate that an SU fuel bowl/needle and seat would struggle with. If anyone wants I'll do a few diagrams of it.

su manifold looks good for a pleumn too andy- ive got one for the lpg mobile, and plan on making a small pleumn with the r31 tb on the front and mixer on the front, needs to sit slightly higer than pleumn though as lpg heavier than air usually for will fall not rise in atmosphere.

get a 2inch off a rover, or even a 1.75 of a 260zz or similar

Thanks again Yeah i kind of pondered that theory regarding each carb supporting 900cc but wasnt sure if that was relative. O.K so maybe i hunt for a 2 inch SU at some point. Meanwhile back to rust repairs on ute.

A good way to look at it (and with no real technical knowledge being applied) you might say the carbs came from say a 1.8lt engine. You're only using one, not two, so it's effectively off a 900cc engine and would be pusing its limits very hard on a turbo 1.6!!

In a draw-through turbo setup, a given carb will support considerably more power than it would on a non-turbo motor. That said 'the bigger the better' so if you can go a a larger SU then that's definitely preferable as a smaller one may limit the amount of boost you can run without going lean.

At some point, each part of your system will become a restriction so it is just a matter of being conscious of that and not pushing the boundaries with a single small carb. I'm not an expert but I believe there are 1.75" and 2" SUs and I'd consider a 1.75" your starting point. I think the factory "SU" (Hitachi) carbs are 40mm which would be smaller again. Will certainly work but as to whether it causes a restriction or allows you to put enough fuel into it for decent boost, I couldn't say.