ok so i am seriously considering supercharging the ute but im looking at the fuel delivery system. now atm im running a 32/36 weber and just wondering what was involded in blow-thru boost prep on this carby? otherwise i'll look into draw-thru. or i can get my hands on some twin sidedraughts soon and what is involed to boost prep these for blow-thru?

TO handle boost pressure, you typically need to drill and fill the floats, they only have atmospheric pressure inside, and so once boost gets into the fuel bowl (which is must in a blowthrough to keep fuel flowing) they'll collapse.

Some of the weber floats seem to be already supported internally, or at least are strong, as posts on the old blowthruturbo mailing list indicated a couple of people testing them. But don't bank on it. To 'fill' them, you get a tiny drill bil and drill 2 holes, one on 1 side, and one opposite side, and then get regular rapid expanding foam spray (from bunnings) and hold the nozzle tight against one hole, You need to spray for a while, till it really floiods out the other hole. Then let it dry in the sun for a good couple of days, then re-seal - with a soldering iron, or possibly araldite (be warned that althoguh solder is 'the go' the heat from the iron will start to burn/melt the foam, so you have to work quick, and you need to clean the outside of the floats 'big time' to get rid of the gel like stuff that will ooze out and touch the float walls on the outside.possibly use emery with a drop of acetone on it. I've heard that you can actually get nitrophyll style floats for some webers, but I haven't seen them in the flesh - so they might just be black plastic as an alternative to brass, and not internally re-inforced - maybe google will turn up something?

If you run a holley instead (and that's what I'd recommend - the fisher price of carbies they may be but they are dead simple to prep and tune for blowthrough) you can get off the shelf floats that are honycomb structure inside and ready made for blowthrough - called 'nitrophyll' floats - they are the dirty black plastic looking ones. Be aware they are a touch heavier, so if you just fit them as is to an existing carby, they will sit lower in the fuel, you'd need to re-adjust the float level (downward) to get back to even stevens (of course this shouldn't be a drama as you'd be starting from scratch with a nitrophyll float).

Other than that the 'big deal' with either of the carbs is to reduce the size of the high speed air bleed (air correctors) Their 'role' in a carb is to reduce the natural phenomemnon of a carb getting richer and richer (all else being equal) as flow through it increases. If you reduce their size, you reduce their scope to lean out the mixture, and hey presto, for the same 'nice' not too rich part throttle cruise jetting
(and I concede that that is also a factor of idle/transfer fuelling too) they'll run richer up top, nice and where you need it for a blowthrough. Reducing their cross section area by 1/2 is about the place to start looking. This in practice is _not_ the same as half the diameter. due to the way that cross section area is calculated, to halve the area you actually multiply the diameter by about 0.7. So if the existing air corrector was 30 thou, you'd go to one that is 21 thou and try from there.

The beauty of it being supercharged is the boost increases with rpm/flow more linearly than with a turbo, so the air corrector trick works even more closely with things.

There is also (with holleys at least) the potential for a smaller air corrector to delay the start of the main metering circuit (which sounds counter intuitive) due to the fact that more air in the circuit initially aerates the fuel and lowers it's resistance to flow (alters the viscosity) and lets the main circuit start flowing earlier. Once it's 'up and running' though the aforementioned richening up top works as decribed. I'm just mentioning that for trivia's sake - I doubt anyone will see it happen to enough of an extent to worry.

If you go with a dgv weber (and more than a few people do) then you can further tweak things, because the primary and secondary don't open at the same rate, nor are they the same size. In this instance you can (and all of this jetting/air corrector talk only works if you do follow it through and tune/spec/jet it properly)_ go a little leaner on the primaries (still reduce the air corrector on the primary) and run the secondary richer which means you might not have to go as far on the secondary air corrector reduction. . Tuning with a wideband is essential to get that perfect, and whilst dynos can setup a very good full power curve, the sheer amt of time needed tends to make it a better bet to try and optimise the part throttle stuff out on the road where you have the time. Of course a wideband ego sensor/logger kit isn't dirt cheap either!

OK once you have that done, of course you need a decent fuel pump, that is capable of an output pressure about 5-7psi above the max boost pressure (which is probably around 20psi pump pressure requirement). Run a bypass/return style rising rate fuel pressure regulator. If you do that, it will bypass all extra fuel, and actually have the pressure between fuel pump and reg a bit lower for normal driving (unlike the dead head holley style regulators) this will reduce load on the pump, extending it's life as well as quietening it down. IF and ONLY if you run a return style regulator, you can actually shim the internal bypass in a holley fuel pump (which opens at around 13psi on teh blue pumps from memory) so that they can supply up to 20psi. I've actually had one putting out nearer 30psi - since the boost pressure was in the low-mid 20s ( on a blowthrough car I had, and it would only see the 30psi pump pressure for about 10-15 seconds (as it would run out of gears and or road before that). It ran for some months and never leaked. I don't think it'd be a great idea if you had it constantly up at that pressure, but for short bursts. That's basically only advice I'm sharing on the basis that you might score a holley pump dirt cheap or free somewhere. If not, there's plenty of other choices.

So you need a higher (than for na Carbs) pressure pump. you also need the rising rate regulator. Some people have nothing but trouble with malpassi's (and you need to get one with an internal spring to suit carb setups, not efi) and some people they work fine for. I was in the latter category, but I'd add that they'd be near the limit of flow for a blown 1.5 litre. Mallory make a brilliant one, that will flow enough for a boosted v8, so the capability (and the price) is a little higher, I think the part number was 2403 or 2407 or something like that - I can double check that if need be). For a holley, you'd run it with about 5-6psi static pressure at idle, and for a weber more like 3-3.5psi . You run the boost reference hose from anywhere on the plumbing between the supercharger and the carb (NOT the inlet manifold).

There are mods to the carb throttle shafts, but I'd strongly suggest trying the carb first as usually fuel seepage there is non existant if the throttle shafts are in good nick (and new holleys are all, at least afaik) sealed in the shafts better than old ones, to meet some californian epa standard or something.

You can either run a carb 'hat' to seal the top of the car for boost (by far the best option) or if you get air leaks everywhere, you can run a complete carb box/enclosure, which then means you have to pull it all apart to make just the smallest adjustment/tweak - avoid it like the plague. If you run a carb hat on the holley, make sure that the air entry isn't 'too low' - have the carb bonnet itself somewhat high. Especially if the carb bonnet air entrance is at the front of the carby. The 'problem' if it's too low and close to the carb mouth, then air rushing in and over the top of the fuel bowl vent will work (like old perfume bottles and some fly spray) to suck air/fuel out of the vent, which depressurises the fuel bowl, and stops fuel flowing. It might not happen at idle or even mid range, but once it passes that threshold, it'll start to lean, then stop fuel altogether. It will make popping sounds from the carb area, and die, comeback to life, die, over and over, unless you lift off the throttle enough. This can even happen NA if the air cleaner lid is too low (actually found this out on the toyota engine I had when it started popping even when run with the turbo disconnected - and a higher carb bonnet air entry fixed the problem 100% never to re-appear.

On the holleys, there are re-usable gaskets made of teflon or similar - they genuinely are reusable (non stick, so they put an end to gasket scraping, and the chance of tiny debris getting into the carb circuits) and they seal the fuel bowl well above 20psi boost. I'd recommend them - but (big but) if you have a _really_ old holley, with damaged or warped surfaces, they _might_ then leak - they are stiffer so they resist blowing out around the fuel bowl gasket, but this also means they squish up a little less, and sometimes the various slots/grooves in the metering blocks don't seal as well. If it's relatively new, forget that, and just run the re-usable ones as is.

Additionally on holleys, they might blowout/rupture the power valve diaphragm. It's not 'dangerous' - if it lets go, it just stays 'open' all the time (well at least in all the ones I have experienced). If that happens, you simply remove the power valve, and run a power valve block off plug. This means it won't be _as_ rich as easily at higher flow rates (newer holleys have a check ball to prevent it blowing out by the way) so you might have to run even smaller air bleeds, or alternatively slightly richer jets. Part throttle cruise economy might not be a huge concern, in which case bigger main jets are 'the go'

Other than that, you might also find that a smaller acc pump squirter nozzle is beneficial (under 28) on 350 holleys, and you might also find it's still over-delivering on the acc pump (it'll feel like it's falling down, but it's not too lean, it's too rich, and you can 'tell' because the natural instinct is to pump the pedal if it seems to fall down and stall, and this only makes it worse (whereas if it was too lean it would help it) - in which case you might have to consider a smaller acc pump cam. I don't remember what the 350s have in std form, nor what is available that is smaller, but at a _guess_ you might find that the cam from a 320 holley (which is basically a 350 re-worked iwth different boosters and metering block to allow better part throttle atomisation and lower emissions, at the cost of some flow and engine output - it's an economy/emissions carb, not for performance per se) delivers less fuel.

On carb sizing, there's a bunch of formula to calculate it, and it's mostly wrong (well more accurately, it's configured to provide a conservative sizing, because it's easier to get fuelling ok on a slightly smaller carb (smaller carb, smaller venturis, stronger signal, improved fuel metering). Based on experience, a 350 holley is definitely not overkill for a 1.2litre. I've run one on a small port headed 3k toyota (and the heads don't flow as well as a datto head - meaning they 'need' or want less carb flow/size) - and even with the turbo not connected, just to get a baseline tune on the holley, the holley didn't lose idle/midrange at all. under 2000rpm it ran just the same as the factory/stock carb, and above 2000rpm it had enough extra output that it didn't need a dyno to show it - it was balatantly obvious. And lastly it extended the usable (NA) rev range about 1000rpm over the factory carb.

For something closer to 1.5 litres and with a better flowing head, you could _certainly_ make a case for a 500 holley in a blowthrough. If a 350 holley comes up cheap, then go for it, no dramas, but if you had the choice between two for the same price, i'd lean toward the 500.

On 2 barrel holleys, there's no support under one half/side of the air cleaner, so if people overtighten the air cleaner, it warps the carb main body/air filter base to buggery - and nothing in the world will allow that to seal the carb bonnet. Probably more than half the 2 barrel holleys on ebay and for sale in general are badly damaged in this area - visible in some pics, or on other adds they do a 'spielberg' and use a camera angle that hides the warpage. The webers in this area are clearly 10000times better and practically impossible for that to happen.

The dgv weber is a touch small for optimal output (but make no mistake, it can still put out a hell of a lot of power with one). You might also consider the 34/34 adm (I think is the letter code) off a mid 1980s ford 6 (crossflow pushrod one), if one comes up cheap. They were way too small for the big ford, but wouldn't be a bad option on a blowthrough smaller engine - they would likely flow about the same as the 32/36 dgv. They have an electric choke, which isn't everyone's cup of tea, but should be easy enough to either disable, or hook up so that it's manually controlled.

And now for the irony - it probably took longer to type (and to read) this post than it would to prep a holley for blowthrough :)

might you be interested in a complete EFI system, with ECU, tuned to 14psi. this includes injectors.

I have mine up for grabs, since I'm installing a twincam20v into my ute.

after reading all that im think im just going to run a draw thru setup. im also curious as to what each oil line fitting is for i.e. inlet, outlet so any help here would be appreciated

I don't think that was the intention.. but some great info in there..

wot type of blower? pics?

yea good info on blowthru for a holley which is obviously what works for jmac but i have got a weber 32/36 so i've just looked around at other options and i rekon drawtrhu 32/36 will be best for me

Add a second Weber. I'm running a Mercedes SC blowing thru 2 weber down draft carbs. I'm getting more than enough fuel for the SC but having to add more when running it with Nitrous.