Essentially here is the deal - most of the heat sucked out of the intake charge (or anywhere else) is only minor whilst the liquid particles stay (*very tiny) liquid. But the heat energy required to turn a liquid into a gas (water into steam) are disproportionate - for just a token 1-2 degrees temperature increase of the H2O as it turns to steam = much much much more than it takes to heat it from, say, 96-98 degrees. This change of state is also the case with petrol and methanol, but they evaporate at relatively lower temperatures (but still with significant latent heat of vaporisation).

What this means inside an engine is actually pretty cool. The methanol will partly (or in the case of it being in a hot intake charge at the turbo compressor outlet, most likey FULLY) evaporate inside the intake tract, or attempt to. So it sucks heat out of the charge in the inlet manifold. Since it does it there, whilst stuff is still flowing into the cylinder, it creates a denser charge, more air in there to support the burning of more fuel, so you get more power from the methanol.

Some (all on a high compression non turbo engine) water won't see a change of state in the intake tract. but once it gets inside the cylinder, and as the piston is rising, well the compression stroke heats the intake charge up massively (for any given pressure, the piston will heat the charge up more than developing that pressure with a turbo or supercharger, which is why they can pack in more air/fuel and make more power.) So instead of cooling the charge, as such, what it actually does is prevent it being heated up so much as the piston rises. A cooler charge (it'll still be hot, just relatively cooler) is less likely to pre-ignite or detonate, so that's why water works the best (aside from being non combustible itself) as an anti detonant, but methanol can add a little power.

It's probably well known that methanol won't mix well with methanol at all. There are things you can add to the mix to make them mix (I think about 1-2% acetone, but don't hold me to it that that is all that is required or the only added chemical needed) So it can't easily be added to fuel in the tank, making its separate method of delivery necessary and worthwhile.

If you happen to be running below the detonation threshold by a long margin, believe it or not, running 10% (on top of petrol being supplied to the extent of getting richer than say 12.5: by itself) methanol might just be enough to actually cost power, because it might burn some of the methanol instead of all of the petrol and it produces less heat energy but uses up more oxygen to get it. that's probably a pretty uncommon occurance, but I am aware of stuff like that happening years back on the jyturbo list (he even experimented with nitromethane after that).

Which is a nice segue into nitromethane. If you were really keen, you could hypothetically run a fairly conservative compression ratio (say around 7-7.5:1 with 4 cylinder engines with alloy heads, and probably 6.5-7:1 on larger or iron headed ones) . Anyway, running say a conservative 10-12psi boost. You'd manage that on pump fuel without water injection (that would be about the limit, so you could always run say 8-10). Anyway, instead of adding more boost, you could instead run a nitromethane injector (this is a hypothetical, so to be honest, storage and supply lines would have to be safe for its use, and it's a little impractical except if you ran it only like that at the drags or something and flushed the system afterward with more normal fuel) - amyhoo, you could add nitromethane. It doesn't like compression, but it does like boost, and unlike traditionally where you run less timing for more boost, nitro is slower burning and actually likes more timing, since it's only partly running on nitro at modest percentages, they cancel one another out, and you end up running the same timing. Nitro essentially wants to run very rich, so for very little oxygen usage, it can release considerable heat energy. Additionally, as it heats up and breaks down, it actually releases oxgen inside the cylinders, so there's more of it available to support combustion. It's almost like nitrous oxide is being magically teleported into the cylinders. It releases enough oxygen, believe it or not, that it can actually burn (not completely mind you) just by itself, if there's enough heat to make it break down and release that oxygen. Which means, unlike the very rare example discussed with methanol, it'll not rob a lot of oxygen that the petrol would otherwise use to combust. So it adds power from both a denser intake charge and then in cylinder more oxygen to support combustion.

Which is essentially why top fuel engines make so much power. Now obviously I'm not suggesting you run 90% nitro or something, but if you kept the boost about the same, and started throwing nitro in there, in approximately the volume you'd feed water in (say 15-20%, you'd see a power increase, probably on the order of 10-15% over and above the power previously made with the same boost and pump fuel and no water. Just to round that out, I'd also add that nitro burns slow enough that some will still be burning as the exhaust valve opens, so it can run th exhaust valve hotter, and as such you'd want to look at wide exhaust valve/seat contact width. You'd also (well probably not if only used at drag meets) find that it'll make the turbo spool quicker, but expose the turbine (ex wheel) to much more heat. As such it'd be perhaps less risky if it was used with supercharging, not turbocharging. Of course if only used for race meets it'd not likely be of any serious concern. I'm curious as to how hard it would be to get it in quantity. Perhaps someone could try the approach that they were absolute RC car fanatics and went through their fuel in sufficient quantity that they wanted to buy in bulk and mix up their own (when sold as car fuel it's combined with methanol in some %age - not sure what but google would likely find that quick - and trace amounts of transmission fluid for lubrication of carb/injection pieces)

Having said all that, when I was first playing turbo holden 6s in the late 80s as a young teenager (actually got started as an apprentice, before I had my learners, let alone old enough for a licence) and there wasn't too much info around, well before we found out we were all 'wrong' and couldn't do it without efi and a massive intercooler (and the prices back then were astronomical, especially so when you consider their cost vs average wage at that time) - well people made exceptionally fast cars with awesome power and torque from their simple drawthroughs and water injection (not even mixed with methanol)

As a final thought if the whole methanol option is too much of a pain, how about e85. It can be bought in drums of 200L (which would likely last a hell of a long time for most people) in places where it isn't available at the pump yet (and might not ever be). It does't have quite the same latent heat of vapourisation as methanol, but it will cool the intake charge over and above petrol. It does 'want' to run richer than petrol, but doesn't have to run anywhere near as much as methanol to run stoich. Which means for the same volume of e85 injected in there as methanol, it wouldn't compete for as much of the available oxygen as the methanol. Hypothetically running e85 or 50 50 e85 and water ought to produce a very nice balance of the two, denser charge, more resistance to detonation and ability to run a bit more boost, but not as expensive (if the last time I compared cost of either.)

just an idea, is it OK to feed the H20, meth, or mix to the ported vacuum at the carb? they provide some level of control, low vacuum at low throttle...

ok so with the draw through setups will i need to do anything to the turbo to make it compatable for this setup and to cope with the fuel that will be passing through it ?

and could i just mount a t25 up to a bog stocker A12 and then plumb it up to the standard carby ? and do i have to run a RRFPR with this setup as blow through ?

and i was going to put my 32/36 on it aswell ,would this be possible with the blow through setup ?

oh and i have a set of L series GX carbys, could i use one of those for the draw through ?

@bakat

You can do this though only on a draw through setup.

@estyre

For a turbo to be draw through compatible you need to rebuild it with a carbon seal or find one with a carbon seal already. You would then need to source a seal (local? or most likely on the net with the right thrust plate). My idea was to pull the turbo apart, find the shaft size then go out to a bearing supplier and find a matching carbon seal and machine my own thrust plate at home/work.

With blow through you really needed build a box around the carby and allow for the fuel to pass through the side of it (weld in a pipe + hose clamp some hose to it) and also for the choke/throttle (use cable glands) and even the ported vac (gland) for boost retard/vacuum advance.

Pressurizing the carb throat (using a carb plenum instead of box) can work but tuning will be very different than in NA situations. On the other hand using the stock carb in the box means there's no need to tune the carb (unless the motor is worked) because the carb will meter fuel correctly to that motor as its got even pressure inside ad out.

You will need a RRFPR, return line and high pressure fuel pump - IHO just added cost when you could run draw through and get basically the same power for less cost.

The 32/36DGV can be used with blow through as the stock carbie can.

Any carb can be used for draw through and any carb can be used for blow though - obviously some are easier than others.

The e85 idea sounds great for those after more boost and power with ease and budget.
I wonder though if making the manifold longer will help with cooling the charge by
sep the radiant heat from the exhaust and making the manifold from thin Steel pipe?
Ive seen thin steel inlet manifolds freeze compared to long alloy ones.
I suppose this is a reason why long manis are now made out of plastic also to avoid
water recirculation to heat it.

pressurising the carb with a carb hat or full carb box won't make any difference to the inherent tunability - because both require that pre venturi boost pressure be supplied to the fuel bowl. On most carbs this is a simple thing, because the fuel bowl vents are inside the region encompassed by the air filter so a carb hat/plenum does the same thing.

In that orientation, in fact, the full carb box is more of a hassle as you have to take it apart to get at the carb. On a holley with a carb hat you can change jets with ease without major work.

I should point out that neither is 'ok' as is. In a blowthrough you can get the off boost running right by tuning with the turbo disconnected (wastegate flap open). But the thing is the carb will _not_ automatically go richer (or at least proportionately so) with increases in boost. In fact it will have a tendency to lean out as boost increases. The only way to adequately combat this, without having to run ridiculously rich off boost (a trade off nobody generally wants, but which is workable for a drag car) is actually simple enough. A venturi tends to get a geometric progression of signal stregnth as flow increases (i.e. as flow goes up, signal stregnth goes up at a higher rate). To combat this, carbs have what are called variously 'high speed air bleeds' or 'air correctors' which bleed off some of the signal (or aerate the fuel being delivered so it's 'diluted' wth air and less actual fuel supplied. All you need to do is reduce the effectiveness. People on the old blowthruturbo list played with this for a while, and a fairly good rule of thumb is to look at what the engine wants off boost (run with gate open) or a similar NA engine would want, and aim for about half the air corrector cross sectional area. not half the diameter, half the area. I think that works out around 0.7 or so of the diameter but don't quote me on that, do the math (area = pi x (radius)^2 [ pi times the radius squared]

It's still not a perfect setup, and you'll have to tweak a little with jetting, esp if you are seeking higher and higher boost ranges, but it's doable. And whether it's in a box, or just a carb hat will have no bearing on that.

ok that makes things a little clearer

would a hitachi/ GX carby of an L sereis work as a draw through and how tuneable are they ?

so for me to run a turbo on a stocker A12 i will have to overcome the problem of the motor leaning out

if i was to run only 5 or so psi could i just richen the fuel mixture up to compensate and then use an O2 sensor to find out how much more fuel ill need when i am on boost ?

i got offered a 48mm dcoe weber a while back and it was on an escort that was running a draw through turbo ,and the turbo was stuffed but the carby was in good condition ,should i go for the weber ? or my L series GX carby ?

you can buy the seal conversion reasonably cheaply, why bother to make one??

If you are running an "SU style" carb in a drawthrough (which includes some of the hitachi/mikuni/whatever carbs) - the leanout as such doesn't quite occur. It's generally limited to those with a 'fixed' venturi size (holley, carter, aisin downdraught, whatever). it can happen n drawthrough holleys and others, ironically because the turbo can 'pull' hard enough under the carb to pull the power valve shut, or metering rods down into the leaner position (whichever method the carb uses). On the SU type in drawthrough, the more it pulls, the more the piston can rise, and it'll pull harder on the jet, no power valve or metering rod (in the traditional sense) to inadvertently pull closed.

So very generally you can tune a drawthrough SU pretty easily - just find a needle that gets the right a/f ratio for off boost running (the thicker 2/3rds or upper 2/3rds of the needle profile) then file down the last 1/3rd progressively to get ricker and richer mixture for when on boost. It's not that hard to do. Essentially you initially run it with say 1-2psi, and check where the mixtures are at (you can usually adjust the actuator to give just 1-2 psi - if not, the workaround is simple, just get a spring, like a throttle return spring, and hook it on the wastegate flap linkage so it is trying to pull the gate open, then it will open sooner, and limit boost to just a few psi. Check the mixtures, file if necessary to ensure a safe a/f ratio and up the boost a psi or two at a time. You can use that 'spring' addition in the other direction to up the max boost by 5psi or more too, cheaper than a wastegate bleed :)

With webers and drawthroughs, they (anecdotally) tend to lean out at higher flows. It's usually due to them being conceived of and designed to see one carb barrel per cylinder, you may find some hassle getting an emulsion tube that 'works' well. Smaller air corrector usually helps along the way. Don't get me wrong, plenty of people ran exceptionally quick with a single big weber on a drawthrough holden years ago. The holleys were just cheaper.

In a blowthrough setup, the webers are usually _very_ difficult to get the emulsion tube selection right for, and seem always to want to run well either on or off boost but seldom both with any one setting. To get around that, some of the people who offered kits (there was a janspeed kit for minis with a dellorto sidedraught blowthrough) they ran restrictor rings at the carb mouths. Basically they were rings, a bit like a 'choke' at the carb mouth. Big enough so that they didn't affect flow or metering off boost. But once flow started to pick up they finally acted as a slight restriction for air entering the carb throat, and as such, since pre carb mouth boost is fed to the fuel bowls, it goes proportionately higher (teh pressure difference between fuel bowl and what pressure there eventually is at the main fuel metering point at the carb venturi proper) and essentially it works well then both on and off boost.

Blowthrough SUs - as used on mg metro turbos and era mini turbos (same motor and box, one in a mini body the other in a ford laser lookalike) well the carb hat had a sleeve in it, that effectively worked as a restrictor ring. A guy on the blowthruturbo list (do a google of 'jukka harkola mini' - I'll bet he's still got a web page up somewhere) tried removing this sleeve/restriction to get more flow, but it never metered fuel properly under boost, the sleeve/restrictor was a necessity.

Given the need for those restrictor rings for those carbs in blowthrough my own preference is that you might as well just bite the bullet and go a holley 2 barrel if you want to go blowthrough. They are just too easy to setup like that.

If you absolutely want to , you can run them without the high speed air bleed size reduction (which isn't actually that hard to do) I certainly have tried it. It won't massively shorten engine life imho, but it will effectively have to have all the enrichment frm the main jets, so it'll be richer off boost than perhaps ideal. It'll basically use more fuel even when driven sedately. That's possibly not a concern to some and if not why worry!

With whats described in the blowthrough I would not bother with a weber or holley when with the su you are only pulling out the needle for fine adjustments. I thinking this fellow whos taken out that ring probably didnt know how to tune the carb any further or the VE of the mini head is maxxed out on the Metro. The datsuns heads are much better and probably could do with more flow.