Lol D, switch on the pedal - as simple as it is thats not a bad idea. After all you can fine tune when it starts to inject. All thats needed extra is a solenoid valve to stop water getting sucked in once the manifold is at vacuum. Then there's the problem of no LED's flashing at you to make it look 'cool' heh.

I know it's a bit late in the thread - but I've run a bunch of blowthrough and drawthrough setups, and honestly, the one to pick is whatever will be easier for you to actually complete. If underbonnet space favours one or the other, or you can get cheap high pressure fuel pumps and rising rate regs or whatever, choose the style that will be less dramas on 'those' terms, because frankly, boost is power, and they'll make sensational power for cheap whether it's blow or drawthrough.

SU carbs are bloody brilliant for drawthrough, very easy to set up. The only reason I have tried other stuff for drawthrough was that I wws running larger engines than datto 4s and quite a bit of boost, and it got to the point that a big 4 barrel holley was less work to setup/dial in than the potential of running 3 SUs (there was a gemini getting around to heathcote occasioanlly with a 202 drawthrough with 3 Sus feeding into the turbo - not mine or anyone I know on a one to one basis, but it has been done). But given the size of the a series engines, I'd not consider anything else but SUs for a drawthrough (well technically there is one exception - I'd consider an impco 200 if it was drawthrough lpg)

I'm quite impressed by the prices of those Ebay parts. I had a hard time even finding a hobbs switch here. People want stupid money for complete "kits" but you could obviously build your own for a decent price. The beauty of the higher pressure pumps is that the anti detonant is able to be better atomised by the metering oriface(s). I would still lean towards injecting it between the carb and the turbo. If using nice high pressure, the mist will be better atomised, So less chance of larger droplets harming the turbo compressor wheel. Also/during after the intake charge being compressed, the antidenonant will begin to absorb some of the heat generated by the act of the compression, as well as being further vapourised by said heat.
With regards to what ratio of water/methanol to run, I've read a few books on the matter. They say that each the water and the alcohol has benifical properties, which each begin to diminish beyond 50%. So 50/50 is the mix I'd use.
They originally discover adding mathanol during the war. The warplanes (spitfires and the like) were overhead cam multivalve supercharged V engines which also used nitrous oxide for high altitute flying where the air was thin. They found that at high altitudes where is was below freezing, the water in their water injection resivoirs would freeze. Methanol was added to prevent this, and they found that it improved the anti knock qualities.

I've done both setups on my 1200. The Blowthrough was more difficult to build and tune but had way better thottle response off the start than my current drawthrough which was easier to build but has lag off the start.
I have yet to run it all out due to some brake issues but hope to race it this Sunday. I am hoping that the nitrous will eliminate the lag issue on the supercharger.
Oh, the brake problem. I forgot to mention. Was having brake problems and I proved it when my car slammed into a brick building this week. I wasn't going fast but enough to jump the curb and slam into it. It rinkled the right front fender but manage to avoid the hood. Luckily I had not yet installed the front grill. I had a pair of fiberglass fenders that have been sitting my garage for years so I threw those on. Front of the car is now black. I may leave it that way. If not, I have some Canary Yellow left over to spray it.
I hope to see some results from this monstrosity this weekend.

Here's Baz's response on seperate water and meth circuits:

"thedevilshands wrote:
Baz - Why seperate water and meth circuits?

L18 stock with L20B head is a cheap combo.
Lots of potential for power, but you will encounter problems along the way with turbo
set ups on L series. So start with a cheap set up( engine wise) & perfect the tubo system.
I did plenty of blow thro systems at dealer level. Mainly SK & HKS systems.
Also played with many wild arse suck tho systems tho these are not my favourites.
Needed to do mods to these for best results. Do not under estimate the power of a blown L18.
Besides they are a good fit in a 120Y. Rev hard & are very durable.

Seperate system of methanol & water.
Water is the best anti detonant available.
Methanol is a fuel.
water is mixed with methanol up to 10% to further increase anti detonation when used
as the primary fuel.
Methanol is added to water to prevent freezing of the water at high altitude in aircraft.

So water is injected to reduce detonation.
As boost increases methanol is injected for more power & additional cooling.
As the point of injection can be controlled you only use the methanol when it is needed.
Cheaper to run this way as well. Water costs nothing.
more water can also be injected to act as a chemical intercooler.
Much, much, easier to tune & set this way.
Allows more ignition advance where you need it.

Note. regardless of detonation problems water injection should be used on all boosted engines to improve drivability.
reduces fuel consumption, up to 20%.
Increases longevity of the engine.
improves throttle responce at low RPMs.

_________________
A little knowledge is a dangerous thing.
www.datsport.com


Good advice ;)

@jmac

That's what I was getting at with carb limitations - when going to a bigger motor than a datto A series 2 inch SU's and flat slides are maxed out so a bigger carb is needed. Holley 4 barrels are a good choice (probably the best carb for mid size engine suck through setups) especially with their double accelerator pumps. Multiple carbs can be setup but its just a PITA, more than one carb to rejet plus syncing them etc.

@thedevilshands
I originally decided to jet the carb a touch lean at WOT (on the main jet) then use the AD injection on boost to compensate and correct the fuel air ratio with how much meth. I added to the water.

However, separate systems seems good as I can see myself buying meth. by 44 gallon drums!

In the war - generally the additive was in fact 50/50 water methanol. Baz is spot on about the difference between water and methanol and the reasons for each being useful etc.

If you could be bothered, there's some test data available from NACA archives

http://naca.central.cranfield.ac.uk/

(NACA was effectively the predecessor to NASA and they pretty much tested/researched anything you care to name regarding planes. There's actually some fascinating stuff to read there - some of the very early articles, about material and starches (or stuff that acted like starch - usually called 'dope' but that name is probably associated with drug slang these days!) for wing and even fuselage coverng. They also have some data on water injection.

They tested and found gains (either in max available boost, or power output, and of note, you can get to a point that although you run more boost, the energy taken to make it starts to negate the gains, esp given the amt of water required to keep it safe. Ironically on modern supercharged piston engined race planes, which still utilise some stuff that dates back to the ww2 era they get to a point where more boost doesn't = more power but they are still faster - believe it or not, the increase in speed is from thrust generated from the short, but curved and rearward opening exhaust tubes!). Anyway NACA tested this stuff and they were finding more gains even up to and slightly over a 1:1 ratio - by which I mean they were injecting as much water as the entire fuel supply (not just 1:1 ratio of water/meth, if it took 30kg of fuel to supply the entire power needs for say 2 minutes, they have run up to and over 30kg water through in the same period). Most water injection setups for cars (admittedly less boost and smaller engines etc) would likely run up around 10-25% maximum added water vs fuel needs. They DID however also see enough oil contamination when water %ages were high, so it's got to be kept more reasonable for a streeter (or if massive rates, change oil after each race meet).

The other interesting thing, since water is essentially free beyond initial injection equipment costs, is that running way rich mixtures helps hold off preignition and detonation, well that effect comes solely from teh extra fuel having a cooling effect. So if you wanted, and never ran it out of water, you can actually run leaner mixtures than you normally would for a turbo setup, and use water injection to replace most of the enrichment fuel and get the same power a little cheaper. You still have to stay richer than stoich for max power even with that hypothetical scenario - not so much for safety of a richer mixture, but because it's unlikely all the fuel particles would be ideally placed to combust with the oxygen around them, so you need a little bit of a surplus of fuel so that each and every oxygen atom is utilised.

Andf to round it off, I accidentally found this (was searching for something else entirely) on youtube

http://www.youtube.com/watch?v=qGZeDrf-5Kk&feature=related

It explains what is needed to make an lpg setup run in blowthrough configuration - yep - just one added hose connecting pre-mixer boost levels to the other side of the main convertor diaphragm. I could probably argue that there are better lpg systems out there that I would have chosen over that example, but the principle, and inherent simplicity of it is the same!

Sounds great, I wont need to use Meth at all just water.

90% of cases dont need meth. as most people only need cooling (so water does this fine), water also acts as a knock suppressor.

The only benefit of meth. is more octane and a tiny bit more cooling as it evaporates quicker. I planned on using the meth in the injection to act as a fuel (ie on boost with out injection I would be lean) so that with the injection the fuel air would be ok.

Most people jet/tune their engines so on boost they are good with fuel air - then inject water and meth. on top of that when they only really needed water alone in the first place. The extra meth. they injected is only so they can tell their mates "my car runs of methanol".

So yeah, you only really need water injection UNLESS you tune to use that extra fuel from the meth. should you inject it. Other wise injecting it over a good fuel air ratio already is pointless.

Thats what I like to hear and also those Flat slide carbs are awesome
but bigger than 48-50mm for an A15 is overkill really.