rx7 SE

iTrader: (5)

I've been doing research on the water/meth injection fad for several months now and have installed a coolingmist kit on my FC (yet to test it on the road). I know practically all the benefits of auxillary injection but there's something that doesn't add up to me.

Correct me if I'm wrong but the whole objective of running a larger intercooler is to lower AIT's, and thus gaining more power because of this. I've seen datalogs of WI bringing AIT's down to where a large intercooler would have done, but yet people say that running water alone will not net you any power, if anything it may initially decrease power until raising boost, tuning, etc.

How is this possible, isn't there a formula stating an additional hp gain per every X amount of AIT lowered? If so, water injection should net you the same gain as installing a larger intercooler, except you won't have the boost drop through the longer pipes. What am I missing ?

Thanks,

~Ant

Sandro

iTrader: (1)

How much power you make mainly depends on how much oxygen you can cram into the combustion chamber.

If you get lower AIT as a result of upstream AI injection only, some of the liquid (water or methanol) must have evaporated and cooled down the air. Evaporation does however cause dilution of oxygen in the air-vapor mixture, which may offset the oxygen "enrichment" from cooldown (increase in density).

Multiple effects, very difficult to predict in a formula. Extreme theoretical cases can be predicted based on ideal gas laws though. For deeper insights, see my thread in this AI section, specifically about this issue https://www.rx7club.com/auxiliary-injection-173/humidity-o2-dilution-887550/

- Sandro

TimeMachine

iTrader: (10)

Correct me if I'm wrong, but I think you gain 1% HP for every 10*F drop in intake temperature (all else being equal).

Trots*88TII-AE*

iTrader: (11)

so... a 1000HP Turbocharged 20B drag car would see the same change in power as a 50cc scooter based on intake temperature drop?

It's not that simple

rx7 SE

iTrader: (5)

Do you think an investment in a larger fmic is necessary with AI? I hope not because that's primarily the reason I went with water/meth injection.

FD3S2005

iTrader: (11)

here is what i think, yea the water injection will cool some of the air and ait's bla bla bla, but having a bigger i/c compared to a smaller i/c both with ai, my theory is that would you have very hot air coming from the turbo going through the smaller i/c cooling very little with the help of ai that does cool it... or a bigger i/c that cools much better and even more with the help of ai

rx7 SE

iTrader: (5)

Good point, I hate how heat soaked my tmic gets too, the car just feels so sluggish after awhile

Hotwheelz

iTrader: (18)

I've been testing my AEM kit that I set up to an on off switch just for testing. Here are my results:

For now I still have the stock intercooler

I have a power fc commander set on the air temp and knock monitor setting

With the w/i off i got my intake air temps up to 60 degrees celcius (140 fahrenheit) on a cool day
I switched on the w/i and i watched the temp drop to a low of 24 degrees celcius (75.2 fahrenheit) and the knock dropped on WOT as well. I did notice however that when driving without boost the w/i system does'nt activate and so the temps rise back untill I boost again.

In my opinion an intercooler will be a plan for me in the future for the fact that it will still cool intake temps when not under boost and the w/i system is not running. Together they would make a killer combo.

There is a huge temp and knock drop with a water methanol set-up and before It was tuned there was a noticable power increase. A quick, crisp boost responce. I know for sure my car loves this stuff in our Houston climate.

For sure the AEM water methanol system I purchased from Bansai Racing was the best
$375.00 I've spent on my car so far.

I posted a thread of my AEM in cab install with lots of how to pictures

Hotwheelz

iTrader: (18)

Since posting the reply above I've obtained a PFS SMIC and installed it on my car

https://www.rx7club.com/3rd-generation-specific-1993-2002-16/smic-install-pictures-897382/

Not only does the intercooler lower the intake temps when not under boost but I saw an all time low air temp of 14c ( 57.2F ) with intercooler and meth injection under 12psi boost. I would definitely suggest buying an intercooler. I got mine here for $380 with the duct

link to the actual water/meth injection set up

https://www.rx7club.com/auxiliary-injection-173/aem-water-meth-how-install-fd-895580/

rx7 SE

iTrader: (5)

Great info! That may be something I look into doing this summer then

PvillKnight7

iTrader: (16)

Two words you need to learn:

Volumetric Efficiency

rx7 SE

iTrader: (5)

Volumetric efficiency deals with how much air an engine can actually flow compared to a theoretical flow, I don't see the relation to lowering air intake temps?

If VE was my goal, then I'd buy an h22. I've heard them make well over 100% VE whereas rotaries are around 85%

PvillKnight7

iTrader: (16)

There is a balance point. Picture a drinking glass. It has 80% air and 20% fuel. If you compress the air you have room for more stuff in the glass. You fill that new found space with water. There is point of diminishing return. It's a chemical balancing act. You can't keep compressing the air by adding more and more water because you will displace the fuel. Hence, lost power. That's why pure meth injection might be better in some situations.

mike_merryguy

iTrader: (8)

IMHO you would have to inject a **** ton of water to actually displace enough fuel to make a difference, and at that point since the stock ECU doesn't know that you are injecting water you would overstuff the compression stroke and maybe pop a seal... but think how much water that would take...

correct me here if i am wrong but you are atomizing the water as its injected, the H20 is then seperated into ATOMS and the stuff is all mixed and cools off the air, well you have left is H2 and 0 and last I checked they are both sources to help fuel out so in turn your theory is wrong, plain water will, if atomized properly.... yep burn (hence the hydrogen car...)

and I am no chemist so I could be wrong this is just what I got out of the articles I read...

I aslo ran only WI on my FC that was pushing 5psi on a supercharger with no problems

Trots*88TII-AE*

iTrader: (11)

If vaporising water separated it into its base molecules, those spray bottle-fan things would be weapons of mass destruction.

Also, if it was that easy, hydrogen combustion engines would be a lot more popular. It's not.

mike_merryguy

iTrader: (8)

LOL thats a good comparison, a fan bottle doesn't spray through a tiny hole at 150 PSI...

ya know i just though it vaporizes not atomizes, whatever it takes it down really far and shouldn't take up enough space to displace fuel thats what i was getting at LOL

classicauto

iTrader: (3)

It both amotizes and vaporizes. But atomization is not reducing a chemical to its atoms. Fog is atomized water, clouds etc. The finer the atomization, the finer the droplets of water, thats all.

It vaporizes into steam (change of state) when it soaks up enough energy to do so. Depending on where you're injecting it that vaporization will take place in different locations. usually in the combustion chamber.

I inject 625cc of water @ roughly 400whp. That is more water then one (FC) stock fuel injector pumps into the engine. So the amounts are not insignificant in regards to displacing fuel. However I would venture to guess without an ignition system thats hooked up to a power grid - you would not be able to fire the mixture long before you'd fill the combustion chamber with water and hydro lock the engine, so its really nothing to worry about.

$lacker

iTrader: (9)

I think by atoms you mean molecules

classicauto

iTrader: (3)

lol yes, molecules I said atoms because the post I was responding to said:


EDIT:


And damnit Taylor I didn't want anyone to see the secret new nozzle setup you bastard - those pics were in confidence!!!

Mike Merry guy is correct but incorrect. Water's base elements will burn, but you are not turning water into hydrogen and oxygen molecules by spraying it out a nozzle - thats all I'm getting at.

Trots*88TII-AE*

iTrader: (11)

I let the cat out of the bag, sorry Joe!

mike_merryguy

iTrader: (8)

well i know the basic principles but just can't explain it scientifically lol