For the first time I got to run my rx-7 with the water injection at the track. My only concern was trap speed as thats more an indication of power to weight , rather than ET which is more driver oriented. I prefer not to discuss my actual numbers as they are irrelevant, but I will discuss the differences in my pre-WI and post WI run.


today I ran 11 lbs of boost and ran 3 times on the same setting on my power FC. My water injection was set to turn on just under 11 lbs. On all three runs my trap speed was within around .30 MPH, so it was very consistent.

Last fall I ran at the same track PRIOR to installing the WI, the same boost settings with the same mods on this car and my trap was exactly the same as I trapped today. Thats right, no differences.

So I learned that water injection by itself at the same boost level does not give you any more power, but I do have some very cool findings.

On my first two runs today I hit the full 11 lbs of boost which was required to activate the water injection. My knock reading on my power FC was 12 on the first run and 15 on the second run. My trap speed/ET were nearly identical. On my third run I did not hit the full 11 lbs of boost, I can only speculate that I hit 10.8 or something close as I know from my boost gauge that I hit 10.X, I just dont know what "X" is. Anyway, since I did not hit the full 11 lbs my water injection did not kick on (and I can confirm cause the red light on my dash did not turn on). the result? Identical trap speed to the first two runs (literally within .30 MPH) and a knock reading of 70. I was pretty damn shocked at the knock reading. I could be coincidence or maybe the water injection really works.

Ok, Im done wasting bandwith.

 

well my firend that you help setup his water injection on his skyline was knocking more when he ran it. why was that?

 

oh yea, the 16 year old kid with the skyline? I have no idea, did he raise the boost beyond what he was running without it? Water injection will only carry you so far. If you spray too much water you can get hesistation in the high rpm's but when its set up correctly it should not cause any knocking.

 

David,

Are you still selling WI kits? I need a new Fd project. Wanna help me with it?

John

 

Hi John....

I actually never, ever sold a kit. I had about 5-6 requests but I turned them all down. I helped a guy from this forum install the water injection after he bought the parts. I'll be glad to do the same for you. Its well worth it, believe me.

 

doesnt it rust out your internals?

 

You were under the impression that it would?

 

No I wasn't under the impression that it would, but I have not seen any tests to back up any theory so I tested it myself.

Some people think due to lower intake temps you should make more power at the same boost level with water injection. Others say the fact that the water takes up room where the air would be, the fact that there is less air in the intake cances out the fact that the intake temps are lower. I wanted to test it, and I did.

 

david as you know I have this on my car....but if I didnt and I just read this post its very confusing. You didnt do a good job advertizing for WI it sounds like it does nothing. When IS it going to give you more power? Never right? unless you tune for it? So basically its a cheap safety measure is all right? keep your engine running cooler and cleaner.

 

Well in theory lower intake temps do lead to higher HP numbers, thats why we all have IC's.

 

hey dude...

I wasn't attempting to advertise for it. To be honest I was hoping I could say that at the same boost level it raised my MPH by 2-3 Miles per hour, but the fact is it didn't. It made no difference.

If you want more power, you can raise the boost a few lbs beyond what you are tuned for (assuming the WI is set up right).

In my 2 runs that I ran with the WI, my intake temps never changed. Even after the runs my intake temps never rose. On the third run when I had the WI off, my intake temps rose like crazy after the run.

So WI eliminates heatsoak and makes you less likely to detonate. Both those claims were supported in my test. It will allow you to run more PSI than you otherwise could without it, thats where it gives you more power.

 

exactly, thats why I wanted to test it out. But you dont have water in your IC taking up space that would otherwise have oxygen in it.

 

you can run a half a point leaner with water injection afr wise than without. this is where you will gain your power.

 

Doesn't water (H2O)evaporate to air of some kind that can cause better or greater mixture of air and fuel....in turn, make more power? I don't know much, so educate me.

Thanks,

POM HB

 

It evaporates to H2O, which is water vapor. I'm not a chemist, so I'm not 100% sure, but the O2 in water vapor is probably not broken down in combustion - only the O2 in the air as oxygen. So the A/F ratios should not change much.

Dave

 

Good post Zero, this makes me seriously consider a WI setup if/when I get the resources down the road.
This sounds like it is a great reliablity mod if done right.
Its always nice to see guys posting their finding good and bad.
Justus

 

WI does NOT work for long term! SHORT term..YES.
in the long run, the internal components will RUST.
im sure all of u know what rust does.

 

WI was used back in the 80s on street racing. the results were proven!!!

 

Just like everything else there's good and bad to water injection. One of the key downsides is that your displacing combustion components (fuel, air) with a substance that takes up space and doesn't contribute to the combustion other than cooling the charge temp a bit because of energy absorbed during evaporation. I'm not certain what the water vapor will do to lubrication internally over the long term, running too rich can "wash down" the walls removing lubricating oils, I suppose steam could do that too.

If you decide that you cannot achieve a safe AF using your fuel system or you're just looking for that charge cooling effect from evaporation then I'd suggest looking into using a combustable substance instead like alcohol etc. but also read up on materials use downstream with stuff like methanol. Bleh sorry I don't have time to go too much into this. : ( You get the idea though.

Kevin T. Wyum

 

Next time I go to the track , which will be in a few weeks I will change my water injection to turn on at 7 PSI. I will then do another comparison. Probably will not make a difference, but should be fun anyway.

 

Everything I've read on this subject says the benefit of the cooling is almost directly offset by the displacement of air by water vapor, at the same boost level. If you don't use water injection to increase boost (or possibly run leaner) there is no benefit. If you increase boost, the combustion chamber cooling should prevent detonation. So, the benefits come from increasing boost safely, not from charge cooling.

 

The only time water injection is going to be a huge benifit is when you want to run a ton of boost. In other words, I'd love to make 500rwhp on pump gas but its hard to do so at 17-18psi (pump gas safe limit). With water injection I know of people runing 22psi of boost on pump gas with no problems.

Other than that I wouldnt worry with it to much. If you do run it you wont gain any power at all unless you tune for it and lean your a/f out....just make REAL sure that you always keep it nice and full cause if you lean out your micture then run out of water your going to be killing the engine.

BTW - My understanding is WI doesnt really do a hole lot for the charge temps (maybe just a little), what it really does is lower combustion temps....like I said though thats just what I've understood. Did you happen to watch your air intake temps on the various runs to see if it was lower when you sprayed?

STEPHEN

 

Stephen,

Water injection does more than just prevent detonation at high boost levels. For one thing, I got a bad tank of gas in my last engine, which is why I believe I popped it on the dyno. WI would have prevented that.
Water injection as you know cleans carbon build up, steam cleans the engine.

As far as intake temps, I run this on my car all the time on the street. I can tell you my intake temps stay at ambient when I am on the highway or driving in the city. on the track I had it set at higher boost, but I can tell you my intake temps stayed at 44C for my first two runs, on my last run the WI was off and the temps went to over 60 after the last run.

It does eliminate heatsoak, thats been proven also.

 

How can it keep your temps at ambient all the time when your driving around if its only comes on when your running 11psi of boost? You dont continually run boost. Also, it must be pretty hot on planet X if your temps are 44C (111F) and thats ambient in the middle of Feb.

For cleaning out the engine you can do the same thing with a bottle of water and a vac line. You just hook it up to a uim nipple and let it take a drink. If your worried about carbon build up you can just do that every do often, maybe when you do a oil change or something.

Water injection wont make up for a bad tank of gas. The reason is water is not combustable, your still going to need something that will combust correctly in the tank. Now maybe if you accedently got 89 instead of 93, then WI would help in that situation.


STEPHEN

 

Steven,

On the street I run the WI around 4-5 psi. I only set it to 11 psi the day before the track and forgot to set back.

thats convenient.

thats what I mean, 86 instead of 91.