Saw an interesting idea on the internet for personal watercraft. The idea is to inject water spray into the exhaust chamber. The cooling effect on the exhaust gasses effectively slows down the the pulses(hot gasses go faster in an exhaust system) which increases back pressure. The whole idea is to allow you to have increased back pressure on a free flowing system,,, like those loud pipes we all like. So as a practical matter you'd need an RPM switch with start/stop like the one from MSD used to safeguard running nitrous past the rev limiter and maybe two relays to sense "motor running and WOT" as well as a pump and nozzle etc.

Hmmm.......

 

That is an interesting idea. It does sort of make sense. The three issues that could raise are: what would this do to the cat? would this increase rust? and I can't imagine that this temperature fluctuation is going to be good for the exhaust system. Maybe that stuff doesn't matter or is insignificant, I don't know. This is something to look into though.

Good points,,,mostly the water through the system shouldn't be a huge problem. Traditional water injection through the intake sends water as steam to the cat and exhaust system. The cat doesn't care and no rust occurs. I do think theres a question of whether the water would be steam before it hit the cat. I think it would be a huge thermal shock to dump liquid water onto the 1200degree catalyst mesh. I also don't see this working for turbos as cooling the exhaust on either side of the charger would translate to lag. Hope somebody tries this idea though. Someone smart and brave and resourcefull,,,Oh Skip,,,are you out there.LOL:D

Where the heck would you keep all the water? If you are talkin about dumping it into an exhaust then you would have to have alot of it and keep on re filling it. Doesn't sound very feasible. Plus you have the added weight. Boz

Boz,

I'm picturing something that only works at very low RPM like crawling or red lights. I slip my clutch a lot rather than fall out of the power band when starting out. It would be nice to mat it at 1000RPM and take off with authority. How much water it takes I don't know. I guess you'd have to calculate the calories your'e trying to extract from the exhaust flow to get a number on water consumption. I do know that racers wrap header pipes to keep temps up by a few percentage points and help flow speed. Regular water injection takes 10-20% of the fuel consumption figures if your'e really using it alot.

MSD Pulse Width Modulated Water Injection System

 

 

MSD PWM WATER INJECTION

 

It's $199.99. Looks interesting!

Well, as for the water becoming steam, what do you think the exhaust gas temperatures are? I'll bet they are way pass the boiling point of water. Since the water is being injected (sprayed)into the exhaust chamber, I have an idea that it would almost instantly vaporize into steam. If I understand the process correctly, this isn't a full time occurrence, so there is no need for a large water tank, as it would only have an 'on demand' requirement. I believe since it was designed for watercraft that there was no thought of the effect to a cat, since most boats don't need them (yet). But since the water would be at a high temp, but lower then normal, it may cause the cat not to reach the desired temperature to be efficient.

Also,You would have to worry about the O2 sensor not reaching temprature. This would tend to mess up the ECU on cars that have them making them run rich......

 

 

 

 

 

Thanks,Ed.....

...The idea is to inject water spray into the exhaust chamber. ...

 

Did you Done That?

You would be cooling off the cat too much and you can damage it. O2 sensors wont really care too much. You can rot out the exhuast system.

 

You would be better off with water injection before combustion.

 

Boats dont have expensive pipes and cats (yet). Not to mention if parts rot out on a boat, its accepted as normal wear and tear.

 

nipper

I dont see how this helps anything, because "backpressure" is nothing deisrable in the slightest.. all that is desirbale from an exhaust system is pulse scavenging, and pulse scavenging is NOT the same as backpressure...

 

I say you get more power from:

 

Water injecting pre combustion, which allows you to run more ignition advance without pinging, which opens up more power for you, and just leaving your exhaust at a more conventional size.

 

than you do from:

 

whatever slightly larger exhaust you can run without losing your scavenging qualities by injecting into the exhaust.

 

I also say: HOLY OLD THREAD, BATMAN!! but this one is actually kinda interesting :-p

I read the info on the MSD site: does not say anything about backpressure there. It does say that the exhaust chamber injection makes the chamber act like it is longer, because the charge is denser, and moves slower. That makes sense to me (particularly on a 2-stroke).