Solofast

Water injection isn't a band aid.....

For any application there is a limiting CR or boost pressure that is based on the octane available. If you aren't over that it doesn't detonate, and above that it does. While you are saying that improved design has increased the tollerance to detoation, that is absolutey true. But once you are out of rope it is going to knock if you don't have the fuel to keep it from detonating. Water injecton simply lets you use more boost or more compression ratio than you would be able to use otherwise. Obvioulsly lots of folks are finding out where that limit is since they are getting detonation. Lots of other folks are at that same limit too, only they don't know it, and are simply loosing power since their konck sensing systems are retarding the spark to keep detonation under control.

But you don't need the higher octane fuel (in fact it hurts fuel economy since it burns slower) at lower power conditions. So if you have high boost you end up octane boosting or buying expensive racing gas to prevent detonation for the 2% of the time when you are at high power. That is expensive and unnecessary since you only need detonation suppression when combustion pressures are high. I would say that adding higher octane gas is more of a "band aid" solution, since it costs you money with every fill up and it does nothing when you aren't at high power. Water injection adds detonation suppression only when it is needed, and lets you have better fuel economy on less expensive lower octane fuel when it isn't.

I agree that it is more work to keep the bottle full, but if the engine is built and is knocking it will be a lot easier to add water injection than tear the engine down or feed it a strict diet of more expensive racing gas or octane booster.

In that sense water injection is a far more elegant solution.

45ACP

"What do you have against the Japanese?"

Their hardware was, at best, second rate. Technologically, the big players were the US, the Brits and the Krauts. The Japanese did ok at first, but as soon as their foes got serious, they fell behind rapidly.



"I go the Reno air races every year and I don't think that have ever seen water injection used. I have seen big doses of N2O which was also used in WWII fighter planes."

It has been a few years since I read much on the subject and so my memory is a little fuzzy, but I recall N2O and water injection being used mostly in bombers. Very, very heavy loads, trying to climb out, etc, etc.


I wouldn't use water injection in a street car. I don't imagine I'd use it in a race car unless the rules required it somehow.

Is this blown up Z06 the guy that wanted to race you last year? The one that figured "that old Vette" would be easy pickings? The same one that learned how horribly wrong he was?

Monty

I agree with what you siad priot to that, I wasn't debating those points or why water or alchol injection would be used and how it works. No debate there.

All I'm saying is that the right thing to do is fix the problem causing the detonation, not slap a band-aid over it and hope you never run out of water or alcohol or a solenoid doesn't fail at the right time and cause damage to a multi-thousand dollar engine. That was my point from the beginning.

I'm just the type of person who would fix the problem the right way, even if that meant disassembling the engine and installing pistons with a slight dish, lower compression height, etc to lower compression. I would consider that the elegant solution.

I've known George for several years now and from what I can tell he's always been the kind of guy that does things the right way too. As George stated in his first post, he solved the problem by installing the appropriate cam with a little more duration and overlap, although he is now inquiring as to whether water injection would have solved the problem. I won't agrue that it probably would have, but at what cost. I'd be willing to bet his engine made more power and torque with the larger, more appropriate cam for his compression ratio, than it would have if he would have simply slapped a banda-d over the problem in the form of a water injection kit. Considering he's getting quotes of $300 for the water injection kit, a new cam won't cost him any more $ since he's a hands on guy and can do it himself.

The main reason most of these water injection kits are still on the market is that so many guys that own newer cars like the C5/C6 want to add bolt on supercharger/turbocharger kits without pulling the engine out or apart. Since these cars already have 10.5+ CR, they are limited to about 6psi of boost on pump gas. So they slap the band aid on the problem, inject water/alcohol, and can now "safely" run more boost. "Safe" until they forget to top the bottle off or a solenoid fails. These are the type of installations that give forced induction a bad name.

The right thing to do, the elegant thing to do, would have been to lower the static compression ratio by replacing the pistons, but that admittedly adds to the cost and complexity of the project.

arnold

At what point of engine operation, whether RPM, power related or whatever/whenever, do you (or Monty or anyone else) know those combustion pressures are high, or more specifically, when detonation probability is highest? Were you referring to the PPP (peak pressure point) itself, or based on my above question, referring to a point of engine operation where the PPP is too close to TDC? Or were you not thinking of PPP at all?

For Monty, you stated "If the engine were properly designed for the application it wouldn't detonate....". Based on the content of your other posts, I am inclined to believe you were making reference to setup based on DCR?

A couple other notes of possible interest. A high octane fuel does not automatically imply a slower burning fuel. An application in point would be a NASCAR high compression 9500+ RPM engine. A slow burning fuel would not be a good choice for that application. Also, anyone ever notice an improvement of power on a very humid or rainy day? Whether you know it or not, you are taking advantage of a passive form of WI.

Guru_4_hire

OK I am gonna try and be solution oriented.

OK water injection is a good idea.

But lets wax philosophic for a minute. You already have an injection system, your carbeurator. Whats fun about the carbeurator, is that its a pretty good distance away so the fuel has a pretty good amount of time to absorb energy. Blow through carbeurated systems can fun a bit more boost because of this effect. fuel injection puts the fuel right at the port so it doesnt have time and space to cool the intake charge. So lets first abuse the things you already have going for you and buy a big *** fuel cooler. maybe a chller kit for it. This way you are atomizing the coolest fuel you can into the engine, which should help with detonation.

Same would go for a water injection system. You could drill some holes in a carb spacer and spray you water/meth into the engine with a signifigant amount of time/space to absorb heat energy. Or most intake manifolds have NOS boss pads at the end of the runners of the intake manifold. You could drill those out and put your injection there, but it doesnt give you time/space for energy to be absorbed.

A good place to start would definitely be a big *** fuel cooler.