I know water methanol injection kits work wonders on vehicles with turbos and superchargers, but has anyone one here done one to a cherokee? They increase the octane rating of normal fuel and lower total motor temps, but the 4.0 is designed for regular octane fuel.....is this a worthy upgrade?? has anyone tried it? let me know Thanks!

 

Basically, you're using the latent heat of evaporation of the injected solution to reduce the temperature of the intake air. Obviously, if you're using some sort of compressor - turbo/supercharger - there will be a significant temperature rise so the meth injection is a poor man's intercooler. (and it's lighter and generally eaiser to plumb.)

It won't matter much on a stock, normally aspirated engine as the air velocity won't be high enough to cause much evaporation and cooling.

 

on a N/A motor, meth injection is useless.

 

Don't bother. By absorbing some of the residual heat after combustion, the use of water/MeOH (or other water/alcohol) fogging reduces "hot spots" in the combustion chamber, helps to keep carbon deposits down, and reduces the ONR (Octane Number Requirement) of a high-compression or forced-induction engine. It won't do squat for a factory naturally aspirated (NA) engine - period. It will do very little for the typical stroker - if you want to do something of benefit to a stroker, have the block decked so that clearance between the piston deck and head deck runs .045-.060" with the head gasket you select (that will do much more.)

Water/MeOH fogging was developed to increase the operational ceiling and high-altitude performance of piston-engine aircraft for WWII, and made its way into hot-rod circles. There's nothing at all wrong with the system (I've set up quite a few!) but it should be used for the purpose intended - like any other tool. You woudn't drive a screw with a mallet, would you? Same thing here.

I've used water/MeOH as a means to reduce ONR for high-boost turbocharged engines, for staged forced-induction engines (turbochargers blowing into a supercharger,) and even to supplement an intercooler for increased adibiatic efficiency of a given compressor system (trying to get as close to a zero-temperature-increase setup as possible. I've actually managed to get a few setups where the intake charge temperature was several degrees below ambient, but that took some creativity to do! And even then, I couldn't do something like that past an atmosphere of boost without some heavy exotic work... The best thermal efficiency I think I've ever managed - and it took some doing! - was getting a 2.5-atm boost charge to within 10*C of ambient after compression...)

NB: The water/MeOH system won't do anything whatever to normal fuel - or to any other fuel, for that matter. If you want to increase your AKI (Anti-Knock Index, or "pump octane number,") there are a couple of ways to go about it:

1) Use high-octane fuel. "Race gas" is available at some service stations up to 100AKI, and you can get 100LL, 110LL, 112LL, and sometimes 120LL aviation gasoline as smaller airfields. Note - if you don't require the higher octane due to higher compression, you'll get minimal to no effect. The AKI of a fuel doesn't have anything at all to do with its net thermal content, it's a measure of the resistance of a fuel to ignition/combustion. It's used to prevent spark knock, preignition, and detonation with high-compression/high-performance engine combinations!

2) Use additives. The original use of TEL (TetraEthyl Lead) was as an anti-knock additive, which was the primary difference between "regular" and "unleaded" fuel - before "regular" was taken off the market. AKI-increasing additives are available at most parts houses - the most common being 104+ and Kickgas (both of which are supposed to take the typical 15-20 gallon automotive tankful of pump gas up to 102-104AKI.)

3) Use additives. Being unconventional, you'll end up doing research into petrochemistry and fuel composition here to see what the refineries use, and then figure out the mix rates of the additive for a given fuel to get a desired AKI. For instance, toluene (a common industrial solvent) is added as an AKI improver to pump gasoline, as it has a "blending octane number" of 112. I've actually built a couple of engines that run on toluene - but it required some major alterations to fuel metering. Most of the lighter alcohols (methanol - MeOH - ethanol - EtOH - propanol - PrOH - and butanol - BuOH - in particular) have blending octane numbers greater than 100. And, most of these solvents are already used as AKI improvers! (Much the same way that acetone is already used as a fuel system cleaner - I merely dump in four ounces to the tankful about every three months to bump up the concentration and keep the system nice and clean. I seem to want to recall that the blending ON of acetone is somewhere in the nineties, and it's already present in gasoline, so I'm just bumping up the AKI a fraction and upping the concentration of a solvent already in use.)

4) Rejet/remeter for a different fuel. A number of lighter liquid hydrocarbons have AKI ratings well over ninety, with several somewhere well north of 100. How do you think they manage to get AKI numbers over 100 for aviation gasoline? AvGas 120LL (Aviation Gasoline, 120AKI, Low Lead) is the highest I've seen, but my granddad used to fly an old Jenny biplane that ran on "grape juice" before he had to have new heads made - "grape juice" was aviation gasoline that was coloured purple for identification, and ran somewhere around 135-140AKI. Ouch!

Whichever path you take, you're either looking at some calculation and trial-and-error, or some serious work and money - so why not just enjoy the ride? If you have a habit of using cheap gas, using a water fogger or a water/MeOH fogger can keep carbon deposits down, but why not just use better gasoline and use a water mist into your idling engine about once a year to make sure you don't get carbon buildup in the chambers? Lot less work that way - and you don't have to remind yourself to fill the "other" tank whenever you fuel up...

 

x2. This guy knows his stuff. Some of the turbo buick guys mix up their own additives...
-Matt

 

Very helpful information! Thanks for all the input guys!

 

Been at it for a little while. Cut my teeth on Corvette/Camaro restos (uncle's collection,) got into AMC/Jeep, and did street/strip, pulling engines, powerboat engines, and even performance one-lunger B&S and Tecumseh engines. Started the practical education about thirty years ago, and started really digging into the theory side of things about twenty years ago. Thermodynamics and petrochemistry came naturally as a result (as well as fluid dynamics, historical research, &c.)

There's a list of recommended reading on my site, but an awful lot of it can be fairly dry...

 

If you are running crazy high compression on a NA setup, you can get gains out of water/meth injection.

You cool the charge overall and allow for more timing and reduce the chance of detonation.

More of a safety feature though. I plan on running a meth injection on my Powerworks SVTF. There it will lower intake temps and should net some decent gains.

 

Impressive write-up and explanation 5-90.

Thanks for taking the time to do that.

 

5-90 i checked out some of the readings on your page and it wasnt to dry even after a full days work lol. Thanks again for putting time into your thorough responce!

 

Glad to help!

One of the books on my list (to write...) is a handbook for the hobbyist on Internal Combustion Engine Theory, but written in the more "conversational" style I try to employ, which seems to work. I had someone review my Power Manual who knew sod-all about engines in the first place, but she told me that she read the whole thing through just because I did manage to make the subject interesting and readable.

That's what I try for!

I'll probably start the theory manual after I hit a plateau on Swappology - which is taking up most of my writing time at the moment (even though it's just the co-ordination of information, more than anything else. The Power Manual was written mostly from memory and experience, but Swappology is something I've already got about eight months' digging into, just for the basic research!)