Introduction and question on water injection

Propane, Butane, LPG, GPL, C3H8, C4H10
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Introduction and question on water injection

Post by TroyT » Wed Apr 24, 2019 4:16 pm

Hi all first post although I have visited many times.

Question is about water or water/meth injection and vaporous propane injection. Does it react the same as it does with gasoline?

Engine info.
Ford 390
Twin T04B turbos
Impco 425 to single 2.5" throttlebody
Direct mounted modified model E.
No intercooler which is why I want to add water injection, question is pre carb or post carb? I'm thinking post carb with an open spacer and a couple nozzles with a progressive controller.

I'm sure I left out some info.

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Re: Introduction and question on water injection

Post by storm » Wed Apr 24, 2019 11:14 pm

G'day Troy

Water or Water/Meth injection has 2 purposes that are closely connected.
1st is to cool the combustion process, which helps to raise the knock threshold.
2nd is to raise the knock threshold of the engine by increasing the octane rating.

With regards to cooling the combustion process it will work the exact same as petrol.
With regards to raising the knock threshold I'd debate how effective this is with LPG. Why? because LPG and Methanol have a similar Octane rating. Methanol is rated at 110 Octane rating while LPG (Propane) is also about 110 Octane rating. LPG that has Butane in the mix is lower so Methanol can help to increase the octane rating but only marginally.

I would think the benefit you will get is from cooling the combustion process which in itself will help to raise the knock threshold.

Pre or post carb? I have only ever seen post carb and would think the closer you can get the injection to the intake valve the better.
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Re: Introduction and question on water injection

Post by TroyT » Thu Apr 25, 2019 10:38 am

I am familiar with water injection on diesel but have never fooled with it on any other fuel. Buddy's pulling tractor has 11 nozzles throughout the system at 1000psi, during a pass it burns more water than fuel!

I have been actively driving the setup as is, so it must be fairly safe. Runs veeery strong. Hope to get it one the chassis dyno this summer.

My main goal is to lower the charge temp and possibly help with cooling the intake valve as well just to add a safety factor. Plan to use the blue windshield washer fluid which is a 30% methanol mix easy to find and cheap.

I don't like the idea of blowing water through the 425, probably be fine but just seems wrong for some reason since it was never designed for wet flow.

Thanks for confirming my thoughts. Very difficult finding information for lpg stateside so this has been mostly a self learning process. Especially anything outside of stationary engines. Its fun though, Ive used lpg on off-road trucks for years but those are mostly thrown together worn out parts.

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Re: Introduction and question on water injection

Post by gottago » Sun Apr 28, 2019 2:33 pm

Noticed your post Troy.. Interesting, an old school 390 with some modern jewelry.. or is that a 351 stroker? What compression ratio are you running? Why not just add an intercooler if concerned? Would like to hear the dyno results too. There was another fellow on here a while back wanting to add a turbo to his big block. Might give him a bit more incentive hearing how well they go.

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Re: Introduction and question on water injection

Post by TroyT » Wed May 01, 2019 11:29 am

It's old school 390 FE. This is an temporary engine, basically a stock worn out low compression truck 390. Probably around 8:1. This engine has been my proof of concept/test bed and doesn't owe me anything. To be eventually replaced with a 360 FE with aftermarket rods and pistons, few other goodies to help it live. Shooting for 9:1 on that engine.

Honestly I do have the room for an intercooler but don't really want to mess with the mounting and charge pipes. Nor do I think it will look good. Another reason my "theory" is that the latent evaporation of the water/meth will help cool the intake valve better then an intercooler would. But that's just a speculation on my part.

The dyno is going to have to wait a little longer then I thought, the current clutch setup will not hold the power. Looks like a new flywheel and clutch setup are in my future. Probably a twin disc. Lay into the throttle in high gear at 55mph as the boost comes on it will flat let go.

First drive was an eye opener to say the least.

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