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Old 04-05-2010, 04:46 PM   #1
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Lean burn cooldown/ Water injection?

I had my car running up to 18:1 air fuel ratio, but backed off because I don't know how hot it can handle. I'm thinking about getting an exhaust temp gauge with some kind of switch that would inject a water mist when it got overly hot.
Any thoughts?
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Old 04-05-2010, 06:51 PM   #2
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Originally Posted by fowljesse View Post
I had my car running up to 18:1 air fuel ratio, but backed off because I don't know how hot it can handle. I'm thinking about getting an exhaust temp gauge with some kind of switch that would inject a water mist when it got overly hot.
Any thoughts?
What kinda of management are you running?

Do you have control of your ignition timing?

I'm not running any egt's but had a temp cht gauge and anything over 17:1 the head temps and coolant temps drop by about two degrees.
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Old 04-05-2010, 08:04 PM   #3
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I have MegaSquirt and Spark. That's interesting that the temps dropped.
My DynoJet AFR gauge only goes as lean as 18:1, and it runs fine past that. I could lean it out until there's some hesitation. I just run it lean at idle, and cruising.
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Old 04-05-2010, 10:24 PM   #4
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Originally Posted by fowljesse View Post
I have MegaSquirt and Spark. That's interesting that the temps dropped.
My DynoJet AFR gauge only goes as lean as 18:1, and it runs fine past that. I could lean it out until there's some hesitation. I just run it lean at idle, and cruising.
That's cool!!! If you can just up the timing and you should be OK.

I adjusted mine on a Chassis dyno by utilizing a Raytek Infrared gun reading the header tubes about two inches from the head. As soon as I upped the timing the temps drop off drastically.

Anything past 17:1 the temps dropped of a ton. I was also was thinking about running a DevilsOwn water/meth injection I had but after the testing I decided it wasn't worth it.

I can run as much as 28:1 without any miss fire but the engine looses to much power and the FE goes down with the power loss. So 22:1 seems to be the sweet spot for my engine.

Its cool to see another home brewed lean burn person on here.

When your running lean what is your manifold pressure at?

Are you N/A or F/I?
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Old 04-06-2010, 12:02 PM   #5
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I wonder if your A/F ratio gauge is accurate?? Advancing the timing and getting cooler exhaust temps means that the fuel is burning in the cylinder instead of the exhaust header because you start it burning sooner - which is a good thing.
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Old 04-06-2010, 12:18 PM   #6
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Hi all,
I have the same opinion as JanGeo.
Having high exhaust temps can mean two things:
- Your ignition is too far retarded.
- Your mixture burns extremely slow
Water injection is normally used only on turbo petrol engines with one goal: avoid knocking by lowering the extreme temperatures in a petrol turbo engine.
If I remember well, the Germans were one of the first to install it in a mass produced engine (Messerschmitt Bf109E fighterplane with compressor and fuel injection).
You don't need this in an atmospheric engine because the temps are not that high. Your problem in the exhaust is the mixture that is still burning. If you can not solve this by changing ignition timing, you past a certain point where you can question the efficiency of lean burn in this engine (mixture burning far too slow). Reasons for burning too slow is e.g. not enough swirl.
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Old 04-06-2010, 12:56 PM   #7
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Originally Posted by JanGeo View Post
I wonder if your A/F ratio gauge is accurate?? Advancing the timing and getting cooler exhaust temps means that the fuel is burning in the cylinder instead of the exhaust header because you start it burning sooner - which is a good thing.
You lost me on this one?

I'm running three Wideband O2 sensors and all three read the same.

I agree with your statement above and that's what happen when I advance the timing, my exhaust temps dropped.

My quote from above.
Quote:
I adjusted mine on a Chassis dyno by utilizing a Raytek Infrared gun reading the header tubes about two inches from the head. As soon as I upped the timing the temps drop off drastically.
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Old 04-06-2010, 01:45 PM   #8
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Great info! I was only guessing that my exhaust temps were high... Better safe than melted! My car is a multi port injected 2.5L V6 with 10:1 compression. I have an MSD Blaster3 coil, and am going to put on my MSD6A capacitive discharge box, when I figure out how to wire it to MegaSquirt. My ignition timing is pretty advanced, but I could mess with it more. My manifold pressure is between about 28, and 35kPa when I lean it out at about 2,000 -3,300 rpm (55-65mph). My spark is between 24-35? BTDC at that time. It has run much leaner than 18:1, because MegaSquirt reads the AFR a little lower than the DynoJet gauge. One time, I leaned it beyond the MegaSquirt gauge, which goes to 19.4:1, and there was no loss in power. The car with me and gas in it weighs about 2450lbs, and will weigh about 2400 this week, and it has a CoEfficient of drag of about .27.

SO, is the general opinion that I can lean it out until I start to lose power, without worrying about burning something? Also to note; it doesn't get hot here in Portland, Oregon, and if it does, I can richen it up, or change the timing, if necessary.
Thanks, people!
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Old 04-06-2010, 03:02 PM   #9
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SO, is the general opinion that I can lean it out until I start to lose power, without worrying about burning something?
The limit will be missfires, or indeed loss of power because of mixture burning to slow.
There's one thing you can burn: exhaustvalves, especially if the valve clearance is not perfect. Valves are cooled because they touch the cylinderhead firm. And they can really burn if there's oxygen and heat around them (lean mixture + ignition to late).
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Old 04-07-2010, 12:19 PM   #10
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That is my concern. The engine has about 10,000 miles on the rebuild, and everything was polished, so hopefully, there are no hot spots.
Is there anything I should know; what to listen/ look for when leaning out, and advancing spark?
Would spark plug heat range make a difference?
Is there an order, or procedure to do this in (example: Advance spark .5?, then lean AFR .3:1, until loss of power, or missfire)?
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