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How lean do you guys go on 50/50?

Old 11-08-17, 03:37 PM
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How lean do you guys go on 50/50?

Just finished installing water injection. Running 1700cc 50/50 water meth, post turbo, pre intercooler. This is approximately 20% of my overall fuel volume being replaced by water meth mixture, of course calculating based off duty cycle's logged from injectors at full WOT usage.

So I'm trying to get an idea of how lean I can run this thing out too. Tuned around a 10.6 AFR right now, and I pulled fuel out to match that 10.6 once kicking the water/meth on-board. But it would be nice to pull it out to an 11.5 or even a 12.0. I've got a little bit if hesitation at 8300-9500rpm range in the tens, and it would probably clean up if we pushed her into the 11's.

I feel like with this volume of water/meth entering the engine, keeping IAT's down under 120F and EGT's under 1700F, there shouldn't be any issue running upwards of 12.0 for cleaner ignition, less carbon build-up, and less fuel consumption?





I ran my 2 rotor at 25psi at an 11.8AFR, on 93 octane with 700cc water/meth on 200psi pump, not a single issue. I would never attempt that on pump gasoline alone. I guess I'm just a little cautious with this engine as the expense is much greater.

Any thoughts??

Oh and the meth is being triggered by ECU dpo at 10psi boost. Engine is running 13.5-14.5 psi with overboost at 15.5psi. I'm about to wire in a fail safe using a fuel pressure transducer that will cut spark or signal a drop in wastegate duty if pressure stop flowing below a threashold under a 10+psi manifold air pressure condition.

Curious if anyone else runs in the high elevens or even the low 12's on AI??? Seems totally doable, but I don't want to find out for myself just yet

Last edited by Monsterbox; 11-08-17 at 03:54 PM.
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Old 11-10-17, 01:33 PM
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Decided to go with a 11.3AFR target at 13.5-14psi with the 18GPH nozzle on 50/50. If this works fire the mixture, Ill switch up to a 25GPH at 50/50 to see how much it affects spark.

This target should give a nice margin of error, while still being significantly leaner than the 10.8 target. We'll see how she pans out on the dyno in a few weeks from 8-9500rpm. Going to try a 0.018 plug gap, down from 0.025 on the r7420
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Old 11-13-17, 06:11 AM
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Are you gapping the R7420s or different plug? What ignition?

you will get best system efficiency with the AI after the intercooler if you can fit it there.
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Old 11-13-17, 11:55 AM
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right now I'm using the rx8 trailing plugs, gapped at 0.025. I'm going to switch to 7420-10 and gap down to 0.020.

Ignition is IGN-1a (aem smart coils) direct fire

Intercooler is integrated into intake manifold, so can't really spray post, unless I did direct port on all 4 runners, but that's way overkill. I think it should do fine pre-intercooler. I really just wanna lean it out to 11.3-4 on water/meth, 10.6 is just way fat for the boost level. But probably going to bump up to 25% of overall fuel volume in w/m first. Which historically has always been fine. Going to give it a shot!

Last edited by Monsterbox; 11-13-17 at 12:06 PM.
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Old 11-13-17, 11:26 PM
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The only problem I can see with your setup would be if water starts pooling in your intercooler. Other then that it's pretty straight forward. Watch for knock and temps while tuning.
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Old 11-14-17, 10:22 PM
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I wish I knew more about water/meth, I skipped straight to E85 and missed the ball. In for learning.

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Old 11-15-17, 01:13 AM
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From memory reading these things ages ago when it was the new new, you target the same AFR you would without running AI.
i.e. same tuning principles as if AI was not present
Your AIT, EGT, and so far 11.3 AFR seems within safe ranges/principles.

Was trying to find posts to support but only decent one i found that remotely answered your question.
https://www.rx7club.com/auxiliary-in...ortant-582856/
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Old 11-20-17, 03:36 AM
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Thanks guys. Going to target an 11.0 without water/meth and a 11.2-11.3 when water meth is engaged!
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Old 11-20-17, 06:26 AM
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Originally Posted by Monsterbox View Post
right now I'm using the rx8 trailing plugs, gapped at 0.025. I'm going to switch to 7420-10 and gap down to 0.020.

Ignition is IGN-1a (aem smart coils) direct fire

Intercooler is integrated into intake manifold, so can't really spray post, unless I did direct port on all 4 runners, but that's way overkill. I think it should do fine pre-intercooler. I really just wanna lean it out to 11.3-4 on water/meth, 10.6 is just way fat for the boost level. But probably going to bump up to 25% of overall fuel volume in w/m first. Which historically has always been fine. Going to give it a shot!
From the amount of years ive used rx8 plugs. I dont recommend them with ig1a coils. The spark plug switch to 7420-10 will be an upgrade. Gapping these plugs tighter would also contribute to better results. Rx8 plugs are weird to gap and are not built the same as race plugs.
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Old 11-20-17, 10:33 AM
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Originally Posted by Sammy Built View Post
From the amount of years ive used rx8 plugs. I dont recommend them with ig1a coils. The spark plug switch to 7420-10 will be an upgrade. Gapping these plugs tighter would also contribute to better results. Rx8 plugs are weird to gap and are not built the same as race plugs.
wow, interesting to hear!!! I guess you get what you pay for. Have a set waiting to throw in, I guess I will finally give them a go! Whats the closest you've ever gapped?
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Old 11-22-17, 04:48 AM
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Originally Posted by Monsterbox View Post
wow, interesting to hear!!! I guess you get what you pay for. Have a set waiting to throw in, I guess I will finally give them a go! Whats the closest you've ever gapped?
NGK states no more than +/- 0.008" for gapping. That's why even on near stock motors when I'm dialing in street tuning (and I see the chance to use 0.035" gap vs. a 0.044" gap), we start with a 0.030-0.032" plug. Snipping is always an option, but especially with iridium micro-tips, it's easy to damage.
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