so, what are the propor readings for a "safe" tune?
12.4 afr, <10psi on 9:1 compression, and no knock (15*btdc)?
I'm just curious. I hear that lots of people tear stuff up on too aggressive of a tune, but I don't see how if its stoichiometric, and no knock. Sorry, I'm a newb. |
At high rpm a car makes max torque at 13:1 and max hp at 12.5:1. I read a sae paper on it one time but I dont have a link to give you. Another reason for a non stoich mixture in boost is because the extra gas actually helps cool the cylinders to help prevent knock. Also, the extra gas helps delay the explosion so that a hot edge or other deposit doesnt pre-ignite the mixture, much like the previous reason.
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Originally Posted by neogenesis2004
(Post 79239)
At high rpm a car makes max torque at 13:1 and max hp at 12.5:1. I read a sae paper on it one time but I dont have a link to give you. Another reason for a non stoich mixture in boost is because the extra gas actually helps cool the cylinders to help prevent knock. Also, the extra gas helps delay the explosion so that a hot edge or other deposit doesnt pre-ignite the mixture, much like the previous reason.
I also read in the megamanual to tune to like 17:1 under cruise. Is that right? what kinda afr's do I want under load for both natural aspiration and fi? Thanks for the help on this. |
also, how do I tune ms for decel and cruise if we don't use a TPS? How will the MAP show this? Do all map's show vaccum?
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17:1 is safe for a cruising, but I wouldnt go over that. I got 32mpg at 15:1 on my MS. Anything at atmospheric or below you would be safe at 14:1 under like 5krpm. I personally would tune to 13:1 above 4.5k below atmo. Above atmo, below 4.5K I have it tune around 13.5:1 and then above I tuned to 12.5:1 above 4.5k. 12.5:1 is optimal but to be safe 11.5:1 is what you should tune for really. I had water cooling and that is why I felt safe to tune that lean in boost. What ended up killing one of my cylinders was my timing adv.
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Originally Posted by neogenesis2004
(Post 79247)
17:1 is safe for a cruising, but I wouldnt go over that. I got 32mpg at 15:1 on my MS. Anything at atmospheric or below you would be safe at 14:1 under like 5krpm. I personally would tune to 13:1 above 4.5k below atmo. Above atmo, below 4.5K I have it tune around 13.5:1 and then above I tuned to 12.5:1 above 4.5k. 12.5:1 is optimal but to be safe 11.5:1 is what you should tune for really. I had water cooling and that is why I felt safe to tune that lean in boost. What ended up killing one of my cylinders was my timing adv.
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additionally, places on the map like the right bottom corner you can run pretty lean because you will only e in that part of the map when you are going downhill and under next to no load at any speed.
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cruise is easily like 70% of the time. You'll hit boost when you want to and going up hills. With the small turbos we have youll easily be under enough load to hit atmo at only like 30% throttle. So boost I'd say is even with decel. But that depends on where you live. I go to school at VT which is in the middle of the appalachin mountains so i go up and down hills all day long when I drive.
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My car made its best power at ~13:1 on the dyno
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ok, so i will set up pulse width to correlate with boost pressure, but how do I get my afr correct since boost and rpm are independent variables? What does "boost is even with decel" mean?
thanks so much for the help, I can't seem to find this info anywhere else. |
Originally Posted by hustler
(Post 79254)
ok, so i will set up pulse width to correlate with boost pressure, but how do I get my afr correct since boost and rpm are independent variables? What does "boost is even with decel" mean?
thanks so much for the help, I can't seem to find this info anywhere else. |
I wouldny try 17:1 on a Miata motor. 17:1 might be ok for an oldy low compression Vette engine with big-bore cylinders, not so for ours. Be on the safe side, stick to 15:1 at cruise.
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Originally Posted by neogenesis2004
(Post 79239)
At high rpm a car makes max torque at 13:1 and max hp at 12.5:1.
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The add to that the variables of what different gauges/senors read. This is why egts are often seen as a valuable tuning tool- just one more thing that can tell you what your changes are doing for combustion. My process is to datalog, then sit down at the computer and compare the log for desired results, make adjustments and then repeat. The key is to make small adjustments to meet your goal.
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Thanks guys. The more I talk about it and get input from here, the more feasible it seems.
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Originally Posted by hustler
(Post 79234)
12.4 afr, <10psi on 9:1 compression, and no knock (15*btdc)?
I'm just curious. I hear that lots of people tear stuff up on too aggressive of a tune, but I don't see how if its stoichiometric, and no knock. Sorry, I'm a newb. Buy a jewelers loupe so you can examine your plugs for specks of piston :) start the timing low and work up until you get scared or you see little balls of metal stuck to the plug and then back it down a bit. Pull them after each run while you let the car cool. But you should also lower timing a few degrees around peak torque. You guys with experience tuning Miatas feel free to shoot that down as the closest I've come has been a turbo MX3, what I've said above is just general crap I've gleaned screwing around with other cars over the years. |
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