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Best A/F for a Single turbo 3rd gen.

 
 
 
 
Old 08-08-03, 10:26 PM
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Best A/F for a Single turbo 3rd gen.

A friend of mine recently bought a 1994 R2 with a single turbo (CBB Turbonetics 60-1) and all the supprting mods plus a G-Force ECU. Also it has a PMS piggyback for fuel adjustments. I was wondering what the reccommended A/F for a rotary is under boost. I have recently been told that as high as 13:1 and I am a little weary. I have a wide band o2 for tuning just curious about what the safest A/F to run is. A little less power is OK for more reiability.

Thanks


Adam
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Old 08-09-03, 12:11 AM
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11.5:1 seems to be a popular target. 13:1 is too lean as your intuition suggested.

Keep in mind how the PFS box works -- it clamps the boost signal to the ECU to ~11 psi or so, leading the stock ECU to give the same injector pulse width for any boost level above that. Then the PFS box applies its enrichment to that signal. So, you will be rich right at that point, but the car will get lean as the boost rises. Thus, you need one level of enrichment for 11 psi, a higher level of enrichment for 13 psi, and an even higher level of enrichment for 15 psi.

-Max
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Old 08-09-03, 07:35 AM
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Re: Best A/F for a Single turbo 3rd gen.

Originally posted by Batty200
. I have recently been told that as high as 13:1 and I am a little weary. I have a wide band o2 for tuning just curious about what the safest A/F to run is. A little less power is OK for more reiability.

Thanks


Adam
Whoever told you 13:1 has no clue about tuning and will blow their rotary very quick. Your best bet is to tune for 11:5:1 on the dyno. On the road the car will be under "load", you will lean out to around 12:1 which is almost perfect.
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Old 08-10-03, 11:43 PM
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Thank you all for your inputs! I have a PMS on my DSM also and I was going to call EFI Systems, the maker of the PMS and see if I could use a 3Bar GM MAP like my DSM does and use that for the boost calibrations. Like I said I appreciate all the help. I will post some dyno number when all done.

Later
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Old 08-10-03, 11:57 PM
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Hey max
Im the owner of the 94 R2 my buddy Batty200 was talking about.
Anywho how would i get around goin lean about 11 psi ?
I can just give it more fuel right?

I want to run about 15 psi on street and 20 psi on track.

thanks

Hai
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Old 08-11-03, 06:59 AM
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You won't be lean at 11 psi, you will be rich at that point if your maximum boost is higher.

The PMS has a fuel cut defencer in it that clamps the boost signal to the stock ECU to keep from hitting fuel cut. Let's call that point C (= 11 or 12 psi). That means the ECU injector signal won't increase at boost levels that are high than C, since the ECU still thinks you are running at boost = C. But, you do need more fuel as the boost goes up, so the remedy is to increase the fuel enrichment in the PMS. However, that will cause you to run rich around point C, since the same injector signal will be delivered at that boost, and the PMS will apply a significant portion of the enrichment adjustment at that level.

Here's an "executive summary" of the situation:
- tune the fuel enrichment map for the maximum boost you plan to run with the map
- you need different maps for different maximum boost levels, since you need more enrichment at higher boost levels (use the Lo-Med-Hi 3-way switch to change maps when you want to run different boost pressures)
- you will run rich around point C when the mixture is right at the maximum boost level

In contrast, systems like the PowerFC, Haltech, etc. allow you to create one fuel map that will work for all boost levels, since there is no clamp on the boost signal to screw things up. They also don't have the issue of running rich just below maximum boost. The PMC works fine for basic programming and people have put down some reasonably decent dyno numbers with it, but you must understand its design to use it effectively.

I attached a spreadsheet that illustrates the issue. Study it to understand what is going on. Play with it to see what happens when you change the numbers.

Be very careful if you want to run a lot of boost. I would be uncomfortable running more than 15 psi with it.

-Max
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Old 08-11-03, 07:12 AM
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Also, I want to make it clear that the numbers in the spreadsheet are just for illustration of the issue and SHOULD NOT BE USED to directly program your ECU. I had to use some numbers to show what happens, but those numbers don't necessarily correspond to real values that you will use to program the ECU. Seek to understand what is going on generally, and then keep it in mind as you program the ECU.

The basic rule of thumb to keep in mind with the PMS is that if you want to run a different boost level, you also need to change the fuel enrichment map. If you don't care to learn the details, keeping this rule in mind will still allow you to program the unit successfully.

A lot of us PMS owners in the past started to wonder why we needed different fuel maps for different boost levels. It's the same engine, right? It seems like one map should work. But we discovered that this boost signal clamping behavior results in the requirement that a different enrichment value needs to be used to run a different boost level. The more boost you want to run, the more fuel you need to add to the injector signal from the stock ECU to get the right mixture at maximum boost. We also learned about the rich hump that this situation creates at boost levels just below the max target.

-Max
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Old 08-11-03, 05:23 PM
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Have any of you guys used the PMS in its standalone mode via the InteraQ software? With this software you can totally eliminate the ecu as far as I know. Also since the PMS is running on top of a G-Force do you know of a way to disable the Fuel cut defencer built in to it since the Gforce most likely eliminates it also. I will be calling EFI Systems to ask them the same questions.

Thanks.

Adam
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Old 08-11-03, 05:48 PM
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yeah we tune my car 11.3 - 11.5 on the dyno

if we are street tuning we try to range 11.7 - 12

Last edited by 87GTR; 08-11-03 at 05:52 PM.
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Old 08-11-03, 07:45 PM
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Wade Lanham did some work with the standalone stuff. I am not sure if he ever got it to work well or not.

You could probably do a little mod to the wiring harness to defeat the fuel cut defenser behavior. Send the MAP sensor signal to both the PMS and the stock ECU, and leave the PMS output that normally goes to the ECU MAP input unconnected, or perhaps grounded through a (100Kohm?) resistor.

-Max
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Old 08-11-03, 11:02 PM
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Max,

Thanks for the help
Greatly appreciated!!

Hai
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Old 08-12-03, 04:57 AM
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Well with water injection I run mine at 13.7:1 or there abouts @ 20psi boost and 472rwhp on pump fuel.

No Water Injection and you will need to fuel "dump" to keep things from melting, breaking, springs loosing tension etc etc.

Cars that run just fuel I set to about 10.5:1 to keep them reliable and tolerate bad fuels and hot days !
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Old 08-12-03, 06:44 AM
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Originally posted by RICE RACING
Well with water injection I run mine at 13.7:1 or there abouts @ 20psi boost and 472rwhp on pump fuel.

No Water Injection and you will need to fuel "dump" to keep things from melting, breaking, springs loosing tension etc etc.

Cars that run just fuel I set to about 10.5:1 to keep them reliable and tolerate bad fuels and hot days !
Great info.

What do you do to the timing with water on compared to water off?

Ken
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Old 08-12-03, 08:09 AM
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For those that tune for road racing (DE events, etc), do you tune for 10.5 - 11.0 on the dyno? How much cushion is required to compensate for high ambient air and intake temperatures during 20-30 minute lapping sessions?

Ramon
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Old 08-12-03, 09:38 AM
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Originally posted by RICE RACING
Well with water injection I run mine at 13.7:1 or there abouts @ 20psi boost and 472rwhp on pump fuel.

No Water Injection and you will need to fuel "dump" to keep things from melting, breaking, springs loosing tension etc etc.

Cars that run just fuel I set to about 10.5:1 to keep them reliable and tolerate bad fuels and hot days !


how much water are you dumping in at 20psi? Im dieing to get my water injections hooked up
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Old 08-12-03, 12:13 PM
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You can run as high as 14:1 when you're cruising (in vacuum range). To run anything over 12:1 range during low boost is too lean. For boost above 5psi and below 10psi, it's a good idea to start tuning for 11.5 or 11.2.
For anything above, try to tune for 10.5.

When you tune for 10.5 on higher boost, it provides some margin for gas irregularities and temperature differences. You should probably be alright on the track.

If you plan to run 20psi or so, you'll need to upgrade your pressure sensor to a 3bar or more sensor.

J
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Old 08-12-03, 05:06 PM
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Originally posted by 87GTR
how much water are you dumping in at 20psi? Im dieing to get my water injections hooked up
I ran about 550cc to 600cc per minute from memory. This is the bare minimum I needed to support my 560odd BHP and at that a/f ratio.

My next application is just going to rely on water alone, no IC at all and ratios of up to 50% of the fuel flow. Basically same as some aviation piston engines.

If you run an IC I found that a flow rate of 12% is the bare minimum to get adequate performance/protection, you can run up to 15% or more. And if you use other "methods" you can inject up to 50% water to fuel ratio. This is extreme but can be and has been done by lots of people. As an example at 50% water to fuel ratio you are only eliminating around 6% volume of air which is not much, especially when you see how far the charge temp goes down !

One example is 30deg C day
50psi boost !
Charge temp 46deg C with a 50% water ratio, all for displacing 6% volume of air with vapourised water. For extreme applications like this Intercoolers (air to air) are a hinderance as they will heat the charge back up to over ambinet temperatures LOL.

If you are using normal set ups MAJORITY OF YOU GUYS I have always stuck to around 10.5:1 especially when being on a dyno as the things tend to run leaner once you get it out onto the track or the road for obvious reasons. I know its maybe not optimal for power, but saftey is the key thing for a majority of users and as such I think its a good ratio to aim for if your running fuel only in you rotary.

For you water injection men you realy need to know your actual fuel use or flow at max power then size/tune your system to deliver the right ratio of water, again 12% to 15% worked well for me even @ 13.7:1

Be warned you need a good spark
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Old 08-12-03, 05:12 PM
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Originally posted by LUV94RX7
Great info.

What do you do to the timing with water on compared to water off?

Ken
I leave timing alone, just trim a/f to suit water injection, depends on engine I guess, but mine has a narrow timing "window" in which it seems to operate the best.

In general I would say just adjust your fuel map to get maximum benifit or just leave it and turn the boost of the clock ! You will have lots of options.
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Old 08-14-03, 04:09 AM
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One example is 30deg C day
50psi boost !
Charge temp 46deg C with a 50% water ratio, all for displacing 6% volume of air with vapourised water.
Hey Pete how are you working out the 6% displacement factor?


For extreme applications like this Intercoolers (air to air) are a hinderance as they will heat the charge back up to over ambinet temperatures LOL.
not if the WI nozzle is after the air to air IC
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