Tip in Acceleration Solved- Need Input for Write-up
 

I have been working over the last three months to resolve a long-standing problem of tip-in acceleration on modified FD's using aftermarket ECU's, in particular the Power FC, but this analysis and subsequent applied fixes may also help solve any tip-in acceleration problems using other aftermarket ECU's. I could have posted this on the Power FC forum or the other ECU forums, but I need input from everyone, even owners of totally stock or near stock cars on the stock ECU to the heavily modified cars using an aftermarket ECU. What I have found through my testing and analysis of tip-in acceleration, is that this function is highly dependent on the air flow or volumetric efficiency of the car's systems, including the engine (mostly porting and 2 mm vs. 3 mm seals), intake (including piping, manifolds, and turbos), exhaust (including manifolds, downpipe, cat, cat-back). I have older Datalogit logs from my car from prior setups which I used and my current logs from my recent extensive air flow modified rebuild. It is very difficult to know or measure true volumetric efficiency in any car, but there is one data point that changes with the intake side of the equation that I can use to help rank different modifications to a rough standard, which is the amount of vacuum developed at idle. In example, my prior setup was a street-ported, 3-mm apex seal 13B with stock UIM, LIM, throttlebody, Efini crossover pipe, Greddy elbow, stock 99' twins, K&N air filters, and Greddy SMIC. On this setup, vacuum at 800 rpm was -400 mmHg and at 1000 was -425 mmHg. My current setup is the same street-ported 3-mm apex seal 13B, extrude honed LIM and UIM, RC ported throttlebody, same Efini crossover pipe, Hitachi HT12-KAI SP turbos, extrude honed Greddy elbow, Autoexec airbox, and Australian dual bank U-type SMIC. With this new setup on the exact same engine(engine not rebuilt), vacuum at 800 rpm is -315 mmHg and at 1000 rpm is -325 mmHg. The added efficiency of moving the air through the air intake system significantly decreased the vacuum. This is the same thing seen with larger engine ports, less vacuum due to added air efficiency.

I have been able to figure out the values used in the three tip-in acceleration tables in Settings 2 of the Power FC. Almost everyone has lean AFR's on tip-in, which leads to poor acceleration and unwanted added engine stress. I now have crisp, almost instantaneous throttle response when I press my gas pedal down, even for mild movement. For passing or more brisk acceleration to WOT, the car leaps forward like I always thought it should. It is amazing the difference it makes. The analysis of these tables and things I found out solved a problem that has almost certainly affected anyone using the Power FC with a lightly to heavily modified car. With this info from all of you, I should be able to recommend changes in the tables for certain modification levels to give each of you the type of new found acceleration to put a big smile on your face and truly know we drive rotary rockets!!

Here is what I need from all of you, if you want to help. I need a simple list of engine porting, 2 mm vs, 3mm apex seals, turbos (single vs. twins), IC(stock, SMIC, FMIC), UIM, LIM, throttlebody, airbox. Then I need vacuum measurements with rpm reading at low idle and your higher idle, preferably between 800-1000 rpm, if possible. From this data, I will hopefully be able to categorize modifications into classes to give my recommendations for changing these tables as a starting points for each of you.
Thanks
Mike

The write-up is coming. Time to light the Rocket!!! LOL

That is awesome, Mike! I'll get that info next time I'm around the car.

I've also found that having the TPS set properly makes a substantial difference. Setting it so the voltages are close to .50v and 1.25v at warm idle makes a substantial difference. Mine was set at 1.00 v and simply going to 1.25v made a very positive difference for me.

Dale

Some of this is from memory, but should be spot on.

My engine is stock port, Mazda 2mm apex seals. Motor is healthy, compression tested with a rotary tester a few months back and it's strong. 99 twins, Blitz front mount, bigger secondary throttle blades on the TB, HKS intake,

Pulling about 390 mm hG (about 15.5") of vacuum at idle. Idle is about 850.

I'll have to find out the high idle/AC vacuum reading.

Dale

Dropping by to give info =)

Vehicle:
Efini RX-7 (JDM)
Stock ports, Stock Apex seals (2 mm I believe), Sequential Twin Turbo, Factory Airbox, Factory SMIC, Factory Cat Converter. (JDM so no precat)

Vehicle Mods Are:
ECU - PowerFC
Fujitsubo Cat Back Exhaust

Idle settings on PFC are:
IDLE A-E OFF - 850 rpm (720 default)
IDLE E/L ON - 900 rpm (850 default)
IDLE A/C ON - 1000 rpm (900 default)

My Idle vacuum readings with the car warmed up and reading 82 c of water temp are:
A-E Off - 850 rpm - 400 mm Hg
E/L On - 900 rpm - 420 mm Hg
A/C On - 1000 rpm - 440 mm Hg

I hope my info assists you

Thanks Dale and Jez. This is helpful. I need others to chime in with more moderate to more heavily air flow modified cars. Once all the data is in, I will try to come up with a snapshot of the settings for all three acceleration tables for respective categories with similar mods and corresponding similar vacuum readings. This will allow someone to plug in the numbers that will be at least close for their respective car. There will be some guesswork on my part since my numbers are specific to my car. Someone with similar vacuum readings and mods to mine should be able to run with it. Others will have to tweak their tables by either logging like I did or by following their AFR closely with acceleration. Once you get the hang of it, it is rather easy to get close but tedious to dial it in tight. My write up explains the tables in detail and how they work. I am a few days from finishing the write up but still need the input from all of you to make it work for you. Coming soon.
Mike

Remember, you don't have to run the Power FC to help the rest of us who do. All I need its the mods list and vacuum readings so I can place my car in the spectrum to figure the needed changes for others.

Forgot one other thing. The changes, which you have to follow correctly, do not cause any car to go lean or raise the AFR. In every case, again if you input the values correctly, the car will go richer every time or lower the AFR to a more ideal number. You can go rich, sometimes too rich if you really over do it, but a rich acceleration should not damage any engine in the short term but can cause rich misfires just like to much fuel and water with aggressive WMI.
Mike

Should have my car going this weekend and i'll get back to you. Stock twins, mild port, 80mm+ full exhaust, v mount. Will list all the details then.

Paging @arghx
This is right up his alley :)

I'm waiting to hear more. My current car is almost completely stock, including stock ECU, so I don't have much to contribute until I hear more details.

I will send some info later this weekend, my car currently is running on the stock ECU because it runs so well with it (albeit somewhat rich), I actually pulled out my PFC due to aggravation with tip in stumble so if this could be solved with some tuning changes that I could do myself I would be all over reinstalling the PFC!

Thanks. It will make a significant difference with tip in acceleration. Once dialed in, with a little tweaking, it is amazing how well the old Power FC can do. The reason, in the past, for the inability for others to make changes that worked is that unknown to them and to me up until the last 4 weekends of testing, is that the Datalogit FC-edit software will let you change the values in the three tables for acceleration that don't actually work. What I mean is that the software will let you enter numbers that you think are legitimate, but are actually unrecognizable by the Power FC program. That means one wrong value and the entire table is messed up and will not work right and you are screwed. I went down so many rabbit holes for the first 6-8 weeks and I was so frustrated that changes I expected didn't work. Once I determined the limitations in each table values, the door was opened and success followed.
Mike

I don't have a Power FC, but a recent datalog of my mostly stock setup (stock airbox, stock seq twin turbos, 3" aftermarket downpipe, stock cat & muffler) shows MAP = 40 kPa at 950 RPM warm idle, and slightly more vacuum (MAP = 38 kPa) at 1500 RPM cold idle. This is approximately 3500 feet, MAP = 89 kPa with the engine off.

Getting tip-in throttle dialed in really helps a car feel comfortable to drive. Another thing that helps drivability is making sure the AFR goes slightly rich (not lean) when you slowly release the clutch to creep forward.

Thanks. This made me think that I will have to state that others will have to account for altitude differences in their vacuum readings to choose the right table values to use.
Mike

Just drove my car around, seeing right at 400 mmHg at 950-1000 RPM (AC on).

Dale

13B-REW FEED Nur Spec porting and rebuild (unknown port size, assume 2mm seals). Stock twins. HKS RS Intake. HKS V Mount w/HKS Elbow. Factory TB and manifolds.

low idle at 850rpm - 380mmHg

el idle at 950rpm - 400mmHg

I am finished with my primary 3-month testing and I am in the fine tuning stage. I have a very brisk acceleration at all RPM's at WOT with no significant lean areas (sometimes a little rich), smooth quick non-lean passing, and non-lean smooth acceleration even with mild pedal pressure. The car now drives very similar to the stock ECU, if not better. Also, my twins spool quicker than before due to the quicker non-lean acceleration with a target AFR of 12.2-12.4 initially in late vacuum and early boost. Turbos can't spool well if your exhaust velocity is not increasing rapidly. This will definitely help all the single turbo cars out there too. Lastly, I really would like to have the mods and vacuum readings for more moderately and heavily modified cars in order to place my car in the spectrum. Thanks you to the several people that have already given me their numbers, but I have yet to have anyone with the same vacuum readings as my car chime in. Without the others, it will be difficult for me give reasonable starting points for the needed changes to the acceleration tables.
Mike

Here are the readings from my car:

Low idle
43.9 cmHg

High idle
45.0 cmHG

Both about +0 / -0.1 cmHg, as measured on a large mechanical dial vacuum gauge.

Altitude is 940 feet elevation.

High idle was obtained from switching on the running lights, no other electrical load. This seemed to allow the highest idle speed compared to other ways, like speed 3 on the fan, etc.

Mods are:

Mazda reman engine, stock ports, compression 106-110psi
Blitz SMIC
OEM intake compression tube
OEM airbox with cheap bastard mod, 99-spec air guide, OEM paper filter
JDM Mazda downpipe
OEM main catalyst
OEM ECM

Thanks again for this effort. Hope this helps.

I will post after driving car tomorrow. I would love of this worked, def have an issue with tip in. to the point where it just dies sometimes under tipin

My car's numbers off the PFC commander:

Low idle @ 824rpm: -432mm
EL idle @ 919rpm: -455mm
AC idle @ 942rpm: -431mm

Altitude @ 1300ft

Rebuilt engine w/ new housings, compression between 119-125psi
Small street port, 2mm E&J seals
All emissions retained
Apexi PFC
Blitz SMIC
OEM airbox w/ cheap mod, paper filter
Bonez downpipe
Bonez CC
Racing Beat catback exhaust

Interesting project, here's some info on my car:

Pettit ECU, readings are from analog gauges
Mild streetport
3mm seals
99 twins
Greddy SMIC
Greddy Elbow
Stock UIM
Stock LIM
Stock throttlebody
Fighters Garage intake (open intake, two K&N filters and heatshield)

No load idle = 800 rpm, 14 inHg = 356 mmHg
E/L = 900 rpm, 15 inHg = 381 mmHg
E/L and A/C = 950-1000 rpm, 13 inHg = 330 mmHg

Oh, the ambient temps were about 60 deg F and the altitude is sea level.

Thanks again for all who have responded with the data. I still need the heavily modified folks to chime in.

I have one more question for the group as a whole. How many of you have a problem with tip in acceleration or the general category of acceleration enrichment with any of the aftermarket ECU's, but particularly the Power FC? I know I did using the Power FC on my old setup, which was more tolerable or livable, and it became a debilitating problem with my new setup after the rebuild. The reason I ask this is that a member of the separate Yahoo tuning group has told me that acceleration enrichment is a very isolated problem with very few reporting any problems at all with aftermarket ECU's. Is this true? To me, if your AFR goes up or leaner by as much as 0.5 or more with any minor or major acceleration, I would consider it a significant problem coming from a non-engineer like myself. If you are like me, I have my car tuned in the cruise areas to AFR's in the high 14's to low 15's to conserve gas and keep carbon buildup in check. From this cruise zone, almost all accelerations occur in everyday lower RPM street driving and you cannot go leaner here like I did with typical AFR's of 16 or 17 and even 20 occurring on many occasions. Now, after the fix, I start the acceleration in the high 14's and my AFR immediately goes to the low to mid 12's and climbs slightly until all the additional fuel from the acceleration tables end. This is the rotary's peak torque range in the mid 12's. What better place to be than in the peak torque band during an acceleration. If you watch your AFR gauge closely when you mash the pedal, from a little to a lot, how many of you experience a rising AFR's (0.5 or greater) and how many show no significance rise or even a decrease in AFR? If you log, check you logs.The members that show an increase in AFR or are leaner and use the Power FC, this new write up to fix the acceleration enrichment tables is for you and you will experience the difference it truly makes. For those with little or no change in AFR, some minor changes to the acceleration tables to lower the AFR into the peak torque band will help some, but you won't experience the same dramatic improvement the others will. Let me know your experience.
Mike

powerfc,stock ports, stock intake manifolds, stock throttlebody, pettit ic, single turbo
idle at 850 -410mmhg
idle with ac 700 rpms -350mmhg

no idle air control or dashpot

I have posted the write up for Acceleration Enrichment Solved for the Power FC in the Power FC forum section. Here is the link.

https://www.rx7club.com/power-fc-for.../#post12344738

I can help answer any questions you may have and help others to achieve much improved accelerations. I was only able to give recommendations for lightly modified cars at this time since I don't have data for other more moderately and heavily modified cars.
Mike

This is awesome! I'll have to try some acceleration logs and see what my car is doing. Hopefully this can help my power when coming out of corners during autox.

Once you get this dialed in, which will take some time making and testing changes, you will be amazed at the difference it makes. You will power out of the corners like a rocket ship!!! LOL
Mike