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Built engine GTX2867R - Poor power and flat spot (W/ Dyno Graph and Logs)
Setup Highlights:
Built motor w/ 8.4 comp
Garrett GTX2867R (w/ .86A/R)
Flyin Miata cast manifold
Full 2.5” exhaust w/ FM Catalytic Converter
DIYPNP
Sealed Power VS855 Valve Springs
Trackspeed Engineering Coil-On-Plug
Flow Force 640cc Injectors
93 pump
Issue:
1. There's a flat spot in torque between 5,300 and 6,700 RPM (You can see the car start to recover at 6,300 RPMS)
2. Car is generally under powered for the PSI it's running.
Next Steps:
I've been tuning the car for weeks now. It seems like the more timing i add, the more power i make, until it starts to knock or miss. I've even scrapped the tune entirely and started with other base maps. (e.g. Right now, I'm working from highly updated Hydra VVT map).
Considering the slow boost, it seems like there's a boost leak. That said, I've run repeated boost leak tests and it seems solid right now PRE-throttle body (Can i run a leak test on the intake manifold somehow?)
I've also checked both Cam and Ignition timing (The latter with a light).
The only think I can think of at this point, is something wrong with the head/valves or I'm missing something major in the tune.
Recent Dyno: Log from that pull (full log attached):
It won't take anymore timing below 6000rpms without knocking? If it will that will help spool a good bit, those 10 degree cells @ 210kpa seem low to me. The boost spike at 5500rpms is definitely contributing to the dip in power from 6000-6500, but it still looks odd. How are you controlling boost?
The 2.5 inch exhaust with cat aren't doing you any favors, but with that turbo at 20psi I think you're right to expect more.
Also, a little constructive criticism on the fuel map. You should interpolate the red portion (which will pull fuel) and add fuel in the black portion. At 6000rpms you're going super lean and stumbling at 2-20% throttle and piggy rich at 60-99% throttle. Those boost but not WOT cells are often overlooked and autotune always tends to pull too much fuel from light throttle high rpm cells.
Check cat for meltage/blockage/restriction, bigger exhaust would = more power, dip is likely lack of ignition timing, I would check AFR calibration too. If it won't take more timing without knocking with 8.4:1 and a big a/r turbine, your exhaust sucks or octane is way too low. My 2cents.
Check cat for meltage/blockage/restriction, bigger exhaust would = more power, dip is likely lack of ignition timing, I would check AFR calibration too. If it won't take more timing without knocking with 8.4:1 and a big a/r turbine, your exhaust sucks or octane is way too low. My 2cents.
I vote exhaust restriction. This can also cause knock in a round about way.
I’m going to pull the midpipe tomorrow (post wideband, pre cat). It's the easiest change and should any exhaust related issues.
Side note: Yes, the AR .86 would NOT be my first choice either. It's what I've got for the time being. That said, I expect the AR to only hinder/delay spool by 500rpm and have no impact >5K
I would actually expect to see a 1000-1500 RPM improvement in the spool. A gtx28R should be between 3500 and 4000 or thereabouts on a well tuned 1.8. The 0.86 is probably helping you right now where you are actually making power.
There looks to be something wrong with your fueling coefficients and/or calibrations. It is most likely either your injector flow or dead time, but it could also be in the MAT, CLT, ...
you have idle VE at 115, and your sub 100kpa cells are all too high. I would highly recommend getting this figured out, and when you re-run VEAL, do it with incorporate AFR. It is difficult to evaluate the fuel table as currently configured.
I would actually expect to see a 1000-1500 RPM improvement in the spool. A gtx28R should be between 3500 and 4000 or thereabouts on a well tuned 1.8. The 0.86 is probably helping you right now where you are actually making power.
There looks to be something wrong with your fueling coefficients and/or calibrations. It is most likely either your injector flow or dead time, but it could also be in the MAT, CLT, ...
you have idle VE at 115, and your sub 100kpa cells are all too high. I would highly recommend getting this figured out, and when you re-run VEAL, do it with incorporate AFR. It is difficult to evaluate the fuel table as currently configured.
I reviewed my setting (and screen captured below).
Some quick notes:
I now see my Injector Size Each (cc) set to 256. Obviously that should be 660. That said, i was under the impression this was only a multiplier for the Fuel VE map and should matter at this point? I will adjust them now and retune the fuel map.
My DIYPNP voltage reading is incorrect. It sits around 17volts (which you can see in the log posted above). I've simply worked around it until this point, but I should learn about the "Calibrate Battery Voltage Settings"
Yes, my Idle VE is very high. I've never had the car idle perfect and seems to need the fuel at all times. Additionally, the hotter the car gets, it the RPMs dip at idle when coming to a stop.
Here're two pulls from this morning with the mid pipe fully removed from the car.
The only adjustments were:
Pulled timing 2 degrees at 3300rpm to 4500rpm between 110 and 160 load.
Adjusted fuel (added a TON - obviously too much in some spots).
I would have made more adjustments but the only actual flat pieces of road available are within ear shot of people at this hour and I didn't want to disturb the peace.
RED Line: Yesterday's pull with cat still installed BLUE Line: Exact same piece of road as RED line but without cat. GREEN Line: Seemingly flat highway entrance ramp
Looks like I'm going catless afterall Maybe i can donate to environmental group so i can sleep better at night? (Although this isn't my DD).
Something doesn't make sense. With a lower than actual injector size the REQ fuel goes up and VE goes down.
if you truly are getting 300+ hp it would probably be advisable to get the configuration as accurate as possible and not allow significant errors to be absorbed into the fundamental tuning parameters. The amount of margin you have for error drops substantially at these power levels.
Something doesn't make sense. With a lower than actual injector size the REQ fuel goes up and VE goes down.
if you truly are getting 300+ hp it would probably be advisable to get the configuration as accurate as possible and not allow significant errors to be absorbed into the fundamental tuning parameters. The amount of margin you have for error drops substantially at these power levels.
100% agreed. I updated Tunerstudio to the correct, 640cc. I was manually adjusting REQ fuel instead of having TunerStudio calculate it (hence why my injector size of 256 really didn't matter).
Additionally: Looking at a few past logs, it's obvious the car likes sub 12.0AFR while spooling. The mid-pipe/cat is now reinstalled so we'll see if I can keep any of that better spool (shown above) by keeping the AFR's down earlier. Will report back later with findings.
Well if the battery voltage reading is off by ~4V, then you will be pulling ~600usec off the top which has to be made up. Get the voltage reading fixed first
After putting the mid pipe back on the car, and again playing with AFR, I was right back where I started with power/spool. (My hope was running the car rich was contributing to the better spool)
I had the axle back off the car a few weeks back and it made zero improvement, leading me to believe my issue is entirely related to catalytic converter, and not necessarily the 2.5inch exhaust.
At this point I can:
Free: Leave the car untouched and just enjoy it.
Cheap: Gut the cat out of my 2.5inch Flyin Miata midpipe
Less Cheap: Replace the 2.5inch 300cell ceramic Magnaflow cat that came with the mid-pipe, with the weld in 3inch 100cell metal Mil Spec cat I have laying around from my Evo days.
Update: going with the "less cheap" option and am going to replace the 2.5inch ceramic 300 cell cat, for a 3inch metal 100 cell cat. Hoping to have the car back on the road within a week.
With the cat no longer being an issue, I don't think the exhaust as a whole will be a restriction and the car should be able to spool quicker and hit the goal of 300whp+ much sooner. I'd love to trap 115 mph before the season is out but will settle for 112. Fingers crossed.
The entire exhaust is 2.5". When I remove the axle back, there's no change in performance. When I remove the cat, there's a huge change in performance - the car will actually make more power than desired.
Thus I'm simply replacing the current cat with a much much better flowing one, I have sitting in my garage. That cat happens to be 3inch.
Is a 2.5inch exhaust with a 3inch cat ideal? Nope. But I'm not replacing the entire exhaust system nor am I running catless. If it doesn't work for some reason, I'll regroup.
The entire exhaust is 2.5". When I remove the axle back, there's no change in performance. When I remove the cat, there's a huge change in performance - the car will actually make more power than desired.
It sounds like you've already got it figured out, but just for reference, removing the axle back while leaving the plugged cat doesn't actually tell you anything about the effect of the axle back on flow. The cat is the bottleneck, so everything after that isn't going to make any difference until you eliminated the bottleneck.
08-19-2017, 05:24 PM
Built engine GTX2867R - Poor power and flat spot (W/ Dyno Graph and Logs)
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Maybe i can donate to environmental group so i can sleep better at night? (Although this isn't my DD).
