Built engine GTX2867R - Poor power and flat spot (W/ Dyno Graph and Logs)
1 Attachment(s)
Setup Highlights:
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:
Recent Dyno: https://cimg0.ibsrv.net/gimg/www.mia...e385c7e4da.jpg Log from that pull (full log attached): https://cimg0.ibsrv.net/gimg/www.mia...b602fa2a55.png |
2.5" exhaust is sure as hell not helping. That boost curve seems so bad.
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6 psi @ 4K rpm... someting wong heow.
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0.86 A/R turbine housing. The 0.64 on the 2867R will spool to 20psi much earlier, but will probably fall off more on the high side.
the 0.86 is a poor choice for a non-compounded/twin application. |
1 Attachment(s)
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. Attachment 229855 |
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.
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Originally Posted by patsmx5
(Post 1434881)
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.
Also, odd as it seems, less fuel helps me spool. |
All, I really really appreciate the feedback. I made a list of recommendations below:
Possible issues:
Thanks again |
Here's a snap shot of the cat.
The second picture is holding the entire pipe above a strong light. I'm going to go drive the car shortly and try and get another log (without getting arrested for the noise). https://cimg1.ibsrv.net/gimg/www.mia...53011a65d3.jpg https://cimg2.ibsrv.net/gimg/www.mia...0e1460a2c7.jpg |
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. |
Originally Posted by Ted75zcar
(Post 1434932)
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. Some quick notes:
https://cimg5.ibsrv.net/gimg/www.mia...eb3daa3812.png |
Here're two pulls from this morning with the mid pipe fully removed from the car.
The only adjustments were:
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 :facepalm: Maybe i can donate to environmental group so i can sleep better at night? (Although this isn't my DD). https://cimg7.ibsrv.net/gimg/www.mia...a525ef4935.jpg |
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. |
Originally Posted by Ted75zcar
(Post 1434942)
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. 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. Thanks again! |
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 ;)
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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:
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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. |
Wait are you installing a 3" mid pipe, and the connecting to your 2.5" axle back?
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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. |
Originally Posted by Carloverx
(Post 1435228)
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.
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Ah! Very true! Fingers crossed replacing the cat maintains most of the performance I saw with the cat removed.
The current axle back setup (in theory) should be pretty free flowing. |
Didn't read the whole thread closely, but here are some observations that will hopefully help:
1) turbo/hotside is terribly sized for the rest of the setup. spool is horrendous 2) the fm bits and 2.5 exhaust is definitely hurting your spool as well, in addition to the stock muffler 3) that "recovery" you reference past 6300 is a very common glitch In the VD software. I really doubt your power actually jumps up past 6300. as you can see in the 2nd plot it noses over hard 4) your tune sucks my conclusion is I don't think your engine is the issue. I think everything else is terribly matched. no offense Just outa curiosity: did you select each part yourself or just bought a random pile of parts? |
Originally Posted by 18psi
(Post 1435309)
Didn't read the whole thread closely, but here are some observations that will hopefully help:
1) turbo/hotside is terribly sized for the rest of the setup. spool is horrendous 2) the fm bits and 2.5 exhaust is definitely hurting your spool as well, in addition to the stock muffler 3) that "recovery" you reference past 6300 is a very common glitch In the VD software. I really doubt your power actually jumps up past 6300. as you can see in the 2nd plot it noses over hard 4) your tune sucks my conclusion is I don't think your engine is the issue. I think everything else is terribly matched. no offense Just outa curiosity: did you select each part yourself or just bought a random pile of parts? Additionally, I'm under the impression the AR .64 vs .86 on this turbo is only good for about 500rpm quicker spool on most setups. I'll take a little more top end over that. I do not have a stock muffler. As for parts selection, it was slowly picking parts here and there over the past two years whenever deals arrived. E.g turbo was used from a 240sx. All fhat said, I still have high hopes for the setup after I get the cat and tune squared away 🙂 |
Maybe I came off way too harsh, my apologies. 370hp is still quite a lot of power
I'm just really shocked at how laggy this setup is. I mean, passing 200tq at 4600 is really late. I think the .86 in your case is doing you zero favors over the .64, but costing you a whole lot of spool/response. The log mani is exacerbating the issue as well. 2.5 exhaust has been proven many times on our cars to reduce spool/response, and as you've learned, the cat is hurting it that much more. I mis-understood some posts and thought you were on stock axleback, my mistake. (although with it spooling so slow, that would have made sense) Can you show me a plot where a .86 hotside clearly makes significant power over the .64 on a Miata? I've seen this on other cars no doubt, but have yet to see it on a Miata. Can you also show me a plot of a Miata performing well with this setup, or as it should? Only other similar setup I can think of is codrus and vtekkiller |
I suspect the cat is hurting you more than the 2.5" exhaust. That said, 3" is definitely better, and there's no reason not to run one that size.
What gear are you doing the Virtual Dyno runs in? IME, 2nd or 3rd is going to give you a very poor estimation of the spool capabilities of the engine. To measure spool, put it in the 1:1 gear and and do a pull from 2000 RPM until it hits full boost (or higher, but going to redline will probably be 120+ in that gear). IMHO, virtual dyno is a lousy way to tune spark, it's much too sensitive to variables that are too hard to control. A proper dyno is the right answer. My car is a .72 ATP exhaust housing with EWG V-band, not a .86. I've also got a GTX2863, so it's a slightly smaller compressor. --Ian |
Originally Posted by 18psi
(Post 1435323)
Maybe I came off way too harsh, my apologies. 370hp is still quite a lot of power
I'm just really shocked at how laggy this setup is. I mean, passing 200tq at 4600 is really late. I think the .86 in your case is doing you zero favors over the .64, but costing you a whole lot of spool/response. The log mani is exacerbating the issue as well. 2.5 exhaust has been proven many times on our cars to reduce spool/response, and as you've learned, the cat is hurting it that much more. I mis-understood some posts and thought you were on stock axleback, my mistake. (although with it spooling so slow, that would have made sense) Can you show me a plot where a .86 hotside clearly makes significant power over the .64 on a Miata? I've seen this on other cars no doubt, but have yet to see it on a Miata. Can you also show me a plot of a Miata performing well with this setup, or as it should? Only other similar setup I can think of is codrus and vtekkiller Regarding providing evidence for the .86 vs .64 on a miata: I have none. 500rpm is my rough estimate based on old dyno graphs from unrelated setups, littered about the internet. (though it does fall in line with the .64 GT2871 ebay charger I previously had on the car). The .86 is NOT helping, I agree. But it just seems like there's a bigger issue in play. Outside of the anecdotally poor spool and power, the other reason I feel the actual setup could do better (even with the mismatch of parts), is due to the seemingly major increase in power I experienced after removing the midpipe/cat. Hence why I'm headed down the path of swapping out the cat. Fingers crossed :) p.s. more details of my nonsense can be found here in my build thread
Originally Posted by codrus
(Post 1435332)
I suspect the cat is hurting you more than the 2.5" exhaust. That said, 3" is definitely better, and there's no reason not to run one that size.
What gear are you doing the Virtual Dyno runs in? IME, 2nd or 3rd is going to give you a very poor estimation of the spool capabilities of the engine. To measure spool, put it in the 1:1 gear and and do a pull from 2000 RPM until it hits full boost (or higher, but going to redline will probably be 120+ in that gear). IMHO, virtual dyno is a lousy way to tune spark, it's much too sensitive to variables that are too hard to control. A proper dyno is the right answer. My car is a .72 ATP exhaust housing with EWG V-band, not a .86. I've also got a GTX2863, so it's a slightly smaller compressor. --Ian I agree the VD is not ideal and had done all it could for me at this point. I recently visited a great shop (ProFab - Chasis & Custom Cars) just a few miles away to setup dyno time. BUT, I haven't made an appointment yet b/c I still felt the car wasn't healthy enough. I genuinely think that after this cat swap, the car will be ready for dyno time. :hsugh: |
Originally Posted by Carloverx
(Post 1435410)
No worries! You may be 100% right, as I have no idea what I'm doing, lol :) That said, I WISH the problem was 370hp - hell, I'd be completely smitten with 330hp! The problem is, as you mentioned, spool is horrific, and power is poor relative to my expectations for the psi/setup (all things considered). With the midpipe still installed, reaching 290whp was like pulling teeth! At the heart of all this is: this car started a casual weekend toy. "Pffff. Certainly I'll never need more than a 2.5 inch exhaust or a cast log manifold" I said, lol. And yet here we are :(
Regarding providing evidence for the .86 vs .64 on a miata: I have none. 500rpm is my rough estimate based on old dyno graphs from unrelated setups, littered about the internet. (though it does fall in line with the .64 GT2871 ebay charger I previously had on the car). The .86 is NOT helping, I agree. But it just seems like there's a bigger issue in play. Outside of the anecdotally poor spool and power, the other reason I feel the actual setup could do better (even with the mismatch of parts), is due to the seemingly major increase in power I experienced after removing the midpipe/cat. Hence why I'm headed down the path of swapping out the cat. Fingers crossed :) p.s. more details of my nonsense can be found here in my build thread I'm running VD in 3rd gear. Unfortunately I can't find a local strip of flat road long enough for a clean 4th gear pulls (damn New Jersey). I agree the VD is not ideal and had done all it could for me at this point. I recently visited a great shop (ProFab - Chasis & Custom Cars) just a few miles away to setup dyno time. BUT, I haven't made an appointment yet b/c I still felt the car wasn't healthy enough. I genuinely think that after this cat swap, the car will be ready for dyno time. :hsugh: |
Update:
https://cimg6.ibsrv.net/gimg/www.mia...ad6ddcde5e.jpg https://cimg8.ibsrv.net/gimg/www.mia...b96c6611f6.png |
New boost curve looks way better, but I'm not sure they're directly comparable given that the gear was different. i.e. different load.
I'm sure that you can tell the difference though. |
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