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Engine, Exhaust, Transmission Discuss the FR-S | 86 | BRZ engine, exhaust and drivetrain.


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Old 02-23-2018, 08:11 PM   #71
Irace86.2.0
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Originally Posted by nikitopo View Post
The dip was created deliberately by factory tune and hardware. Not just with tune.

The blue line below is the torque curve of the "mother" engine. It is the FB20 engine which was used as a base to design our engine. My daily car has this engine and it has no torque dip at all. Do you see any dip in the curve? Do you think they could avoid the dip in the older engine and not in the newer?
I don't know if they did it for economy. It is certainly possible, and I have even said that same theory in the past, but it was only conjecture. What evidence is there for that? If they cared so much about mileage to create a torque dip then why would they change the final drive on the 2017 to be more aggressive?

I'm of the belief that the torque dip is a product of a 12.5:1 compression motor trying to avoid knock, something that could be alleviated with a long tube catless header, but they need a precat, and they need to heat the precat fast during cold starts for emissions, something that a long tube header doesn't allow.
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Old 02-23-2018, 08:21 PM   #72
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Originally Posted by CSG Mike View Post
It doesn't.

A stock FA20 tuned on Motec, still exhibits the dip.
Sorry, I'm fairly naive about the details of tuning...

Are you saying the Motec system doesn't use the knock sensors to automatically adjust timing/etc to avoid knock?...that the Motec system only runs on set parameters like open tune only (maf only)?...did I butcher that?
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Old 02-23-2018, 08:23 PM   #73
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At least we know the solution. Imo Toyota could come out and explain the torque curve to us and we'd still argue it. For whatever reason, the oem header was/is a compromise.
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Old 02-23-2018, 09:22 PM   #74
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Originally Posted by Irace86.2.0 View Post
If my theory from earlier holds any water then the reason why a tune can't fix the dip alone is because the motor will try to avoid knock regardless of the basic parameters set by the tune, and knock may be problematic on some high compression NA motors at low rpms where slow exhaust speeds increase combustion chamber temperatures from residual exhaust gases.

If my theory is true then trying to hard tune out the dip without a header could be dangerous or increase the chance of engine knock.



The FB20 is a stroked FA20 (minus port injection). The FB20 has a lower compression, so it would make a good apples to apples comparison for comparing the effects of compression ratio on low end torque (to demonstrate my theory true or false), but it isn't a good apples to apples comparison because the engine is undersquare (longer stroke and smaller piston diameter than our square setup). Usually a stroked motor will have more low end torque, so any dip alleviation from not being as high compressed could just as likely be from being stroked. Thus, I agree with you that the FB20 isn't an apples to apples comparison for my theory or for his theory.
I am aware of the differences in the FB20 and not fully discrediting your opinion because there is merit to the idea. I'm just making observations based on the charts I have seen.

E85 is much more knock resistant. Still has dip.
http://www.ft86club.com/forums/showthread.php?t=52326

It is pretty easy to discredit the thought that the factory tune causes the dip, when tuned cars still have it.

There is so much more that we don't have answers for so there are a lot of assumptions. I know bore to stroke changes VE. We also do not know how the FB is cammed vs the FA which would also play a large role. I have a feeling it is significantly different just based on what red line is between the two.
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Old 02-23-2018, 09:47 PM   #75
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Originally Posted by Lantanafrs2 View Post
At least we know the solution. Imo Toyota could come out and explain the torque curve to us and we'd still argue it. For whatever reason, the oem header was/is a compromise.
Correct, either way it's not just in the tune as someone else said previously. In another thread on here all they did was punch out the internals of the cat and torque dip was gone. Don't think it gets any more conclusive than that.
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Old 02-23-2018, 09:50 PM   #76
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Originally Posted by Irace86.2.0 View Post
I don't know if they did it for economy. It is certainly possible, and I have even said that same theory in the past, but it was only conjecture. What evidence is there for that? If they cared so much about mileage to create a torque dip then why would they change the final drive on the 2017 to be more aggressive?

I'm of the belief that the torque dip is a product of a 12.5:1 compression motor trying to avoid knock, something that could be alleviated with a long tube catless header, but they need a precat, and they need to heat the precat fast during cold starts for emissions, something that a long tube header doesn't allow.
Best theory I've heard however I had a catted el header that took care of the torque curve. Only issue was a power reduction below 3 grand.
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Old 02-23-2018, 11:05 PM   #77
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Originally Posted by Irace86.2.0 View Post
I'm of the belief that the torque dip is a product of a 12.5:1 compression motor trying to avoid knock,
If this were true, wouldn't it be easily recognizable when datalogging the stock car at WOT, and be readily accepted by this point?
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Old 02-23-2018, 11:14 PM   #78
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Originally Posted by NoHaveMSG View Post
I am aware of the differences in the FB20 and not fully discrediting your opinion because there is merit to the idea. I'm just making observations based on the charts I have seen.

E85 is much more knock resistant. Still has dip.
http://www.ft86club.com/forums/showthread.php?t=52326

It is pretty easy to discredit the thought that the factory tune causes the dip, when tuned cars still have it.

There is so much more that we don't have answers for so there are a lot of assumptions. I know bore to stroke changes VE. We also do not know how the FB is cammed vs the FA which would also play a large role. I have a feeling it is significantly different just based on what red line is between the two.
I would say that does throw a wrinkle in things because E85 does reduce knock and does decrease temperatures. Maybe all it is then is the poor flowing cat and header.

Quote:
Originally Posted by Lantanafrs2 View Post
Best theory I've heard however I had a catted el header that took care of the torque curve. Only issue was a power reduction below 3 grand.
High flow cat though, right? Dyno?
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Old 02-23-2018, 11:17 PM   #79
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Originally Posted by gtengr View Post
If this were true, wouldn't it be easily recognizable when datalogging the stock car at WOT, and be readily accepted by this point?
Like what would be seen during datalogging?...can you data log residual exhaust gases in the combustion chamber, or exhaust escape velocity out the headers? Really, I dunno, can you?
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Old 02-23-2018, 11:41 PM   #80
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Originally Posted by Irace86.2.0 View Post
Like what would be seen during datalogging?
You would look at everything related to ignition timing and see that the engine is protecting itself from knock during the torque dip if your theory was true.
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Old 02-24-2018, 01:02 AM   #81
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Say bye to that dip! Good riddance!

Also, how did you get the car to rev to 8k?
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Old 02-24-2018, 01:04 AM   #82
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Say bye to that dip! Good riddance!

Also, how did you get the car to rev to 8k?
You can set the rev-limiter in the tune. Mine is at 7800rpm.
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Old 02-24-2018, 01:12 AM   #83
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Originally Posted by Irace86.2.0 View Post
I don't know if they did it for economy. It is certainly possible, and I have even said that same theory in the past, but it was only conjecture. What evidence is there for that? If they cared so much about mileage to create a torque dip then why would they change the final drive on the 2017 to be more aggressive?
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Originally Posted by NoHaveMSG View Post
There is so much more that we don't have answers for so there are a lot of assumptions. I know bore to stroke changes VE. We also do not know how the FB is cammed vs the FA which would also play a large role. I have a feeling it is significantly different just based on what red line is between the two.
You have answers and these are not assumptions. Toyota insisted to keep the dip and have a more economic and environmental friendly car. They never wanted to fix the dip. Maybe to provide a refinement, but never to fix. This is the most official reply you can get:

http://www.ft86club.com/forums/showp...8&postcount=51

Last edited by nikitopo; 02-24-2018 at 01:46 AM.
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Old 02-24-2018, 01:23 AM   #84
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Originally Posted by nikitopo View Post
You have answers and these are not assumptions. It looks that Toyota insisted to keep the dip and have a more economic and environmental friendly car. They never wanted to fix the dip. Maybe to provide a refinement, but never to fix. This is the most official reply you can get:

http://www.ft86club.com/forums/showp...8&postcount=51
So. Why. Is. There. No. Dyno. Of. A. Stock. Car. That. Has. Been. Tuned. By. The. Aftermarket. That. Has. No. Torque. Dip?

I don't know how much more simple to put it then that. Not trying to flame you, or say that your wrong. But if there is not an aftermarket tuner that has removed the dip on a stock car I would say this is not true. There are plenty of examples of tuned stock cars. Still have the dip.

Man I am really sorry to the OP. I always thought the ACE header was kind of over blown but after seeing all the charts, without even bothering to look at the numbers, it obviously works well.
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