Originally Posted by nikitopo (Post 3048775)

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?

Originally Posted by CSG Mike (Post 3048995)

It doesn't.

A stock FA20 tuned on Motec, still exhibits the dip.

Originally Posted by Irace86.2.0 (Post 3048973)

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.

Originally Posted by Lantanafrs2 (Post 3049009)

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.

Originally Posted by Irace86.2.0 (Post 3049001)

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.

Originally Posted by Irace86.2.0 (Post 3049001)

I'm of the belief that the torque dip is a product of a 12.5:1 compression motor trying to avoid knock,

Originally Posted by NoHaveMSG (Post 3049032)

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.

Originally Posted by Lantanafrs2 (Post 3049048)

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.

Originally Posted by gtengr (Post 3049070)

If this were true, wouldn't it be easily recognizable when datalogging the stock car at WOT, and be readily accepted by this point?

Originally Posted by Irace86.2.0 (Post 3049076)

Like what would be seen during datalogging?

Originally Posted by airjonny (Post 3049110)

Say bye to that dip! Good riddance!

Also, how did you get the car to rev to 8k?

Originally Posted by Irace86.2.0 (Post 3049001)

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?

Originally Posted by NoHaveMSG (Post 3049032)

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.

Originally Posted by nikitopo (Post 3049114)

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