Throttle % spike with bigger throttle body

[malamri424]

Hey everyone

**NOOB ALERT**

I have a 2015 Grand Cherokee SRT with a non-MDS cam, CAI, and hellcat throttle body hooked to a 92mm to 84mm adapter.

The issue I'm having is that with the bigger TB I get a noticeable spike in throttle opening even though I'm gradually pushing the pedal. This issue doesn't occur to the same extent with the stock TB.

A couple of logs are attached and my stock and current tunes as well.

With the big TB I've tried multiplying the airflow throttle model by 1.05 and doing a throttle re-learn with no noticeable change in the spike behavior.

Please advice. My goal is to have the big TB behave like the stock TB by gradually opening before spiking aggressively to the WOT position.

Thanks!

[PurpleRam]

There?s few good threads on here talking about bigger TB?s ....... leave everything under . 7v stock, Start reducing every thing above 1.0 , start small, the upper end of the air flow table can us as much as a 55% reduction...... .7 to 1.0v is the gray area ,

[malamri424]

There?s few good threads on here talking about bigger TB?s ....... leave everything under . 7v stock, Start reducing every thing above 1.0 , start small, the upper end of the air flow table can us as much as a 55% reduction...... .7 to 1.0v is the gray area ,

Thank you so much bro... I will apply this approach and log it for others to learn.

[PurpleRam]

Search “bigger throttle body”, about4 or 5 threads down there’s a good thread actually called bigger throttle body, in it there’s a great explanation of why we reduce airflow #s

[PurpleRam]

These are the Major take away from the thread I was referring to, the author is

Hemituna


“Take the factory flow numbers with a grain of salt. Don’t be afraid to play with them. I have a 700whp Whippled 6.4 with a hellcat 95mm TB that has the max TB airflow number as 400.Why?? because P/T responsiveness/drivability is soooooo much better with smaller numbers. The factory numbers above 1v are too big. Above 1.5- 2v, they are waaaay tooo big. Fit a larger TB and drive it and it will feel bet ter...Add 10-15% to TB tables as you 'should' do and it goes back to feeling like it did prior to the mod. So try a bigger TB and smaller numbers and hey it now feels even better... go figure!!The idle areas 0 -.5v will sometimes need adjusting to a slightly larger number to get that area correct.

“Let me explain the above a little more.........A stock 6.4L tune has the WOT airflow limit as 353 g/but the TB table goes to 1100 g/s ??So how does that work?? Now, if you log max airflow on a stock 6.4, the biggest number will be 350-360 g/so 350 g/s makes 475hp it seems....So why is everyone using 1000 - 1500 g/s to make 100-300hp more???The factory it seems has imbedded an airflow model in the PCM, hence why you must designate an engine capacity. Now this model only affects P/T operation. Between the TB airflow and what they deem the engine requires at P/T, the TB will track an airflow target. Now WOT is WOT and the TB will open 100% no matter what the numbers are in the tables. But P/T between 25 - 75% throttle, you are limited to the numbers in the model. So if the 6.4 is in P/T mode it will never open the TB past353 g/s whether at 30% pedal or 70%. Most never notice this. If you move WOT threshold lower, you notice it less. BUT, if you make the airflow tables bigger, the gap between P/T and WOT gets even greater. If you make the numbers bigger, the TB will be opened less until it goes WOT. If you try and increase the ETC tables, what often happens is the ETC opens the TB, the airflow exceeds what's allowed and the ETC is forced to close the TB. So you get this strange surging effect. Why the factory has done this is to give the engine the amount of TB that they feel it needs at certain rpm to maintain velocity/airflow/smooth the torque curve or whatever! However, when modding or adding a blower, this is now not ideal. So following their lead with TB flow tables often wont get the result you are after. On a blower engine, 50% pedal, wont give enough TB opening to make much boost so you don't get 50% power. so you keep leaning on the pedal till finally it goes WOT and BAM - full boost and look out! The often talked about light-switch effect! This same response is felt when NA also.The trick I have found is to lower (a lot!) the 3 TB airflow tables in the .75 -1v and above areas. This will give a much more linear pedal to the point where the transition to WOT is seamless. The added benefit is that you no longer hit lots of Airflow/Tq mgmt limits! Keep in mind the stock airflow max numbers and give it a try. We can talk more about NOV and Wheel Power tables later.......”

[malamri424]

These are the Major take away from the thread I was referring to, the author is

Hemituna


?Take the factory flow numbers with a grain of salt. Don?t be afraid to play with them. I have a 700whp Whippled 6.4 with a hellcat 95mm TB that has the max TB airflow number as 400.Why?? because P/T responsiveness/drivability is soooooo much better with smaller numbers. The factory numbers above 1v are too big. Above 1.5- 2v, they are waaaay tooo big. Fit a larger TB and drive it and it will feel bet ter...Add 10-15% to TB tables as you 'should' do and it goes back to feeling like it did prior to the mod. So try a bigger TB and smaller numbers and hey it now feels even better... go figure!!The idle areas 0 -.5v will sometimes need adjusting to a slightly larger number to get that area correct.

?Let me explain the above a little more.........A stock 6.4L tune has the WOT airflow limit as 353 g/but the TB table goes to 1100 g/s ??So how does that work?? Now, if you log max airflow on a stock 6.4, the biggest number will be 350-360 g/so 350 g/s makes 475hp it seems....So why is everyone using 1000 - 1500 g/s to make 100-300hp more???The factory it seems has imbedded an airflow model in the PCM, hence why you must designate an engine capacity. Now this model only affects P/T operation. Between the TB airflow and what they deem the engine requires at P/T, the TB will track an airflow target. Now WOT is WOT and the TB will open 100% no matter what the numbers are in the tables. But P/T between 25 - 75% throttle, you are limited to the numbers in the model. So if the 6.4 is in P/T mode it will never open the TB past353 g/s whether at 30% pedal or 70%. Most never notice this. If you move WOT threshold lower, you notice it less. BUT, if you make the airflow tables bigger, the gap between P/T and WOT gets even greater. If you make the numbers bigger, the TB will be opened less until it goes WOT. If you try and increase the ETC tables, what often happens is the ETC opens the TB, the airflow exceeds what's allowed and the ETC is forced to close the TB. So you get this strange surging effect. Why the factory has done this is to give the engine the amount of TB that they feel it needs at certain rpm to maintain velocity/airflow/smooth the torque curve or whatever! However, when modding or adding a blower, this is now not ideal. So following their lead with TB flow tables often wont get the result you are after. On a blower engine, 50% pedal, wont give enough TB opening to make much boost so you don't get 50% power. so you keep leaning on the pedal till finally it goes WOT and BAM - full boost and look out! The often talked about light-switch effect! This same response is felt when NA also.The trick I have found is to lower (a lot!) the 3 TB airflow tables in the .75 -1v and above areas. This will give a much more linear pedal to the point where the transition to WOT is seamless. The added benefit is that you no longer hit lots of Airflow/Tq mgmt limits! Keep in mind the stock airflow max numbers and give it a try. We can talk more about NOV and Wheel Power tables later.......?

Yeah I found it... He referred to "3 TB tables" but I can only find one where these numbers are applicable, the "throttle body model" ==> "airflow" as shown in the picture.
What are the other two?

[PurpleRam]

Large range and small range tables

[PurpleRam]

Large range and small range tables

for the most part don't concern yourself with those, they are more of a Fine tuning thing and most times there is no need to deal with them.

[malamri424]

Tried lowering the airflow numbers above 1v as mentioned. Didn't seem to do much (log and tune attached as "tb low"), when I tried to go even lower I got a "service throttle body" message.

Throttle position jumps from 30% to WOT.

I tried going the other way and multiplied the stock numbers by 1.15 (log and tune attached as "tb high"). Still no apparent difference... Throttle jumps from 30% to WOT.

Haven't touched the low and high range tables yet.

Any indeas?

Thanks!

[HaasExp]

It seems like that step to WOT may be caused by the pedal voltage passing the WOT threshold in the tune.

However, your logs don't have the PIDs to properly analyse this.

Add the following PIDs to your logs:

Relative Pedal
Relation Throttle

Both of these parameters should max out at around 3.84V