How streetable can you get a 6.1-based turbo build?

[Grant]

I recently added a manual transmission and larger cam to the 6.1-based 7.4L hemi in my SRT8 Magnum. As I tune out the plethora of drivability issues (mostly with the throttle body range tables), I've been trying to figure out how PCM translates accelerator pedal voltage into throttle body voltage.

It seems to me the PCM computes requested torque from accel pedal voltage. Then it looks at current RPM, VE and the throttle body range tables to figure out how much throttle angle it needs to provide that torque. So what happens if you throw turbo spool into this? Does the PCM freak out, or is it all manageable somehow?

Everything would certainly be a lot easier if you could just map pedal voltage to throttle voltage, like a cable throttle... This wouldn't be great for an automatic car of course.

Thanks for any help. I originally wanted to get a Hellephant, but it doesn't seem like I'll be able to get my hands on one. So now I'm thinking I'll have my current block built for turbos.

[Bullet300]

There are tables that map pedal position to throttle position. When turbo spools and you have your tables scaled acordingly it will adjust as the map reads more pressure. The main hing to get correct is the tipping point into boost. This depends alot on your throttle reaction and trigger voltage for wide open throttle.

[Grant]

So it is possible to get these PCMs to drive like stock with a turbocharger? Or will you always be chasing some drivability issue?

[Bullet300]

Mine drives like a nice cammed car under boost then when it comes on all hell breaks loose. It takes time to get it right. If you do it yourself there is alot to learn. Or just get a reputable tuner who knows there stuff to dial it in for you.

[McCloud]

I'm not by any stretch of the means an expert tuner but this is what I know.

These tables should align and be based on the bench flow of your TB.

- AirFlow/Electronic Throttle/Throttle body Model/Ariflow 35035
- AirFlow/Electronic Throttle/FeedForward Control/ Small Range 44388
- AirFlow/Electronic Throttle/FeedFoward Control/Large Range 44387

Torque Management/Driver Demand/Power % Request 35060 drives the pedal sensitivity/TB opening. The more aggressive you are with your Power % Request the more sensitive your gas pedal is.


As for when the turbo spools up you will need to make sure you have your power enrichment, transient, and VE tables setup correctly to account for the turbo spooling up.

Again not an expert but thought I could at least get you pointed in the right direction.

[Grant]

I'm not by any stretch of the means an expert tuner but this is what I know.

These tables should align and be based on the bench flow of your TB.

- AirFlow/Electronic Throttle/Throttle body Model/Ariflow 35035
- AirFlow/Electronic Throttle/FeedForward Control/ Small Range 44388
- AirFlow/Electronic Throttle/FeedFoward Control/Large Range 44387

My car (naturally aspirated) drives like total crap unless the Small / Large Range tables differ from the TB Airflow Model. I need to adjust them to give more throttle on tip-in at low airflows, or it dies or surges on small pedal voltages.

I wish I knew what was going on here. I'm in the process of creating a model for the ETC system, and hoping that will shed more light on things.

As for when the turbo spools up you will need to make sure you have your power enrichment, transient, and VE tables setup correctly to account for the turbo spooling up.

Yeah, I've done all that on cable throttle cars before. It's the ETC I'm scared of, because it sometimes seems to do crazy things. Like this:
https://forum.hptuners.com/showthrea...l=1#post636523

[Grant]

Mine drives like a nice cammed car under boost then when it comes on all hell breaks loose. It takes time to get it right. If you do it yourself there is alot to learn. Or just get a reputable tuner who knows there stuff to dial it in for you.

Thanks, do you have any problems with the ETC doing funny things when you're trying to modulate the throttle in lower gears? Or is it all smooth and progressive?

[Bullet300]

Thanks, do you have any problems with the ETC doing funny things when you're trying to modulate the throttle in lower gears? Or is it all smooth and progressive?

Mine is smooth as silk. Do you have an aftermarket thottle body? If so this can make it more difficult to dial in.

[McCloud]

I was playing around with the air tables at one point to improve throttle response based on the posts in here with reducing the numbers in the tables. I ran into the issue your experiencing. I went back to the stock tune settings but bumped up the air under .3v by 20%. My theory behind that is I have a bigger cam and need more air around idle and tip in. It did smooth it all out, but ended up with poor throttle response so then I bumped up all of the numbers in the % request and I ended up with great throttle response.

Messing around with the Air tables works, but I personally feel like it all works better with the correct airflow and adjusting how you want the throttle to feel with the % request settings. Setting the air tables low just tricks the TB into opening wider sooner, you get the same result from bumping up the % to v ratio in the % request table. Seems like a cleaner way to do it. That's just my opinion and what works for me, I don't mean to discredit the other process.

So long story short you may just need adjustments .3 volt and under. Another thought is the TB could have issues. Maybe measure the v to TB % open?

[Grant]

Mine is smooth as silk. Do you have an aftermarket thottle body? If so this can make it more difficult to dial in.

Yes, an Arrington 90mm on a 449 ci motor. Smoothness I can tune in, but I have not yet been able to get the throttle to behave in a linear manner at higher pedal voltages (see link above).

I was playing around with the air tables at one point to improve throttle response based on the posts in here with reducing the numbers in the tables. I ran into the issue your experiencing. I went back to the stock tune settings but bumped up the air under .3v by 20%. My theory behind that is I have a bigger cam and need more air around idle and tip in. It did smooth it all out, but ended up with poor throttle response so then I bumped up all of the numbers in the % request and I ended up with great throttle response.

Bigger cams definitely need more air, but this should be reflected in the VE tables (which affects aircharge and thus torque calcs). It feels like there are important parts of the calibration we can't access.

Messing with low throttle volts also works for me in some places, but seems to create issues where I didn't have any before, like changes with weather, hanging on decel, or over-corrections at idle. I think I'm going to go correct Arrington TB settings (roughly stock + 27%) and try to increase torque in more specific areas with other tables. Like friction torque. This approach seems like it will have fewer side effects on other areas.

Messing around with the Air tables works, but I personally feel like it all works better with the correct airflow and adjusting how you want the throttle to feel with the % request settings. Setting the air tables low just tricks the TB into opening wider sooner, you get the same result from bumping up the % to v ratio in the % request table. Seems like a cleaner way to do it. That's just my opinion and what works for me, I don't mean to discredit the other process.

Agreed.

[DakBuilder]

Very good information here guys. I'm planning on referencing it as I get closer to firing up my TT build. Much appreciated

Jay