Project Turbo Deathkart

[etravoda]

I'm currently working on the tuning for the turbo build on my Deathkart. I started the car project around 3 years ago, based off a 95 Camaro. I'm pretty familiar with all things car-mechanical, but boost and tuning is a new world for me. I've been learning a LOT by reading (and reverse engineering) in recent months and its cool world. It was neat to find this forum and its small collection of wisdom (something it seems is lost in modern forums). Huge thanks to "Skinny Pedal" for uploading his turbo tune that I could reference. A few pictures attached for fun.

www.youtube.com/watch?v=IPfetGYSSrI

Specs:
- All stock LT1 (other than cam)
- CC503 Cam and beehive springs
- Block hugger headers flipped and modified with all other exhaust being custom
- T76 eBay Turbo
- Tial 44mm Wastegate
- GT500 injectors (not yet installed)
- Shooting for 450 WHP to start... we'll see how long that lasts


Things I've updated so far:
- Tweaked open loop AFR for MAP scaling
- Tweaked Fuel Transient for MAP scaling (I noticed Skinny Pedal just did away with transient fueling all together)
- Took 5% VE off of crank eff table (for camshaft, this is a total guess)
- Disabled MAF
- Changed minimum spark advance to 15 deg from 4k rpm up (I noticed Skinny Pedal didn't change the default value of 23 deg)
- Tweaked main spark advance and extended spark advance
- Spark coolant temp correction updated
- Zeroed all EGR spark advance correction
- Low octane retard vs map
- Max knock retard



I've got several questions and will add more as I continue to tune. I'd also love to get feedback on the tune when I can get it uploaded.
- I've read about the barometric press reset. Sounds like most people zero this value but I've also heard to drop it to 1500 rpm so it continues to function out of boost. Which is preferred?
- What's a good target peak timing for ~8 psi of boost? Seems the LT1's really like timing, but I want to stay conservative.
- Right now its all on stock fuel system so I can make sure I can get the tune to run right with the 2-bar MAP (not changing too much at one time). What other tune values should I be looking at?
- Should I be modifying the BLM cell boundaries?
- I thought I had read there was a minimum injector pulse value somewhere, I anticipate I'll need that for bigger injectors?
- I've got a ballpark VE table for the camshaft from modifying based on fuel trims (its still on the MAF). Can I use these values once I do fueling mods and just halve the injector value I put into the ECM? (24.5 lb injectors for my 49 lb that will go in it)


Any help appreciated!

---

Photo credit for the last image goes to my little brother who owns www.differentialimagery.com

[steveo]

- What's a good target peak timing for ~8 psi of boost? Seems the LT1's really like timing, but I want to stay conservative.

they like timing while n/a but under boost you definitely want to be conservative to say the least. 8psi is actually a lot for the stock LT1 compression and the brittle stock pistons. a few pings under load can really break stuff. most people call it a day at 6psi

- Should I be modifying the BLM cell boundaries?

if your closed loop cruise operating range is higher you can raise them up a bit, analyze the number of events per blm cell and see if they're actually getting used during real driving

I've got a ballpark VE table for the camshaft from modifying based on fuel trims (its still on the MAF). Can I use these values once I do fueling mods and just halve the injector value I put into the ECM? (24.5 lb injectors for my 49 lb that will go in it)

why would you halve the injector flow constant? that will push twice as much fuel as it should, makes no sense. you need to halve the scale of the map axis of the VE table and anything that references the MAP sensor. the injector flow rate is a constant.

any changes you've made to the VE table based on trims from the MAF are no good, you'll need to chuck that table and tune it again with the maf disabled. is your goal to run a maf, or to run speed density? if you're going to pull through the maf and keep it that way, just tune the VE table enough as a backup so you can get home if your MAF dies

[etravoda]

they like timing while n/a but under boost you definitely want to be conservative to say the least. 8psi is actually a lot for the stock LT1 compression and the brittle stock pistons. a few pings under load can really break stuff. most people call it a day at 6psi

if your closed loop cruise operating range is higher you can raise them up a bit, analyze the number of events per blm cell and see if they're actually getting used during real driving

why would you halve the injector flow constant? that will push twice as much fuel as it should, makes no sense. you need to halve the scale of the map axis of the VE table and anything that references the MAP sensor. the injector flow rate is a constant.

any changes you've made to the VE table based on trims from the MAF are no good, you'll need to chuck that table and tune it again with the maf disabled. is your goal to run a maf, or to run speed density? if you're going to pull through the maf and keep it that way, just tune the VE table enough as a backup so you can get home if your MAF dies

I'm planning to start at 4.5 psi (lowest wastegate spring I can run) and step it up to around 6 psi for now. I'm assuming at some point my self control will fade and I will turn it up to 8 though traction will likely be an issue before that's ever the case. Is 18 deg excessive?

Seems reasonable to watch BLM events and try to balance them to some degree, thank you!

Doesn't tricking the ECU into running in a different portion of all MAP values in speed density require halving the injector value as well? I know the tune I'm using as a reference as 15 lb injectors as a constant and he was running 30lb if I remember correctly.


One other curiosity for now: Is the primary controlling factor for closed loop fueling on a MAF system the MAF frequency calibration? I see stoich inputs (which I presume it uses as a target?) and a lot of other inputs for open loop/PE/etc

[steveo]

Doesn't tricking the ECU into running in a different portion of all MAP values in speed density require halving the injector value as well? I know the tune I'm using as a reference as 15 lb injectors as a constant and he was running 30lb if I remember correctly.

no it doesn't. the only reason you might decrease the injector constant is if you run speed density and exceed 100% VE which i guess is unavoidable with a turbo, however halving it (so 100% VE is actually 200% VE) might be a bit extreme. it would require scaling the entire VE table by the same amount. if you were running a maf there should be no need to do that. every single other thing in your calibration will get screwed up too.

One other curiosity for now: Is the primary controlling factor for closed loop fueling on a MAF system the MAF frequency calibration? I see stoich inputs (which I presume it uses as a target?) and a lot of other inputs for open loop/PE/etc

maf calibration tables and ve tables have really nothing to do with open loop and closed loop fueling methods. in a maf system the maf table is how it estimates airflow. in a speed density system the VE table is how it estimates airflow. that's a primary factor in how much fuel it injects for sure, but it has the same effect whether you're in open loop, closed loop, power enrichment, or whatever.

[etravoda]

no it doesn't. the only reason you might decrease the injector constant is if you run speed density and exceed 100% VE which i guess is unavoidable with a turbo, however halving it (so 100% VE is actually 200% VE) might be a bit extreme. it would require scaling the entire VE table by the same amount. if you were running a maf there should be no need to do that. every single other thing in your calibration will get screwed up too.

maf calibration tables and ve tables have really nothing to do with open loop and closed loop fueling methods. in a maf system the maf table is how it estimates airflow. in a speed density system the VE table is how it estimates airflow. that's a primary factor in how much fuel it injects for sure, but it has the same effect whether you're in open loop, closed loop, power enrichment, or whatever.

I'm probably not articulating myself quite well enough but I think you understood (and now that I've made sense in my own mind). Yes by going to the 2-bar MAP I'll need to scale the VE values lower in order to not exceed 100% under the boost portion of the map.

Just trying to wrap my head around tuning (for both speed density and MAF-based tunes in general).

Also just realized you're THE EEHack guy! Thank you for all your work on the flashing/data software, its incredibly well put together! I'm sure it's a huge effort for you and amazing you've provided it all for free.

[steveo]

with all the work you're putting into this toy, have you considered just changing the damn pistons? you could lower your static compression and increase your ability to handle some minor detonation really easily at the same time. i don't understand why you would do all this work with the stock pistons and CR as changing pistons on a SBC is just as easy as swapping the cam, which you already did. you could just quickly ball hone it and skip the machine shop too if you really wanted to save some money and it would probably be fine. might only take an afternoon and a couple hundred bucks to reach your boost goals on pump gas. i don't think there is a way you're going to get 8psi or higher reliable on that thing with pump gas and the stock compression ratio, and if you do you're going to have to retard timing so much you'll be making negative gains